Total Synthesis of Aflastatin A A dissertation presented by Jason James Beiger to The Department of Chemistry and Chemical Biology in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Chemistry Harvard University Cambridge, Massachusetts May, 2013 © 2013 by Jason James Beiger All rights reserved. Dissertation Advisor: Professor David A. Evans Jason James Beiger Total Synthesis of Aflastatin A Abstract The syntheses of aflastatin A (1) and its C3–C48 degradation fragment (2) are described. The syntheses feature several complex diastereoselective fragment couplings, including a C35–C36 anti-Felkin-selective boron-mediated oxygenated aldol reaction, a C15– C16 Felkin-selective trityl-catalyzed Mukaiyama aldol reaction, and a C26–C27 chelatecontrolled aldol reaction involving soft enolization with magnesium. Careful comparison of the spectroscopic data for the synthetic aflastatin A C3–C48 degradation fragment (2) to that reported by the isolation group revealed a structural misassignment in the lactol region of the naturally derived degradation product. The cause of the mismatch was initially believed to be stereochemical in origin. Ultimately, the data reported for the naturally derived aflastatin A C3–C48 degradation lactol (2, R = H) was attributed to its derivative lactol trideuteriomethyl ether (R = CD3). Further, the absolute configurations of six stereogenic centers (C8, C9 and C28–C31) in aflastatin A (1) were formally revised by the isolation group prior to completion of its total synthesis. The synthesis of the aflastatin A C3–C48 lactol trideuteriomethyl ether and its spectroscopic match to the naturally derived C3–C48 degradation fragment confirm the stereochemical revision. The synthesis of a degradation product containing the tetramic acid and two overlapping stereocenters (C4 and C6) was also achieved. Its spectroscopic match to the corresponding naturally derived degradation fragment verified the absolute configuration of iii the aflastatin A C5' stereocenter. When combined with previous degradation fragment syntheses, and eventually the total synthesis of aflastatin A, the revised stereochemical assignment of aflastatin A was fully affirmed. OH O Me N Me 2' 5' OH 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 35 OH OH OH 39 O Me Me Me OH Me Me Me Me Me OH OH H O C9H19 Aflastatin A (1) OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH OR 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 Aflastatin A C3–C48 Degradation Fragment (2, R = H) iv Table of Contents Chapter 1: Introduction to Aflastatin A I. Aflatoxins II. Isolation and Biological Activity III. Structural Elucidation IV. Stereochemical Revision V. Synthesis Achievements Made Prior to the Stereochemical Revision A. The C35–C36 Oxygenated Aldol Reaction C. The C15–C16 Mukaiyama Aldol Reaction Chapter 2: Synthesis of the C3–C48 Degradation Fragment of Aflastatin A I. Synthesis Plans Involving C28–C29 Bond Formation A. Initial Structure of Aflastatin A B. Revised Structure of Aflastatin A II. Synthesis Plans Involving C26–C27 Bond Formation A. Initial Structure of Aflastatin A B. Revised Structure of Aflastatin A III. Synthesis of the C3–C26 Ketone A. Synthesis of the C3–C15 Aldehyde B. Syntheses of the C16–C26 Enolsilane and C3–C26 Ketone IV. Synthesis of the C27–C48 Aldehyde V. Synthesis of the C3–C48 Degradation Fragment VI. Graphical Summary Chapter 3: Structural Revision of the C3–C48 Degradation Fragment of Aflastatin A I. Development of a Model for the C27–C48 Lactol Region II. Syntheses of the epi-C39 and epi-C33–C37 Lactols A. Synthesis of the epi-C39 Lactol 51 56 57 19 19 23 25 25 27 33 34 37 40 47 49 1 3 4 7 11 11 16 B. The C18–C19 Aldol Reaction and Synthesis of the C9–C27 Degradation Fragment 13 v B. Synthesis of the epi-C33–C37 Lactol III. Syntheses of Three Diastereomeric epi-C36 Lactols A. Synthesis of the epi-C34,C36 Lactol B. Synthesis of the epi-C35,C36 Lactol C. Synthesis of the epi-C36 Lactol IV. A Solution to the Structural Problem V. Syntheses of the C3–C48 Degradation Fragments VI. Spectroscopic Analysis of the C3–C48 Degradation Fragments VII. Graphical Summary VIII. Experimental Section Chapter 4: Synthesis of Aflastatin A I. Installation of the Tetramic Acid II. Revised Synthesis of the C27–C48 Aldehyde III. Completion of the Synthesis of Aflastatin A IV. Graphical Summary V. Experimental Section Appendix 1: Spectral Data Comparisons Appendix 2: 1H- and 13C-NMR Spectra Chapter 3 Chapter 4 58 62 63 66 68 71 74 80 85 88 130 140 143 148 159 191 206 207 235 vi Acknowledgments First and foremost, I would like to thank my research advisor, Prof. David A. Evans, for accepting me into his research group, providing intellectual and financial support, and most importantly, showing a great amount of patience. I think we both knew we were in for the long haul when he referred to my work on the aflastatin project as occurring on a geological timescale (lab members affectionately call this "Beiger time"). I hope you understand that I needed this time to make sure we got our work done to the best of our ability. I believe I speak for every member of the aflastatin project in saying that it has been a true privilege to work not only within this group, but on a molecule that stands to be the last polyketide natural product completed by this laboratory. I can only hope that it provides a satisfactory final chapter to the rich aldol legacy that you and this group will leave behind. I would also like to acknowledge the members of my thesis and graduate advising committees for their time and support: Profs. Matthew D. Shair, Yoshito Kishi, and Tobias Ritter. In particular, I thank Matt for his guidance and support in applying for a postdoctoral research position and funding, as well as the discussions we've had through the years about research and departmental (GPC-related) activities. I am also extremely grateful for the work that Prof. Kishi and his group did to assist the reassignment of aflastatin, and am honored to have been able to share with him the work he so strongly influenced. Finally, I thank Tobias for his help and understanding, especially as I rotated through his lab my first year. I am deeply indebted to those who worked alongside and before me on the aflastatin project, without whose work and dedication this dissertation would not have been possible. I particularly enjoyed the healthy collaboration that I shared with Drs. Peter Fuller, Egmont Kattnig and Joseph Young, and am grateful for the precedent laid forth by Drs. Frank Glorius, vii Bill Trenkle, Jing Zhang, Jason Burch, David Thaisrivongs, Victor Cee and Sarah Siska. Outside of the aflastatin project, I must thank the entire Evans research group for providing personal support and maintaining a wonderful academic and working environment. In particular, I am thankful for the strong friendships that my classmates, Joseph Wzorek and Alex Speed, shared through the years. Although I feel as though I am leaving you behind, I look forward to sharing a beer with you again in the future. I also am thankful to my baymate Dr. Simone Bonazzi for keeping me on my feet this final year. I am very proud of your recent synthesis achievement and wish you the greatest of success at Novartis. I also have to thank the last remaining group members – Art, Simone, Bichu and SusAnn – for holding the fort with me as the ranks grew thin. I also had the privilege of mentoring two undergraduates – Tamara Halkina and Doug Duquette – and wish them success as they complete their own degrees. As fellow graduate students, Drew, Joe Y., Jon L., and Keith were particularly influential during my early graduate years. Overall, it been a true privilege to work alongside a talented group of baymates (Joe Y., Tom, Keith, Torsak, Pete, Hyun-Ji, Simone), graduate students (Pavel, Keith, George, Jon L., Joe Y., Drew, Hyun-Ji, Yimon, Eugene, Torsak, Alex Speed, Joe W., Bichu, Hung-Chieh), postdocs (Lizbet, Egi, Christian, Shizue, Andrew, SusAnn, Martin, Matt, Tom, Pete, Simone, Dennie, Paulo, Daniel, Florian, Thomas, Joe P., David M., Alex Sherlock, Sebastian, Art, Pascal), undergraduates (Toma, Doug, Christina, Peyton, Adelaide, David T., Jon M., Justin), and visiting scholars (Lenni, Danny G., David W.). I will especially miss group activities such as Rhino League Volleyball (Dung Cup Champions 2009 and Rhino Cup Final Four 2011), wiffle ball, poker, Charles River runs, beer o'clocks, meals (at Border, Boca, the Common, etc.), Horse Latitudes shows, and so on. Outside of the Evans research family, I have to thank the many departmental members viii that enriched my graduate life here. Profs. Dieter Seebach, Eric N. Jacobsen, and the entire Jacobsen group are acknowledged for their participation in joint group meetings. Next, my work was inspired by the many natural product syntheses that were completed both within my group and by graduate students throughout the department, with special mention of nakadomarin (Simone, Bichu), himgaline/GB13 (Drew), salvinorin (Jon L.), peloruside (Alex S., Dennie; Meredeth, Matt S.), azaspiracid (Lizbet), oasomycin (Pavel), fastigiatine (Brian L.), hibarimicinone (Ben, Brian L.), hyperforin (Brian S.), reserpine (Naomi), cortistatin (Alec, Chong; Hong), trioxacarcin (Dan, Jakub, Nick), stephacidin (Seth), and finally banyaside (Corinna, ETH), which had its own distinctive flavor of structural mayhem. All of your work was truly inspirational and drove me to give my own project a fitting end. This work would also not have been possible without the support of many departmental staff members. In particular, Drs. Shaw Huang and Bill Collins are thanked for their assistance with NMR experiments. Friendship and support from facilities (Jerry, Mike, Jon, Ricky, Chris and Pat), the financial office (Michelle, Lisa, Liz), and front office administration (Tony, Allen Helen, Kathy, Barbara) is also gratefully acknowledged, especially as our laboratory faced contraction and years without a formal administrative assistant. I thank Joseph, Martin and Valia for their administrative services early on. I also must not forget my previous research advisors and mentors who got me to where I am today. Just about thirteen years ago, I was invited as a high school student to work in the laboratory of Professor Iwao Ojima (SUNY – Stony Brook). Since then I have been fortunate enough to work as an undergraduate researcher for Professor Amos B. Smith, III (Penn), and twice as a summer intern at OSI Pharmaceuticals, Inc. I thank both professors for granting me such wonderful research opportunities, as well as their support through the years. I also am ix indebted to the many mentors I have had: Mrs. Schoch (Kings Park HS), Drs. Xudong (Deric) Geng and Xinyuan (Ed) Wu (Stony Brook), Drs. Adam Charnley and Jason Cox (Penn), and Drs. Arno Steinig and Meizhong Jin (OSI). I also lament the recent closure of OSI (Farmingdale, NY), and hope that all affected friends and acquaintances find new work soon. To continue, I must acknowledge Dr. Michael Strem (Strem Chemicals, Inc.) and the NESACS-GDCh Student Exchange Program for providing an amazing graduate school experience. The opportunity to present my research at an international conference in Rostock, Germany not only forced me to get a passport, but also resulted in many friendships on both sides of the Atlantic. I am especially grateful to have shared this experience with a special group of Boston-area exchange participants (Chris, Greg, Heidi, Colin, Ania, Kevin, Emily, Nick, Gowri, Xin, Patrick, John), as well as many conference organizers and attendees (Elisabeth, Andi, Isabella, Mike, Johannes, etc.). I also enjoyed the welcome diversion that sports such as departmental basketball ("Chemball"), Jacobsen group frisbee, NERC summer softball tournaments, and the Penn/Columbia alumni softball team had to offer. I also frequented Hemenway gym to attend group exercise classes and play basketball, and am thankful to the trainers who helped keep me in shape (Wendy, Melissa, Kerry, Elyse, Kate, Brian, Mike), as well as the many friends who took classes and played basketball with me (Mike P., Dave, Harrison, Tory; Sendhil, Heather, Laura, Tom, Lorenzo, Paul, Frank and others from the economics department). I also value the close friendships that I have with Rebecca, Harrison, and Diana. They are representative of the many friends from Harvard, Penn and my hometown (Kings Park, NY) who have helped me during the most trying phases of my graduate career. I am also thankful to Heather, whose outside (or non-chemistry) perspective has helped keep me sane x during the final stages of writing, and to all those who have hosted me outside of Boston when I simply needed exposure to some place that was not Converse 306B: Melanie (Philadelphia), Melody (Chicago), and Jon (Atlanta). In the end, I am indebted to many friends not listed here who have positively influenced my life (by way of teaching, band, dormitory living, eateries, happy hours, etc.), and it is to those not explicitly named that I offer my sincerest gratitude now. Finally, I would like to express my gratitude to my family – notably my mom, dad, and brother Justin – for their continuous care, support, and understanding, and without whom none of this would have been possible. I am extremely proud of Justin and the work that he does for the NYPD – especially in light of the recent tragedy surrounding the Boston Marathon – and I wish for his continued safety. xi To Mom, Dad and Justin. xii "We few, we happy few, we band of brothers." – Henry V, William Shakespeare xiii List of Abbreviations Å Ac aq AsA 9-BBN BcA BINAP Bn BOM box Bu Bz calcd cat Cbz cm–1 CSA cod COSY Cy δ d DDQ DIBALH DMAP DMF DMSO d.r. E ee angstrom acetyl aqueous aflastatin A 9-borabicyclo[3.3.1]nonane blasticidin A 2,2'-bis(diphenylphosphino)-1,1'-dinaphthyl benzyl benzyloxymethyl bisoxazoline butyl benzoyl calculated catalytic benzyloxycarbonyl wavenumber(s) camphor sulfonic acid 1,5-cyclooctadiene correlation spectroscopy cyclohexyl chemical shift day(s) 2,3-dichloro-5,6-dicyano-1,4-benzoquinone diisobutylaluminum hydride 4-(dimethylamino)pyridine N,N-dimethylformamide dimethyl sulfoxide diastereomeric ratio entgegen (German) enantiomeric excess xiv ent epi eq equiv ESI Et g h HMPA HMBC HMQC HPLC HRMS HSQC Hz IBX IR J KHMDS L LDA LiHMDS 2,6-lut. M m-CPBA Me MHz min mol MOP MS enantiomeric epimeric equation equivalent electrospray ionization ethyl gram(s) hour(s) hexamethylphosphoramide heteronuclear multiple bond correlation heteronuclear multiple quantum correlation high-pressure liquid chromatography high-resolution mass spectrometry heteronuclear single quantum correlation hertz ortho-iodoxybenzoic acid infrared coupling constant potassium bis(trimethylsilyl)amide liter(s), or ligand lithium diisopropylamide lithium bis(trimethylsilyl)amide 2,6-lutidine (2,6-dimethylpyridine) molar, or metal meta-chloroperoxybenzoic acid methyl megahertz minute(s) mole(s) 2-methoxypropan-2-yl molecular sieves xv MTPA m/z n NaHMDS NOE NMR Nu Ph Piv PMB PMP ppm PPTS Pr p-TsOH py quant. quinox R Ref. ROE rt sat. SM TBDPS TBS t or tert TEMPO TFA THF TIPS α-methoxy-α-(trifluoromethyl)phenylacetyl mass-to-charge ratio normal sodium bis(trimethylsilyl)amide nuclear Overhauser effect nuclear magnetic resonance nucleophile phenyl pivaloyl (trimethylacetyl) para-methoxybenzyl 1,2,2,6,6-pentamethylpiperidine parts per million pyridinium para-toluenesulfonate propyl para-toluenesulfonic acid (monohydrate) pyridine quantitative 2-(4,5-dihydro-2-oxazolyl)quinoline alkyl group (generic) reference rotating frame Overhauser effect room temperature saturated starting material tert-butyldiphenylsilyl tert-butyldimethylsilyl tertiary 2,2,6,6-tetramethyl-1-piperidinyloxy, free radical trifluoroacetic acid tetrahydrofuran triisopropylsilyl xvi TMS TOF TPS Tr TS v/v wt% Z ))) trimethylsilyl time-of-flight triphenylsilyl trityl transition state volume per unit volume weight percent zusammen (German) sonication xvii Chapter 1 Introduction to Aflastatin A I. Aflatoxins The aflatoxins represent a group of mycotoxins produced by fungi of the Aspergillus genus (Figure 1.1).1 Aflatoxins produced by strains of A. flavus and A. parasiticus regularly contaminate food and feedstock derived from infected corn, cotton, grain and peanut crops.2 Contamination of agricultural commodities is problematic because aflatoxins exhibit potent toxicity and carcinogenicity in mammals.3 Limiting the amount of aflatoxin that enters our food supply is important for protecting human and animal health while minimizing economic loss.4 As an example, aflatoxin levels are regulated within the United States by the Food and Drug Administration (FDA), and must not exceed 20 parts-per-billion in food destined for                                                                                                                 (1) (2) Goldblatt, L., Ed. Aflatoxin, Scientific Background, Control, and Implications; Academic Press, New York, NY, 1969. (a) Detroy, R.W.; Lillehoj, E.B.; Ciegler, A. Aflatoxin and Related Compounds. In Microbial Toxins: Fungal Toxins; Ciegler, A., Kadis, S., Ajl, S.J., Eds.; Academic Press: New York, 1971; Vol. 6, pp 3–178; (b) Diener, U.L.; Cole, R.J.; Sanders, T.H.; Payne, G.A.; Lee, L.S.; Klich, M.A. Annu. Rev. Phytopathol. 1987, 25, 249–270. (a) Squire, R.A. Science 1981, 214, 877–880; (b) Eaton, D.L., Groopman, J.D., Eds.; The Toxicology of Aflatoxins: Human Health, Veterinary, and Agricultural Significance; Academic Press: San Diego, CA, 1994; (c) Newberne, P.M.; Butler, W.H. Cancer Res. 1969, 29, 236–250. (a) Payne, G.A. Process of Contamination by Aflatoxin-Producing Fungi and Their Impact on Crops. In Mycotoxins in Agriculture and Food Safety; Sinha, K.K., Bhatnagar, D., Eds.; Marcel Dekker: New York, 1998; pp 279–306. (b) Bennett, J.W.; Klich, M. Clin. Microbiol. Rev. 2003, 16, 497–516. (3) (4)   1 human consumption.5 O O O O OMe O O OMe O O O O O Aflatoxin B1 Aflatoxin G1 Figure 1.1. Representative aflatoxins. Few methods exist for protecting agricultural products from aflatoxin contamination. Traditionally, fungicides have been used to control the propagation of aflatoxigenic fungi, but they are often toxic to mammals, and provoke the emergence and pervasion of resistant strains. More recently, non-aflatoxigenic strains of A. flavus were developed to displace aflatoxinproducing strains from crop fields, but application timing, cost, and overall effectiveness of this technology are limiting.6 Alternatively, specific inhibitors of aflatoxin biosynthesis that lack fungicidal activity are desirable.7 Since aflatoxins do not appear to be essential for fungal growth and viability, it should be possible to inhibit their synthesis without selecting for resistant strains. Aflatoxin production inhibitors should also provide new insight into the mechanism and regulation of aflatoxin biosynthesis by fungi on the molecular level. Study in this area should aid the development of more effective and economically practical means of minimizing aflatoxin contamination.                                                                                                                 (5) (6) (7) U.S. Food and Drug Administration. Action Levels for Aflatoxins in Animal Feeds. Compliance Policy Guide, Sec. 683.100, 1979 (revised 1994). (a) Dorner, J.W.; Lamb, M.C. Mycotoxin Res. 2006, 22, 33–38; (b) Cotty, P.J. Phytopathology 1994, 84, 1270–1277. (a) Zaika, L.L.; Buchanan, R.L. J. Food Prot. 1987, 50, 691–708; (b) Wheeler, M.H.; Bhatnagar, D. Pestic. Biochem. Physiol. 1995, 52, 109–115; (c) Wheeler, M.H.; Bhatnagar, D.; Rojas, M.G. Pestic. Biochem. Physiol. 1989, 35, 315–320; (d) Dutton, M.F.; Anderson, M.S. J. Food Prot. 1980, 43, 381–384.   2 II. Isolation and Biological Activity Aflastatin A (AsA, 1) was discovered during a screen of microbial metabolites that specifically targeted aflatoxin production in A. parasiticus (Figure 1.2).8 AsA was isolated by Sakuda and coworkers from the mycelial extract of the bacterium Streptomyces sp. MRI142, which in turn was isolated from a soil sample collected in Zushi-shi, Kanagawa prefecture, Japan. Similarly, blasticidin A (BcA, 2) was isolated by Fukunaga, Yonehara and their respective coworkers from the soil bacterium Streptomyces griseochromogenes.9 BcA was initially reported to show antifungal activity towards the rice blast pathogen Pyricularia oryzae. Later, Sakuda and coworkers reevaluated BcA as an inhibitor of aflatoxin production after noticing homologous physicochemical properties between it and AsA.10 OH O Me N Me 2' OH 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 35 OH OH OH 39 O Me Me Me OH Me Me Me Me Me OH OH H O C9H19 Aflastatin A (1) OH O Me N 2' OH 3 7 HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 25 29 33 OH OH OH 37 O Me Me Me OH Me Me Me OH OH H O C10H21 Blasticidin A (2) Figure 1.2. Structures of aflastatin A (1) and blasticidin A (2).                                                                                                                 (8) (a) Sakuda, S.; Ono, M.; Furihata, K.; Nakayama, J.; Suzuki, A.; Isogai, A. J. Am. Chem. Soc. 1996, 118, 7855–7856; (b) Ono, M.; Sakuda, S.; Suzuki, A.; Isogai, A. J. Antibiotics 1997, 50, 111–118; (c) Ono, M.; Suzuki, A.; Isogai, A.; Sakuda, S. Production Aflastatin A from Streptomyces sp., A Pharmaceutical Composition and Methods of Use. U.S. Patent 5,773,263, June 30, 1998. (a) Fukunaga, K.; Misato, T.; Ishii, I.; Asakawa, M. Bull. Agric. Chem. Soc. Jpn. 1955, 19, 181–188; (b) Kōno, Y.; Takeuchi, S.; Yonehara, H. J. Antibiotics 1968, 21, 433–438. (9) (10) (a) Sakuda, S.; Ono, M.; Ikeda, H.; Inagaki, Y.; Nakayama, J.; Suzuki, A.; Isogai, A. Tetrahedron Lett. 1997, 38, 7399–7402; (b) Sakuda, S.; Ono, M.; Ikeda, H.; Nakamura, T.; Inagaki, Y.; Kawachi, R.; Nakayama, J.; Suzuki, A.; Isogai, A.; Nagasawa, H. J. Antibiotics 2000, 53, 1265–1271. (c) Ono, M.; Suzuki, A.; Isogai, A.; Sakuda, S. Aflatoxin Contamination Inhibitor and Aflatoxin ContaminationInhibiting Method. U.S. Patent 6,121,310, September 19, 2000.   3 Owing to their similar chemical properties, AsA and BcA exhibit comparable biological activities.11 AsA and BcA inhibit production of both aflatoxin B and G groups by A. parasiticus (IC50 = 0.07 and 0.04 µM, respectively) without significantly affecting fungal growth. They also reduce production of the pentaketide-derived melanin in the fungus Colletotrichum lagenarium. 12 Biological assays reveal that AsA and BcA suppress the expression of enzymes (i.e. PKS1) and a regulatory protein (AflR) involved in early steps of the biosyntheses of aflatoxin and melanin,13 but exact molecular targets for these natural products have yet to be identified. Collectively, AsA and BcA exhibit antibiotic activity against various fungi, bacteria and yeast. Independently, AsA inhibits propagation of subcutaneously transplanted mouse adenocarcinoma,8c whereas BcA suppresses ribosomal protein synthesis in the yeast Saccharomyces cerevisiae.14 III. Structure Elucidation Aflastatin A is a 3-acyltetramic acid natural product that bears a highly oxygenated and long alkyl chain.8a It contains 29 stereogenic centers, one stereodefined (E) alkene (C2– C3), a six-membered lactol (C33–C37), and is capped by a D-alanine-based tetramic acid moiety (N1’–C6’) that is subject to both rotameric and tautomeric equilibria. As a polyketide, AsA bears hydroxyl groups at several unexpected positions (C8, C28, C30, C34, and C36), but this unusual oxidation pattern can be explained by the incorporation of five glycolic acid                                                                                                                 (11) Sakuda, S. Mycotoxins 2010, 60, 79–86. (12) Okamoto, S.; Sakurada, M.; Kubo, Y.; Tsuji, G.; Fujii, I.; Ebizuka, Y.; Ono, M.; Nagasawa, H.; Sakuda, S. Microbiology 2001, 147, 2623–2628. (13) (a) Kondo, T.; Sakurada, M.; Okamoto, S.; Ono, M.; Tsukigi, H.; Suzuki, A.; Nagasawa, H.; Sakuda, S. J. Antibiotics 2001, 54, 650–657; (b) Sakuda, S. Mycotoxins 2002, 52, 153–159; (c) Sakuda, S.; Kondo, T.; Yoshinari, T.; Nagasawa, H. Mycotoxins 2003, Suppl. 3, 99–105; (d) Yoshinari, T.; Akiyama, T.; Nakamura, K.; Kondo, T.; Takahashi, Y.; Muraoka, Y.; Nonomura, Y.; Nagasawa, H.; Sakuda, S. Microbiology 2007, 153, 2774–2780. (14) Yoshinari, T.; Noda, Y.; Yoda, K.; Sezaki, H.; Nagasawa, H.; Sakuda, S. J. Antibiotics 2010, 63, 309–314.   4 subunits during its biosynthesis.15 Sakuda and coworkers first reported preliminary structural information for AsA in concert with its isolation.8a They used a combination of spectroscopic and degradation experiments to elucidate its molecular formula, structural connectivity, and relative stereochemistry in the C33–C37 lactol region. The same group later assigned the complete relative and absolute stereochemistry of AsA as represented by structure 3 (Figure 1.3).16 They ultimately corrected the configuration of six stereogenic centers (C8, C9 and C28–C31), which will be discussed in due course. OH O Me N Me 2' OH 3 HO HO HO HO HO HO HO HO HO HO HO HO HO 8 9 15 19 23 27 28 29 30 31 35 OH OH OH 39 O Me Me Me OH Me Me Me Me 3 Me OH OH H O C9H19 Figure 1.3. Initial structural assignment of aflastatin A (AsA). The initial stereochemical assignment of AsA (3) relied upon its chemical degradation and spectroscopic analyses of the resultant fragments (Scheme 1.1). The absolute configurations of the smallest degradation fragments were determined as follows: N-methylD-alanine (6) by Marfey’s method, β-hydroxyacid 11 by comparison of its optical rotation data to literature value, and both dibenzoate 7 and tribenzoate 10 by comparison of their respective circular dichroism spectra and optical rotation values to data obtained from authentic samples. The relative stereochemistry of the C9–C27 and C3–C48 degradation                                                                                                                 (15) Ono, M.; Sakuda, S.; Ikeda, H.; Furihata, K.; Nakayama, J.; Suzuki, A.; Isogai, A. J. Antibiotics 1998, 51, 1019–1028. (16) Ikeda, H.; Matsumori, N.; Ono, M.; Suzuki, A.; Isogai, A.; Nagasawa, H.; Sakuda, S. J. Org. Chem. 2000, 65, 438–444.   5 fragments 9 and 8, respectively, was elucidated by J-based configuration analysis17 and partly supplemented with ROE correlation data. The absolute and relative configurations of the degradation fragments were then connected to provide a complete stereochemical depiction of AsA. Scheme 1.1. Degradation of aflastatin A (4). OH O Me N Me O Me N Me 2' 2' OH 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 35 OH OH OH 39 O Me Me Me a OH Me Me Me Me Me 4 OH OH H n–r O C9H19 s OH BzO 3 7 O 33 OH 39 OH k–m BzO 10 O b–c Me 5 Me Me d–f OBz g–j H OBz HO C9H19 11 OH OH OH OH OH OH OH OH BzO 3 7 Me H N O 5' HO 9 15 21 27 OH OH Me 7 Me Me Me Me Me Me Me 6 9 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH OH 39 Me Me OH Me Me Me Me Me 8 OH OH H O C9H19 Reagents and conditions: (a) NaIO4; NaBH4; (b) NaIO4; (c) HCl (aq.); (d) O3; Me2S; (e) LiAlH4; (f) BzCN, nBu3N; (g) HCl, MeOH; (h) O3; NaBH4; (i) Ac2O, py, DMAP; (j) NaOMe; Dowex-50W (H+); (k) NaIO4; NaBH4; (l) Ac2O, py, DMAP; (m) NaOMe; (n) HCl, MeOH; (o) NaIO4; (p) NaBH4; (q) HCl (aq.); (r) BzCl, py, DMAP; (s) NaIO4. The relative stereochemistry of C9–C27 degradation fragment 9 was reinforced by [13C]acetonide analysis,18 and its absolute configuration elucidated by Mosher ester analysis19 (Scheme 1.2).20 First, pentaacetonide 12 and tetraacetonide 14 were synthesized and analyzed                                                                                                                 (17) Matsumori, N.; Kaneno, D.; Murata, M.; Nakamura, H.; Tachibana, K. J. Org. Chem. 1999, 64, 866–876. (18) Rychnovsky, S.D.; Rogers, B.N.; Richardson, T.I. Acc. Chem. Res. 1998, 31, 9–17. (19) Dale, J.A.; Mosher, H.S. J. Am. Chem. Soc. 1973, 95, 512–519. (20) Sakuda, S.; Ikeda, H.; Nakamura, T.; Nagasawa, H. Biosci. Biotechnol. Biochem. 2004, 68, 407–412.   6 to establish 1,3-syn diol relationships across the entire C9–C27 region. Second, the MTPA esters of carbinol 13 were prepared to determine the absolute configuration at C13. Taken together, these derivations provided additional support for the initial absolute configuration assignment of C3–C48 degradation fragment 8, and therefore AsA. Scheme 1.2. Derivitization of AsA C9–C27 degradation fragment 9. Me Me OH OH OH OH OH OH OH OH OH OH 9 15 21 27 Me Me O O 15 Me Me O O Me Me O 21 Me Me O O 27 a O 9 O O Me Me Me 9 Me Me b–c Me Me Me Me Me 12 Me Me O 9 Me Me OH O 13 15 Me Me O O 21 Me Me O O OTr 27 Me Me OTr O 9 Me Me O 15 Me Me O O 21 Me Me O O OTr 27 O O O O Me Me Me Me Me 13 Me Me Me Me Me 14 Reagents and conditions: (a) 2,2-dimethoxypropane, CSA, acetone, rt; Et3N; (b) TrCl, py, DMAP, MeCN, rt; (c) Me2C(OMe)2, p-TsOH, DMF, rt; Et3N. IV. Stereochemical Revision Aflastatin A attracted the attention of the Kishi group during their development of a universal NMR database as a tool for the stereochemical assignment of acyclic regions of natural products.21 The structural array of contiguous carbinols seen in the C27–C31 region of AsA was particularly suited for comparison with their library of 1,2,3,4,5-pentaols. Kishi and coworkers observed that each pentaol diastereomer exhibited a distinct spectroscopic profile. Specifically, comparison of their spin-coupling profiles to the reported data (Figure 1.4A) compelled them to suggest that the relative stereochemistry in the C27–C31 pentaol region of AsA degradation fragment 8 be revised from syn/syn/syn/syn (Figure 1.4B) to anti/syn/syn/syn (Figure 1.4C).                                                                                                                 (21) (a) Kobayashi, Y.; Tan, C.-H.; Kishi, Y. Helv. Chim. Acta 2000, 83, 2562–2571; (b) Higashibayashi, S.; Czechtizky, W.; Kobayashi, Y.; Kishi, Y. J. Am. Chem. Soc. 2003, 125, 14379–14393.   7 A R OH OH OH OH 27 31 R H R B R OH OH OH 27 31 C R OH OH OH 27 31 R R OH OH 3J OH OH syn syn syn syn 10 8 (Hz) (Hz) 6 4 2 0 (in methanol-d4) OH OH syn syn syn anti 10 8 6 4 2 0 (in methanol-d4) (in methanol-d4) anti syn syn syn Bond C27–C28 C28–C29 C29–C30 C30–C31 H,H (Hz) 3J (in pyridine-d5) Figure 1.4. Spin-coupling constant comparison of the C27–C31 pentaol region of AsA degradation fragment 8 (A) to Kishi's database pentaols (B,C). Somewhat concurrently, Sakuda and coworkers deciphered the structure of blasticidin A (BcA). 22 As with AsA, they used a combination of spectroscopic and degradation experiments to elucidate its relative and absolute stereochemistry. Unlike AsA, however, they took greater caution in assigning stereochemistry to the C8–C9 diol and C25–C29 pentaol regions, as purposefully left ambiguous in structure 15 (Scheme 1.3). Scheme 1.3. Degradation of blasticidin A (15) to C3–C47 fragment 16. OH O Me N 2' OH 3 HO HO HO HO HO HO HO HO HO HO HO HO 8 9 15 19 25 26 27 28 29 3J 7.5 3.0 5.0 3.0 H,H H,H 33 OH OH OH 37 O Me Me a–d Me OH Me Me Me 15 OH OH H O C10H21 OH HO HO HO HO HO HO HO HO HO HO HO HO 33 OH OH OMe 37 HO 3 7 11 15 19 25 29 Me Me OH Me Me Me 16 OH OH H O C10H21 Reagents and conditions: (a) HCl, MeOH; (b) O3; NaBH4; (c) Ac2O, py, DMAP; (d) NaOMe; Dowex-50W (H+). Sakuda and coworkers relied on BcA C3–C47 degradation fragment 16 to determine                                                                                                                 (22) Sakuda, S.; Ikeda, H.; Nakamura, T.; Kawachi, R.; Kondo, T.; Ono, M.; Sakurada, M.; Inagaki, H.; Ito, R.; Nagasawa, H. J. Antibiotics 2000, 53, 1378–1384.   8 the absolute configuration of these positions.23 They used J-based configuration analysis17 in combination with the NMR database method21 to assign the relative configurations from C23– C25 as syn, and C25–C29 as anti/syn/syn/syn. Less expected was that they assigned the absolute configurations of C8 and C9 to be opposite those proposed for AsA. During their analysis, they discovered that in the C8–C9 diol region, the spin-coupling profile of BcA degradation fragment 16 (Figure 1.5A) was very similar to that of AsA fragment 8. Such spectral similarity allowed them to correct a coupling constant value (3JH-9,H-10) attributed previously to AsA fragment 8 (Figure 1.5B), and prompted them to revise their previous assignments for C8 and C9 in AsA. Ultimately, Sakuda and coworkers revised the configuration of six stereogenic centers (C8, C9 and C28–C31) in AsA to match the corresponding stereocenters in BcA. A 8 OH R 9 B R 8 OH R 9 R revision R OH 8 9 R OH Me syn/syn BcA (2007) Bond C8–C9 C9–C10 3J H,H (Hz) OH Me syn/anti AsA (2000) Bond C8–C9 C9–C10 3J H,H (Hz) OH Me syn/syn AsA (2007) Bond correction C8–C9 C9–C10 3J H,H (Hz) 4.2 4.2 4.0 8.0 4.0 4.0 (in pyridine-d5) (in pyridine-d5) (in pyridine-d5) Figure 1.5. Stereochemical assignment of the C8–C9 diol region of BcA degradation fragment 16 (A) and revision of AsA fragment 8 (B). To support their assignment of the C8–C11 region of BcA (and reassignment of AsA), Sakuda and coworkers synthesized four model diastereomers 17a–d (Figure 1.6A).23 Among the models, only the coupling constant values observed for syn/syn diastereomer 17a and the C8–C10 region of BcA degradation fragment 16 were comparable.                                                                                                                 (23) (a) Sakuda, S.; Matsumori, N.; Furihata, K.; Nagasawa, H. Tetrahedron Lett. 2007, 48, 2527–2531; (b) Sakuda, S.; Yoshinari, T.; Nakamura, K.; Akiyama, T.; Takahashi, Y.; Muraoka, Y.; Nonomura, Y.; Nagasawa, H. Mycotoxins 2006, Suppl. 4, 135–140.   9 A 8 OH OH HO 9 OH OH OH 8 OH OH OH (ent) 8 OH OH OH (ent) 8 HO 9 HO 9 HO 9 OH OH Me 17a syn/syn B 8 OH Me 17b syn/anti OH OH OH OH Me 17c anti/syn OH Me 17d anti/anti OH OH OH 8 15 BnO 3 9 OH BnO 3 9 15 OH Me Me OH Me 18a syn/syn Me Me Me Me OH Me 18b syn/anti Me Me OH OH OH 8 8 9 15 OH OH OH OH BnO 3 9 15 BnO 3 OH Me Me OH Me 18c anti/syn Me Me Me Me OH Me 18d anti/anti Me Me Figure 1.6. Sakuda’s (A) and Evans’ (B) models for the C8–C9 diol region of AsA and BcA. Nevertheless, the NMR databases suggest that interactions between structural motifs that are two (but potentially four) carbons away are significant.21 Because our group had been actively pursuing the synthesis of AsA since its initial stereochemical assignment, we desired stronger evidence for the reassignment of C8 and C9 and synthesized the corresponding C3– C15 model diastereomers 18a–d (Figure 1.6B).24 The syn/syn diastereomer (18a) provided not only the closest spectral match, but also assurance that redirecting future synthesis efforts toward revised structures 1 and 19 was appropriate (Figure 1.7). OH O Me N Me 2' OH 3 HO HO HO HO HO HO HO HO HO HO HO HO HO 8 9 15 19 23 27 28 29 30 31 35 OH OH OH 39 O Me Me Me OH Me Me Me Me 1 Me OH OH H O C9H19 OH HO HO HO HO HO HO HO HO HO HO HO HO HO 8 28 9 15 19 23 27 29 30 31 35 OH OH OH 39 HO 3 Me Me OH Me Me Me Me 19 Me OH OH H O C9H19 Figure 1.7. Revised structural assignment of AsA (1) and C3–C48 degradation fragment 19.                                                                                                                 (24) Young, J.M. Studies Toward the Synthesis of Aflastatin A. Ph.D. Thesis, Harvard University, 2008.   10 V. Synthesis Achievements Made Prior to the Stereochemical Revision The Evans group has a long-standing interest in the use of aldol reactions for the construction of polyacetate and polypropionate natural products. We selected aflastatin A (3) as a synthesis target due to the challenges posed by its densely oxygenated structure. We were attracted by the opportunity to develop aldol chemistry for the construction of natural products containing contiguous polyols. Despite uncertainty surrounding the initial stereochemical assignment, our laboratory made enduring advances toward the synthesis of AsA prior to the stereochemical revision. These include the developments of: (1) an antiFelkin-selective C35–C36 oxygenated aldol reaction, (2) a Felkin-selective C18–C19 anti aldol reaction and its application to the synthesis of C9–C27 degradation fragment 9, and (3) a Felkin-selective C15–C16 Mukaiyama aldol reaction. A. The C35–C36 Oxygenated Aldol Reaction25 The C33–C37 lactol region of AsA presented us the opportunity to investigate diastereoselective construction of the C33–C36 anti/syn/anti tetraol by aldol reaction of an oxygenated enolate.26 Concerns over controlling enolate geometry, enolization regioselectivity, and aldehyde facial selectivity were abated by the discovery of a highly selective C35–C36 oxygenated aldol reaction (Scheme 1.4). We observed exclusive formation of desired anti/syn/anti aldol adduct 23 by linking together the α- and β-oxygens of model aldehyde 20 with an acetonide protecting group. We propose that anti-Felkin addition of the more reactive (E) enolate27 of ketone 21 to this aldehyde is favored and proceeds via Zimmerman-Traxler28                                                                                                                 (25) This section represents the culminative work of Drs. Frank Glorius, Jing Zhang, and Jason D. Burch. (26) (a) Glorius, F. Development of α-Oxygenated Aldol Methodology and Progress Towards the Synthesis of Aflastatin A. Postdoctoral Report, Harvard University, 2001; (b) Evans, D.A.; Glorius, F.; Burch, J.D. Org. Lett. 2005, 7, 3331–3335. (27) Evans, D.A.; Nelson, J.V.; Vogel, E.; Taber, T.R. J. Am. Chem. Soc. 1981, 103, 3099–3111.   11 transition state 22. By contrast, we anticipate that the Felkin rotamer of aldehyde 20 destabilizes transition state 24 by introducing nonbonding interactions between the aldehyde side chain and the incoming enolate nucleophile. Scheme 1.4. The C35–C36 oxygenated aldol reaction. H O TBSO Me O Me 20 O OTBS 39 H O 35 R R O O Cy B Cy TBSO H 1. Cy2BCl (1.1 equiv.) Me2EtN (2.0 equiv.) pentane, 0°C 2. aldehyde (0.5 equiv.) –78 °C to –20 °C 86%, dr > 95:05 H TBSO Me Me O O Me O Me OH O 36 35 OTBS 39 35 C9H19 36 O OTBS H anti-Felkin TS 22 O O O H 23 anti/syn/anti H R H TBSO Felkin TS 24 H Me Me O B Cy Cy O TBSO Me O Me OH O 36 35 39 C9H19 OTBS C9H19 OTBS 21 35 36 OTBS R 25 anti/anti/anti Ultimately, we determined that aldol diastereoselectivity was strongly dependent upon protecting group identity. As applied to the synthesis of AsA, installation of an acetonide protecting group at C33/C34 would be essential for anti-Felkin-selective C35–C36 bond formation. Upon satisfying this requirement, we successfully applied the oxygenated aldol reaction to the syntheses of AsA lactol region subunits 27 (eq 1)29 and 29 (eq 2).26b,30 Me Me O O 31 Me Me O O 35 ketone 21, Cy2BCl, Me2NEt H pentane 85%, dr > 95:05 O O 31 O OH O 36 35 OTBS 39 C9H19 (1) Me O Me 26 Me O Me 27 OTBS                                                                                                                                                                                                                                                                                                                                                           (28) Zimmerman, H.E.; Traxler, M.D. J. Am. Chem. Soc. 1957, 79, 1920–1923. (29) Zhang, J. Studies Toward the Total Synthesis of (–)-Aflastatin A. Postdoctoral Report, Harvard University, 2003. (30) Burch, J.D. Complex Aldol Reactions for Polyketide Synthesis: I. Total Synthesis of Callipeltoside A. II. Synthesis of the C27–C48 Subunit of Aflastatin A. Ph.D. Thesis, Harvard University, 2005.   12 TBSO BzO 27 O O 35 ketone 21, Cy2BCl, Me2NEt H pentane 73%, dr > 95:05 O TBSO BzO 27 31 O OH O 36 35 OTBS 39 O BzO Me O Me Me Me 28 O 31 C9H19 (2) O BzO Me O Me Me Me 29 OTBS Recently, Ramana and coworkers reported an alternative approach to constructing the AsA lactol region. 31 Their syntheses featured the palladium-mediated 6-endo-dig cycloisomerization of alkynones directly obtained from the oxidation of alkynols 30 and 33 (Scheme 1.5). They then installed the requisite stereochemistry at C33 and C34 via faceselective hydroboration of intermediate dihydropyrans 31 and 34. Their efforts ultimately led to the construction of lactol methyl ethers 32 and 35, respectively. Scheme 1.5. Ramana’s syntheses of the AsA lactol region. OBn OBn 31 35 OBn OBn OBn 39 OBn OBn OBn 39 a,b 54%, 2 steps OBn 31 35 c,d 65%, 2 steps BnO AcO 31 35 OBn OBn 39 HO 30 C9H19 O OMe 31 C9H19 H O OMe 32 C9H19 OBn BnO O Me Me O 27 OBn OBn OBn a,b 53%, 2 steps R OBn 31 35 OBn OBn OBn c,d 61%, 2 steps AcO BnO R 31 35 OBn 31 35 OBn OBn O 33 HO O 34 OMe O H OMe 35 Reagents and conditions: (a) IBX, EtOAc, reflux; (b) Pd(OAc)2, MeOH, rt, 54% (31, 2 steps), 53% (34, 2 steps); (c) BH3•Me2S, THF, 0 °C; H2O2, NaOH (aq.), rt; (d) Ac2O, py, CH2Cl2, rt, 65% (32, 2 steps), 61% (35, 2 steps). B. The C18–C19 Aldol Reaction and Synthesis of the C9–C27 Degradation Fragment32 Soon after Kishi and coworkers questioned the initial stereochemical assignment of AsA,21b the Evans group prioritized confirmation of the relative and absolute stereochemistry of C9–C27 degradation fragment 9 by chemical synthesis. Our strategy was based on the                                                                                                                 (31) (a) Narute, S.B.; Kiran, N.C.; Ramana, C.V. Org. Biomol. Chem. 2011, 9, 5469–5475; (b) Narute, S.B.; Ramana, C.V. Tetrahedron 2013, 69, 1830–1840. (32) This section represents the culminative work of Drs. William C. Trenkle and Jing Zhang.   13 Felkin-selective anti aldol addition of ethyl ketone 37 to α,β-syn-aldehyde 36 (Scheme 1.6).33 Despite the non-reinforcing relationship between vicinal substituents on the aldehyde,34 Felkin adduct 39 is still formed with high diastereoselection due to the inherent Felkin bias of the preformed (E) enolate.33b As seen in transition state 40, formation of undesired anti-Felkin product 41 is disfavored due to a syn pentane interaction that develops during C–C bond formation. Scheme 1.6. Precedent for the C18–C19 anti aldol reaction. 37 Me non-reinforcing O Me Felkin Me TS 38 H iPr H Me H via (E) enolate iPr syn OTBS O O B L L Me O 18 OH OTBS 19 iPr Me Me Me Me O H 19 OTBS iPr Me 36 Cy2BCl, Et3N 79%, dr = 94:06 39 Felkin/1,3-syn anti iPr Me Me H OP H iPr H O O H L B L Me O 18 OH OTBS 19 iPr Me Me Me anti-Felkin TS 40 41 anti-Felkin/1,3-anti Our group then successfully applied this anti aldol reaction to the synthesis of AsA C9–C27 degradation fragment 9.29,35 Addition of the (E) enolate of ethyl ketone 42 to aldehyde 43 provided the desired anti adduct 44 and its C18 epimer in moderate yield and excellent Felkin diastereoselectivity (Scheme 1.7). The undesired diastereomer arose from unfortunate epimerization of the major product under the reaction conditions. We then converted aldol adduct 44 to degradation fragment 9 and its derivative peracetate, compared their analytical data with authentic samples,15,16 and concluded that Sakuda and coworkers had                                                                                                                 (33) (a) Dart, M.J. Diastereoselective Aldol Addition Reactions. Ph.D. Thesis, Harvard University, 1995; (b) Evans, D.A.; Dart, M.J.; Duffy, J.L.; Rieger, D.L. J. Am. Chem. Soc. 1995, 117, 9073–9074. (34) Evans, D.A.; Dart, M.J.; Duffy, J.L.; Yang, M.G. J. Am. Chem. Soc. 1996, 118, 4322–4343. (35) Evans, D.A.; Trenkle, W.C.; Zhang, J.; Burch, J.D. Org. Lett. 2005, 7, 3335–3338.   14 correctly assigned the relative and absolute stereochemistry of the AsA C9–C27 degradation fragment 9. Scheme 1.7. Synthesis of AsA C9–C27 degradation fragment 9. Me Me PMBO Ph 42, R = TBS 9 Me Me OR O 15 O O O H Me OR O 21 O 27 OPMB OTIPS Me Me Me Me 43, R = TBS Cy2BCl, Et3N, Et2O –78 °C to –20 °C Me Me PMBO Ph 9 49%, dr = 82:18 (+ 39% SM) syn Me Me O OPMB OTIPS O O OR O 18 15 OH OR O 19 23 27 Me Me Me Me Me 44, R = TBS 31%, 7 steps OH OH OH OH OH OH OH OH HO 9 15 21 27 OH Me Me Me Me Me 9 More recently, Robles and McDonald reported an alternative approach to constructing the pentaacetonide derivative of AsA degradation fragment 9. 36 Their strategy for the synthesis of the C9–C27 polyketide region relied on iterative additions of lithium acetylides to epoxides, followed by regio- and stereoselective functionalization of the resultant internal alkynes (Scheme 1.8). Their efforts resulted in the modular synthesis of pentaacetonide 51, which matched original spectral data provided by the isolation group.                                                                                                                 (36) (a) Robles, O.; McDonald, F.E. Org. Lett. 2008, 10, 1811–1814; (b) Robles-Resendiz, O. Modular Synthesis of Polyketide Natural Products: Synthesis of the C9–C27 Degradation Product of Aflastatin A and Total Synthesis of Fostriecin. Ph.D. Thesis, Emory University, 2009.   15 Scheme 1.8. McDonald’s synthesis of AsA C9–C27 degradation fragment 51. Me Me PMBO 19 Me Me n-BuLi, BF3•OEt2 73% TIPS Me Me O PMBO 19 O 23 O O 27 O 27 OH 22 23 48 63%, 6 steps TIPS 45 Me H 46 Me Me Me O O 27 47 Me Me O 9 O OTMS 13 O H PMBO 19 O O 23 n-BuLi, BF3•OEt2 86% Me 49 Me Me Me 48 Me Me O O Me Me O O 15 Me Me Me Me O 9 Me Me O O 27 Me Me O O Me Me O 21 Me Me O O 27 PMBO OR OH 16 13 17 O 21 O O O Me Me Me Me 50, R = TMS 20%, 8 steps 9 Me Me Me Me Me 51 C. The C15–C16 Mukaiyama Aldol Reaction37 The C18–C19 aldol reaction was key to providing us access to degradation fragment 9 and verification of its structural assignment. Nevertheless, we desired a more convergent fragment coupling for the synthesis of AsA, and found recourse in a Felkin-selective C15– C16 Mukaiyama aldol reaction. Our approach was based on the trityl-catalyzed38 addition of enolsilane 53 to syn aldehyde 52 to selectively form Felkin aldol adduct 54 despite nonreinforcing α,β-stereoinduction (Scheme 1.9).34 We propose that sterically demanding Lewis acids such as the trityl cation increase the influence of the α-methyl stereocenter by promoting addition through antiperiplanar transition state 56, 39 perhaps with an altered nucleophile trajectory.40                                                                                                                 (37) This section represents the culminative work of Drs. William C. Trenkle, Jing Zhang, and Joseph M. Young. (38) (a) Mukaiyama, T.; Kobayashi, S.; Murakami, M. Chem. Lett. 1984, 13, 1759–1762; (b) Denmark, S.E.; Chen, C.-T. Tetrahedron Lett. 1994, 35, 4327–4330. (39) Heathcock, C.H.; Walker, M.A. J. Org. Chem. 1991, 56, 5747–5750 and references therein. (40) Heathcock, C.H.; Flippin, L.A. J. Am. Chem. Soc. 1983, 105, 1667–1668.   16 Scheme 1.9. Precedent for the C15–C16 Mukaiyama aldol reaction. non-reinforcing PMBO iPr 13 O H Me 53 OTMS Me Lewis acid, CH2Cl2 BF3•OEt2 Ph3CClO4 syn anti PMBO iPr OH O 16 15 PMBO Me iPr OH O 16 15 PMBO antiperiplanar TS 56 Me H Me C O Ph Ph Ph H H C H iPr H OTMS C Me Me 54 Felkin/1,3-syn 17 89 Me 55 anti-Felkin/1,3-anti 83 11 52 : : Our initial attempts at the trityl-catalyzed C15–C16 Mukaiyama aldol addition of enolsilane 58 to aldehyde 57 were met with decomposition (eq 3).41 We later identified that the likely origin of decomposition was the C27 PMB ether of enolsilane 58.24 Since the trityl cation is known to oxidize unhindered PMB ethers via hydride abstraction,42 new aldol coupling partners were designed to exclude this protecting group. Ultimately, addition of enolsilane 61 to aldehyde 60 provided the desired Felkin aldol adduct 62 as a single C15 diastereomer (eq 4). This result demonstrated that construction of the AsA C3–C26 polyketide region could be achieved with greater convergence and efficiency. Me Me PMBO TIPSO 9 Me Me O H Me Ph3CPF6, CH2Cl2 TMSO O 19 Me Me O 23 O O 13 O O 27 OPMB OTIPS 57 Me Me Me Me 58 (3) Me Me O 23 decomposition Me Me Me Me PMBO TIPSO O 11 O OH O 16 15 O 19 O O 27 OPMB OTIPS Me Me Me Me Me 59                                                                                                                 (41) Trenkle, W.C. Progress Towards the Synthesis of Aflastatin A. Postdoctoral Report, Harvard University, 2002. (42) For examples, see: (a) Fujioka, H.; Sawama, Y.; Kotoku, N.; Ohnaka, T.; Okitsu, T.; Murata, N.; Kubo, O.; Li, R.; Kita, Y. Chem. Eur. J. 2007, 13, 10225–10238; (b) Yadav, V.K.; Agrawal, D. Chem. Commun. 2007, 5232–5234; (c) Doddi, V.R.; Kokatla, H.P.; Pal, A.P.J.; Basak, R.K.; Vankar, Y.D. Eur. J. Org. Chem. 2008, 5731–5739.   17 Me Me 60, R = TBS BnO 3 7 Me Me O 15 OR O 11 O TMSO H O 19 O OR 23 Me Me Me OR Me Me Me Me Me 61, R = TBS (4) Ph3CPF6, CH2Cl2, –78 °C 62, R = TBS BnO 3 7 81%, dr > 95:05 Me Me O 19 Me Me syn OR O 11 O OH O 16 15 O OR 23 Me Me Me OR Me Me Me Me Me Shortly after our discovery of a competent C15–C16 Mukaiyama aldol reaction, Sakuda and coworkers revised the initial stereochemical assignment of AsA.23 In response, we prioritized the synthesis of C3–C48 degradation fragment 19 as a means of confirming the relative and absolute stereochemistry of AsA. Although the structural reassignment required us to revisit our synthesis plans, we were confident in the structural identity of the C9–C27 region, and could use both the C35–C36 oxygenated aldol and C15–C16 Mukaiyama aldol reactions in our future synthesis efforts. Our synthesis of AsA C3–C48 degradation fragment 19 will be discussed in Chapter 2.   18 Chapter 2 Synthesis of the C3–C48 Degradation Fragment of Aflastatin A I. Synthesis Plans Involving C28–C29 Bond Formation The structure of aflastatin A (AsA) presented our group the opportunity to develop aldol chemistry for the construction of its densely oxygenated C27–C31 and C33–C37 regions. In addition to developing an anti-Felkin-selective C35–C36 oxygenated aldol reaction, our group targeted the C27–C31 pentaol as a site for major fragment coupling. Initially, our retrosynthesis plan hinged on the development of a C28–C29 oxygenated aldol reaction, but was later transformed by the discovery of a C26–C27 chelate-controlled aldol addition. A. Initial Structure of Aflastatin A1 Our first retrosynthesis plan for the initial structure of AsA (1) involved disconnection at C2–C3 to produce tetramic acid derivative 2 (Scheme 2.1).2 We planned to install the tetramic acid by a Horner-Wadsworth-Emmons reaction3 as late in the synthesis as possible                                                                                                                 (1) (2) (3) This section represents the culminative work of Dr. William C. Trenkle and Dr. Jing Zhang. Trenkle, W.C. Progress Towards the Synthesis of Aflastatin A. Postdoctoral Report, Harvard University, 2002. (a) Horner, L.; Hoffman, H.; Wippel, H.G.; Klahre, G. Chem. Ber. 1959, 92, 2499–2505; (b) Wadsworth, W.S., Jr.; Emmons, W.D. J. Am. Chem. Soc. 1961, 83, 1733–1738.   19 because we expected that the C5’ stereocenter would be readily epimerizable. 4 Having removed this base-sensitive moiety, we next focused on an aldol-based assemblage of the C3– C48 polyketide backbone. For the major fragment coupling, we decided to investigate the double-stereodifferentiating syn aldol addition of ketone 4 to dialdehyde synthon 3 as a means of forming the C28–C29 bond. Scheme 2.1. First retrosynthesis plan for structure 1. OH O Me N Me 2' OH 2 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 28 11 15 19 23 29 35 OH OH OH 39 O Me Me Me OH Me Me Me 1 Me Me OH OH oxygenated aldol addition HO HO HO 31 H O C9H19 olefination OH O 2 P(OR) 2 O 2 H 3 7 11 OH 35 O Me N Me 5' OH OH OH 39 Me O HO HO HO HO HO HO HO HO HO HO 15 19 23 27 O H O H O 4 C9H19 Me Me OH Me Me Me Me Me 3 At the time, double-stereodifferentiating syn aldol additions of α’-oxygenated ketones to α-oxygenated aldehydes were undocumented. Although syn aldol reactions of chiral α’oxygenated ketones with achiral aldehydes were known to favor the formation of 1,3-syn products,5 the effect of introducing a second stereocontrol element at the aldehyde’s αposition was not well understood. As per the polar Felkin-Anh model,6 we predicted that the aldehyde α-alkoxy stereocenter at C27 would establish a matched relationship with the C31                                                                                                                 (4) (5) Royles, B.J.L. Chem. Rev. 1995, 95, 1981–2001 and references therein. (a) Masamune, S.; Choy, W.; Kerdesky, F.A.J.; Imperiali, B. J. Am. Chem. Soc. 1981, 103, 1566–1568; (b) Marco, J.A.; Carda, M.; Falomir, E.; Palomo, C.; Oiarbide, M.; Ortiz, J.A.; Linden, A. Tetrahedron Lett. 1999, 40, 1065–1068; (c) Carda, M.; Murga, J.; Falomir, E.; González, F.; Marco, J.A. Tetrahedron 2000, 56, 677–683. (a) Chérest, M.; Felkin, H.; Prudent, N. Tetrahedron Lett. 1968, 9, 2199–2204; (b) Anh, N.T.; Eisenstein, O. Nouv. J. Chim. 1977, 1, 61–70; (c) Anh, N.T. Top. Curr. Chem. 1980, 88, 145–162. (6)   20 stereocenter of (Z) enolate 6. Aldol reaction via transition state 7 would effect diastereoselective C28–C29 bond formation, and thereby lead to the desired syn/syn/syn adduct 8 (Scheme 2.2). We envisioned that transition state 7 would be favored since it features hyperconjugative stabilization of the forming C28–C29 bond, dipole-dipole minimization between the C31 α'-alkoxy stereocenter and the transforming enolate, and minimization of nonbonding interactions between the reacting partners. Scheme 2.2. Proposed C28–C29 oxygenated aldol reaction. H OPMB H O 5 OR' (Z) R'O R H dipole minimization 31 27 polar Felkin-Anh TS 7 OPMB O O M H R L R 28 1,3-syn PMBO R'O R'O L 29 R 27 R'O 31 R R OML2 6, R' = TBS or Bn H OH O 8, R' = TBS or Bn syn/syn/syn R'O Model studies of the C28–C29 oxygenated aldol reaction were then performed to evaluate our stereochemical prediction.7 Our desires to control enolization regioselectivity and produce geometrically-defined (Z) enolates of general structure 6 were satisfied by reports of chlorodicyclohexylborane-mediated syn aldol additions of ketones bearing both chelating alkyl and bulky silyl protecting groups at their α’-oxygen position (C31).8 Disappointingly, reaction of ketone 9 with aldehyde 10 under these conditions proceeded poorly in both yield and diastereoselectivity (eq 1). Boron-mediated enolization of advanced C29–C48 ketone 12 was also attempted, but reactivity – and similarly poor levels of diastereoselection – was observed only upon formation of the corresponding lithium enolates (eq 2).                                                                                                                 (7) (8) Zhang, J. Studies Toward the Total Synthesis of (–)-Aflastatin A. Postdoctoral Report, Harvard University, 2003. Murga, J.; Falomir, E.; Carda, M.; González, Marco, J.A. Org. Lett. 2001, 3, 901–904.   21 Me Me OBn OBn OBn 31 35 Cy2BCl, Et3N; aldehyde 10 OBn 30%, dr ~ 1:1:1:1 Me Me 10 O 23 O 23 O OR OBn OBn OBn 28 29 35 OBn (1) O 9 OBn OH O 11, R = PMB OBn O 27 OPMB H O Me Me O 23 RO RO RO 31 OTMS OR 35 OR H O OMe 39 LiHMDS, –78 °C; aldehyde 10 40%, dr ~ 1:1:1:1 RO O R'O RO RO 28 29 OTMS OR 35 OR H O 39 C9H19 O OH O OMe C9H19 (2) 12, R = TBS 13, R = TBS, R' = PMB During the course of these studies, related work in the Evans group demonstrated that the modified Cornforth model provides a more accurate description of enolate additions to αalkoxy aldehydes than the polar Felkin-Anh model.9 Shortly thereafter, Marco, Carda and coworkers reported double-stereodifferentiating boron aldol reactions of an erythulosederived α,α’-dioxygenated ketone with both enantiomeric series of α-oxygenated aldehydes 15 (Scheme 2.3).10 Addition of (Z) boron enolate 14 to aldehydes 15 having the same relative stereochemistry required for the C28–C29 aldol reaction produced a complex mixture of aldol adducts 17, thus agreeing with our model studies. Reaction of the same chiral enolate with enantiomeric aldehyde ent-15 established a matched stereorelationship between these reacting partners and resulted in the formation of anti/syn/syn aldol adducts 19 in high yield and excellent diastereoselectivity.                                                                                                                 (9) (a) Evans, D.A.; Siska, S.J.; Cee, V.J. Angew. Chem., Int Ed. 2003, 42, 1761–1765; (b) Siska, S.J. Construction of Polyhydroxylated Stereoarrays Using the Aldol Reaction. Ph.D. Thesis, Harvard University, 2005. (10) (a) Marco, J.A.; Carda, M.; Díaz-Oltra, S.; Murga, J.; Falomir, E.; Roeper, H. J. Org. Chem. 2003, 68, 8577–8582; (b) Díaz-Oltra, S.; Murga, J.; Falomir, E.; Carda, M.; Peris, G.; Marco, J.A. J. Org. Chem. 2005, 70, 8130–8139.   22 Scheme 2.3. Double stereodifferentiating aldol reactions that support the Cornforth model. OR' R 15 Me Me O O TBSO 31 27 H O Cornforth TS 16 O Cy B Cy H O R 27 OTBS OR' H dipole minimization 31 mismatched complex mixture R Me Me OR' OR" O O 28 29 Et2O H H OH O R = Me, BOM R' = TBDPS, Bn R" = TBS anti O H 27 17 OBCy2 14 R = Me, BOM R' = TBDPS, Bn Cornforth TS 18 O Cy B Cy R O Et2O OR' R ent-15 27 OTBS OR' H dipole minimization 31 syn Me Me matched 73–89%, dr > 95:05 R OR' OR" O 28 29 O H O H H OH O 19 anti/syn/syn O B. Revised Structure of Aflastatin A11 Overall, these experiments provided support for the modified Cornforth model in aldol additions of substituted enolates to α-oxygenated aldehydes. As a result, we deemed that proposed transition state 7 (Scheme 2.2) was likely invalid, and realized that relying upon a C28–C29 oxygenated aldol reaction for construction of the initially proposed structure of AsA (1) was untenable. Fortunately, the stereochemical revision of the C27–C31 pentaol region of AsA12 provided us an opportunity to revisit this disconnection as an alternative to the C26– C27 aldol chemistry that will be described in due course. One of our retrosynthesis plans for AsA C3–C48 degradation fragment 2013 involved disconnection at C28–C29 to produce aldehyde 21 and the C31-epimer 22 of the original ketone fragment (Scheme 2.4).14                                                                                                                 (11) The synthesis of C27–C31 pentaol derivative 25 (vide infra) was performed by the author in collaboration with Dr. Joseph M. Young and Dr. Egmont Kattnig. (12) (a) Higashibayashi, S.; Czechtizky, W.; Kobayashi, Y.; Kishi, Y. J. Am. Chem. Soc. 2003, 125, 14379– 14393; (b) Sakuda, S.; Matsumori, N.; Furihata, K.; Nagasawa, H. Tetrahedron Lett. 2007, 48, 2527–2531; (c) Sakuda, S.; Yoshinari, T.; Nakamura, K.; Akiyama, T.; Takahashi, Y.; Muraoka, Y.; Nonomura, Y.; Nagasawa, H. Mycotoxins 2006, Suppl. 4, 135–140. (13) Ikeda, H.; Matsumori, N.; Ono, M.; Suzuki, A.; Isogai, A.; Nagasawa, H.; Sakuda, S. J. Org. Chem. 2000, 65, 438–444. (14) Young, J.M. Studies Toward the Synthesis of Aflastatin A. Ph.D. Thesis, Harvard University, 2008.   23 Scheme 2.4. C28–C29 aldol-based retrosynthesis plan for C3–C48 degradation fragment 20. OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 28 3 7 11 15 19 23 29 35 OH OH OH 39 Me Me OH Me Me Me 20 Me Me OH OH oxygenated aldol addition H O C9H19 OH HO HO HO 35 HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 OH OH OH 39 H O O 31 Me Me OH Me Me Me Me Me H O C9H19 21 22 Synthesis of the AsA C27–C31 anti/syn/syn/syn pentaol region by this doublestereodifferentiating aldol strategy required selection of protecting groups that did not interfere with reactivity or diastereoselectivity. Previous experiments revealed that sterically encumbered ketones (such as 12, eq 2) resist enolization by chlorodicyclohexylborane,7 and that bulky aldehydes display limited reactivity with simple boron enolates.15 We alleviated these concerns by tying back both the C27 and C31 stereocenters as their respective 1,3-syn acetonides. Gratifyingly, the model reaction of the dicyclohexylboron enolate of α-silyloxy ketone 24 with aldehyde 23 produced the desired aldol adduct with high levels of conversion and diastereoselection (eq 3). The intermediate β-hydroxy ketone was subsequently reduced with diisobutylalane16 to afford the desired pentaol derivative 25 in good overall yield. one step from diol (NaIO4) Me Me O O 27 BnO 23 H O 1. Cy2BCl, Et3N, Et2O; dr ≥ 93:07 BnO 23 Me Me O O 28 29 Me Me OR O O 35 23 Me Me TBSO O 31 OBn (3) O (2 equiv.) 35 2. DIBALH, PhMe; 66–71%, 3 steps OH OH 25, R = TBS anti/syn/syn/syn OBn O 24                                                                                                                 (15) Burch, J.D. Complex Aldol Reactions for Polyketide Synthesis: I. Total Synthesis of Callipeltoside A. II. Synthesis of the C27–C48 Subunit of Aflastatin A. Ph.D. Thesis, Harvard University, 2005. (16) Kiyooka, S.; Kuroda, H.; Shimasaki, Y. Tetrahedron Lett. 1986, 27, 3009–3012.   24 This result demonstrated the potential of oxygenated enolate chemistry in constructing the C27–C31 pentaol region of AsA. As a major fragment coupling, however, we noted that the C28–C29 aldol addition was limited by both the relative stoichiometry and protecting group requirements of its reacting partners. We therefore refocused our efforts on the development and implementation of a C26–C27 chelate-controlled aldol addition. II. Synthesis Plans Involving C26–C27 Bond Formation A. Initial Structure of Aflastatin A17 As experimental support for the modified Cornforth model grew, our group began to explore other possibilities for major fragment coupling within the C27–C31 pentaol region. Our second retrosynthesis plan for the initial structure of AsA (1) abandoned the idea of a C28–C29 oxygenated aldol reaction and instead focused on forming the C26–C27 bond by boron-mediated aldol addition of methyl ketone 26 to poly-hydroxylated aldehyde synthon 27 (Scheme 2.5).15 Scheme 2.5. Second retrosynthesis plan for structure 1. OH O Me N Me 2' OH 2 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 26 11 15 19 23 27 35 OH OH OH 39 O Me Me Me OH Me Me Me 1 Me Me OH OH boron-mediated aldol addition HO O HO HO Me H 27 31 H O C9H19 OH 35 O H 3 7 OH OH OH OH OH OH OH OH O 11 15 19 23 OH OH OH 39 Me Me OH Me Me Me Me Me 26 OH OH H O 27 C9H19 The newly proposed disconnection at C26–C27 was borne out of our group's systematic study of methyl ketone aldol additions to α,β-bisoxygenated aldehydes under                                                                                                                 (17) This section represents the culminative work of Drs. Victor J. Cee, Sarah J. Siska, and Jason D. Burch.   25 nonchelating conditions.18 We observed synthetically useful levels of diastereoselectivity for the desired 1,2-syn aldol adducts 30 when enolboranes were added to syn aldehyde 28, in which both α- and β-oxygen substituents were protected as TBS ethers (eq 4). syn OBBN R R = Me, iPr, t-Bu O H TBSO 29 OTBS Me Me CH2Cl2 87–91%, dr ≥ 93:07 R O 26 27 OH OTBS Me Me (4) TBSO 28 29, R = Me, iPr, t-Bu This reaction was then extended to model substrates that possessed the full oxygenation pattern present in the C28–C31 region of AsA. Aldol addition of 9-BBN enolate 30 derived from isobutyl methyl ketone to aldehyde 31 afforded the desired 1,2-syn adduct with slightly diminished diastereoselection (eq 5).15 Notably, the size of the protecting groups on C30 and C31 was minimized (benzoates were selected instead of TBS ethers) to ensure reactivity. syn Me Me 23 OBBN H O 27 OR' OBz 31 enolate 30, –78 °C Ph dr = 85:15 Me Me 23 O 26 OH OR' OBz 27 31 Ph (5) 30 OR OBz 31, R = TES, R' = TBS OR OBz 32, R = TES, R' = TBS To our surprise, reaction of the same enolborane with fully elaborated C27–C48 aldehyde 33 proceeded with inverted diastereoselectivity (eq 6), even though the first point of difference between aldehydes 31 and 33 occurred at C33.15 This experiment showed that formation of the C33–C37 lactol prior to major fragment coupling could have an adverse effect on reaction diastereoselectivity. As a result, future synthesis plans centered upon C26– C27 bond formation as the major fragment coupling would involve additions to the open-                                                                                                                 (18) Evans, D.A.; Cee, V.J.; Siska, S.J. J. Am. Chem. Soc. 2006, 126, 9433–9441.   26 chain form of the C27–C48 lactol region. Lactol formation would then be delayed until a later stage in the synthesis, such as global deprotection. OR RO O R'O BzO H 27 31 35 OR OR' OR 39 enolate 30 dr ~ 1:2 Me Me 23 RO O HO R'O BzO 26 27 31 35 OR' OR 39 OR OBz H O OH C9H19 OR OBz H O OH C9H19 (6) 33, R = TES, R' = TBS 34, R = TES, R' = TBS B. Revised Structure of Aflastatin A19 As before, the stereochemical revision of the C27–C31 pentaol region of AsA provided us an opportunity to modify our major fragment coupling strategy. However, before completing the total synthesis of AsA, we sought to confirm its stereochemical reassignment12 by way of C3–C48 degradation fragment 20.13 We envisioned polyol 20 to arise from the diastereoselective aldol addition of C3–C26 ketone 35 to C27–C48 aldehyde 36 (Scheme 2.6).14,20 Aldehyde 36, possessing both α- and β-oxygenation, offered us the possibility of using chelation control21 to establish the stereocenter at C27 with high diastereoselection. We expected that nucleophilic addition to a six-membered chelate would afford the desired 1,3anti relationship. Since silyl ethers generally disfavor chelation,22,23 we planned to induce chelation between the carbonyl and β-benzyloxy substituent (at C29) by protecting the C28 carbinol as its silyl ether.                                                                                                                 (19) This section represents the culminative work of Drs. Victor J. Cee, and Egmont Kattnig. Dr. Kattnig is credited with the discovery and development of the chelate-controlled/soft enolization-based C26–C27 aldol reaction (vide infra). (20) Kattnig, E. An Aldol Approach Toward Aflastatin A – Synthesis of the C3–C48 Polyol. Postdoctoral Report, Harvard University, 2011. (21) (a) Reetz, M.T. Angew. Chem. 1984, 96, 542–555; Angew. Chem., Int. Ed. 1984, 23, 556–569; (b) Reetz, M.T. Acc. Chem. Res. 1993, 26, 462–468 and references therein. (22) Keck, G.E.; Boden, E.P. Tetrahedron Lett. 1984, 25, 265–268. (23) For exceptions, see: a) Evans, D.A.; Allison, B.D.; Yang, M.G.; Masse, C.E. J. Am. Chem. Soc. 2001, 123, 10840–10852; b) Stanton, G.R.; Kauffman, M.C.; Walsh, P.J. Org. Lett. 2012, 14, 3368–3371 and references therein.   27 Scheme 2.6. C26–C27 aldol-based retrosynthesis plan for C3–C48 degradation fragment 20. HO HO HO HO HO HO HO HO HO HO HO HO HO 26 1,3-anti OH 35 OH OH 39 HO 3 7 11 15 19 23 27 31 Me Me OH Me Me Me Me Me 20 OH OH H O OH C9H19 chelate-controlled aldol addition OH OH OH OH OH OH OH OH O HO 3 7 11 15 19 23 Me 36 O 28 Me Me OH Me Me Me 35 Me Me OBn OH OH OH O 29 31 35 OH 39 H R3SiO C9H19 OH OH OH In developing this strategy, we were encouraged by our earlier systematic study24 of methyl ketone Mukaiyama aldol additions25 to α,β-bisoxygenated aldehydes under chelating conditions.26 For these experiments, magnesium(II) iodide was chosen as the Lewis acid because it was known to chelate heteroatom-substituted aldehydes and promote highly diastereoselective Mukaiyama aldol reactions.27 Gratifyingly, enolsilane additions to syn αsilyloxy, β-alkoxy aldehyde 37 in the presence of freshly prepared MgI2 proceeded in high yield to afford the desired 1,3-anti products 39 as single diastereomers (Scheme 2.7).28 The observed selectivity is consistent with 1,3-chelate model 38, whereby nucleophilic addition to the carbonyl occurs preferentially from the less sterically hindered face of the six-membered chelate. In this model, the two stereocenters of the syn diastereomer are reinforcing, as aldol                                                                                                                 (24) Cee, V.J. I. Asymmetric Induction in Heteroatom-Substituted Aldehydes. II. Total Synthesis of (+)Casuarine. Ph.D. Thesis, Harvard University, 2003. (25) (a) Mukaiyama, T.; Narasaka, K.; Banno, K. Chem. Lett 1973, 1011–1014; (b) Mukaiyama, T.; Banno, K.; Narasaka, K. J. Am. Chem. Soc. 1974, 96, 7503–7509; (c) Mukaiyama, T. Angew. Chem. 2004, 116, 5708– 5733; Angew. Chem., Int. Ed. 2000, 43, 5590–5614. (26) For the analogous study under nonchelating conditions, see: Ref. 18. (27) For an example, see: Corey, E.J.; Li, W.; Reichard, G.A. J. Am. Chem. Soc. 1998, 120, 2330–2336. (28) The stereochemistry of the newly formed stereogenic center was determined by Mosher ester analysis. See: (a) Dale, J.A.; Mosher, H.S. J. Am. Chem. Soc. 1973, 95, 512–519; (b) Hoye, T.R.; Jeffrey, C.S.; Shao, F. Nat. Protoc. 2007, 2, 2451–2458.   28 addition to the Re face of aldehyde 37 is blocked by both the α-silyloxy and β-alkyl substituents.23a Having realized the feasibility of using a chelate-controlled Mukaiyama aldol addition to form the C26–C27 bond, we opted to investigate the coupling of more complex substrates. Scheme 2.7. Precedent for C26–C27 chelate-controlled aldol addition. 1,3-anti OTMS R 25 O 28 H TBSO OPMB Me 29 MgI2, CH2Cl2, 0 °C R 90–93%, dr ≥ 99:01 PMB M O iPr O TBSO H Nu H H 38 O 26 OH OPMB Me 27 29 Me 37 TBSO Me R = Me, iPr, t-Bu 39, R = Me, iPr, t-Bu β-alkoxy chelate 1,3-anti Our model studies began with the further elaboration of aldehyde fragment 37 (eq 7). The influence of additional oxygen-based stereocenters (and therefore protecting groups) at C30 and C31 on the diastereoselectivity of the fragment coupling was unknown. Aldehyde 40 was chosen as a suitable model since it featured the first four stereocenters (C28–C31) present in subunit 36, while maintaining the requisite α-silyloxy and β-alkoxy substituents at C28 and C29, respectively. In an effort to minimize any potential steric effects on aldehyde reactivity, we also protected the neighboring stereocenters (C30 and C31) as benzyl ethers. Addition of the enolsilane derived from 3-methyl-2-butanone to aldehyde 40 in the presence of MgI2 again produced the desired aldol adduct 41 in good yield and excellent diastereoselectivity, but we noted that freshly prepared MgBr2•OEt2 was more efficient at promoting this reaction.29 In either experiment, the remote benzyloxy substituents at C30 and C31 did not                                                                                                                 (29) For another example in which MgBr2•OEt2 was found to be superior to MgI2, see: Evans, D.A.; Kvœrnø, L.; Dunn, T.B.; Beauchemin, A.; Raymer, B.; Mulder, J.A.; Olhava, E.J.; Juhl, M.; Kagechika, K.; Favor, D.A. J. Am. Chem. Soc. 2008, 130, 16295–16309.   29 significantly diminish the 1,3-anti diastereoselectivity of the aldol addition, and ultimately provided us a viable protecting group strategy for the C28–C31 stereotetrad during the key fragment coupling. 1,3-anti OTMS iPr 25 O H 27 TBSO OBn OBn Me 31 MgII salt iPr CH2Cl2, 0 °C MgI2 MgBr2•OEt2 O 26 OH OBn OBn Me 27 31 Me 40 Me 41 (7) OBn TBSO OBn 68%, dr = 93:07 80%, dr = 95:05 Our model studies continued with an investigation into the reactivity of model enolsilane 42 which incorporates the C23 carbinol of ketone fragment 35 protected as its silyl ether (Scheme 2.8). Magnesium-promoted aldol addition of enolsilane 42 to aldehyde 40 proceeded with excellent 1,3-anti diastereoselectivity, but unexpectedly resulted in elimination of the C23 silyloxy substituent to produce enone 44. Formation of this undesired elimination product might be explained by the intermediacy of oxocarbenium ion 43.25 When silylation of the nascent C27 oxyanion is slowed by steric hindrance,30 we propose that this alkoxide may instead abstract a proton from C24, ultimately resulting in departure of the vicinal silyloxy group. Further inspection of our previous reactions (eq 7) revealed the formation of enolsilane 45 prior to workup, presumably via an analogous deprotonation pathway.31 When various attempts to prevent elimination by facilitating silyl transfer or quenching magnesium aldolate 43 in situ were unsuccessful, we found recourse in soft enolization.                                                                                                                 (30) Intermolecular silyl transfer may be operative. For examples, see: Carreira, E.M.; Singer, R.A.; Tetrahedron Lett. 1994, 35, 4323; Denmark, S.E.; Chen, C.-T. Tetrahedron Lett. 1994, 35, 4327. (31) Our group noted the formation of similar byproducts during the synthesis of azaspiracid. See: Dunn, T.B. Synthesis of the C21–C40 Fragment of Azaspiracid-1. Ph.D. Thesis, Harvard University, 2005.   30 Scheme 2.8. Model C26–C27 Mukaiyama aldol reaction. 1,3-anti TBSO BnO 23 OTMS aldehyde 40, MgBr2•OEt2 BnO CH2Cl2, 0 °C 43%, dr = 95:05 R X H 24 26 O 23 OH OBn OBn Me 27 31 Me 42 aldol addition 44 Ln TBSO OBn Mg O OBn R' elimination TBSO 43 TMSO HO BnO BnO Me 27 31 Me Me 45 27 O TMS TBSO Me TBSO BnO Soft enolization32 is a powerful method for generating metal enolates under mild conditions. Our lab has previously demonstrated33 that enolizable carbonyl compounds may be deprotonated by weak trialkylamine bases in the presence of suitable magnesium(II)-based Lewis acids to enable highly efficient C–C bond-forming reactions. Excited by the prospect of maintaining aldehyde facial selectivity while suppressing the formation of undesired enone 44, we imagined assembling polyol 20 by way of a chelate-controlled aldol reaction involving soft enolization with MgBr2•OEt2.34 Albeit promising, the reversible nature of soft enolization with magnesium raised new concerns about enolate regioselectivity, substrate dimerization, and aldehyde epimerization. Fortunately, addition of ketone 46a (1.1 equiv) to aldehyde 47 (1.0 equiv) in the presence of MgBr2•OEt2 (4.0 equiv) and Hünig base (2.0 equiv) produced the desired aldol adduct 49a in modest yield and excellent diastereoselectivity (Scheme                                                                                                                 (32) For the earliest examples of magnesium-based soft enolization, see: (a) Rathke, M.W.; Cowan, P.J.; J. Org. Chem. 1985, 50, 2622–2624; (b) Rathke, M.W.; Nowak, M. J. Org. Chem. 1985, 50, 2624–2626; (c) Tirpak, R.E.; Olsen, R.S.; Rathke, M.W. J. Org. Chem. 1985, 50, 4877–4879; (d) Olsen, R.S.; Fataftah, Z.A.; Rathke, M.W. Synth. Commun. 1986, 16, 1133–1139. (33) Evans, D.A.; Tedrow, J.S.; Shaw, J.T.; Downey, C.W. J. Am. Chem. Soc. 2002, 124, 392–393; (b) Evans, D.A.; Downey, C.W.; Shaw, J.T.; Tedrow, J.S. Org. Lett. 2002, 4, 1127–1130. (34) For previous examples of direct aldol additions involving soft enolization with MgBr2•OEt2, see: (a) Wei, H.-X.; Li, K.; Zhang, Q.; Jasoni, R.L.; Hu, J.; Paré, P.W. Helv. Chim. Acta 2004, 87, 2354–2358; (b) Yost, J.M.; Zhou, G.; Coltart, D.M. Org. Lett. 2006, 8, 1503–1506; (c) Zhou, G.; Yost, J.M.; Coltart, D.M. Synthesis 2007, 478–482; (d) Yost, J.M.; Alfie, R.J.; Tarsis, E.M.; Chong, I.; Coltart, D.M. Chem. Commun. 2011, 47, 571–572.   31 2.9).28,35 In contrast to the Mukaiyama aldol example (Scheme 2.8), only a trace amount of enone byproduct was formed under these soft enolization conditions. We propose that elimination of the C23 silyloxy substituent is disfavored due to the stability of intermediate magnesium aldolate complex 48. Furthermore, use of a bulky amine base curtailed aldehyde epimerization36 while enforcing a desirable level of enolate regioselection. Scheme 2.9. Model C26–C27 soft enolization-based aldol reaction. TBSO BnO 23 O Me O H 27 TBSO OBn Me 31 MgBr2•OEt2, EtN(iPr)2 CH2Cl2, 0 °C 45%, dr = 95:05 1,3-anti Me 46a X Mg TBSO BnO 21 OBn 47 Ln O 26 27 31 O OBn Me Me (workup) BnO TBSO 23 O OH OBn Me 27 31 Me 48 TBSO OBn 49a TBSO OBn Despite using nearly equimolar amounts of substrate, ketone dimerization37 posed a formidable challenge to improving reaction yield. We envisioned disfavoring this pathway by enlarging the C23 silyloxy substituent (OTPS, OTIPS > OTBS), and consequently observed increased yields of aldol adducts 49b and 49c (eq 8). During the course of our optimization studies, we also noted that increasing the size of the trialkylamine base to PMP (1,2,2,5,5pentamethylpiperidine) appeared to completely suppress aldehyde epimerization. As before, we used excess base (2.0 equiv) and Lewis acid (4.0 equiv) to reach high conversions over                                                                                                                 (35) Reformatsky-type aldol addition of the corresponding a-bromoketone to aldehyde 47 in the presence of SmI2 in THF at –78 °C also produced the desired aldol adduct 49a in 85% yield but with slightly diminished diastereoselectivity (dr = 90:10). See: Ref. 20. (36) In the absence of ketone 46a, less than 10% epimerization of aldehyde 47 was observed after 0.5 h under the same reaction conditions. (37) In the absence of aldehyde 47, complete ketone dimerization was observed within 10 min under the reaction conditions defined in Scheme 2.9.   32 short reaction times (ca. 6 min at –5 °C),38 then rapidly quenched the mixtures to avoid decomposition of the desired aldol adducts. 1,3-anti OR O BnO 23 O Me H 27 TBSO OBn Me 31 MgBr2•OEt2, PMP BnO CH2Cl2, –5 °C OR O 26 23 OH OBn Me 27 31 Me Me (8) OBn 47 TBSO OBn 46b, R = TIPS 46c, R = TPS 49b, R = TIPS, 68%, dr = 95:05 49c, R = TPS, 70%, dr = 95:05 Now confident in our ability to construct the C26–C27 bond of polyol 20 using a merged chelate-controlled/soft enolization-based aldol approach, we turned our attention to the syntheses of subunits 35 and 36 (Scheme 2.6). III. Synthesis of the C3–C26 Ketone39 Our synthesis plan for C3–C26 ketone fragment 50 was inspired by the Felkin- selective C15–C16 Mukaiyama aldol reaction that we discovered before the structural revision (Scheme 2.10).14 We envisioned that trityl-catalyzed40 addition of the enolsilane of ketone 52 to aldehyde 51 would selectively form the corresponding Felkin aldol adduct despite non-reinforcing α,β-stereoinduction.41 We anticipated that the same strategy could be used to assemble C16–C26 ketone 52 from aldehyde 55 and Chan's diene42 (56). Finally, we                                                                                                                 (38) Temperatures lower than –5 °C significantly limited conversion, even after extended reaction times. (39) This section represents the culminative work of Drs. William C. Trenkle, Jing Zhang, Joseph M. Young, and Peter H. Fuller. (40) (a) Mukaiyama, T.; Kobayashi, S.; Murakami, M. Chem. Lett. 1984, 13, 1759–1762; (b) Denmark, S.E.; Chen, C.-T. Tetrahedron Lett. 1994, 35, 4327–4330. (41) Evans, D.A.; Dart, M.J.; Duffy, J.L.; Yang, M.G. J. Am. Chem. Soc. 1996, 118, 4322–4343. (42) (a) Chan, T.-H.; Brownbridge, P. J. Chem. Soc., Chem. Commun. 1979, 578–579; (b) Brownbridge, P.; Chan, T.-H.; Brook, M.A.; Kang, G.J. Can. J. Chem. 1983, 61, 688–693.   33 expected that chelate-controlled addition43 of the alkyllithium derivative of iodide 53 to αalkoxy aldehyde 55 would set the 1,2-syn diol relationship seen in C3–C15 aldehyde 51. Scheme 2.10. Retrosynthesis plan for C3–C26 ketone 50. OR OR OR OR OR OR OR OR O 16 RO 3 7 11 15 19 23 Me Me Me OR Me Me Me Me 50 Me 1,2-syn Felkin-selective aldol addition 51 RO 8 3 7 OR OR OR O 9 11 15 O H Me 17 OR OR OR 22 21 25 Me Me Me OR Me Me Me Me Me 52 chelate-controlled alkylmetal addition Me Me OBn O O O 15 Felkin-selective aldol addition 17 TBSO O 21 OR OR H 25 BnO 3 7 I H O 11 Me 53 Me Me Me 54 Me N Me OMe OMe Me 55 Me 56, R = TMS A. Synthesis of the C3–C15 Aldehyde Our synthesis of C3–C15 aldehyde synthon 51 began with the preparation of C3–C7 iodide 53 44 (Scheme 2.11). The copper-catalyzed, enantioselective hetero-Diels–Alder reaction 45 of enol ether 57 46 and α-ketoester 58 47 produced the desired cycloadduct with excellent enantio- and diastereoselection. Substrate-controlled hydrogenation of dihydropyran 60 then afforded the corresponding 1,3-syn dimethyl product as a single diastereomer.                                                                                                                 (43) (a) Cram, D.J.; Abd Elhafez, F.A. J. Am. Chem. Soc. 1952, 74, 5828–5835; (b) Cram, D.J.; Kopecky, K.R. J. Am. Chem. Soc. 1959, 81, 2748–2755; (c) Cram, D.J.; Leitereg, T.H. J. Am. Chem. Soc. 1968, 90, 4019– 4026. (44) The synthesis of C3–C7 iodide 53 was previously achieved in 7 steps via a pair of auxiliary-controlled enolate alkylations. See: Vong, B.G.; Abraham, S.; Xiang, A.X.; Theodorakis, E.A. Org. Lett. 2003, 5, 1617–1620. (45) (a) Evans, D.A.; Olhava, E.J.; Johnson, J.S.; Janey, J.M. Angew. Chem., Int. Ed. 1998, 37, 3372–3375; (b) Evans, D.A.; Johnson, J.S.; Olhava, E.J. J. Am. Chem. Soc. 2000, 122, 1635–1649. (46) Prepared in one step by isomerization of allyl ethyl ether. See: Ref. 31 and references cited therein. (47) Prepared in one step by mono-addition of isopropenylmagnesium bromide to diethyl oxalate. See: (a) Ref. 31; (b) Rambaud, M.; Bakasse, M.; Duguay, G.; Villieras, J. Synthesis 1988, 564–566.   34 Reduction of ethyl ester 61 and iodination of the resultant primary carbinol proceeded in good yield. Ring fragmentation of iodide 62 was then induced by lithium-halogen exchange to provide acyclic enol 63.48 Benzylation, ozonolysis with reductive workup, and iodination ultimately provided C3–C7 iodide 53 in good overall yield and 11 total steps from commercially available material. Scheme 2.11. Synthesis of C3–C7 iodide 53. O EtO Me 57 3 3 O OEt a 96% ee, dr = 98:02 EtO 4 O 7 O OEt Me b 78%, 2 steps, dr > 95:05 EtO 4 O H 6 O OEt Me c,d,e 70% Me 58 O H 7 Me 5 Me 61 i 60 f HO 3 7 I Me g,h BnO 3 7 OH 85% BnO 3 7 I Me 62 Me 63 Me 75%, 3 steps Me 64 Me Me 53 Me Me Me O N t-Bu H2O Cu OH2 OTf N t-Bu O TfO (S,S)-59 Reagents and conditions: (a) (S,S)-59, 3 Å MS, Et2O, –78 °C, 96% ee, dr = 98:02; (b) H2, Pd/C, EtOAc, rt, dr > 95:05, 78% (2 steps); (c) Et3SiH, BF•OEt2, CH2Cl2, –10 °C to 0 °C; (d) LiAlH4, Et2O, 0 °C; (e) PPh3, I2, imidazole, MeCN, PhH, 55 °C, 70% (3 steps); (f) t-BuLi, Et2O, –78 °C; (g) BnBr, NaH, DMF, 0 °C; (h) O3, Na2CO3, Sudan III, EtOH, CH2Cl2, –78 °C; NaBH4, –78 °C to rt, 75% (3 steps); (i) PPh3, I2, imidazole, CH2Cl2, 0 °C to rt, 85%. Our synthesis of the C3–C15 aldehyde continued with the preparation of C8–C15 aldehyde 54 (Scheme 2.12). The syn aldol reaction of cinnamaldehyde (65) and oxazolidinone 66 produced the desired adduct in very good yield and excellent diastereoselectivity. 49 Benzylation of the C9 carbinol and net reduction of imide 67 to its corresponding aldehyde                                                                                                                 (48) The catalytic, enantioselective synthesis of ent-63 was previously developed by our group and applied to the synthesis of (+)-azaspiracid-1. See: (a) Evans, D.A.; Dunn, T.B.; Kvœrnø, L.; Beauchemin, A.; Raymer, B.; Olhava, E.J.; Mulder, J.A.; Juhl, M.; Kagechika, K.; Favor, D.A. Angew. Chem., Int. Ed. 2007, 46, 4698–4703; (b) Ref. 29.; (c). Ref. 31. (49) Evans, D.A.; Bartroli, J.; Shih, T.L. J. Am. Chem. Soc. 1981, 103, 2127–2129.   35 proceeded in very good yield. Boron-mediated aldol addition of β-ketoimide 6950 to aldehyde 68 was immediately followed by silylation of the nascent C11 carbinol to produce adduct 70 in good yield and excellent diastereoselectivity. Diastereoselective reduction of the C13 carbonyl with zinc borohydride gave the desired anti/anti/syn C11–C14 stereotetrad with excellent selectivity.51 Transamidation of the intermediate imide, acetonide formation, and ozonolysis of styryl derivative 71 completed the synthesis of C8–C15 aldehyde 54 in 11 linear steps and very good overall yield. Scheme 2.12. Synthesis of C8–C15 aldehyde 54. O Ph 65 OBn O Ph 68 9 9 O H 11 O a N O 66 O N O 75%, dr > 95:05 86%, dr > 95:05 Ph 67 OH O 10 9 O b,c,d N O 80% Me Bn O H 13 Me Bn OBn OR O 8 12 11 15 O e,f Ph O N O O g,h,i,j 43% Me Me 69 Me Bn Me Me Me Bn 70, R = TES Me Me O N Me OMe 92% k H O OBn O 9 Me Me OBn O Ph 9 O 13 O 13 O OMe N Me Me Me 71 Me Me Me 54 Me Reagents and conditions: (a) Bu2BOTf, Et3N, CH2Cl2, –78 °C to 0 °C, dr > 95:05, 86%; (b) Me(MeO)NH•HCl, AlMe3, THF, –78 °C, 87%; (c) BnBr, NaH, DMF, –10 °C, 99%; (d) LiAlH4, Et2O, 0 °C to rt, 93%; (e) Cy2BCl, EtNMe2, Et2O, –78 °C, dr > 95:05; (f) TESOTf, 2,6-lut., CH2Cl2, –78 °C, 75% (2 steps); (g) Zn(BH4)2, Et2O, CH2Cl2, –55 °C to –25 °C, 59%; (h) Me(MeO)NH•HCl, AlMe3, THF, –78 °C to 0 °C, 80%; (i) AcOH, THF, H2O, rt; (j) Me2C(OMe)2, PPTS, CH2Cl2, rt, 91% (2 steps); (k) O3, py, Sudan III, EtOH, CH2Cl2, –78 °C; Me2S, – 78 °C to rt, 92%.                                                                                                                 (50) Evans, D.A.; Ng, H.P.; Clark, J.S.; Rieger, D.L. Tetrahedron 1992, 48, 2127–2142. (51) (a) Halstead, D.P. Total Syntheses of Miyakolide & Discodermolide. Ph.D. Thesis, Harvard University, 1998; (b) Nakata, T.; Oishi, T. Tetrahedron Lett. 1980, 21, 1641–1644; (c) Nakata, T.; Oishi, T. Acc. Chem. Res. 1984, 17, 338–344.   36 Our synthesis of C3–C15 aldehyde 74 concluded with union of the C3–C7 and C8– C15 fragments (Scheme 2.13).52 Chelate-controlled addition of alkyllithium 72 to α-alkoxy aldehyde 54 yielded the desired 1,2-syn diol derivative 73 as a single diastereomer in very good yield. Silylation of the C8 carbinol and reduction of the Weinreb amide produced C3– C15 aldehyde 74 in excellent yield and overall convergency (14 longest linear steps, 25 overall). Scheme 2.13. Synthesis of C3–C15 aldehyde 74. Me Me OBn O a 53, R = I 72, R = Li BnO 3 7 O O 15 R H 8 11 Me Me O Me Me 54 Me OMe N Me b 86%, dr > 95:05 Me Me Me Me OBn O 8 O O 15 OBn O N Me OMe c,d 94% BnO 3 7 11 O O 15 BnO 3 7 11 H Me Me OH Me 73 Me Me Me Me OR Me Me Me 74, R = TBS Reagents and conditions: (a) t-BuLi, Et2O, pentane, –78 °C; (b) MgBr2•OEt2, CH2Cl2, –78 °C, dr > 95:05, 86%; (c) TBSOTf, 2,6-lut., CH2Cl2, –78 °C to 0 °C, 97%; (d) LiAlH4, Et2O, 0 °C, 97%. B. Syntheses of the C16–C26 Enolsilane and C3–C26 Ketone Our synthesis of C3–C26 ketone synthon 50 continued with the preparation of the enolsilane of C16–C26 ketone synthon 5253 via C16–C21 aldehyde 5554 (Scheme 2.14). Syn aldol reaction55 of methacrolein (75) and oxazolidinone 66 was followed by silylation of the nascent C19 carbinol to produce adduct 76 in very good yield and excellent                                                                                                                 (52) This reaction sequence was performed by Dr. Peter H. Fuller. The synthesis of the corresponding C3 TBS ether of C3–C15 aldehyde 74 was achieved by Dr. Joseph M. Young. See: Ref. 14. (53) The synthesis of C16–C26 enolsilane 83 (vide infra) was previously achieved by Dr. Joseph M. Young in 13 steps via a pair of auxiliary-controlled aldol reactions. See: Ref 14. (54) The synthesis of C16–C21 aldehyde 55 in 7 steps from methyl (S)-(+)-3-hydroxy-2-methylpropionate was previously reported. See: Mínguez, J.M.; Kim, S.-Y.; Giuliano, K.A.; Balachandran, R.; Madiraju, C.; Day, B.W.; Curran, D.P. Bioorg. Med. Chem. 2003, 11, 3335–3357. (55) Evans, D.A.; Fitch, D.M. J. Org. Chem. 1997, 62, 454–455.   37 diastereoselectivity. Substrate-controlled hydroboration 56 selectively established the C18 methyl stereocenter and afforded γ-lactone 77 in very good yield upon oxidative workup. Oxidative ring opening, C16–C17 olefination, and reduction of Weinreb amide 78 gave aldehyde 55 in good overall yield. Scheme 2.14. Synthesis of C16–C21 aldehyde 55. O 19 O H 21 O a,b N O 66 86% dr > 95:05 OR O 20 19 O c N O 84%, dr = 95:05 Me 75 O Me 18 Me Bn O 21 Me Me Bn 76, R = TBS d,e,f 74% 17 16 21 TBSO O N Me OMe g 77% 17 TBSO O 21 Me OTBS 77 H Me Me 78 Me 55 Me Reagents and conditions: (a) Bu2BOTf, EtN(iPr)2, –78 °C to 0 °C, dr > 95:05, 88%; (b) TBSOTf, 2,6-lut., CH2Cl2, –78 °C to –20 °C, 98%; (c) 9-BBN, THF, 0 °C; aq H2O2, pH 7 buffer, EtOH, 0°C to rt; cat. KOt-Bu, THF, 0 °C to rt, dr = 95:05, 84%; (d) Me(MeO)NH•HCl, AlMe3, THF, –40 °C to 0 °C; (e) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to 0 °C; (f) Ph3PPMeBr, NaHMDS, THF, –78 °C to 0 °C, 74% (3 steps); (g) DIBALH, CH2Cl2, –78 °C, 77%. The synthesis of C16–C26 enolsilane 83 57 continued with the trityl-catalyzed40 addition of Chan's diene42 (56) to C16–C21 aldehyde 55 to form Felkin aldol adduct 79 in very good yield and excellent diastereoselectivity (Scheme 2.15). Prasad 1,3-syn reduction58 was followed by cerium-mediated conversion of ester 80 to its corresponding allylsilane59 and global desilylation to produce triol 81 in good yield. Selective protection of the C23 carbinol                                                                                                                 (56) (a) Still, W.C.; Barrish, J.C. J. Am. Chem. Soc. 1983, 105, 2487–2489; (b) Midland, M.M.; Kwon, Y.C. J. Am. Chem. Soc. 1983, 105, 3725–3727. (57) The synthesis of C16–C26 enolsilane 83 from methyl ester 80 was designed in collaboration with Dr. Peter H. Fuller, and executed by Dr. Fuller. (58) Chen, K.-M.; Hardtmann, G.E.; Prasad, K.; Repič, O; Shapiro, M.J. Tetrahedron Lett. 1987, 28, 155–158. (59) (a) Anderson, M.B.; Fuchs, P.L. Synth. Commun. 1987, 17, 621–635; (b) Narayanan, B.A.; Bunnelle, W.H. Tetrahedron Lett. 1987, 28, 6261–6264; (c) Lee, T.V.; Channon, J.A.; Cregg, C.; Porter, J.R.; Roden, F.S.; Yeoh, H.T.-L. Tetrahedron 1989, 45, 5877–5886; (d) Bunnelle, W.H.; Narayanan, B.A. Org. Synth. 1990, 69, 89–92; Org. Synth. 1993, Coll. Vol. 8, 602–605.   38 as its triisopropylsilyl ether, 1,3-syn acetonide formation and Wacker oxidation60 of the C16– C17 alkene produced methyl ketone 82 in good overall yield and 15 linear steps. The synthesis was capped by formation of enolsilane 83 in preparation for the C15–C16 Mukaiyama aldol reaction. Scheme 2.15. Synthesis of C16–C26 enolsilane 83. 17 TBSO O 21 OR OR H 25 a 84%, dr > 95:05 17 TBSO HO 22 21 O O 25 b OMe 87%, dr > 95:05 OMe Me 55 Me 56, R = TMS TBSO HO HO 19 23 Me Me 79 O c,d,e OMe 80 76% 17 OH OH OH f,g,h 21 25 Me 73% Me Me Me Me 81 Me Me O Me O 19 Me Me OR 23 O i Me 99% TMSO 17 O O 21 OR 25 Me Me Me 82, R = TIPS Me Me 83, R = TIPS Reagents and conditions: (a) Ph3PCPF6 (5 mol%), CH2Cl2, –78 °C; PPTS, MeOH, 0 °C to rt, dr > 95:05, 84%; (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to –50 °C; aq H2O2, pH 7 buffer, MeOH, –50 °C to rt, dr > 95:05, 87%; (c) TMSOTf, 2,6-lut., CH2Cl2, –78 °C to rt; (d) TMSCH2MgBr, CeCl3, THF, Et2O, –78 °C to rt; (e) HF•py, CH2Cl2, 0 °C to rt, 76% (3 steps); (f) TIPSCl, imidazole, DMF, rt to 45 °C, 91%; (g) Me2C(OMe)2, PPTS, acetone, rt, 93%; (h) PdCl2(quinox), AgSbF6, aq t-BuOOH, CH2Cl2, 0 °C to rt, 86%; (i) TMSOTf, Et3N, CH2Cl2, –78 °C to –20 °C, 99%. Our synthesis of C3–C26 ketone 85 concluded with merging of the C3–C15 and C16– C26 fragments (Scheme 2.16). Encouraged by results obtained before the structural revision, the trityl-catalyzed40 addition of enolsilane 83 to aldehyde 74 proceeded in similar fashion to produce the desired Felkin aldol adduct 84 as a single C15 diastereomer in very good yield. Prasad 1,3-syn reduction58 was followed by acetonide formation and ozonolysis to provide C3–C26 ketone 85 in good overall yield and 20 linear steps.                                                                                                                 (60) Michel, B.W.; Camelio, A.M.; Cornell, C.N.; Sigman, M.S. J. Am. Chem. Soc. 2009, 131, 6076–6077.   39 Scheme 2.16. Synthesis of C3–C26 ketone 85. Me Me 74, R = TBS BnO 3 7 Me Me O 15 OBn O 11 O TMSO H O 19 O OR' 23 Me Me Me OR Me Me Me a Me 84%, dr > 95:05 Me Me OH O 16 15 Me 83, R' = TIPS 84, R = TBS R' = TIPS BnO 3 7 Me Me OBn O 11 O O 19 O OR' 23 Me Me Me OR Me Me Me b,c,d Me Me 60%, dr > 95:05 Me Me O 19 85, R = TBS R' = TIPS BnO 3 7 Me Me OBn O 11 Me Me O 15 O O O OR' O 23 Me Me Me OR Me Me Me Me Me Reagents and conditions: (a) Ph3PCPF6 (3 x 10 mol%), CH2Cl2, –78 °C; PPTS, MeOH, 0 °C, dr > 95:05, 84%; (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to –20 °C; aq H2O2, pH 7 buffer, MeOH, –20 °C to rt, dr > 95:05, 87%; (c) Me2C(OMe)2, PPTS, acetone, rt, 85%; (d) O3, py, EtOH, CH2Cl2, –78 °C; Me2S, –78 °C to rt, 81%. IV. Synthesis of the C27–C48 Aldehyde61 Our synthesis plan for C27–C48 aldehyde fragment 86 was designed to take advantage of the anti-Felkin selective α-oxygenated aldol reaction developed specifically for the C33– C36 stereochemical array (Scheme 2.17).62 We presumed that the intervening structural revision would have minimal impact on reaction diastereoselectivity, and therefore decided to target the same C35–C36 aldol bond disconnection. This act produced C36–C48 ketone 88 and C27–C35 aldehyde 87, the latter of which could be accessed stereoselectively from C27– C31 aldehyde 91 via a series of allylation, ring-closing metathesis and dihydroxylation steps.                                                                                                                 (61) The synthesis of C27–C48 aldehyde 117 was designed and performed by the author in collaboration with Dr. Egmont Kattnig. (62) (a) Glorius, F. Development of α-Oxygenated Aldol Methodology and Progress Towards the Synthesis of Aflastatin A. Postdoctoral Report, Harvard University, 2001; (b) Evans, D.A.; Glorius, F.; Burch, J.D. Org. Lett. 2005, 7, 3331–3335.   40 Scheme 2.17. Retrosynthesis plan for C27–C48 aldehyde 86. O OBn OR OR OR O 36 31 35 OR 39 oxygenated aldol addition 87 OBn OR O 31 O 35 O H OTBS OTBS 39 H 27 R3SiO RO C9H19 OR OR 86 1,2-syn O RO 27 R3SiO RO C9H19 88 Me O Me 91 BnO 30 O 31 chelatecontrolled addition H O 34 OBn O 32 RCM OBn O RO 27 R3SiO RO 31 33 O O TBSO 27 TBSO BnO RO 27 R3SiO RO 31 Me Me 90 89 Two syntheses of C36–C48 ketone 88 were achieved before the structural revision (Scheme 2.18). The first route62a featured the copper-catalyzed, enantioselective aldol addition of silylketene acetal 93 to benzyloxy acetaldehyde (92). 63 The resulting absolute stereochemistry of the C37 carbinol was then relayed to C39 by Evans-Tishchenko 1,3-anti reduction,64 and ultimately produced gram-scale quantities of ketone 88 in 9 steps, 46% overall yield and 98% ee. A shorter, second route65 was based upon the enantioselective methallylation66 of decanal, providing the desired fragment in 6 steps, 36% unoptimized overall yield and 96% ee. Our synthesis of the C27–C48 aldehyde began with the preparation of C27–C31 aldehyde 91 from methyl α-D-(+)-glucopyranoside (99) (Scheme 2.19). Regioselective dibenzylation,67 iodination68 and silylation produced pyranoside 101 in good overall yield.                                                                                                                 (63) (a) Evans, D.A.; Murry, J.A.; Kozlowski, M.C. J. Am. Chem. Soc. 1996, 118, 5814–5815; (b) Evans, D.A.; Kozlowski, M.C.; Murry, J.A.; Burgey, C.S.; Campos, K.R.; Connell, B.T.; Staples, R.J. J. Am. Chem. Soc. 1999, 121, 669–685; (c) Allison, B.D. Chelate Control: A Pivotal Design Element in Asymmetric Synthesis. Ph.D. Thesis, Harvard University, 2001. (64) Evans, D.A.; Hoveyda, A.H. J. Am. Chem. Soc. 1990, 112, 6447–6449. (65) Thaisrivongs, D.A. Synthesis of the C5'–C2 and C36–C48 Subunits of Aflastatin A. A.B. Thesis, Harvard University, 2007. (66) (a) Keck, G.E.; Tarbet, K.H.; Geraci, L.S. J. Am. Chem. Soc. 1993, 115, 8467–8468; (b) Keck, G.E.; Krishnamurthy, D.; Grier, M.C. J. Org. Chem. 1993, 58, 6543–6544; (c) Keck, G.E.; Krishnamurthy, D. Org. Synth. 1998, 75, 12–18. (67) Français, A.; Urban, D.; Beau, J.-M. Angew. Chem., Int. Ed. 2007, 46, 8662–8665.   41 Zinc-mediated fragmentation69 and in situ reduction produced an intermediate enol that was silylated and oxidatively cleaved, ultimately furnishing C27–C31 aldehyde 91 in eight steps and 52% overall yield. Scheme 2.18. Previous syntheses of C36–C48 ketone 88. O 37 OTMS H 39 a 93%, 98% ee OH O 38 37 b,c,d,e St-Bu 58% OH O 39 f,g,h,i C9H19 86%, dr > 99:01 O TBSO OTBS 39 St-Bu 93 OBn 92 SnBu3 Me 37 OBn 95 OTBS 96 OTBS 39 C9H19 88 O H 39 j C9H19 Me 74%, 96% ee OH 38 39 k,l Me 83% O m,n,o 58% C9H19 C9H19 97 98 2 SbF6– O N Ph N Cu O N Ph (S,S)-94 H2O OH2 Reagents and conditions: (a) (S,S)-94, CH2Cl2, –78 °C; aq HCl, THF, rt, 93%, 98% ee; (b) Me(MeO)NH•HCl, AlMe3, THF, –15 °C to rt, 97%; (c) Pd/C, H2, EtOAc, rt, 98%; (d) TBSCl, imidazole, THF, CH2Cl2, 0 °C, 92%; (e) C9H19MgBr, THF, 0 °C to rt, 66%; (f) SmI2, iPrCHO, THF, –10 °C, dr > 99:01, 91%; (g) TBSOTf, 2,6-lut., CH2Cl2, 0 °C, 99%; (h) DIBALH, PhMe, –78 °C, 97%; SO3•Py, Et3N, DMSO, CH2Cl2, –55 °C to 0 °C, 98%; (j) (S)-(–)-1,1'-bi-2-naphthol, Ti(OiPr)4, 4 Å MS, CH2Cl2, –78 °C to –20 °C, 74%, 96% ee; (k) TBSCl, imidazole, DMF, rt, 83%; (l) O3, py, CH2Cl2, MeOH, –78 °C; Me2S, –78 °C to rt, quant.; (m) LDA, THF; TMSCl, Et3N, – 78 °C to rt; (n) m-CPBA, NaHCO3, CH2Cl2, 0 °C to rt; aq HCl, THF, H2O, rt; (o) TBSCl, imidazole, DMF, rt to 50 °C, 58% (3 steps). Scheme 2.19. Synthesis of C27–C31 aldehyde 91. H a,b,c 82% 99, R = H 100, R = Bn HO 31 O 27 OMe OH H d,e 97% I 31 O 27 OMe OTBS f,g,h 76% BnO TBSO 27 TBSO BnO 91 O 31 RO OR BnO OBn 101 H Reagents and conditions: (a) TMSCl, py, CH2Cl2, 0 °C to rt, quant.; (b) PhCHO, Cu(OTf)2, CH2Cl2, MeCN; Et3SiH, 0 °C to rt; (c) BH3•THF, Cu(OTf)2, 82% (2 steps); (d) PPh3, I2, imidazole, PhMe, MeCN, rt, 97%; (e) TBSCl, imidazole, CH2Cl2, 0 °C to rt, quant.; (f) Zn, THF, H2O, ))), 45 °C; NaBH4, 0 °C, 88%; (g) TBSCl, imidazole, CH2Cl2, 0 °C to rt, 92%; (h) O3, py, CH2Cl2, MeOH, –78 °C; PPh3, –78 °C to rt, 94%.                                                                                                                                                                                                                                                                                                                                                           (68) (a) Garegg, P.J.; Samuellson, B. J. Chem. Soc., Perkin Trans. I. 1980, 2866–2869; (b) Garegg, P.J.; Johansson, R.; Ortega, C.; Samuellson, B. J. Chem. Soc., Perkin Trans. I. 1982, 681–683. (69) Skaanderup, P.R.; Hyldtoft, L.; Madsen, R. Monatsh. Chem. 2002, 133, 467–472.   42 Our synthesis of the C27–C48 aldehyde continued with the stereoselective allylation of syn α,β-bisalkoxy aldehyde 91 (Scheme 2.20). Although both α- and β-oxygen substituents were available for chelation,70 the rate of reaction of allylmagnesium bromide with the five-membered chelate43 was significantly faster,71 producing homoallylic alcohol 102 in 96% yield and excellent diastereoselectivity (dr ≥ 93:07). We observed that the nature of the nucleophile20,24 and distal carbinol protecting groups (at C27 and C28)20 were important for maintaining excellent diastereoselection. Scheme 2.20. Synthesis of C27–C35 aldehyde 106. BnO TBSO 27 TBSO BnO 91 O OBn O TBSO TBSO BnO 27 31 34 O 31 a H 96%, dr ≥ 93:07 OBn OH 32 b,c 86% TBSO 27 TBSO BnO 102 31 O d,e 33 OBn O TBSO TBSO BnO 27 31 35 O O Me Me f,g,h 72% 69%, dr ≥ 95:05 103 OBn OBn O i,j,k,l TBSO 27 TBSO BnO 105 31 35 104 OBn OBn O OPiv 66% TESO 27 TBSO BnO 106 31 O 35 H Me O Me Me O Me Reagents and conditions: (a) MgBr2•OEt2, allylMgBr, CH2Cl2, Et2O, PhMe, –78 °C, 96%, dr ≥ 93:07; (b) acrylic pivalic anhydride, EtN(iPr)2, DMAP, THF, PhH, rt, 94%; (c) (Ph3P)2Cl2Ru=CHPh, PhH, 65 °C, 92%; (d) RuCl3, CeCl3•7H2O, NaIO4, EtOAc, MeCN, H2O, 0 °C, dr ≥ 95:05; (e) Me2C(OMe)2, PPTS, acetone, 30 °C, 69% (2 steps); (f) LiBH4, THF, H2O, 0 °C to rt; (g) PivCl, py, 0 °C to rt, 78% (2 steps); (h) BnBr, NaH, nBu4NI, THF, 0 °C to rt, 92%; (i) HF•py, py, THF, 0 °C to rt, 85%; (j) TESOTf, 2,6-lut., CH2Cl2, 0 °C, 91%; (k) DIBALH, CH2Cl2, PhMe, –78 °C, 90%; (l) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C, 95%.                                                                                                                 (70) The possibility of bicyclic chelates involving the aldehyde carbonyl and both oxygen substituents cannot be ruled out. See: (a) Charette, A.B.; Mellon C.; Rouillard, L.; Malenfant, E. Pure Appl. Chem. 1992, 64, 1925–1931; (b) Charette, A.B.; Mellon C.; Rouillard, L.; Malenfant, E. Synlett 1993, 81–82. (71) For examples that suggest five-membered magnesium chelates react much faster than six-membered chelates, see: (a) Frye, S.V.; Eliel, E.L.; Cloux, R. J. Am. Chem. Soc. 1987, 109, 1862–1863; (b) Williams, D.R.; Klingler, F.D. Tetrahedron Lett. 1987, 28, 869–872; (c) Keck, G.E.; Andrus, M.B.; Romer, D.R. J. Org. Chem. 1991, 56, 417–420; (d) Burgess, K.; Chaplin, D.A. Tetrahedron Lett. 1992, 33, 6077–6080.   43 Acryloylation 72 of the nascent C31 carbinol, and ring-closing metathesis 73 of the intermediate diene then furnished unsaturated lactone 103. Stereoselective dihydroxylation74,75 and acetonide formation produced lactone 104 as a single diastereomer. Reduction to the diol, selective protection of the primary carbinol, and benzylation yielded pivalate ester 105. Silyl protecting group exchange at C27 was necessary at this stage because selective removal of the TBS ether76 after C35–C36 aldol coupling would later prove difficult. Reductive removal of the ester and Parikh-Doering oxidation77 ultimately provided C27–C35 aldehyde 106 in 12 steps and 27% overall yield from aldehyde 91. With scalable routes to C36–C48 ketone 88 and C27–C35 aldehyde 106 in hand, the synthesis of the C27–C48 fragment was nearly complete. At this juncture, it was unclear how the revised stereochemistry (C28–C31) of aldehyde 106 would influence the diastereoselectivity of our planned C35–C36 aldol reaction. Addition of the corresponding (E) enolate of ketone 88 to this aldehyde produced the desired anti-Felkin product 107 in fairly good isolated yield but with unexpectedly diminished diastereoselection (Scheme 2.21, eq 9). A similar result was observed for an aldehyde (108) having the same relative configuration between C31 and C33 (Scheme 2.21, eq 10).20 Both examples deviated from the good yields                                                                                                                 (72) Tanaka, A.; Suzuki, H.; Yamashita, K. Agric. Biol. Chem. 1989, 53, 2253–2256. (73) Schwab, P.; France, M.B.; Ziller, J.W.; Grubbs, R.H. Angew. Chem. 1995, 107, 2179–2181; Angew. Chem., Int. Ed. 1995, 34, 2039–2041. (74) (a) Plietker, B.; Niggemann, M. J. Org. Chem. 2005, 70, 2402–2405; (b) Plietker, B. Synthesis 2005, 2453– 2472. (75) For examples of the diastereoselective dihydroxylation of related α,β-unsaturated δ-lactones using Upjohn conditions (OsO4, NMO), see: (a) Ghosh, A.K.; Kim, J.-H. Tetrahedron Lett. 2003, 44, 3967–3969; (b) Ramachandran, P.V.; Prabhudas, B.; Chandra, J.S.; Reddy, M.V.R. J. Org. Chem. 2004, 69, 6294–6304; (c) Bhaket, P.; Stauffer, C.S.; Datta, A. J. Org. Chem. 2004, 69, 8594–8601. (76) Selective desilylation of the C27 carbinol was achieved under specific buffered conditions. See: Hu, T.; Takenaka, N.; Panek, J.S. J. Am. Chem. Soc. 2002, 124, 12806–12815. (77) Parikh, J.R.; Doering, W.v.E. J. Am. Chem. Soc. 1967, 89, 5505–5507.   44 and excellent diastereoselectivities obtained prior to the C28–C31 stereochemical revision (Scheme 2.21, eqs 11,12).7,15 Scheme 2.21. C35–C36 oxygenated aldol reactions. OBn OBn O TESO 27 TBSO BnO 106 27 31 O 35 a H 66%, dr = 86:14 OBn OBn O TESO 27 TBSO BnO 31 OH O 36 35 OTBS 39 C9H19 (9) Me O Me O 35 Me O OTBS Me 107 OH O 36 31 35 39 OBn OBn O 31 b H 65%, dr = 84:16 O Me 27 OBn OBn O OTBS C9H19 (10) O Me O BnO Me 108 Me O Me O BnO Me Me O OTBS Me 109 O OH O 36 31 35 39 27 TBSO BzO 31 O O 35 c H 73%, dr > 95:05 O Me 27 TBSO BzO OTBS C9H19 (11) O Me O BzO Me Me O Me 110 O O 35 O BzO Me Me O OTBS Me 111 OH O 36 35 Me Me O 112 O 31 Me Me d H 81%, dr > 95:05 O O 31 O OTBS 39 C9H19 113 (12) Me O Me Me O Me OTBS Reagents and conditions: (a) ketone 88, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 106, pentane, PhMe, – 78 °C to –20 °C, 66%, dr = 86:14; (b) ketone 88, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 108, pentane, PhMe, –78 °C to –20 °C, 65%, dr = 84:16; (c) ketone 88, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 110, pentane, PhMe, –78 °C to –20 °C, 73%, dr > 95:05; (d) ketone 88, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 112, pentane, –78 °C to –20 °C, 81%, dr > 95:05. The reduced diastereoselection for the anti-Felkin product may be attributed to the inversion of relative configuration between the C31 and C33 carbinol stereocenters. When these stereocenters exist in a 1,3-anti relationship, anti-Felkin transition state 114 benefits both from dipole-dipole minimization and extension of the aldehyde's alkyl chain away from the reaction center (Figure 2.1A). When this relationship is inverted, the transition states (115–117) that lead to desired anti-Felkin products 107 and 109 become destabilized by unfavorable steric and/or electrostatic interactions, regardless of C31–C32 rotational isomer (Figure 2.1B).   45 A 1,3-anti H O 35 33 OR' H 31 OR' O 33 R BCy2 R R 31 H Me O Me 110 or 112 B H TBSO Me Me O OR' O 31 OH O 36 35 OTBS 39 35 R" O O C9H19 36 O H anti-Felkin TS 114 H 31 Me O Me OTBS 111 or 113, dr > 95:05 H 33 R'O H TBSO Me Me O 35 R BCy2 R" O O 36 O H H C31–C32 bond rotation anti-Felkin TS 115 R H 31 1,3-syn OR' O 33 O 35 33 OR' BCy2 R R 31 H Me O Me 106 or 108 H TBSO Me Me O OR' O 31 OH O 36 35 OTBS 39 35 R" O O C9H19 36 O H H C31–C32 bond rotation anti-Felkin TS 116 OR' R 31 Me O Me OTBS 107 or 109, dr ≤ 86:14 33 H BCy2 H TBSO Me Me O 35 R" O O 36 O H anti-Felkin TS 117 Figure 2.1. C35–C36 oxygenated aldol anti-Felkin transition state possibilities. Our synthesis of C27–C48 aldehyde 118 was completed in short order (Scheme 2.22). Silylation of aldol adduct 107 was followed by selective deprotection and oxidation77 at C27. This sequence provided C27–C48 fragment 118 in good overall yield and 24 linear steps. Scheme 2.22. Synthesis of C27–C48 aldehyde 118. OBn OBn O TESO 27 TBSO BnO 31 OH O 35 OTBS a,b,c 39 O OBn OBn O 31 OR O 35 OTBS 39 C9H19 76% Me O OTBS Me 107 H 27 TBSO BnO C9H19 Me O Me OTBS 118, R = TES Reagents and conditions: (a) TESOTf, 2,6-lut., CH2Cl2, 0 °C, 87%; (b) PPTS, CH2Cl2, MeOH, 0 °C to rt, quant.; (c) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C, 87%.   46 V. Synthesis of the C3–C48 Degradation Fragment78 Having completed the syntheses of both the C3–C26 and C27–C48 fragments, we ventured forward with the key aldol coupling (Scheme 2.23).20 Satisfyingly, chelatecontrolled addition of ketone 85 to aldehyde 118 under our soft enolization conditions delivered the desired β-hydroxy ketone 119 with excellent diastereoselection.28 We reduced the aldol adduct under Prasad's conditions58 to afford the corresponding 1,3-syn diol in good yield. Both steps were completely chemoselective and eliminated the need to mask the C37 carbonyl. To conclude the synthesis of the target structure, the intermediate diol was subjected to a two-step deprotection sequence. We found that removal of the acetonide and silyl protecting groups was best achieved with hexafluorosilicic acid,79 but noted that removal of the C36 TBS ether was particularly troublesome and limited yield. Deprotection over longer reaction times, with larger excess reagent, or with resubjection of incompletely deprotected material to the original reaction conditions increased overall conversion at the cost of decomposition. Ultimately, the remaining benzyl ethers were cleaved to unveil C3–C48 degradation fragment 20 in modest overall yield and 28 linear steps.                                                                                                                 (78) The synthesis of C3–C48 degradation fragment 20 was first performed by Dr. Egmont Kattnig in collaboration with Dr. Peter H. Fuller and the author. (79) (a) Pilcher, A.S.; Hill, D.K.; Shimshock, S.J.; Waltermire, R.E.; DeShong, P. J. Org. Chem. 1992, 57, 2492–2495; (b) Pilcher, A.S.; Shimshock, S.J. J. Org. Chem. 1993, 58, 5130–5134.   47 Scheme 2.23. Synthesis of C3–C48 degradation fragment 20. Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' O 23 O Me OBn OBn O 31 OR" O 35 OTBS 39 Me Me OR Me Me Me Me Me a Me Me O 19 H 27 TBSO BnO 60%, dr = 95:05 C9H19 85, R = TBS, R' = TIPS Me Me OBn O BnO 3 7 11 Me O OTBS Me 118, R" = TES Me Me O 15 O O O OR' O 26 23 OH OBn OBn O 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me RO BnO 24%, dr = 95:05 Me O Me OR 119, R = TBS, R' = TIPS, R" = TES b,c,d OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me Me Me 20 OH OH H O OH C9H19 Reagents and conditions: (a) MgBr2•OEt2, PMP, CH2Cl2, –5 °C, 60%, dr = 95:05; (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to –55 °C; aq H2O2, pH 7 buffer, MeOH, 0 °C to rt; pinacol, MeOH, 50 °C, 68%, dr = 95:05; (c) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt; (d) H2, Pd black, dioxane, H2O, rt, 35% (2 steps). Careful comparison of our NMR spectroscopic data for C3–C48 degradation fragment 20 to that reported by the isolation group for the naturally derived degradation product revealed a structural misassignment.20 To our surprise, the chemical shifts of the reassigned stereocenters (C8, C9, C28–C31) were in reasonable agreement with our data, but significant differences were observed in the C33–C39 lactol (hemiketal) region. The solution to this structural curiosity and our structural reassignment of naturally derived degradation product 20 will be discussed in Chapter 3.   48 VI. Graphical Summary Synthesis of C27–C31 Lactone 104 H HO 31 O 27 OMe OH quant. H TMSO 31 O 27 OMe Ph H O 31 O 27 OMe OH HO OH 99 TMSO OTMS OTMS 120 O 121 OBn 82%, two steps OMe 27 H I 31 O 27 OMe OTBS quant. H I 31 O H HO 97% 31 O 27 OMe OH BnO 101 OBn 88% BnO BnO OBn 122 OH BnO OBn 100 BnO 31 31 BnO 94% TBSO 27 TBSO BnO 91 O 31 HO 27 TBSO BnO 123 O OBn O TBSO 27 TBSO BnO 103 31 35 92% TBSO 27 TBSO BnO 124 O OBn O 35 H 96%, dr ≥ 93:07 OBn OH 94% TBSO 27 TBSO BnO 102 O 31 92% TBSO 27 TBSO BnO 31 125 O dr ≥ 95:05 OBn O TBSO 27 TBSO BnO 126 31 35 OH OH OBn O 69%, 2 steps TBSO 27 TBSO BnO 31 35 O O Me Me 104   49 Synthesis of C27–C48 Aldehyde 118 OBn OH O 104 TBSO 27 TBSO BnO 31 35 OBn OH O OH 78%, 2 steps TBSO 27 TBSO BnO 128 92% 31 35 OPiv Me O Me 127 Me O Me OBn OBn O TESO 27 TBSO BnO 130 31 OPiv 35 OBn OBn O 91% HO 27 TBSO BnO 129 31 OPiv 35 OBn OBn O 85% TBSO 27 TBSO BnO 105 31 OPiv 35 Me O Me 90% Me O Me Me O Me OBn OBn O TESO 27 TBSO BnO 131 31 35 OBn OBn O OH 95% TESO 27 TBSO BnO 106 31 O 35 O H OTBS 88 OTBS 39 C9H19 Me O Me Me O Me 66%, dr = 86:14 OBn OBn O RO 27 TBSO BnO 31 OR O 35 OTBS 39 OBn OBn O 87% TESO 27 TBSO BnO 31 OH O 35 OTBS 39 C9H19 C9H19 Me O Me OTBS Me O Me 107 OTBS 132, R = TES quant. OBn OBn O HO 27 TBSO BnO 31 OR O 35 OTBS 39 O 87% OBn OBn O 31 OR O 35 OTBS 39 C9H19 Me O Me OTBS H 27 TBSO BnO C9H19 Me O Me OTBS 133, R = TES 118, R = TES   50 Chapter 3 Structural Revision of the C3–C48 Degradation Fragment of Aflastatin A I. Development of a Model for the C27–C48 Lactol Region1 We anticipated that synthesis of C3–C48 degradation fragment 1 and comparison of its NMR spectroscopic data to that reported by the isolation group2 would corroborate the stereochemical revision of aflastatin A (AsA).2b,3 Despite favorable agreement between our data4 and the chemical shifts of the reassigned stereocenters in the C8–C9 diol and C27–C31 pentaol regions, we became disappointed when significant differences appeared in the region loosely bound by C33 and C39 (Figure 3.1). Our analysis revealed a structural misassignment in the lactol region of naturally derived degradation fragment 1.4 Since the isolation group reported mass spectrometry data for this molecule,2a we believed the correct structure to be an isomer of C53H106O22. We could                                                                                                                 (1) (2) A model for the C27–C48 lactol region was developed by Dr. Egmont Kattnig in collaboration with Dr. Peter H. Fuller and the author. (a) Ikeda, H.; Matsumori, N.; Ono, M.; Suzuki, A.; Isogai, A.; Nagasawa, H.; Sakuda, S. J. Org. Chem. 2000, 65, 438–444; (b) Sakuda, S.; Matsumori, N.; Furihata, K.; Nagasawa, H. Tetrahedron Lett. 2007, 48, 2527–2531. Higashibayashi, S.; Czechtizky, W.; Kobayashi, Y.; Kishi, Y. J. Am. Chem. Soc. 2003, 125, 14379–14393. Kattnig, E. An Aldol Approach Toward Aflastatin A – Synthesis of the C3–C48 Polyol. Postdoctoral Report, Harvard University, 2011. (3) (4)   51 not rule out the possibility of constitutional isomerism, but the body of two-dimensional NMR, degradation and isotopic labeling experiments conducted by Sakuda and coworkers2,5 strongly suggested that the structural problem was stereochemical in origin. 1H-NMR Data HO HO HO HO HO HO HO HO HO HO HO HO HO OH 35 OH OH 39 HO 3 7 11 15 19 23 27 31 Me Me OH Me Me Me Me Me 1 OH OH H O OH C9H19 |Δδ| ≥ 0.1 ppm 13C-NMR Data HO HO HO HO HO HO HO HO HO HO HO HO HO OH 35 OH OH 39 HO 3 7 11 15 19 23 27 31 Me Me OH Me Me Me Me Me 1 OH OH H O OH C9H19 |Δδ| ≥ 1 ppm Figure 3.1. NMR data comparisons of synthetic to naturally derived degradation fragment 1. We further analyzed the available data to better confine the suspected stereochemical misassignment to the C33–C39 region. At first we used Kishi's NMR database of 1,3,5,7tetraols6 to deduce the absolute configuration of the C27 stereocenter (Table 3.1).4 To begin, the absolute configurations of the C23 and C25 stereocenters had previously been established by Mosher ester and [13C]acetonide analyses,5c as well as the independent chemical syntheses of the AsA C9–C27 degradation fragment and its derivatives. 7 We anticipated that the chemical shifts of the C23 and C25 carbon atoms would largely depend upon 1,3stereochemical relationships within the C21–C27 tetraol region, and be negligibly influenced by the surrounding polypropionate and pentaol regions. Comparison of the corresponding                                                                                                                 (5) (a) Sakuda, S.; Ono, M.; Furihata, K.; Nakayama, J.; Suzuki, A.; Isogai, A. J. Am. Chem. Soc. 1996, 118, 7855–7856; (b) Ono, M.; Sakuda, S.; Ikeda, H.; Furihata, K.; Nakayama, J.; Suzuki, A.; Isogai, A. J. Antibiotics 1998, 51, 1019–1028; (c) Sakuda, S.; Ikeda, H.; Nakamura, T.; Nagasawa, H. Biosci. Biotechnol. Biochem. 2004, 68, 407–412. Kobayashi, Y.; Tan, C.-H.; Kishi, Y. Helv. Chim. Acta 2000, 83, 2562–2571. (a) Evans, D.A.; Trenkle, W.C.; Zhang, J.; Burch, J.D. Org. Lett. 2005, 7, 3335–3338; (b) Robles, O.; McDonald, F.E. Org. Lett. 2008, 10, 1811–1814. (6) (7)   52 values for AsA to Kishi's tetraols revealed a syn/syn/syn stereoarray. Additionally, the chemical shifts of C23 and C25 for the naturally derived2 and synthetic4 C3–C48 degradation fragments (1) were all within 0.6 ppm of each other, suggesting like syn/syn relationships about each carbon. If a syn/syn/anti stereochemical relationship existed in this region, we expected that the chemical shift of C25 would be approximately 69 ppm, or roughly 2 ppm lesser than C23.8 Since the absolute configurations of the C23 and C25 stereocenters were known, and the relative 1,3-syn relationship between C25 and C27 duly established, our analysis supported Sakuda's assignment for the C27 stereocenter. Table 3.1. Chemical shift analysis of the C21–C27 1,3,5,7-tetraol region.a Carbon C21 C23 C25 C27 C28 a Kishi Tetraol (syn/syn/syn)b – ~ 68 ~ 68 – – Sakuda Aflastatin Ab 73.5 67.9 67.5 67.9 74.3 Sakuda 1 2000c 76.2 70.8 73.1d 76.2e 72.2e Sakuda 1 2007 Correctionc – – 71.1 72.2 76.2 b Evans 1c syn 76.3 70.7 71.3 72.3 76.1 c OH OH OH OH R 21 23 25 27 R syn/syn/syn All chemical shifts (δ) are reported in ppm. misreported. e Values misassigned. Measured in DMSO-d6. Measured in pyridine-d5. d Value We then compared the spectroscopic profiles of the C27–C31 pentaol regions of naturally derived2 and synthetic4 C3–C48 degradation fragments 1 (Table 3.2). Their vicinal proton-proton spin-coupling profiles were similar and suggested that the relative stereochemistry in this region be assigned as anti/syn/syn/syn, according to Kishi's NMR database of 1,2,3,4,5-pentaols.3 We did note that the C30 carbon atoms differed in chemical shift by 1.2 ppm, but suspected that such disagreement was an artifact of some stereochemical                                                                                                                 (8) We assumed that our distribution of chemical shifts in pyridine-d5 would be similar to those observed by Kishi and coworkers in DMSO-d6 and methanol-d4. We did not expect intramolecular interactions (i.e. hydrogen-bonding networks) to significantly impact our analysis.   53 anomaly in the C33–C39 region.9 In the end, we trusted the coupling constant analysis and relayed the absolute stereochemistry of the C27 carbinol through the C27–C31 pentaol region, thereby supporting Sakuda's stereochemical revision of the C28–C31 stereocenters. Table 3.2. Data analysis of the C27–C31 pentaol region.a Coupling Constant Analysisa Protons Sakuda 1c Evans 1c Chemical Shift Analysisb Carbon C27 Sakuda 1c 72.2d 76.2d 71.5 75.4 70.9 b Evans 1c 72.3 76.1 71.4 74.2 71.0 OH OH OH R 27 31 H27–H28 H28–H29 H29–H30 H30–H31 7.5 3.0 5.0 3.0 7.0 C28 2.5 C29 5.5 C30 2.5 C31 R OH OH anti/syn/syn/syn a c All coupling constants (3JH,H) are reported in Hertz (Hz). Measured in pyridine-d5. d Values reassigned in 2007. All chemical shifts (δ) are reported in ppm. The preceding analyses (Tables 3.1 and 3.2) allowed us to relay the absolute configurations of C23 and C25 to C27 and eventually the entire C27–C31 pentaol region. As such, we limited the potential stereochemical problem to the C33–C39 region wherein the largest contiguous spectral discrepancies existed. We next developed a model for the C33–C39 region to help us solve the structural curiosity.4 The model needed to be large enough so that the site of truncation would not affect the chemical shifts of the stereocenters in question. The NMR databases demonstrated that interactions between structural motifs connected directly (α) or with one bridging carbon (β) were significant.6 Although the influence of structural motifs located outside this "selfcontained box" was often negligible, the effects of the γ- and δ-positions on chemical shift profiles were recognizable in some cases.3 When applied to the C33–C39 region, we identified a self-contained box spanning from C29 to C43. Fortunately, our model studies did                                                                                                                 (9) Medium coupling constant values (3JH,H and 2JC,H) were observed by Sakuda and coworkers about the C29– C30 bond. Due to uncertainty in their J-based configuration analysis and our C30 chemical shift comparison, we could not fully exclude the possibility of an anti/syn/anti/syn relationship in this region.   54 not require consumption of advanced intermediate C3–C26 ketone. Rather, we quickly accessed C27–C48 lactol region model 3a from an intermediate used in the synthesis of C3– C48 degradation fragment 1 (Scheme 3.1). Scheme 3.1. Synthesis of model C27–C48 lactol 3a. OH OBn OBn O 27 OH O 35 OTBS a,b 39 HO HO HO HO 27 31 35 OH OH 39 O Me O BnO Me 31 C9H19 44% Me O Me 2 OTBS OH OH H O 3a OH C9H19 Reagents and conditions: (a) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt; (b) H2, Pd black, dioxane, H2O, rt, 44% (2 steps). As hoped, the chemical shifts for model lactol 3a and synthetic C3–C48 degradation fragment 1 were in good agreement, except at those positions (C27–C29) closest to the site of truncation (Figure 3.2).4 It followed that similar discrepancies in spectral data for the C33– C39 region were seen between naturally derived2 C3–C48 degradation 1 and the truncated C27–C48 polyol 3a. OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH 39 Me 1H-NMR Me OH Me Me Me OH Me Me 1 13C-NMR OH OH Data HO HO HO HO 28 27 29 31 H O OH C9H19 Data HO HO HO OH 35 35 OH OH 39 OH OH 39 HO 28 27 29 31 OH OH |Δδ| ≥ 0.05 ppm H O OH 3a C9H19 OH OH |Δδ| > 1 ppm H O OH 3a C9H19 Figure 3.2. NMR data comparisons of model C27–C48 lactol 3a to synthetic C3–C48 degradation fragment 1. As such, we determined that diastereomers of truncated polyol 3a could serve as suitable models of the lactol region in our future studies toward the stereochemical revision of AsA. Ideally, once a spectral match was obtained, we could parlay our work on that model diastereomer into the synthesis of a revised C27–C48 aldehyde fragment.   55 II. Syntheses of the epi-C39 and epi-C33–C37 Lactols We revisited the chemical shift discrepancies between synthetic4 and naturally derived2 degradation fragments 1 and were intrigued that the largest numerical differences occurred from C36–C39 in the carbon spectra, and at H33, H38 and H39 in the proton spectra. These observations prompted us to question the stereochemical relationships between the C27–C31 pentaol region and the C33–C37 lactol, as well as the C33–C37 lactol and the isolated C39 stereocenter. The absolute configurations at C39 and C33 of AsA were determined by optical rotation analyses of small degradation fragments 410 and 5, respectively (Figure 3.3).2a We noticed that the J-based configuration analysis11 used to link the absolute configurations of C31 and C33 before the stereochemical revision of AsA was later discarded.2b With this in mind, we decided to check the validity of the optical rotation data through chemical syntheses of epi-C39 and epi-C33–C37 lactol regions 3b and 3c, respectively. The latter diastereomer was designed to be epimeric at C33 and by necessity throughout the entire C33–C37 region in order to preserve the relative stereochemistry within the lactol ring, as supported by published coupling constant and NOE data.5a,b degradation fragments HO 4 inversion of configuration OH model C27–C48 lactols HO 27 O OH 39 5 BzO BzO 33 31 C9H19 H OBz OH OH OH 39 HO HO HO 31 35 HO HO HO 33 35 OH OH 39 OH OH H O OH C9H19 HO 27 31 OH OH H O OH C9H19 3b, epi-C39 3c, epi-C33–C37 Figure 3.3. Design of model C27–C48 lactols 3b and 3c to probe optical rotation data.                                                                                                                 (10) Vining, L.C.; Taber, W.A. Can. J. Chem. 1962, 40, 1579–1584. (11) Matsumori, N.; Kaneno, D.; Murata, M.; Nakamura, H.; Tachibana, K. J. Org. Chem. 1999, 64, 866–876.   56 A. Synthesis of the epi-C39 Lactol12 The first truncated polyol that we targeted was the C39 epimer (3b). Our synthesis plan for this diastereomer targeted the same C35–C36 aldol bond disconnection,13 except that enantiomeric ketone ent-7 would be added to common aldehyde intermediate 6 (Scheme 3.2). Scheme 3.2. Synthesis plan for epi-C39 lactol 3b. OH HO HO HO HO 27 31 36 35 OH OH 39 oxygenated aldol addition RO 6 27 OR OR O 31 O 35 O H OTBS OTBS 39 OH OH H O OH C9H19 C9H19 RO RO 3b, epi-C39 Me O Me ent-7 We took this opportunity to further improve the synthesis of the C36–C48 ketone (Scheme 3.3).14 Our route featured the iridium-catalyzed transfer hydrogenative allylation15 of 1-decanol to give homoallylic carbinol ent-8 in very good yield and excellent enantioselection. Silylation and dihydroxylation16 afforded diol ent-9. Regioselective silylation and ParikhDoering oxidation17 then gave α-silyloxyketone ent-7 in five steps and good overall yield. Scheme 3.3. Synthesis of C36–C48 ketone ent-7. 37 OH OAc 39 a 81%, 95% ee OH 38 39 b,c 84%, dr ~ 1:1 OH OTBS 39 d,e 79% O OTBS 39 C9H19 C9H19 C9H19 C9H19 ent-8 OH ent-9 OTBS ent-7 Reagents and conditions: (a) [Ir(cod)Cl]2 (2.5 mol%), (R)-(+)-BINAP, Cs2CO3, m-NO2BzOH, THF, 100 °C, 81%, 95% ee; (b) TBSCl, imidazole, DMF, 0 °C to rt; (c) RuCl3, CeCl3•7H2O, NaIO4, EtOAc, MeCN, H2O, 0 °C, dr ~ 1:1, 84% (2 steps); (d) TBSCl, imidazole, DMF, 0 °C to rt, 93%; (e) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –10 °C to 10 °C, 85%.                                                                                                                 (12) The synthesis of epi-C39 lactol 3b was achieved by the author in collaboration with Drs. Egmont Kattnig and Peter H. Fuller. (13) (a) Glorius, F. Development of α-Oxygenated Aldol Methodology and Progress Towards the Synthesis of Aflastatin A. Postdoctoral Report, Harvard University, 2001; (b) Evans, D.A.; Glorius, F.; Burch, J.D. Org. Lett. 2005, 7, 3331–3335. (14) This reaction sequence was designed and performed by Dr. Peter H. Fuller. (15) Kim, I.S.; Ngai, M.-Y.; Krische, M.J. J. Am. Chem. Soc. 2008, 130, 14891–14899. (16) (a) Plietker, B.; Niggemann, M. J. Org. Chem. 2005, 70, 2402–2405; (b) Plietker, B. Synthesis 2005, 2453– 2472. (17) Parikh, J.R.; Doering, W.v.E. J. Am. Chem. Soc. 1967, 89, 5505–5507.   57 With C27–C35 aldehyde 10 in hand,4 the synthesis of epi-C39 lactol 3b was three steps from completion (Scheme 3.4). Addition of the corresponding (E) enolate of ketone ent7 to aldehyde 10 produced the desired anti-Felkin product 11 in poor isolated yield18 but with a similar level of diastereoselection previously observed en route to lactol 3a (dr = 84:16). The inverted stereochemistry (C39) at the β'-position of ketone ent-7 had a minimal impact on C35–C36 aldol reaction diastereoselectivity. Ultimately, removal of the acetonide, silyl and benzyl protecting groups provided epi-C39 lactol 3b in serviceable yield. Scheme 3.4. Synthesis of epi-C39 lactol 3b. OBn OBn O 27 O 35 O H OTBS OTBS a 27 39 OBn OBn O O 16%, dr ~ 77:23 Me O BnO Me 31 OH O 36 35 OTBS 39 O Me O BnO Me 31 C9H19 C9H19 Me O Me ent-7 Me O Me b,c OH OTBS 11 10 3b, epi-C39 HO 27 HO HO HO 31 35 OH OH 39 OH OH H O OH C9H19 Reagents and conditions: (a) ketone ent-7, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 10, PhMe, –78 °C to – 25 °C, 16%, dr ~ 77:23; (b) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt, 50%; (b) H2, Pd black, dioxane, H2O, rt. B. Synthesis of the epi-C33–C37 Lactol19 The second truncated polyol that we targeted was the C33–C37 epimer (3c). Our synthesis plan for this diastereomer again targeted the C35–C36 aldol bond disconnection13 because inversion of the entire lactol preserved the anti/syn/anti relationship required for this transform (Scheme 3.5). Additionally, we expected the diastereoselectivity of this reaction to be restored to the excellent levels seen before the revision since the relative configuration                                                                                                                 (18) The quality of the chlorodicyclohexylborane used in this reaction was questionable. For the best results, we distilled Cy2BCl at least once every 3 months and stored it under argon in a Schlenck flask at –20 °C. (19) The synthesis of epi-C33–C37 lactol 3c was achieved by the author in collaboration with Drs. Egmont Kattnig and Peter H. Fuller.   58 between the C31 and C33 carbinol stereocenters was again 1,3-anti.13b,20 The C27–C35 fragment 14 would in turn be assembled via the double stereodifferentiating syn aldol addition of α,α'-bisoxygenated ketone 15 21 to β-oxygenated aldehyde 16. We expected excellent diastereoselection due to the matched relationship between the ketone α'-stereocenter and the aldehyde β-stereocenter. Dipole-dipole minimization within both ketone 22 and aldehyde 23 would determine their respective facial selectivities, and bond formation would occur on each reactant's less sterically hindered face. Scheme 3.5. Synthesis plan for epi-C33–C37 lactol 3c. OH HO HO HO HO 27 31 36 35 OH OH 39 oxygenated aldol addition RO 12 27 OR OR O 31 O 35 O H OTES OTBS 39 OH OH O 27 H O OH C9H19 C9H19 13 RO RO O H 31 3c, epi-C33–C37 O 35 Me O Me O 30 1,3-anti oxygenated aldol addition OPMB 16 RO 27 OH O 31 35 O Me O Me 15 OTES OR 14 Me O Me RO RO 1,3-anti Me O Me We took this opportunity to modify the protecting group scheme of the C36–C48 ketone. We finally decided to protect the C36 carbinol as its TES ether24 rather than its TBS ether because removal of the latter protecting group during our previous fragment and model                                                                                                                 (20) (a) Zhang, J. Studies Toward the Total Synthesis of (–)-Aflastatin A. Postdoctoral Report, Harvard University, 2003; (b) Burch, J.D. Complex Aldol Reactions for Polyketide Synthesis: I. Total Synthesis of Callipeltoside A. II. Synthesis of the C27–C48 Subunit of Aflastatin A. Ph.D. Thesis, Harvard University, 2005. (21) Chlorodicyclohexylboron-mediated aldol reactions of α-triethylsilyloxyketone 15 were known to produce syn products via the corresponding (Z) enolate. See: (a) Marco, J.A.; Carda, M.; Falomir, E.; Palomo, C.; Oiarbide, M.; Ortiz, J.A.; Linden, A. Tetrahedron Lett. 1999, 40, 1065–1068; (b) Carda, M.; Murga, J.; Falomir, E.; González, F.; Marco, J.A. Tetrahedron 2000, 56, 677–683; (c) Ribes, C.; Falomir, E.; Carda, M.; Marco, J.A. Org. Lett. 2007, 9, 77–80. (22) (a) Masamune, S.; Choy, W.; Kerdesky, F.A.J.; Imperiali, B. J. Am. Chem. Soc. 1981, 103, 1566–1568; (b) Heathcock, C.H.; Arseniyadis, S. Tetrahedron Lett. 1985, 26, 6009–6012; (c) Bernardi, A.; Capelli, A.M.; Comotti, A.; Gennari, C.; Gardner, M.; Goodman, J.M. Paterson, I. Tetrahedron 1991, 47, 3471–3484. (23) Evans, D.A.; Dart, M.J.; Duffy, J.L.; Yang, M.G. J. Am. Chem. Soc. 1996, 118, 4322–4343. (24) Boron-mediated aldol reactions of α-triethylsilyloxyketones were known. For examples, see: Ref. 21.   59 syntheses was difficult.4 The synthesis of C36–C48 ketone 13 (Scheme 3.6) was achieved in similar fashion to its pseudo-enantiomer ent-7 (Scheme 3.3). As a point of difference, regioselective triethylsilylation of diol 9 and oxidation17 of the intermediate C37 carbinol gave C36–C48 ketone 13 in five steps and good overall yield. Scheme 3.6. Synthesis of C36–C48 ketone 13. 37 OH OAc 39 a 72%, ≥ 90% ee OH 38 39 b,c 66%, dr ~ 1:1 OH OTBS 39 d,e 89% O OTBS 39 C9H19 C9H19 C9H19 C9H19 8 OH 9 OTES 13 Reagents and conditions: (a) [Ir(cod)Cl]2 (2.5 mol%), (S)-(+)-BINAP, Cs2CO3, m-NO2BzOH, THF, 100 °C, 72%, ≥ 90% ee; (b) TBSCl, imidazole, DMF, 0 °C to rt, 90%; (c) RuCl3, CeCl3•7H2O, NaIO4, EtOAc, MeCN, H2O, 0 °C, dr ~ 1:1, 73%; (d) TESCl, EtN(iPr)2, CH2Cl2, –60 °C to –20 °C, 90%; (e) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C, 99%. The synthesis of epi-C33–C37 lactol 3c began with the preparation of ketone 15 in six steps from L-ascorbic acid,25 and aldehyde 16 in five steps from (–)-2,3-O-isopropylidene-Derythronolactone26 (Scheme 3.7). Addition of the (Z) boron enolate derived from ketone 15 to aldehyde 16 provided adduct in good yield with excellent diastereoselection. 27 Prasad reduction,28,29 protecting group manipulation, and oxidation17 provided aldehyde 19 in good overall yield. As expected, anti aldol addition of ketone 13 to this aldehyde provided adduct 20 as a single diastereomer in good overall yield. Ultimately, the now standard two-step deprotection sequence yielded epi-C33–C37 lactol 3c.                                                                                                                 (25) Marco, J.A.; Carda, M.; González, F.; Rodríguez, S.; Murga, J. Liebigs Ann. Chem. 1996, 1801–1810. (26) For steps related to the synthesis of aldehyde 16, see: (a) Choi, W.J.; Park, J.G.; Yoo, S.J.; Kim, H.O.; Moon, H.R.; Chun, M.W.; Jung, Y.H.; Jeong, L.S. J. Org. Chem. 2001, 66, 6490–6494; (b) Pirrung, F.O.H.; Hiemstra, H.; Speckamp, W.N.; Kaptein, B.; Schoemaker, H.E. Synthesis 1995, 458–472; (c) Brown, H.C.; Mandal, A.K.; Kulkarni, S.U. J. Org. Chem. 1977, 42, 1392–1398; (d) Kang, S.-K.; Jung, K.Y.; Chung, J.-U.; Namkoong, E.-Y.; Kim, T.-H. J. Org. Chem. 1995, 60, 4678–4679. (27) The stereochemistry of the newly formed stereogenic center was determined by Mosher ester analysis. See: (a) Dale, J.A.; Mosher, H.S. J. Am. Chem. Soc. 1973, 95, 512–519; (b) Hoye, T.R.; Jeffrey, C.S.; Shao, F. Nat. Protoc. 2007, 2, 2451–2458. (28) Chen, K.-M.; Hardtmann, G.E.; Prasad, K.; Repič, O; Shapiro, M.J. Tetrahedron Lett. 1987, 28, 155–158. (29) The stereochemistry of the newly formed stereogenic center was determined by [13C]acetonide analysis. See: Rychnovsky, S.D.; Rogers, B.N.; Richardson, T.I. Acc. Chem. Res. 1998, 31, 9–17.   60 Scheme 3.7. Synthesis of epi-C33–C37 lactol 3c. O 27 O H 31 O a 35 27 O OPMB 16 78%, dr ≥ 95:05 30 OH O b,c 31 35 O Me O Me 15 OBn OBn O 27 30 31 O Me O Me O 35 OPMB 66%, dr ≥ 95:05 OTES Me O Me RO Me O Me O 17, R = TES OTBS OBn OBn O d,e 35 27 O Me O BnO Me 18 OPMB 30 31 f H OTES OH HO HO HO 35 39 O Me O BnO Me 19 C9H19 13 56%, 3 steps, dr ≥ 95:05 Me O Me Me O Me OBn OBn O 27 OH O 36 35 OTBS g,h 39 OH OH 39 O Me O BnO Me 31 C9H19 HO 27 31 Me O Me OTES 20 OH OH H O OH C9H19 3c, epi-C33–C37 Reagents and conditions: (a) Cy2BCl, Et3N, Et2O, –78 °C to 0 °C, dr ≥ 95:05, 78% (2 steps); (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to 0 °C; aq H2O2, pH 7 buffer, MeOH, 0 °C to rt, 92%, dr ≥ 95:05; (c) CsF, THF, 70 °C; BnBr, NaH, nBu4NI, 0 °C to rt, 72%; (d) DDQ, CH2Cl2, pH 7 buffer, 0 °C, no hν, 81%; (e) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C; (f) ketone 13, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 19, Et2O, –78 °C to –25 °C, dr ≥ 95:05, 56% (3 steps); (g) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt; (h) H2, Pd black, dioxane, H2O, rt. After completing the syntheses of lactols 3b and 3c, we once again compared spectroscopic data. Coupling constant analysis (3JH31–H32) revealed that the stereochemical relationship between C31 and the lactol was correct in diastereomers 3a and 3b, but not epiC33–C37 lactol 3c (Table 3.3). As expected, the degradation fragments and model lactols all exhibited similar spin-coupling profiles around the C33–C37 lactol. Table 3.3. Coupling constant analysis of the C31–C36 region.a OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH OH 39 HO HO HO HO 27 31 35 HO HO HO HO 27 31 35 OH OH 39 OH OH H O OH 3a C9H19 OH OH H O OH C9H19 OH OH H O OH C9H19 3b, epi-C39 Synthetic 1b 6.6, 7.8 3.0, 10.2 9.6 9.6 3.0 Lactol 3ac 6.3, 7.6 2.9, 10.2 9.7 9.5 3.4 Lactol 3bc 5.5, 7.3 2.7, 9.5 9.5 9.5 3.4 Lactol 3cc 2.9, 10.0 2.9, 10.0 9.7 9.5 3.4 3c, epi-C33–C37 Protons H31–H32 H32–H33 H33–H34 H34–H35 H35–H36 a d Sakuda 1 6.0, 8.0b 3.5, 10.0b OH HO HO R 31 35 OH 38 9.5d 9.5d 3.0d H O R OH All coupling constants (3JH,H) are reported in Hertz (Hz). b Measured in pyridine-d5. c Measured in methanol-d4. Measured in DMSO-d6.   61 Chemical shift analysis in the C38–C39 region was not as conclusive (Table 3.4). We were hard pressed to explain the relative positional flip of the H38 protons throughout the series. Ultimately, we surmised that the absolute configurations at both C33 and C39 were assigned properly.30 Table 3.4. Chemical shift analysis of the C38–C39 region. Protons H38ac H38bd H39 a Sakuda 1b 2.45 2.19 4.18 Synthetic 1b 2.14 2.73 4.72 Lactol 3ab 2.16 2.74 4.73 Lactol 3bb 2.48 2.62 4.59 Lactol 3cb 2.38 2.70 4.56 OH HO R 32 35 OH OH 39 H O OH R All chemical shifts (δ) are reported in ppm. b Measured in pyridine-d5. c Observed peak a doublet of doublets having two large coupling constants. d Observed peak a doublet of doublets having one large and one small coupling constant. III. Syntheses of Three Diastereomeric epi-C36 Lactols Having substantiated the stereochemical assignments at C33 and C39 with our own data, we refocused on the remaining structural ambiguities in the lactol region. We reasoned that due to conformational and anomeric effects, the configuration at C33 should control C37, thus leaving three stereocenters (C34–C36) in question (Figure 3.4A). Now limited to eight possible diastereomers, we scrutinized the published spectra for further guidance. Out of all the peaks associated with the C34–C36 triol, one distinct doublet of doublets (dd) was identified in the 1H-NMR spectrum (Figure 3.4B).2a Assuming a chair conformation, the requirement that a proton within the lactol ring exhibit one large (L) and one small (S) coupling constant (or be anti and gauche to vicinal protons, respectively) reduced the field to four diastereomers (Figure 3.4C), one of which was the originally assigned structure (3a). Our highest priority became the synthesis of a structure (3d) that agreed with the proposed                                                                                                                 (30) The corresponding C31 and C37 stereocenters of blasticidin A were assigned the same absolute configuration. See: (a) Sakuda, S.; Ono, M.; Ikeda, H.; Inagaki, Y.; Nakayama, J.; Suzuki, A.; Isogai, A. Tetrahedron Lett. 1997, 38, 7399–7402; (b) Sakuda, S.; Ono, M.; Ikeda, H.; Nakamura, T.; Inagaki, Y.; Kawachi, R.; Nakayama, J.; Suzuki, A.; Isogai, A.; Nagasawa, H. J. Antibiotics 2000, 53, 1265–1271.   62 assignment of this peak to H35 (Figure 3.4D). Should we suspect that the two-dimensional NMR correlation data had been misinterpreted and the peak actually corresponds to H34, both structures 3e and 3g would become viable synthesis candidates. We were open to this possibility because a similar error may have led to the correction (and formal swap) of chemical shift data sets for C27 and C28 when the stereochemical revision was reported.2b A OH HO HO HO HO 34 R 27 31 35 36 OH OH 39 D 35 H H 36 33 H O OH OH R HO 27 OH OH H O OH C9H19 HO HO 34 HO HO HO 31 H OH 35 OH OH 39 8 possible diastereomers B 1H-NMR H R 2 possible diastereomers if dd is H35 H H HO 36 33 OH OH H O OH C9H19 3a (AsA) H OH 35 OH R HO HO HO HO 27 31 Inset of 1 (Sakuda 2000, in pyridine-d5) 35 (dd, J = 9.5, 3.0 Hz, 1H) HO H 34 OH OH 39 R OH H O OH OH H O OH C9H19 3d, epi-C34,C36 H OH 35 δ (ppm) 35 OH OH H HO 36 33 4 possible diastereomers C Expected Lactol Splitting Patterns Isomer 3a 3b 3c 3d H33 ddd2L,1S ddd1L,2S ddd2L,1S ddd2L,1S H34 tL tS dd dd H35 dd dd tS tS H36 dS dS dL dS HO H 34 R O HO 27 HO HO HO 31 OH OH 39 H R H 2 possible diastereomers if dd is H34 OH H 36 33 OH OH H O OH C9H19 3e, epi-C35,C36 H OH 35 H O OH OH R HO 27 35 HO H 34 HO HO HO 31 OH OH 39 H R OH OH H O OH C9H19 3g, epi-C35 Figure 3.4. Design of model C27–C48 lactols 3d, 3e and 3g to probe two-dimensional NMR correlation data. Abbreviations: d = doublet, t = triplet, S = having a small J value(s), L = having a large J value(s). A. Synthesis of the epi-C34,C36 Lactol31 Under this rationale, we first targeted the synthesis of epi-C34,C36 lactol 3d. Since the relative stereochemistry of the C33–C36 tetraol region was changed, we could no longer form                                                                                                                 (31) The synthesis of epi-C34,C36 lactol 3d was achieved by Dr. Peter H. Fuller in collaboration with the author.   63 the C35–C36 bond by anti-Felkin-selective oxygenated aldol addition.13 Instead, we tried to form this bond by the Cornforth-selective syn aldol addition32 of ketone 13 to aldehyde 21, but these efforts were stymied by an unexpected reversal in enolate regioselectivity33 (eq 1). Me Me OBn O MOPO 27 TBSO BnO 31 Me Me O 35 O ketone 13, 9-BBN-OTf, iPr2NEt H Et2O 71%, dr ≥ 95:05, regioselection 94:06 OBn O MOPO 27 TBSO BnO 31 O OH O 35 OTES 36 (1) OBn 21 22 BnO TBSO C9H19 We then modified our synthesis plan such that the assembly of the C33–C36 syn/anti/syn tetraol relied on the diastereoselective syn dihydroxylation16 of enone 24 according to Kishi's empirical rule34 (Scheme 3.8). The C35–C36 bond of enone 24 would in turn be formed by the Horner-Wadsworth-Emmons reaction35 of β-ketophosphonate 26 and aldehyde 25. Then, given the success of our newly developed chelate-controlled aldol reaction, we anticipated applying our soft-enolization based method4 to the formation of the C32–C33 bond via 1,2-chelate-controlled addition of ketone 27 to aldehyde 28. Based upon the Cram chelate model,36 we expected excellent selectivity for the desired 1,2-syn diastereomer via exclusive formation of five-membered chelate 29 and nucleophilic addition to the less sterically hindered face.                                                                                                                 (32) (a) Cornforth, J.W.; Cornforth, R.H.; Mathew, K.K. J. Chem. Soc. 1959, 112–127; (b) Evans, D.A.; Siska, S.J.; Cee, V.J. Angew. Chem., Int Ed. 2003, 42, 1761–1765; (c) Cee, V.J. I. Asymmetric Induction in Heteroatom-Substituted Aldehydes. II. Total Synthesis of (+)-Casuarine. Ph.D. Thesis, Harvard University, 2003. (33) Products resulting from α'-enolization were not observed in earlier chlorodicyclohexylboron-mediated aldol additions of C36–C48 ketones. See: Ref. 13. (34) (a) Cha, J.K.; Christ, W.J.; Kishi, Y. Tetrahedron Lett. 1983, 24, 3943–3946; (b) Cha, J.K.; Christ, W.J.; Kishi, Y. Tetrahedron 1984, 40, 2247–2255. (35) (a) Horner, L.; Hoffman, H.; Wippel, H.G.; Klahre, G. Chem. Ber. 1959, 92, 2499–2505; (b) Wadsworth, W.S., Jr.; Emmons, W.D. J. Am. Chem. Soc. 1961, 83, 1733–1738. (36) (a) Cram, D.J.; Abd Elhafez, F.A. J. Am. Chem. Soc. 1952, 74, 5828–5835; (b) Cram, D.J.; Kopecky, K.R. J. Am. Chem. Soc. 1959, 81, 2748–2755; (c) Cram, D.J.; Leitereg, T.H. J. Am. Chem. Soc. 1968, 90, 4019– 4026.   64 Scheme 3.8. Synthesis plan for epi-C34,C36 lactol 3d. OH HO HO HO HO 27 31 35 OH OH 39 1,2-syn lactol formation RO 27 OR OR OR OR O 36 31 35 OR 39 OH OH 1,2-syn H O OH C9H19 C9H19 RO RO OR OR dihydroxylation 3d, epi-C34,C36 25 RO 27 23 OR OR OR O 32 33 35 H O (EtO)2P O 37 OTBS C9H19 HWE RO 27 OR OR OR 31 35 O 36 OR 39 C9H19 RO RO chelate-controlled aldol addition 27 OR 26 RO RO OR 24 OBn O 31 O 34 1,2-syn OTBS OBn 28 α-alkoxy chelate Bn 29 O R M O H Nu H 34 O Me O Me Me H 33 OBn 27 The synthesis of lactol 3d began with the preparation of ketone 27 in eight steps from methyl α-D-(+)-glucopyranoside, 37 aldehyde 28 in six steps from glycidol, 38 and βketophosphonate 26 in three steps from diol 9 (Scheme 3.9). 39 1,2-Chelation-controlled addition of ketone 27 to aldehyde 28 under soft enolization conditions proceeded with excellent diastereoselection. Prasad reduction28 of the intermediate adduct to diol 30, acetonide formation, desilylation and oxidation17 at C35 yielded aldehyde 32. Barium hydroxide-mediated addition40 of phosphonate 26 to this aldehyde provided (E) enone 33 as a single isomer in good overall yield. As predicted by Kishi's empirical rule,34 dihydroxylation16 provided the desired 1,2-syn diol 34 in good yield and diastereoselection. Finally, the standard deprotection sequence gave epi-C34,C36 lactol 3d.                                                                                                                 (37) The synthesis of the C27–C31 aldehyde precursor to ketone 27 will be discussed in due course. (38) (a) Kolakowski, R.V.; Williams, L.J. Tetrahedron Lett. 2007, 48, 4761–4764; (b) Furrow, M.E.; Schaus, S.E.; Jacobsen, E.N. J. Org. Chem. 1998, 63, 6776–6777. (39) For an analogous synthesis of a structurally related β-ketophosphonate, see: Traoré, M.; Maynadier, M.; Souard, F.; Choisnard, L.; Vial, H.; Wong, Y.-S. J. Org. Chem. 2011, 76, 1409–1417. (40) (a) Alvarez Ibarra, C.; Arias, S.; Fernández, M.J.; Sinisterra, J.V. J. Chem. Soc., Perkin Trans. II 1989, 503–508; (b) Paterson, I.; Yeung, K.-S.; Smaill, J.B. Synlett 1993, 774–776.   65 Scheme 3.9. Synthesis of epi-C34,C36 lactol 3d. 27 OBn O 31 O Me H 35 a,b OTBS 56%, dr ≥ 95:05 O Me OBn 28 27 OBn OH OH 32 33 c,d OTBS 95% O Me O Me 27 OBn Me Me O Me O 35 OBn 30 O (EtO)2P OBn Me Me e 35 27 27 OBn O 31 O OH OBn O 31 O O 37 OTBS f C9H19 65%, 2 steps O Me O Me 31 O Me O Me H OBn OBn Me Me OBn 32 OBn 26 Me Me 27 OBn O 31 O 35 O 36 OTBS 39 g 76%, dr ≥ 90:10 O Me 27 OBn O 31 O OH O 36 35 OTBS 39 O Me O Me C9H19 C9H19 OBn OBn 33 O Me OBn h,i OBn OH 34 OH 3d, epi-C34,C36 HO 27 HO HO HO 31 35 OH OH 39 OH OH H O OH C9H19 Reagents and conditions: (a) MgBr2•OEt2, PMP, CH2Cl2, –5 °C, dr ≥ 95:05; (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to 0 °C; aq H2O2, NaOH, MeOH, 0 °C to rt, dr ≥ 95:05, 56% (2 steps); (c) Me2C(OMe)2, PPTS, acetone, rt, quant.; (d) Et3N•HF, THF, 0 °C to rt, 95%; (e) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C; (f) Ba(OH)2, THF, H2O, 0 °C to 10 °C, 65% (2 steps); (g) RuCl3, CeCl3•7H2O, NaIO4, EtOAc, MeCN, H2O, 0 °C, 76%, dr ≥ 90:10; (h) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt, ~70%; (i) H2, Pd black, dioxane, H2O, rt. After completing the synthesis of lactol 3d, we were initially disappointed by how poorly its spectroscopic data matched that of polyol 1. Upon further analysis, we did observe a favorable exchange of the H38 resonances, most likely resulting from the inverted configuration at C36, and decided this effect deserved further investigation. Accordingly, we prioritized the synthesis of epi-C35,C36 lactol 3e over that of epi-C35 lactol 3g. B. Synthesis of the epi-C35,C36 Lactol41 Somewhat serendipitously, a precursor to epi-C35,C36 lactol 3e had already been isolated as the minor (Felkin) diastereomer in the earlier anti aldol addition of ketone 7 to aldehyde 35 (Scheme 3.10). Two-step global deprotection of this aldol product provided epiC35,C36 lactol 3e.                                                                                                                 (41) The synthesis of epi-C35,C36 lactol 3e was achieved by the author in collaboration with Dr. Peter H. Fuller.   66 Scheme 3.10. Synthesis of epi-C35,C36 lactol 3e. OBn OBn O TESO 27 TBSO BnO 35 b,c OH 3e, epi-C35,C36 HO 27 31 O 35 O H OTBS OTBS 39 a dr = 14:86 OBn OBn O TESO 27 TBSO BnO 31 OH O 36 35 OTBS 39 C9H19 7 C9H19 36 Me O Me Me O Me OTBS HO HO HO 31 35 OH OH 39 OH OH H O OH C9H19 Reagents and conditions: (a) ketone 7, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 35, PhMe, –78 °C to – 20 °C, 66%, dr = 14:86; (b) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt, 53%; (c) H2, Pd black, dioxane, H2O, rt. Comparison of the spectroscopic data for lactol 3e with naturally derived2 degradation polyol 1 produced the best chemical shift match to date for the methylene protons at C32 and C38 while maintaining the same beneficial interchange of H38 resonances that were observed for lactol 3d. The excellent overlay of these diagnostic peaks suggested that the relative stereochemistries in lactol 3e between the C34 stereocenter and the C27–C31 pentaol region, and the C36 stereocenter and the isolated C39 stereocenter, were correct. Disappointingly, much of the spectroscopic data within the lactol ring itself still exhibited poor overlay. We hypothesized that this could be rectified by inverting the stereochemistry at C35 to its originally assigned configuration (Figure 3.5). In doing so, we discredited a coupling constant that was assigned to this region (3JH-35,H-36 = 3 Hz).5a The possibility that a coupling constant had been measured incorrectly was not so unreasonable since the correction of one value (3JH-9,H-10) by the isolation group led to the stereochemical revision of the AsA C8–C9 diol region.2b Unfortunately, this possibility was also inconsistent with our previous spectral analysis, namely the assumption that a doublet of doublets (having one small J value of about 3 Hz) corresponds to either H34 or H35. Out of both desperation and curiosity, we proceeded anyway with the synthesis of lactol 3f.   67 OH HO HO HO 34 HO 27 31 35 OH OH 36 39 inversion at C35 HO 27 OH HO HO HO 34 31 35 36 OH OH 39 OH OH H O OH C9H19 OH OH H 35 H O OH C9H19 3e, epi-C35,C36 H 36 33 3f, epi-C36 H OH R 3J H35,H36 35 OH OH H HO 36 33 HO H 34 R O 3J H35,H36 HO HO 34 H R H = 3 Hz H R O OH = ? Hz Figure 3.5. Design of epi-C36 lactol 3f to probe the H35–H36 coupling constant. C. Synthesis of the epi-C36 Lactol42 Our synthesis plan for epi-C36 lactol 3f relied on the formation of the C36–C37 and C32–C33 bonds by a series of chelation-controlled additions (Scheme 3.11). We began with formation of the C36–C37 bond via 1,2-chelate-controlled addition of the organomagnesiate of vinyl bromide 39 to α-benzyloxy aldehyde 38.43 Based upon the Cram chelate model,36 we expected excellent selectivity for the desired 1,2-syn diastereomer via exclusive formation of a five-membered chelate. Similarly, we expected that addition of ketone 27 to the sixmembered chelate of aldehyde 40 would afford the desired 1,3-anti relationship in C27–C36 fragment 38. Scheme 3.11. Synthesis plan for epi-C36 lactol 3f. OH HO HO HO HO 27 31 35 OH OH 39 1,2-syn lactol formation RO 37 OR OR OR OR 36 29 33 37 OR 39 OH OH H O OH C9H19 C9H19 RO RO chelate-controlled aldol addition OTES 40 RO 27 OR OR 1,3-anti 3f, epi-C36 OBn O 31 27 O Me H 33 OBn 36 OR OR OR OBn 32 33 36 chelate-controlled vinylmetal addition OTBS H Br 39 39 O Me O Me 27 C9H19 OBn OTBS RO RO 38 R3SiO O                                                                                                                 (42) The synthesis of epi-C36 lactol 3f was achieved by the author in collaboration with Dr. Peter H. Fuller. (43) For similar chelation-controlled additions of vinylmagnesium reagents, see: (a) Heathcock, C.H.; McLaughlin, M.; Medina, J.; Hubbs, J.L.; Wallace, G.A.; Scott, R.; Claffey, M.M.; Hayes, C.J.; Ott, G.R. J. Am. Chem. Soc. 2003, 125, 12844–12849; (b) Terrell, L.R. The Total Synthesis of the Assigned Structure of Amphidinolide A. Ph.D. Thesis, Michigan State University, 2001.   68 The synthesis of lactol 3f began with the preparation of aldehyde 40 in five steps from cinnamaldehyde44 (Scheme 3.12). 1,3-Chelation-controlled addition of ketone 27 to aldehyde 40 under soft enolization conditions4 proceeded with excellent diastereoselection. Prasad reduction28 of the intermediate adduct furnished diol 41. Acetonide formation, desilylation and oxidation17 at C36 yielded aldehyde 43. Addition of the magnesiated carbanion of vinyl bromide 3945 to this aldehyde provided the desired 1,2-syn adduct as a single diastereomer in very good overall yield. Silylation and ozonolysis were followed by the standard deprotection sequence to give epi-C36 lactol 3f. Scheme 3.12. Synthesis of epi-C36 lactol 3f. 27 OBn O 31 O Me H OBn 35 O Me O Me 27 OTES a,b dr ≥ 94:06 Me Me O Me 27 OBn OH OH OBn 32 33 OTES OTBS c,d 73%, 4 steps OBn Me Me OTBS 40 O OBn 35 O Me OBn 41 27 OBn O 31 O Me O Me 42 OH e O Me 27 OBn O 31 O OBn 35 OTBS H Br 39 Me Me 39 f 85%, 2 steps, dr ≥ 95:05 C9H19 OBn OTBS Me Me O Me OBn TBSO 43 O 27 OBn O 31 O OBn 36 37 OTBS C9H19 44 g,h 42% O Me 27 OBn O 31 O OBn O OTBS C9H19 O Me O Me OBn TBSO OH O Me OBn TBSO i,j OH HO HO HO OTES 45 3f, epi-C36 HO 27 35 OH OH 39 31 OH OH H O OH C9H19 Reagents and conditions: (a) MgBr2•OEt2, PMP, CH2Cl2, –5 °C, dr ≥ 94:06; (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to 0 °C; aq H2O2, pH 7 buffer, MeOH, 0 °C to rt, dr ≥ 95:05; (c) Me2C(OMe)2, PPTS, acetone, rt; (d) PPTS, CH2Cl2, MeOH, 0 °C to rt, 73% (4 steps); (e) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C; (f) bromide 39, t-BuLi, Et2O, pentane, –78 °C; MgBr2•OEt2, Et2O, PhH, –78 °C to 0 °C; aldehyde 43, CH2Cl2, – 78 °C to 0 °C, dr ≥ 95:05, 85% (2 steps); (g) TESCl, imidazole, nBu4NI, DMF, 0 °C to 60 °C, 73%; (h) O3, py, CH2Cl2, MeOH, –78 °C; PPh3, –78 °C to rt, 58%; (i) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt, 61%; (c) H2, Pd black, dioxane, H2O, rt.                                                                                                                 (44) Evans, D.A.; Cee, V.J.; Siska, S.J. J. Am. Chem. Soc. 2006, 128, 9433–9441. (45) Vinyl bromide 39 may be prepared in two steps from decanal. See: Zhang, Z.; Huang, J.; Ma, B.; Kishi, Y. Org. Lett. 2008, 10, 3073–3076.   69 Comparison of the spectroscopic data for lactol 3f with naturally derived2 degradation polyol 1 produced a better chemical shift match than lactol 3e for the H32 methylene protons, but an unexpectedly greater mismatch for the H38 protons (Table 3.5). Full comparison of the three diastereomeric epi-C36 lactols indicated that the absolute configuration of C34 in lactols 3e and 3f (as originally assigned) was correct. Unfortunately, chemical shift analysis of the C38 protons was not conclusive regarding the relationship between the C36 and C39 stereocenters. Although we observed a beneficial interchange of H38 resonances across the series, we could never achieve a full spectroscopic profile match for the lactol region of naturally derived2 degradation fragment 1. At this point in our search, we judged that we had exhausted all reasonable stereochemical possibilities and decided to discontinue the syntheses of more C27–C48 lactol diastereomers. Table 3.5. Chemical shift analysis of C32 and C38 for epi-C36 lactols 3d–f.a,b OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH OH 39 HO HO HO HO 27 31 35 HO HO HO HO 27 31 35 OH OH 39 OH OH H O OH C9H19 OH OH H O OH C9H19 OH OH H O OH C9H19 3d, epi-C34,C36 Protons H32a H32b H38a H38b a 3e, epi-C35,C36 Lactol 3d 2.94 2.69 2.64 2.05 Lactol 3e 3.09 2.51 2.45 2.16 Lactol 3f 3.21 2.51 2.67 2.06 3f, epi-C36 Sakuda 1 3.17 2.49 2.45 2.19 Synthetic 1 3.21 2.56 2.14 2.73 OH HO HO R 32 35 OH OH 38 H O OH R All chemical shifts (δ) are reported in ppm. b Measured in pyridine-d5.   70 IV. A Solution to the Structural Problem46 Despite achieving the syntheses of model C27–C48 lactol 3a and five of its diastereomers (3b–3f), we were left without a suitable spectroscopic match for naturally derived2 C3–C48 degradation product (née "lactol") 1. Prior comparisons of proton chemical shift data left the relationship between the C33–C37 lactol and the isolated C39 stereocenter unclear, so we shifted focus to the chemical shift of the C37 lactol carbon. Having believed the structural issue to be stereochemical in origin for so long, we were delighted to realize that our data for the C37 lactol carbon of model C27–C48 lactol 3a closely matched that reported for the C35 lactol carbon of the structurally related blasticidin A (BcA) C3–C47 degradation lactol 47 (Table 3.6).47 Generally speaking, the chemical shift of the C37 carbon in all model C27–C48 diastereomers more closely matched that of the BcA C35 lactol carbon than the C37 carbon of naturally derived2 AsA C3–C48 degradation product 1. Furthermore, literature data for the C37 carbon of naturally derived AsA degradation product 1 closely matched that reported for the BcA degradation lactol methyl ether 48.47,48 These observations prompted us to formally convert model C27–C48 lactol 3a to its lactol methyl ether 51a (Scheme 3.13). The synthesis of model C27–C48 lactol methyl ether 51a was accomplished in four steps from aldol adduct 49. Removal of the acetonide and silyl protecting groups was interrupted to ease the subsequent purification of lactol methyl ether 50. Cleavage of the C36 TBS ether was followed by debenzylation to give lactol methyl ether 51a.                                                                                                                 (46) The solution to the structural problem was discovered by the author in collaboration with Dr. Peter H. Fuller. (47) Sakuda, S.; Ikeda, H.; Nakamura, T.; Kawachi, R.; Kondo, T.; Ono, M.; Sakurada, M.; Inagaki, H.; Ito, R.; Nagasawa, H. J. Antibiotics 2000, 53, 1378–1384. (48) For a complete comparison of tabulated spectral data for naturally derived and synthetic AsA C3–C48 degradation lactols 1, see: Appendix 1.   71 Table 3.6. Chemical shift analysis of AsA C37 (BcA C35) for lactols and lactol methyl ethers.a Model C27–C48 Lactols HO HO HO HO 27 31 OH 35 37 OH OH OH 39 HO HO HO HO 27 31 35 OH OH 37 39 OH OH H O OH 3a C9H19 OH OH H O OH C9H19 3b–3f OH 35 Aflastatin A (AsA) C3–C48 Degradation Fragments HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH OH 37 39 Me Me OH Me Me Me Me Me OH OH H O OR C9H19 1, R = H 46a, R = Me OH 33 Blasticidin A (BcA) C3–C47 Degradation Fragments HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 25 29 OH OH 35 37 Me Group Evans Me OH Me Me Lactol(s) 3a 3b–3f 1 1 47 48 Me R H H H "H" H Me δ (ppm) 100.2 99.8–100.8b 101.2c 103.2 100.1 103.3 OH OH H O OR C10H21 47, R = H 48, R = Me Carbon AsA C37 AsA C37 AsA C37 OH HO HO R' H O OH OH OR R' Sakuda AsA C37 BcA C35 BcA C35 AsA C37/BcA C35 a Measured in pyridine-d5. b Average δ = 100.2 ppm. c Later corrected to δ = 100.1 ppm. Scheme 3.13. Syntheses of model C27–C48 lactol methyl ethers 51a and 51b. OH OBn OBn O TESO TBSO BnO 31 OH O 35 OTBS a,b 39 HO BnO BnO HO 27 31 35 OR OH 39 C9H19 32% Me O Me 49 OTBS OH OBn c,d HO HO HO H O OMe C9H19 50, R = TBS OH 35 OH OH 39 e 51a, R = CH3 51b, R = CD3 HO 27 31 OH OH H O OR C9H19 Reagents and conditions: (a) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt, 50%; (b) PPTS, CH2Cl2, MeOH, rt, 63%; (c) nBu4NF, THF, 0 °C; TMSOMe; (d) H2, Pd black, dioxane, H2O, rt; (e) Dowex 50x8 (H+), CD3OD, rt. The chemical shift of the C37 carbon of model C27–C48 lactol methyl ether 51a correlated nicely with that reported for naturally derived2 AsA C3–C48 degradation product 1   72 (Table 3.7). We then became curious why the resonances belonging to the newly incorporated methyl group were absent from their NMR spectra of naturally derived degradation product 1. We hypothesized that during the course of their NMR spectroscopic studies,2a the isolation group dissolved AsA degradation lactol methyl ether 46a in methanol-d4 and inadvertently exchanged the methyl ether for its trideuteriomethyl ether (46b). To substantiate this proposal, we converted model lactol methyl ether 51a to trideuteriomethyl ether 51b in the presence of trace acid (Dowex) (Scheme 3.13). Table 3.7. Chemical shift analysis of AsA C37 for model lactol 3a, lactol methyl ethers 51a and 51b, and degradation fragment 1.a Group Evans Lactol 3a 51a 51b Sakuda a R H CH3 CD3 "H" δ (ppm) 100.2 103.3 103.3 103.2 OH HO HO HO HO 27 31 35 OH OH 39 1 OH OH H O OR C9H19 3a, R = H 51a, R = CH3 51b, R = CD3 Measured in pyridine-d5. As expected, the chemical shift of the C37 carbon of model lactol trideuteriomethyl ether 51b correlated nicely with that reported for naturally derived AsA C3–C48 degradation product 1 (Table 3.7). In fact, model lactol ethers 51a and 51b were spectroscopically indistinct with the exception of the obvious resonances. Furthermore, the spectroscopic data for lactol trideuteriomethyl ether 51b provided us the best profile match for naturally derived degradation fragment 1 in the C27–C48 lactol region (Figure 3.6). The only data point that concerned us was the chemical shift of C36, but resolution of this difference between the two structures will be discussed in due course.   73 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me Me Me 1 13C-NMR OH OH H O OH C9H19 1H-NMR Data HO HO HO OH 35 Data HO HO HO OH 35 36 OH OH 39 OH OH 39 HO 28 27 29 31 OH OH |Δδ| ≥ 0.05 ppm H O OCD3 51b C9H19 HO 28 27 29 30 31 OH OH |Δδ| ≥ 0.5 ppm H O OCD3 51b C9H19 Figure 3.6. NMR data comparison of naturally derived C3–C48 degradation lactol 1 to model C27–C48 lactol trideuteriomethyl ether 51b. V. Syntheses of the C3–C48 Degradation Fragments Now confident that we had found a solution to our structural problem, we pursued the syntheses of AsA C3–C48 degradation lactol methyl ether 46a and its trideuteriomethyl ether analogue (46b). Rather than retrace the route we had originally used to synthesize C3–C48 degradation lactol 1, we decided to modify our synthesis plan for C27–C48 aldehyde 52 (Scheme 3.14). We began with the usual C35–C36 aldol bond disconnection13 to produce C27–C35 aldehyde 6 and C36–C48 ketone 13. In this iteration, we decided to install a triethylsilyl ether at the C36 carbinol position of ketone 13,24 as we had in the synthesis of epi-C33–C37 lactol 3c, to facilitate global deprotection. Then, given the success of our newly developed 1,3-chelate-controlled aldol reaction, we anticipated extending our soft enolizationbased method4 to the formation of the C31–C32 bond via 1,2-chelate-controlled addition of ketone 54 to aldehyde 53. Based upon the Cram chelate model,36 we expected excellent selectivity for the desired 1,2-syn diastereomer via exclusive formation of five-membered chelate 55 and nucleophilic addition to the less sterically hindered face.   74 Scheme 3.14. Synthesis plan for C3–C48 degradation fragment 46a. OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 26 3 7 11 15 19 23 27 31 35 OH OH 39 Me 1,2-syn Me OH Me Me Me Me Me 46a OH OH chelate-controlled aldol addition O H O OMe C9H19 6 RO 27 OR OR O 32 31 O 35 O H OTES OTBS 39 oxygenated aldol addition OBn OR OR OR O 36 31 35 OR 39 C9H19 13 1,2-syn RO RO Me O Me H 27 R3SiO RO C9H19 OR OR 52 chelate-controlled aldol addition TESO 27 30 31 O H Me O OTBDPS OPMB 35 O α-alkoxy chelate H Nu M R O 30 Bn 55 O Me O Me 53 OBn H 54 The synthesis of C27–C35 aldehyde 5349 commenced with the glycolate aldol addition of oxazolidinone 5750 to aldehyde 56,51 which afforded the desired syn adduct 58 in good yield and excellent diastereoselectivity (Scheme 3.15). Silylation and net reduction afforded α-benzyloxyaldehyde 53 in good overall yield. Chelate-controlled addition of C32–C35 ketone 5452 to this C27–C31 aldehyde under our soft enolization conditions delivered the desired β-hydroxy ketone 59 on multigram scale.53 As before, our magnesium-promoted aldol process was found to exhibit exceptionally high asymmetric induction.27,54 Diastereoselective                                                                                                                 (49) The synthesis of C27–C35 aldehyde 67 was first achieved by Dr. Egmont Kattnig using a chelationcontrolled/soft enolization-based approach. The synthesis of C27–C48 aldehyde 71 from redesigned C36– C48 ketone 13 was then completed by the author in collaboration with Dr. Peter H. Fuller (vide infra). (50) Evans, D.A.; Gage, J.R.; Leighton, J.L.; Kim, A.S. J. Org. Chem. 1992, 57, 1961–1963. (51) Aldehyde 56 was prepared in two steps from L-gulonic acid γ-lactone. See: Hubschwerlen, C.; Specklin, J.L.; Higelin, J. Org. Synth. 1995, 72, 1–5. (52) Ketone 54 was prepared in six steps from L-serine. See: Hirth, G.; Walther, W. Helv. Chim. Acta 1985, 68, 1863–1871. (53) Chelate-controlled Mukaiyama aldol addition of the corresponding enolsilane of ketone 54 to aldehyde 53 was again unsuccessful. (54) To make a more efficient synthesis, we would prefer to protect the C29 oxygen as its benzyl ether, but reaction of the corresponding aldehyde with ketone 54 under our soft enolization conditions produced an   75 carbonyl reduction55 was followed by desilylation to produce triol 60. Installation of the C33,C34 acetonide to produce the fully protected C27–C35 fragment 61 required three protecting group manipulations: PMP acetal formation,56 dibenzylation, and acetal exchange. Scheme 3.15. Synthesis of C27–C35 fragment 61. 27 O H O BnO O 31 O a N O 70%, dr > 95:05 57 O Me Me OH O 30 29 O b–d N O 72% O Me Me O 31 O BnO Bn 58 O 32 31 Bn 56 O TESO 27 TESO HO e 27 f,g OTBDPS OPMB 35 O Me O Me 53 H Me OBn OTBDPS OPMB 35 O 72%, dr = 97:03 Me O Me OBn 59 58%, dr = 93:07 54 OH OH OH h–j 31 OBn OBn O 27 27 O Me O Me OBn 60 35 OTBDPS OPMB O 69% Me O BnO Me 31 35 OTBDPS Me O Me 61 Reagents and conditions: (a) (nBu)2BOTf, Et3N, PhMe, –78 °C to –40 °C, dr > 95:05, 70%; (b) TESCl, imidazole, DMF, rt, 84%; (c) LiBH4, H2O, THF, 0 °C to rt, 92%; (d) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –40 °C to –10 °C, 93%; (e) MgBr2•OEt2, PMP, CH2Cl2, –5 °C, dr = 97:03, 72%; (f) Zn(BH4)2, CH2Cl2, Et2O, –78 °C, dr = 93:07, 86%; (g) PPTS, CH2Cl2, MeOH, 0 °C, 68%; (h) DDQ, 4 Å MS, CH2Cl2, 0 °C, 83%; (i) BnBr, NaH, nBu4NI, THF, 0 °C to rt, 88%; (j) Me2C(OMe)2, PPTS, acetone, 55 °C, 95%. Alternatively, the fully protected C27–C35 fragment 61 may be accessed from dibenzylglucopyranoside 62 57 in twelve steps (Scheme 3.16). Iodination, 58 zinc-mediated fragmentation,59 in situ reduction, and protection of the resultant 1,2-diol produced acetonide 63 in good overall yield. Ozonolysis and stereoselective allylation of the resultant syn α,βbisalkoxy aldehyde produced homoallylic alcohol 64 in moderate yield. We also observed a                                                                                                                                                                                                                                                                                                                                                           unfavorable mixture of diastereomers (dr = 49:51), whereas allylmagnesium bromide addition produced homoallylic carbinol 64 in very good diastereoselectivity (dr = 89:11) (vide infra). (55) Oishi, T.; Nakata, T. Acc. Chem. Res. 1984, 17, 338–344 and references therein. (56) Oikawa, Y.; Nishi, T.; Yonemitsu, O. Tetrahedron Lett. 1983, 24, 4037–4040. (57) Français, A.; Urban, D.; Beau, J.-M. Angew. Chem., Int. Ed. 2007, 46, 8662–8665. (58) (a) Garegg, P.J.; Samuellson, B. J. Chem. Soc., Perkin Trans. I. 1980, 2866–2869; (b) Garegg, P.J.; Johansson, R.; Ortega, C.; Samuellson, B. J. Chem. Soc., Perkin Trans. I. 1982, 681–683. (59) Skaanderup, P.R.; Hyldtoft, L.; Madsen, R. Monatsh. Chem. 2002, 133, 467–472.   76 diminished level of diastereoselection (dr = 89:11) when compared to our previous synthesis in which the aldehyde substrate had silyl protecting groups at C27 and C28. Acryloylation60 of the nascent C31 carbinol, and ring-closing metathesis 61 of the intermediate diene then furnished unsaturated lactone 65. Stereoselective dihydroxylation62,63 and acetonide formation produced lactone 66 as a single diastereomer. Reduction to the diol, selective protection of the primary carbinol, and benzylation yielded common intermediate 61. Desilylation and oxidation17 of the resultant carbinol ultimately provided C27–C35 aldehyde 67. Scheme 3.16. Alternative synthesis of C27–C35 aldehyde 67. H HO 31 O 27 OMe OH a,b,c 68% O O Me BnO 27 31 d,e 56%, dr = 89:11 O 27 27 OBn OH 32 31 f,g 71% 64 BnO 62 OBn O Me O Me Me Me O Me h,i OBn 63 OBn 27 OBn O 31 34 OBn O 31 35 O O 66 j,k,l 90% O Me O Me 65 33 OBn 66%, dr ≥ 95:05 OBn OBn O O Me O Me OBn 27 m,n 31 35 27 OBn OBn O 31 O 35 O Me O BnO Me 61 OTBDPS 96% O Me O BnO Me 67 H Me O Me Me O Me Reagents and conditions: (a) PPh3, I2, imidazole, PhMe, MeCN, rt, 97%; (b) Zn, THF, H2O, ))), 45 °C; NaBH4, 0 °C, 78%; (c) Me2C(OMe)2, PPTS, acetone, rt, 90%; (d) O3, py, CH2Cl2, MeOH, –78 °C; PPh3, –78 °C to rt; (e) MgBr2•OEt2, allylMgBr, CH2Cl2, Et2O, –78 °C to –40 °C, dr = 89:11, 56% (2 steps); (f) acrylic pivalic anhydride, EtN(iPr)2, DMAP, THF, PhH, rt, 80%; (g) (Ph3P)2Cl2Ru=CHPh (4 x 5 mol%), PhH, 65 °C, 89%; (h) RuCl3, CeCl3•7H2O, NaIO4, EtOAc, MeCN, H2O, 0 °C, 85%, dr ≥ 95:05; (i) Me2C(OMe)2, PPTS, acetone, 30 °C, 78%; (j) LiBH4, H2O, THF, 0 °C to rt, quant.; (k) TBDPSCl, imidazole, DMF, 0 °C, 95%; (l) BnBr, NaH, nBu4NI, DMF, –20 °C, 95%; (m) nBu4NF, THF, 0 °C, quant.; (n) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C, 96%.                                                                                                                 (60) Tanaka, A.; Suzuki, H.; Yamashita, K. Agric. Biol. Chem. 1989, 53, 2253–2256. (61) Schwab, P.; France, M.B.; Ziller, J.W.; Grubbs, R.H. Angew. Chem. 1995, 107, 2179–2181; Angew. Chem., Int. Ed. 1995, 34, 2039–2041. (62) (a) Plietker, B.; Niggemann, M. J. Org. Chem. 2005, 70, 2402–2405; (b) Plietker, B. Synthesis 2005, 2453– 2472. (63) For examples of the diastereoselective dihydroxylation of related α,β-unsaturated δ-lactones using Upjohn conditions (OsO4, NMO), see: (a) Ghosh, A.K.; Kim, J.-H. Tetrahedron Lett. 2003, 44, 3967–3969; (b) Ramachandran, P.V.; Prabhudas, B.; Chandra, J.S.; Reddy, M.V.R. J. Org. Chem. 2004, 69, 6294–6304; (c) Bhaket, P.; Stauffer, C.S.; Datta, A. J. Org. Chem. 2004, 69, 8594–8601.   77 Scheme 3.17. Synthesis of C27–C48 aldehyde 71. OBn OBn O 27 O 35 O H OTES OTBS 39 a 77%, dr = 91:09 O Me O BnO Me 67 31 C9H19 13 Me O Me OBn OBn O 27 OH O 36 35 OTBS b 39 OBn OBn O HO 88% 27 31 OR O 35 OTBS c,d 39 O Me O BnO Me 31 C9H19 C9H19 73% Me O Me OTES 68 HO BnO Me O Me OR 69, R = TES OBn OBn O AcO 27 TBSO BnO 31 OR O 35 OTBS 39 e,f 80% O OBn OBn O 31 OR O 35 OTBS 39 C9H19 Me O Me OR 70, R = TES H 27 TBSO BnO C9H19 Me O Me OR 71, R = TES Reagents and conditions: (a) ketone 13, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 67, Et2O, –78 °C to – 25 °C, dr = 91:09, 77%; (b) TESOTf, 2,6-lutidine, CH2Cl2, 0 °C; TMSOTf; aq H2SO4, 88%; (c) AcCl, 2,4,6collidine, CH2Cl2, –78 °C to 0 °C, 98%; (d) TBSOTf, 2,6-lutidine, CH2Cl2, 0 °C, 74%; (e) DIBALH, CH2Cl2, – 78 °C, 84%; (f) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C, 95%. Having completed the syntheses of both the C3–C26 and C27–C48 fragments, we ventured forward with the key aldol coupling (Scheme 3.18). 64 Satisfyingly, chelatecontrolled addition of ketone 72 to aldehyde 71 under our soft enolization conditions4 delivered the desired β-hydroxy ketone with excellent diastereoselection. We immediately reduced the aldol adduct65 under Prasad's conditions28 to afford 1,3-syn diol 73 as a single diastereomer in good overall yield. Both steps were completely chemoselective and eliminated the need to mask the C37 carbonyl.                                                                                                                 (64) The syntheses of the C3–C48 degradation fragments were achieved by the author in collaboration with Dr. Peter H. Fuller. (65) We observed that the intermediate aldol adduct is subject to retro-aldolization on silica gel. For higher overall yields of diol 73, we performed the aldol addition and reduction in tandem before purification.   78 Scheme 3.18. Synthesis of C3–C48 degradation fragments 1, 46a, and 46b. Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' O 23 O Me OBn OBn O 31 OR" O 35 OTBS 39 Me Me OR Me Me Me Me Me a,b H 27 TBSO BnO C9H19 72, R = TBS, R' = TIPS Me Me OBn O BnO 3 7 11 70%, dr = 95:05 Me O Me OR" 71, R" = TES Me Me O 15 Me Me O 19 O O O OR' OH OH OBn OBn O 26 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me c 58% RO BnO Me O Me OH 35 OR" 73, R = TBS, R' = TIPS, R" = TES HO RO HO HO HO HO HO HO HO HO HO RO RO RO 3 7 11 15 19 23 27 31 OH OH 39 Me Me OH Me Me Me Me Me d e,f g OH OR 1, R = R' = H 74, R = Bn, R' = H 46a, R = H, R' = CH3 46b, R = H, R' = CD3 53% 29% 79% H O OR' C9H19 Reagents and conditions: (a) MgBr2•OEt2, PMP, CH2Cl2, –5 °C, dr = 95:05; (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to –55 °C; aq H2O2, aq NaOH, MeOH, 0 °C, dr ≥ 95:05, 70% (2 steps); (c) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt, 58%; (d) H2, Pd black, dioxane, H2O, rt, 53%; (e) Dowex 50x8 (H+), MeOH, 30 °C, 39%; (f) H2, Pd black, dioxane, H2O, rt, 74%; (g) Dowex 50x8 (H+), CD3OD, rt, 79%. We concluded the synthesis of C3–C48 degradation lactol methyl ether 46a in three steps from diol 73. As before, removal of the acetonide and silyl protecting groups was best achieved with hexafluorosilicic acid.66 We obtained pentabenzyl ether 74 in higher yield and purity than previously due to the increased lability of the C36 triethylsilyl ether. The nascent lactol was then converted to its lactol methyl ether, and the remaining benzyl ethers cleaved to unveil C3–C48 degradation lactol methyl ether 46a in modest yield. Transetherification of lactol methyl ether 46a was performed in the presence of methanol-d4 and trace acid (Dowex) to afford C3–C48 trideuteriomethyl ether 46b in good yield. Finally, we achieved our second synthesis of C3–C48 degradation fragment 1 in two steps and better overall yield from pentabenzyl ether 74 via the standard two-step deprotection sequence.                                                                                                                 (66) (a) Pilcher, A.S.; Hill, D.K.; Shimshock, S.J.; Waltermire, R.E.; DeShong, P. J. Org. Chem. 1992, 57, 2492–2495; (b) Pilcher, A.S.; Shimshock, S.J. J. Org. Chem. 1993, 58, 5130–5134.   79 VI. Spectroscopic Analysis of the C3–C48 Degradation Fragments67 Upon completion of the syntheses of degradation fragments 1, 46a, and 46b (Figure 3.7), we proceeded with their full spectroscopic analysis. Our data for lactol trideuteriomethyl ether 46b correlated nicely with those tabulated for naturally derived2 degradation product 1. All chemical shift values in the proton and carbon spectra were within 0.03 ppm and 0.2 ppm of each other, respectively, with one caveat. In conjunction with the stereochemical revision of AsA, the chemical shift of C25 of naturally derived degradation product 1 was revised from 73.1 ppm to 71.1 ppm.2b However, our data for model C27–C48 lactol trideuteriomethyl ether 46b indicated that the value of 73.1 ppm should be assigned to C36. As a result, we believe the chemical shift value of 71.5 ppm originally reported for C36 should instead be revised to 71.1 ppm. Then, the carbon data for these two atoms, as well as the proton data for H25 and H36, should be switched. We believe this error resulted from misinterpretation of two-dimensional NMR correlation (i.e. COSY, HMQC, and HMBC) data,2a as the proton signals are very close in chemical shift. Our proposed correction is supported by the corresponding data for BcA C3–C47 degradation lactol methyl ether 48.47 Upon making this correction, we make two important conclusions: 1) The data reported by the isolation group for naturally derived AsA C3–C48 degradation lactol 1 should in fact be attributed to its derivative lactol trideuteriomethyl ether 46b; and 2) Our synthesis of lactol trideuteriomethyl ether 46b and its spectroscopic match to naturally derived C3–C48 degradation fragment 1 confirm the revised stereochemical assignment of AsA.                                                                                                                 (67) The spectroscopic analysis of C3–C48 degradation lactol 1 was first performed by Dr. Egmont Kattnig and later revised by the author. The spectroscopic analyses of C3–C48 degradation lactol methyl ethers 46a and 46b were performed by the author in collaboration with Dr. Peter H. Fuller.   80 Model C27–C48 Lactols and Lactol Methyl Ethers HO HO HO HO 27 31 OH 35 37 OH OH 39 OH OH Aflastatin A (AsA) C3–C48 Degradation Fragments H O OR C9H19 3a, R = H 51a, R = CH3 51b, R = CD3 OH 35 HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH OH 37 39 Me Me OH Me Me Me Me Me OH OH H O OR C9H19 1, R = H 46a, R = CH3 46b, R = CD3 OH 33 Blasticidin A (BcA) C3–C47 Degradation Fragments HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 25 29 OH OH 35 37 Me Me OH Me Me Me OH OH H O OR C10H21 47, R = H 48, R = CH3 Figure 3.7. Structures of AsA model lactol 3a, model lactol methyl ethers 51a and 51b, C3– C48 degradation fragments 1, 46a, and 46b, and BcA C3–C47 degradation fragments 47 and 48. In continuation of our analysis, the data for trideuteriomethyl ether 46b and lactol methyl ether 46a were spectroscopically indistinct with the exception of the obvious resonances. By extension, our data for lactol methyl ether 46a also matched naturally derived2 degradation product 1 apart from the resonances belonging to the methyl group. We hypothesized that during the course of their NMR spectroscopic studies, the isolation group dissolved degradation fragment 46a (née 1) in methanol-d4 and inadvertently exchanged the methyl ether for its trideuteriomethyl ether 46b in the presence of trace acid.68 Our hypothesis is reasonable because structural elucidation of the corresponding AsA C9–C27 degradation fragment was conducted in methanol-d4 or a mixture of methanol-d4 and pyridine-d5. Unfortunately, we have no evidence that C3–C48 degradation lactol methyl ether 46a was ever dissolved in methanol-d4 because the NMR spectra are reported in pyridine-d5.                                                                                                                 (68) In our hands, simple filtration of model C27–C48 lactol methyl ether 51a through Dowex 50x8 (H+) resin and dissolution in methanol-d4 resulted in little to no ether exchange (<10% conversion to lactol trideuteriomethyl ether 51b by 1H-NMR over one week at room temperature).   81 We explicitly propose that the isolation group synthesized lactol trideuteriomethyl ether 46b by transetherification of lactol methyl ether 46a, which we noted is experimentally more facile in the presence of trace acid (Dowex) than the ketalization of parent lactol 1. As a result, we suspect that the isolation group did not synthesize aflastatin A C3–C48 degradation lactol 1 as reported. Our notion is supported by inconsistencies between experimental procedures disclosed for the degradations of AsA and BcA to their respective lactols 1 and 47. In the case of AsA, the last reported chemical step is the saponification of the peracetate of lactol 1, followed by neutralization of the crude product mixture by passing it through an acidic Dowex column. In the case of BcA, saponification was performed on the peracetate of lactol methyl ether 48, and hydrolysis of lactol methyl ether 48 to its parent lactol 47 required an extra step, namely exposure to strong aqueous acid. We expect that the hydrolysis of AsA C3–C48 degradation lactol methyl ether 46a to its corresponding lactol 1 requires similar acidic conditions. In the end, we suspect that lactol trideuteriomethyl ether 46b was mistaken for lactol 1 upon acquisition of NMR spectra that lacked resonances corresponding to the proper product, lactol methyl ether 46a. The NMR data that we present for AsA C3–C48 degradation product 1 is the first to be reported for this structure. Our second synthesis of this structure allowed us to revise our own chemical shift data for the C37 carbon from 101.2 ppm to 100.1 ppm, thus bringing it into excellent agreement with model C27–C48 lactol 3a and BcA C3–C47 degradation lactol 47 (Table 3.6). Overall, our NMR data for AsA C3–C48 degradation lactol 1 may best be described as a rough overlay of the C3–C27 and C40–C48 regions of naturally derived AsA C3–C48 degradation fragment 46a (née 1) and the C20–C41 (or C22–C43 by AsA numbering) region of BcA C3–C47 degradation lactol 47 (Appendix 1, Tables 7 and 8). As   82 such, we are confident that our data for AsA C3–C48 degradation product 1 is correct and not attributable to any other structure. As final proof of structure, the high-resolution mass spectrometry (HRMS) data that we measured for AsA C3–C48 degradation lactol 1 predicts the correct molecular formula, C53H106O22. Although this result was expected, we could not explain Sakuda's matching HRMS data for naturally derived degradation fragment 1, which we structurally reassigned as lactol trideuteriomethyl ether 46b. Looking to resolve this issue, we scrutinized their published spectra for any recognizable amount of lactol 1, but only observed a lopsided mixture of lactol trideuteriomethyl and lactol methyl ethers 46b and 46a, respectively.69 We then tested the possibility that HRMS data for lactol 1 could be obtained from such a mixture. We succeeded, but were unable to reproduce the accuracy of the isolation group's measurement.70 At the conclusion of our spectroscopic analyses, we had successfully revised the structure of the naturally derived AsA C3–C48 degradation fragment from lactol 1 to its lactol trideuteriomethyl ether derivative 46b. We believe that the misassignment of this fragment provided us the opportunity to test structural curiosities while displaying the true power of chemical synthesis. In particular, our accumulated work involving soft enolization with magnesium clearly demonstrated the reliability of our chelate-controlled aldol method in complex settings, as well as its potential applicability to the large-scale production of chiral                                                                                                                 (69) The tabulated NMR data for degradation product 1 (Ref. 2a) is devoid of resonances corresponding to the methyl group of lactol methyl ether 46a. However, these resonances appear to be attenuated in the published spectra. Therefore, spectral analysis was presumably completed on some mixture of lactol methyl and lactol triodeuteriomethyl ethers 46a and 46b, respectively. (70) High-resolution mass spectrometry (HRMS) data corresponding to lactol 1 (m/z calcd for C53H106NaO22 [M+Na]+: 1117.7068) may be obtained from a sample containing lactol methyl ether 46a (TOF, found: 1117.7279) or lactol trideuteriomethyl ether 46b (TOF, found: 1117.7353). As such, we believe it possible that MS data corresponding to degradation lactol 1 (Ref. 2a) may be obtained from a mixture of lactol methyl ether 46a and its derivative lactol trideuteriomethyl ether 46b.   83 building blocks for stereoselective organic synthesis. Now, with the syntheses of the AsA degradation fragments behind us, and the structural revision duly confirmed, we were ready to tackle the synthesis of the natural product. Our work toward the installation of the tetramic acid and the completion of the total synthesis of aflastatin A will be discussed in Chapter 4.   84 VII. Graphical Summary Synthesis of C27–C35 Aldehyde 67 H HO 31 O 27 OMe OH quant. H TMSO 31 O 27 OMe Ph H O 31 O 27 OMe OH 82%, two steps H HO 31 O 27 OMe OH HO OH 75 TMSO OTMS OTMS 76 O OBn 77 BnO OBn 62 BnO 27 31 BnO 31 H I 78% 31 97% O 27 OMe OH O Me O Me OBn 63 90% HO 27 HO BnO 79 BnO OBn 78 O 27 OBn O 27 31 OBn OH 31 27 OBn O 31 35 O Me O Me H dr = 89:11, 56%, 2 steps O Me O Me OBn 80 O OBn 64 O 80% O Me O Me 81 OBn 89% O 27 OBn O 31 35 O O 66 O Me O Me Me Me 27 OBn O 31 35 OH 27 OBn O 31 35 78% O Me O Me OH 82 OBn quant. OBn 85%, dr ≥ 95:05 O Me O Me 65 OBn 27 OBn OH O 31 35 27 OBn OH O 31 35 27 OBn OBn O 31 35 O Me O BnO Me 83 OH 95% O Me O BnO Me OR 95% O Me O BnO Me quant. OR Me O Me Me O Me Me O Me 84, R = TBDPS 61, R = TBDPS 27 OBn OBn O 31 O 35 27 OBn OBn O 31 35 O Me O BnO Me H 96% O Me O BnO Me OH Me O Me 67 Me O Me 85   85 Synthesis of C3–C48 Degradation Fragment 1 27 OBn OBn O 31 O 35 O H OTES 13 OTBS 27 39 OBn OBn O 31 OH O 35 OTBS 39 O Me O BnO Me 67 C9H19 Me O Me 77%, dr = 91:09 O Me O BnO Me 68 C9H19 Me O Me OTES 88% OBn OBn O AcO 27 31 OR O 35 OTBS 39 OBn OBn O HO 98% 27 31 OR O 35 OTBS 39 C9H19 C9H19 HO BnO 86, R = TES Me O Me OR 74% OR O 35 HO BnO Me O Me OR 69, R = TES OTBS 39 OBn OBn O AcO 27 TBSO BnO 70, R = TES Me Me OBn O BnO 3 7 11 31 OBn OBn O 84% HO 27 TBSO BnO 87, R = TES 31 OR O 35 OTBS 39 C9H19 C9H19 Me O Me OR Me O Me OR 95% Me Me O 15 Me Me O 19 O O O OR' O 23 O Me OBn OBn O 31 OR" O 35 OTBS 39 Me Me OR Me Me Me Me Me H 27 TBSO BnO dr = 95:05 C9H19 Me O Me OR" 71, R" = TES 72, R = TBS, R' = TIPS Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' O 23 OH OBn OBn O 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me RO BnO dr ≥ 95:05, 70%, 2 steps Me O Me OR" 88, R = TBS, R' = TIPS, R" = TES Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' OH OH OBn OBn O 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me 58% RO BnO Me O Me OH OR" 73, R = TBS, R' = TIPS, R" = TES HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me 74 Me Me 53% OH OBn H O OH C9H19 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me Me Me 1 OH OH H O OH C9H19   86 Synthesis of C3–C48 Degradation Fragments 46a and 46b OH HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me 74 Me Me 39% OH OBn H O OH C9H19 OH HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me 89 Me Me 74% OH OBn H O OCH3 C9H19 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me 46a Me Me 79% OH OH H O OCH3 C9H19 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH 39 Me Me OH Me Me Me 46b Me Me OH OH H O OCD3 C9H19   87 VIII. Experimental Section General Information Reactions in anhydrous solvents were carried out in glassware that was flame-dried or oven-dried. Unless noted, reactions were magnetically stirred and conducted under an atmosphere of nitrogen or argon. Air-sensitive reagents and solutions were transferred via syringe or cannula, and were introduced to reaction vessels through rubber septa. Reactions conducted below ambient temperature were cooled by external baths: dry ice/acetone for –78 °C to –5 °C, sodium chloride/ice water for –5 °C, and ice water for 0 °C. Reactions requiring more than 8 h at temperatures between –55 °C and 0 °C were chilled using an immersion cooler. Reactions conducted above ambient temperature were heated by a silicone oil bath. Analytical thin layer chromatography (TLC) was performed on EMD Reagent silica gel 60 F254 plates (210–270 µm layer thickness). Visualization was accomplished with ultraviolet light (254 nm) followed by heating after staining the plate with ceric ammonium molybdate or potassium permanganate solution. Extraction and chromatography solvents were reagent grade or HLPC grade, and were used without further purification. Brine solution refers to a saturated aqueous solution of sodium chloride. Product purification was performed by flash column chromatography71 using Sorbent Technologies, Whatman, or Dynamic Adsorbents silica gel (32–63 µm, 230–400 mesh). Reversed-phase chromatography was performed using a Teledyne Isco CombiFlash® Rf 200 UV/Vis purification system and RediSep® Rf Gold C18 column (5.5 g, 20–40 µm). Materials Tetrahydrofuran, diethyl ether, toluene, and dichloromethane employed as reaction solvents were dried by passage through a column of activated alumina under an argon atmosphere.72 Benzene, acetonitrile, and pentane employed as reaction solvent were distilled from calcium hydride prior to use. Methanol was distilled from magnesium methoxide prior to use. EMD DriSolv dimethyl sulfoxide and N,N-dimethylformamide were used without further purification. Triethylamine, Hünig’s base, 2,6-lutidine, pyridine, dimethylethylamine, diisopropylamine, hexamethyldisilazane, and chlorotrimethylsilane were distilled from                                                                                                                 (71) (72) Still, W.C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923–2925. Pangborn, A.B.; Giardello, M.A.; Grubbs, R.H.; Rosen, R.K.; Timmers, F.J. Organometallics 1996, 15, 1518–1520.   88 calcium hydride prior to use. Organolithium reagents (e.g. n-butyllithium, t-butyllithium, methyllithium) were purchased from commercial suppliers and were titrated prior to use using 2-butanol with 1,10-phenanthroline as indicator.73 Grignard reagents were titrated using I2 in THF. Dicyclohexylchloroborane was distilled under reduced pressure and stored under argon in a Schlenk flask. Trimethylsilyl, triethylsilyl, and t-butyldimethylsilyl trifluoromethanesulfonates, as well as boron trifluoride diethyl etherate were distilled from calcium hydride and stored under argon in Schlenk flasks. Benzyl bromide was purified by passage through a column of activated neutral alumina. Me(MeO)NH•HCl was dried azeotropically with benzene immediately prior to use. 2,3-Dichloro-5,6-dicyano-1,4benzoquinone (DDQ) was recrystallized from benzene and chloroform and stored under argon at –20 °C in a foil-wrapped vial. (R)-(–)and (S)-(+)-α-methoxy-α- (trifluoromethyl)phenylacetyl chlorides were purchased from the Sigma-Aldrich Chemical Company, and their absolute configurations were confirmed by optical rotation. Chloroform-d and benzene-d6 were stored over 4Å molecular sieves.74 Other reagents were purified, if necessary, according to the published methods.75 Analytical Information Unless otherwise stated, all isolated and characterized compounds were >95% pure as judged by 1H-NMR spectroscopic analysis. 1H-NMR spectra were recorded at room temperature on an Agilent DD2 600 spectrometer (600 MHz), a Varian Inova 600 spectrometer (600 MHz), a Varian Inova 500 spectrometer (500 MHz), or a Mercury 400 spectrometer (400 MHz). 1H-NMR data are reported in the following format: chemical shift (multiplicity, coupling constant(s), integration, proton assignment). Chemical shifts are reported in parts per million (ppm) from tetramethylsilane (δ scale) with the residual solvent resonance as internal standard (7.26 ppm for CDCl3, 7.15 for C6D6, 3.30 for CD3OD, and 7.55 pm for the middle peak of C5D5N). Multiplicity is abbreviated as follows: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad, app = apparent. Proton assignments are referenced to the aflastatin A numbering system, and were made with the aid of 2D-COSY                                                                                                                 (73) (74) (75) Watson, S.C.; Eastham, J.F. J. Organomet. Chem. 1967, 9, 165–168. (a) Burfield, D.R.; Gan, G.H.; Smithers, R.H. J. Appl. Chem. & Biotechnol. 1978, 28, 23–30. (b) Burfield, D.R.; Goh, E.H.; Ong, E.H.; Smithers, R.H. Gazz. Chim. Ital. 1983, 113, 841–843. Armarego, W.L.F.; Chai, C.L.L. Purification of Laboratory Chemicals, 6th Ed. Butterworth-Heinemann: Oxford, 2009.   89 experiments. NOEs were measured by 2D-NOESY experiments or pulsed-field-gradient assisted 1D NOE experiments. 13 C-NMR spectra were recorded at room temperature on a Varian Inova 500 spectrometer (125 MHz), or a Mercury 400 spectrometer (100 MHz) with broadband proton decoupling. Chemical shifts are reported in ppm from tetramethylsilane (δ scale) with the residual solvent resonance as internal standard (77.0 ppm for CDCl3, 128.0 for C6D6, 49.0 for CD3OD, and 135.5 pm for the middle peak of C5D5N). Carbon assignments are referenced to the aflastatin A numbering system, and were made with the aid of 2D-HSQC experiments. Infrared spectra were recorded as thin films on NaCl plates using a Perkin Elmer 1600 series FT-IR spectrometer at a resolution of 4 cm–1. Optical rotations were measured on a T Jasco P-2000 series digital polarimeter with a sodium lamp, and are reported as [α] D (°C) XX° (c (g/100 mL), solvent). High-resolution mass spectra were obtained on Agilent 6210 TOF or Bruker micrOTOF-Q II spectrometers at Harvard University’s Small Molecule Mass Spectrometry Facility or Laukien-Purcell Instrumentation Center, respectively. Spectroscopic Data for Model C27–C48 Lactols and Lactol Methyl Ethers OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH H 3a O C9H19 Aflastatin A Model C27–C48 Lactol (3a). White solid; [α] 23 +12.8° (c = 0.50, CH3OH); IR D (neat) 3428 (br), 1638 cm–1; 1H-NMR (600 MHz, pyridine-d5) δ 7.06 (br s, 1H, one of –OH), 6.80–5.80 (br s, 8H, eight of –OH), 5.00 (app dt, J = 7.0, 7.0, 2.0 Hz, 1H, C31-H), 4.95 (br s, 1H, one of –OH), 4.89 (app dt, J = 10.0, 10.0, 3.0 Hz, 1H, C33-H), 4.79 (dd, J = 9.5, 3.0 Hz, 1H, C35-H), 4.76 (m, 1H, C39-H), 4.72 (dd, J = 4.5, 3.5 Hz, 1H, C29-H), 4.62–4.59 (m, 2H, C28H and C30-H), 4.50 (d, J = 3.0 Hz, 1H, C36-H), 4.41 (app t, J = 9.5, 9.5 Hz, 1H, C34-H), 4.35– 4.30 (m, 2H, C27-H2), 3.22 (ddd, J = 13.2, 8.0, 3.0 Hz, 1H, one of C32-H), 2.75 (dd, J = 14.4, 1.8 Hz, 1H, one of C38-H), 2.58 (ddd, J = 13.2, 10.0, 7.0 Hz, 1H, one of C32-H), 2.15 (dd, J = 14.4, 10.9 Hz, 1H, one of C38-H), 1.68–1.61 (m, 1H, one of C40-H), 1.56–1.45 (m, 2H, one of C40-H and one of C41-H), 1.39–1.34 (m, 1H, one of C41-H), 1.30–1.13 (m, 12H, C42–47-H2),   90 0.83 (t, J = 7.2 Hz, 3H, C48-H3); 13C-NMR (125 MHz, pyridine-d5) δ 100.2 (C37), 75.2 (C36), 73.8 (C34), 73.7 (C30), 73.5 (C29), 72.9 (C28 and C35), 71.6 (C31 and C33), 69.0 (C39), 64.6 (C27), 42.6 (C38), 39.6 (C40), 37.5 (C32), 32.1 (C46), 30.1 (C43 or C44), 29.9 (C43 or C44), 29.8 (C42), 29.6 (C45), 25.8 (C41), 22.9 (C47), 14.3 (C48); HRMS (ESI-TOF) m/z calcd for C22H44NaO11 [M+Na]+: 507.2776, found: 507.2788. OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH H 3b O C9H19 epi-C39 Model C27–C48 Lactol (3b). White solid; 1H-NMR (600 MHz, pyridine-d5) δ 6.84 (br s, 1H, one of –OH), 6.55 (br s, 2H, two of –OH), 6.44–6.22 (br m, 3H, three of –OH), 6.14 (br s, 1H, one of –OH), 5.98 (br s, 2H, two of –OH), 5.87 (br s, 1H, one of –OH), 4.88 (dd, J = 9.2, 2.8 Hz, 1H, C35-H), 4.87 (app dt, J = 9.4, 9.4, 2.6 Hz, 1H, C33-H), 4.83 (m, J = 7.3, 4.1 Hz, 1H, C31-H), 4.59 (d, J = 2.8 Hz, 1H, C36-H), 4.59 (m, 1H, C39-H), 4.56 (dd, J = 3.8, 3.2 Hz, 1H, C29-H), 4.54 (m, J = 3.5 Hz, 1H, C28-H), 4.43 (m, 1H, C30-H), 4.41 (app t, J = 9.1 Hz, 1H, C34-H), 4.34–4.28 (m, J = 5.4, 4.5 Hz, 2H, C27-H2), 3.07 (ddd, J = 14.2, 4.1, 3.4 Hz, 1H, one of C32-H), 2.62 (dd, J = 14.2 Hz, 1H, one of C38-H), 2.53 (ddd, J = 14.2, 8.8, 7.9 Hz, 1H, one of C32-H), 2.48 (dd, J = 14.2, 10.1 Hz, 1H, one of C38-H), 1.77–1.73 (m, 1H, one of C40-H), 1.62–1.56 (m, 2H, one of C40-H and one of C41-H), 1.47–1.42 (m, 1H, one of C41H), 1.27–1.11 (m, 12H, C42–47-H2), 0.82 (t, J = 7.2 Hz, 3H, C48-H3); 13C-NMR (125 MHz, pyridine-d5) δ 100.3 (C37), 74.8 (C30), 74.2 (C36), 74.1 (C28), 73.3 (C29), 73.1 (C35), 72.93 (C33), 72.87 (C34), 72.4 (C31), 67.6 (C39), 64.6 (C27), 45.3 (C38), 39.1 (C40), 37.3 (C32), 32.1 (C46), 30.04 (C43 or C44), 29.99 (C43 or C44), 29.8 (C42), 29.6 (C45), 26.2 (C41), 22.9 (C47), 14.3 (C48); 1H-NMR (600 MHz, CD3OD) δ 4.01 (ddd, J = 7.3, 5.5, 3.1 Hz, 1H, C31H), 3.94 (m, 1H, C39-H), 3.85 (dd, J = 9.5, 3.4 Hz, 1H, C35-H), 3.83 (ddd, J = 9.7, 9.5, 2.7 Hz, 1H, C33-H), 3.79 (m, J = 3.4 Hz, 1H, C28-H), 3.74 (dd, J = 4.7, 3.4 Hz, 1H, C29-H), 3.68 (d, J = 3.4 Hz, 1H, C36-H), 3.67–3.61 (m, 2H, C27-H2), 3.63 (dd, J = 4.7, 3.1 Hz, 1H, C30-H), 3.42 (dd, J = 9.5, 9.4 Hz, 1H, C34-H), 2.17 (ddd, J = 14.4, 5.5, 2.7 Hz, 1H, one of C32-H), 1.88 (dd, J = 14.5, 1.9 Hz, 1H, one of C38-H), 1.78 (dd, J = 14.6, 10.0 Hz, 1H, one of C38-H), 1.73 (ddd, J = 14.4, 9.5, 7.3 Hz, 1H, one of C32-H), 1.50–1.23 (m, 16H, C40–47-H2), 0.89 (t, J = 7.0 Hz, 3H, C48-H3).   91 OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH H 3c O C9H19 epi-C33–C37 Model C27–C48 Lactol (3c). White solid; 1H-NMR (600 MHz, pyridine-d5) δ 8.03 (br s, 1H, one of C37–OH), 6.90 (br s, 1H, one of –OH), 6.51 (br s, 2H, two of –OH), 6.44–6.21 (br m, 3H, three of –OH), 6.12–6.01 (br m, 3H, three of –OH), 5.04 (ddd, J = 9.4, 9.2, 2.8 Hz, 1H, C33-H), 4.91–4.90 (m, 2H, C30-H and C31-H), 4.64 (dd, J = 3.7, 3.2 Hz, 1H, C29-H), 4.58 (d, J = 2.6 Hz, 1H, C36-H), 4.58–4.54 (m, 2H, C28-H and C39-H), 4.38 (m, J = 9.4, 9.1 Hz, 1H, C34-H), 4.35–4.26 (m, 3H, C27-H2 and C35-H), 3.11 (m, J = 2.6 Hz, 1H, one of C32-H), 2.70 (dd, J = 13.2 Hz, 1H, one of C38-H), 2.38 (dd, J = 14.2, 10.3 Hz, 1H, one of C38H), 2.32 (m, J = 11.8, 9.2 Hz, 1H, one of C32-H), 1.76–1.72 (m, 1H, one of C40-H), 1.62–1.56 (m, 2H, one of C40-H and one of C41-H), 1.48–1.41 (m, 1H, one of C41-H), 1.26–1.05 (m, 12H, C42–47-H2), 0.82 (t, J = 7.2 Hz, 3H, C48-H3); 13C-NMR (125 MHz, pyridine-d5) δ 100.2 (C37), 76.1 (C35), 74.03 (C29), 73.99 (C36), 73.3 (C30), 73.2 (C28), 73.0 (C34), 71.1 (C33), 69.9 (C31), 67.9 (C39), 64.6 (C27), 44.8 (C38), 39.0 (C40), 38.5 (C32), 32.1 (C46), 30.04 (C43 or C44), 29.99 (C43 or C44), 29.8 (C42), 29.6 (C45), 26.2 (C41), 22.9 (C47), 14.3 (C48); 1HNMR (600 MHz, CD3OD) δ 3.97 (ddd, J = 10.3, 3.5, 3.1 Hz, 1H, C31-H), 3.94 (m, 1H, C39H), 3.88 (dd, J = 9.5, 3.4 Hz, 1H, C35-H), 3.87 (ddd, J = 9.7, 9.7, 2.8 Hz, 1H, C33-H), 3.78 (ddd, J = 6.2, 5.0, 3.5 Hz, 1H, C28-H), 3.73 (dd, J = 4.5, 3.5 Hz, 1H, C29-H), 3.70 (d, J = 3.4 Hz, 1H, C36-H), 3.66 (d, J = 11.1, 5.0 Hz, 1H, one of C27-H), 3.63 (d, J = 11.1, 6.2 Hz, 1H, one of C27-H), 3.57 (dd, J = 4.2, 4.0 Hz, 1H, C30-H), 3.40 (dd, J = 9.7, 9.5 Hz, 1H, C34-H), 2.15 (ddd, J = 14.4, 10.0, 2.6 Hz, 1H, one of C32-H), 1.93 (dd, J = 14.6, 1.9 Hz, 1H, one of C38-H), 1.75 (dd, J = 14.6, 10.0 Hz, 1H, one of C38-H), 1.61 (ddd, J = 14.4, 9.8, 2.9 Hz, 1H, one of C32-H), 1.50–1.38 (m, 2H, C40-H2), 1.37–1.23 (m, 14H, C41–47-H2), 0.89 (t, J = 7.1 Hz, 3H, C48-H3). OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH H 3d O C9H19   92 epi-C34,C36 Model C27–C48 Lactol (3d). White solid; 1H-NMR (600 MHz, pyridine-d5) δ 7.46 (br s, 1H, one of –OH), 6.96 (br s, 1H, one of –OH), 6.54 (br s, 1H, one of –OH), 6.38– 6.28 (br m, 2H, two of –OH), 6.25–6.12 (br m, 4H, four of –OH), 5.07 (ddd, J = 7.5, 6.9 Hz, 1H, C33-H), 4.85 (m, 1H, C31-H), 4.69 (m, 1H, C39-H), 4.68 (dd, J = 3.4, 3.2 Hz, 1H, C30-H), 4.59 (m, J = 3.5 Hz, 1H, C28-H), 4.56 (dd, J = 10.1, 3.1 Hz, 1H, C35-H), 4.48 (m, 1H, C29-H), 4.44 (m, 1H, C34-H), 4.38 (d, J = 9.7 Hz, 1H, C36-H), 4.35–4.29 (m, 2H, C27-H2), 2.96 (ddd, J = 13.5, 8.1, 7.9 Hz, 1H, one of C32-H), 2.69 (ddd, J = 13.4, 6.7, 5.9 Hz, 1H, one of C32-H), 2.64 (dd, J = 14.1, 11.3 Hz, 1H, one of C38-H), 2.04 (dd, J = 13.9 Hz, 1H, one of C38-H), 1.64–1.59 (m, 1H, one of C40-H), 1.51–1.42 (m, 2H, one of C40-H and one of C41-H), 1.38– 1.31 (m, 1H, one of C41-H), 1.26–1.11 (m, 12H, C42–47-H2), 0.82 (t, J = 7.1 Hz, 3H, C48-H3); 13 C-NMR (125 MHz, pyridine-d5) δ 100.1 (C37), 74.3 (C36), 74.2 (C29), 73.9 (C28), 73.5 (C30), 72.5 (C35), 72.1 (C34), 70.6 (C31), 69.3 (C33), 68.2 (C39), 64.5 (C27), 43.8 (C38), 39.2 (C40), 35.7 (C32), 32.0 (C46), 30.0 (C43 or C44), 29.9 (C43 or C44), 29.8 (C42), 29.5 (C45), 25.8 (C41), 22.9 (C47), 14.2 (C48). OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH H 3e O C9H19 epi-C35,C36 Model C27–C48 Lactol (3e). White solid; 1H-NMR (600 MHz, pyridine-d5) δ 7.52 (br s, 1H, one of –OH), 7.32 (br s, 1H, one of –OH), 7.07 (br s, 1H, one of –OH), 6.47– 6.37 (br m, 4H, four of –OH), 6.09–6.03 (br m, 3H, three of –OH), 4.96–4.90 (m, J = 9.8, 3.4 Hz, 2H, C31-H and C33-H), 4.74–4.66 (m, 2H, C29-H and C35-H), 4.62–4.55 (m, 2H, C28-H and C39-H), 4.55–4.49 (m, 1H, C30-H), 4.37–4.28 (m, 2H, C27-H2), 3.92–3.89 (m, 1H, C36-H), 3.86 (m, J = 8.6 Hz, 1H, C34-H), 3.09 (ddd, J = 14.2, 5.9, 3.4 Hz, 1H, one of C32-H), 2.51 (ddd, J = 14.1, 9.8, 7.1 Hz, 1H, one of C32-H), 2.45 (dd, J = 14.3, 10.5 Hz, 1H, one of C38-H), 2.16 (dd, J = 14.2 Hz, 1H, one of C38-H), 1.69–1.64 (m, 1H, one of C40-H), 1.60–1.47 (m, 2H, one of C40-H and one of C41-H), 1.46–1.39 (m, 1H, one of C41-H), 1.26–1.11 (m, 12H, C42–47-H2), 0.82 (t, J = 7.2 Hz, 3H, C48-H3); 13C-NMR (125 MHz, pyridine-d5) δ 100.8 (C37), 74.4 (C35), 74.00 (C30), 73.95 (C28), 73.5 (C29), 73.1 (C34), 71.8 (C36), 71.6 (C31), 67.8 (C39), 67.3 (C33), 64.6 (C27), 45.7 (C38), 38.9 (C40), 37.2 (C32), 32.1 (C46), 30.1 (C43 or C44), 29.9 (C43 or C44), 29.8 (C42), 29.6 (C45), 26.0 (C41), 22.9 (C47), 14.3 (C48); 1H-NMR (600   93 MHz, CD3OD) δ 4.07 (ddd, J = 6.7, 6.6, 2.7 Hz, 1H, C31-H), 4.03 (ddd, J = 9.8, 9.8, 3.1 Hz, 1H, C33-H), 4.03–3.98 (m, 1H, C39-H), 4.01 (dd, J = 3.1, 2.9 Hz, 1H, C35-H), 3.79 (ddd, J = 6.3, 5.1, 3.1 Hz, 1H, C28-H), 3.78–3.75 (m, 1H, C30-H), 3.68 (dd, J = 5.0, 2.7 Hz, 1H, C29-H), 3.67–3.62 (m, 2H, C27-H2), 3.34 (d, J = 3.1 Hz, 1H, C36-H), 3.28 (dd, J = 9.8, 2.9 Hz, 1H, C34H), 2.21 (ddd, J = 14.1, 6.7, 3.1 Hz, 1H, one of C32-H), 1.86 (dd, J = 14.6, 10.4 Hz, 1H, one of C38-H), 1.70 (ddd, J = 14.2, 9.7, 6.6 Hz, 1H, one of C32-H), 1.67 (dd, J = 14.5, 1.8 Hz, 1H, one of C38-H), 1.45–1.22 (m, 16H, C40–47-H2), 0.90 (t, J = 7.0 Hz, 3H, C48-H3). OH HO HO HO HO 27 31 35 OH OH OH 39 OH OH H 3f O C9H19 epi-C36 Model C27–C48 Lactol (3f). White solid; 1H-NMR (600 MHz, pyridine-d5) δ 7.53 (br s, 1H, one of –OH), 6.99–6.96 (br m, J = 4.2, 4.0 Hz, 2H, two of –OH), 6.84 (br s, 1H, one of –OH), 6.58 (br s, 1H, one of –OH), 6.53–6.49 (br s, 2H, two of –OH), 6.10–6.05 (br m, 2H, two of –OH), 5.98 (br d, J = 4.0 Hz, 1H, one of –OH), 4.95 (m, 1H, C31-H), 4.90 (ddd, J = 9.8, 9.7, 3.1 Hz, 1H, C33-H), 4.72–4.66 (m, 2H, C29-H and C39-H), 4.61–4.56 (m, J = 9.8, 7.6 Hz, 3H, C28-H, C30-H and C35-H), 4.34–4.28 (m, 2H, C27-H2), 3.94 (ddd, J = 9.8, 9.2, 3.6 Hz, 1H, C34-H), 3.91 (dd, J = 8.2, 7.8 Hz, 1H, C36-H), 3.21 (ddd, J = 13.8, 7.0, 3.4 Hz, 1H, one of C32-H), 2.67 (dd, J = 14.2, 11.1 Hz, 1H, one of C38-H), 2.51 (ddd, J = 13.8, 10.0, 6.6 Hz, 1H, one of C32-H), 2.06 (dd, J = 12.9 Hz, 1H, one of C38-H), 1.66–1.60 (m, 1H, one of C40-H), 1.54–1.46 (m, 2H, one of C40-H and one of C41-H), 1.42–1.34 (m, 1H, one of C41-H), 1.26–1.11 (m, 12H, C42–47-H2), 0.82 (t, J = 7.2 Hz, 3H, C48-H3); 13 C-NMR (125 MHz, pyridine-d5) δ 99.8 (C37), 77.8 (C36), 77.1 (C34), 75.8 (C29), 73.8 (C30), 73.6 (C28), 73.1 (C35), 71.5 (C31), 70.7 (C33), 68.3 (C39), 64.5 (C27), 43.8 (C38), 39.2 (C40), 37.6 (C32), 32.0 (C46), 30.1 (C43 or C44), 29.9 (C43 or C44), 29.8 (C42), 29.5 (C45), 25.8 (C41), 22.9 (C47), 14.2 (C48); 1H-NMR (600 MHz, CD3OD) δ 4.08–4.02 (m, J = 8.3, 6.3, 2.3 Hz, 2H, C31-H and C39-H), 3.89 (ddd, J = 10.0, 9.8, 2.9 Hz, 1H, C33-H), 3.79–3.76 (m, J = 5.1, 3.1 Hz, 2H, C28-H and C29-H), 3.68–3.62 (m, J = 8.2, 6.1 Hz, 2H, C27-H2), 3.67 (dd, J = 5.1, 2.5 Hz, 1H, C30-H), 3.58 (app t, J = 9.2 Hz, 1H, C35-H), 3.10 (d, J = 9.4 Hz, 1H, C36-H), 3.09 (app t, J = 9.4 Hz, 1H, C34-H), 2.23 (ddd, J = 13.9, 7.5, 2.9 Hz, 1H, one of C32-H), 1.93 (dd, J = 14.5, 10.8 Hz, 1H, one of C38-H), 1.66 (ddd, J = 13.9, 10.1, 6.3 Hz, 1H, one of C32-H), 1.62 (dd, J =   94 14.4, 1.9 Hz, 1H, one of C38-H), 1.48–1.24 (m, 16H, C40–47-H2), 0.89 (t, J = 7.0 Hz, 3H, C48H3). OH HO HO HO HO 27 31 35 OH OH OMe 39 OH OH H 51a O C9H19 Aflastatin A Model C27–C48 Lactol Methyl Ether (51a). White solid; [α] 24 +19.8° (c = D 0.30, CH3OH); IR (neat) 3362 (br), 2926, 2855, 1456, 1377, 1206, 1102, 1063 cm–1; 1H-NMR (600 MHz, pyridine-d5) δ 6.87 (br s, 1H, one of –OH), 6.48 (br s, 2H, two of –OH), 6.42–5.99 (br m, 6H, six of –OH), 4.94 (m, J = 6.2, 2.9 Hz, 1H, C31-H), 4.70–4.66 (m, J = 3.6 Hz, 2H, C29-H and C36-H), 4.65 (ddd, J = 5.6, 5.1, 3.5 Hz, 1H, C28-H), 4.58 (dd, J = 9.3, 3.6 Hz, 1H, C35-H), 4.52 (dd, J = 3.5, 3.4 Hz, 1H, C30-H), 4.38–4.32 (m, J = 10.8, 4.5 Hz, 2H, C27-H2), 4.33 (app t, J = 9.1 Hz, 1H, C34-H), 4.26 (app dt, J = 9.2, 9.2, 2.8 Hz, 1H, C33-H), 4.22–4.17 (m, J = 7.3, 5.0 Hz, 1H, C39-H), 3.37 (s, 3H, C56-H3), 3.20 (ddd, J = 14.2, 6.4, 2.7 Hz, 1H, one of C32-H), 2.50 (ddd, J = 14.6, 8.9, 5.9 Hz, 1H, one of C32-H), 2.46 (dd, J = 15.1, 9.3 Hz, 1H, one of C38-H), 2.23 (app d, J = 14.9 Hz, 1H, one of C38-H), 1.71–1.64 (m, 1H, one of C40-H), 1.63–1.53 (m, 2H, one of C40-H and one of C41-H), 1.52–1.43 (m, 1H, one of C41-H), 1.32– 1.14 (m, 12H, C42–47-H2), 0.82 (t, J = 7.0 Hz, 3H, C48-H3); 13C-NMR (125 MHz, pyridine-d5) δ 103.3 (C37), 74.3 (C30), 73.9 (C28), 73.6 (C29), 73.1 (C36), 72.8 (C33), 72.7 (C35), 72.4 (C34), 71.3 (C31), 67.0 (C39), 64.7 (C27), 47.9 (C56), 39.42 (C38 or C40), 39.36 (C38 or C40), 37.5 (C32), 32.1 (C46), 30.03 (C43 or C44), 29.97 (C43 or C44), 29.8 (C42), 29.5 (C45), 26.0 (C41), 22.9 (C47), 14.2 (C48); HRMS (ESI-TOF) m/z calcd for C23H46NaO11 [M+Na]+: 521.2932, found: 521.2926. OH HO HO HO HO 27 31 35 OH OH OCD3 39 OH OH H 51b O C9H19 Aflastatin A Model C27–C48 Lactol Trideuteriomethyl Ether (51b). White solid; [α] 24 D +22.9° (c = 0.38, CH3OH); IR (neat) 3365 (br), 2926, 2855, 2072, 1456, 1418, 1260, 1207, 1114, 1062 cm–1; 1H-NMR (600 MHz, pyridine-d5) δ 6.13 (br s, 9H, nine of –OH), 4.94 (app   95 dt, J = 6.2, 6.2, 3.2 Hz, 1H, C31-H), 4.70–4.66 (m, J = 3.6 Hz, 2H, C29-H and C36-H), 4.65 (ddd, J = 5.7, 5.3 Hz, 1H, C28-H), 4.58 (dd, J = 9.2, 3.7 Hz, 1H, C35-H), 4.52 (dd, J = 3.8, 3.4 Hz, 1H, C30-H), 4.38–4.32 (m, J = 10.8, 5.3 Hz, 2H, C27-H2), 4.33 (app t, J = 9.5 Hz, 1H, C34H), 4.26 (app dt, J = 9.2, 9.2, 2.6 Hz, 1H, C33-H), 4.21–4.17 (m, J = 5.9 Hz, 1H, C39-H), 3.20 (ddd, J = 14.1, 6.4, 2.8 Hz, 1H, one of C32-H), 2.50 (ddd, J = 14.6, 8.7, 5.9 Hz, 1H, one of C32H), 2.46 (dd, J = 15.3, 9.3 Hz, 1H, one of C38-H), 2.22 (app d, J = 14.9 Hz, 1H, one of C38-H), 1.71–1.64 (m, 1H, one of C40-H), 1.63–1.53 (m, 2H, one of C40-H and one of C41-H), 1.52– 1.43 (m, 1H, one of C41-H), 1.32–1.14 (m, 12H, C42–47-H2), 0.82 (t, J = 7.0 Hz, 3H, C48-H3); 13 C-NMR (125 MHz, pyridine-d5) δ 103.3 (C37), 74.3 (C30), 73.9 (C28), 73.6 (C29), 73.1 (C36), 72.8 (C33), 72.6 (C35), 72.4 (C34), 71.3 (C31), 66.9 (C39), 64.6 (C27), 39.42 (C38 or C40), 39.36 (C38 or C40), 37.5 (C32), 32.1 (C46), 30.03 (C43 or C44), 29.97 (C43 or C44), 29.8 (C42), 29.5 (C45), 26.0 (C41), 22.9 (C47), 14.2 (C48); HRMS (ESI-TOF) m/z calcd for C23H43D3NaO11 [M+Na]+: 524.3121, found: 524.3100. Synthesis of the C27–C35 Aldehyde H HO 31 O 27 OMe OH H I 31 O 27 OMe OH BnO OBn 62 BnO OBn 78 (2S,3R,4R,5S,6S)-4,5-Bis(benzyloxy)-6-(iodomethyl)-2-methoxytetrahydro-2H-pyran-3-ol (78). To a solution of diol 62 (9.8 g, 26 mmol, 1.0 equiv), imidazole (5.4 g, 79 mmol, 3.0 equiv), and triphenylphosphine (10.7 g, 40.7 mmol, 1.55 equiv) in 2:1 PhMe/MeCN (131 mL, 0.2 M wrt 62) at rt was added iodine (10 g, 39 mmol, 1.5 equiv) in three portions. The reaction mixture was stirred at rt for 3 h, quenched with brine (100 mL), and then diluted with H2O (10 mL) and Et2O (50 mL). The layers were separated and the aqueous layer extracted with Et2O (3 x 100 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 5:1 → 4:1 → 3:1 hexanes/EtOAc) afforded iodide 78 (12.3 g, 97% yield) as a white solid. [α] 25 +95.4° (c = D 2.3, CH2Cl2); IR (neat) 3424 (br), 3029, 2924, 1497, 1453, 1399, 1361, 1325, 1214, 1192, 1140, 1087, 1046, 733, 696 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.39–7.30 (m, 10H, ArH), € 4.95 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 4.94 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.84   96 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.78 (d, J = 3.8 Hz, 1H, C27-H), 4.72 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 3.80 (dd, J = 9.2, 8.9 Hz, 1H, C29-H), 3.71 (ddd, J = 8.8, 8.6, 3.8 Hz, 1H, C28-H), 3.51 (dd, J = 10.5, 2.6 Hz, 1H, one of C32-H), 3.48 (ddd, J = 9.1, 6.4, 2.6 Hz, 1H, C31-H), 3.48 (s, 3H, –OCH3), 3.36 (dd, J = 9.2, 8.9 Hz, 1H, C30-H), 3.32 (dd, J = 10.5, 6.3 Hz, 1H, one of C32-H), 2.16 (d, J = 8.6 Hz, 1H, C28-OH); 13C-NMR (125 MHz, CDCl3) δ 138.4, 137.9, 128.5, 128.5, 127.9, 127.9, 127.8, 99.3, 82.8, 81.2, 75.4, 75.3, 73.1, 69.7, 55.5, 7.3; HRMS (ESI-TOF) m/z calcd for C21H25INaO5 [M+Na]+: 507.06389, found: 507.06416. H I 31 O OMe 27 OBn HO 27 31 BnO OBn 78 OH OH OBn 79 ((2S,3R,4R)-3,4-Bis(benzyloxy)hex-5-ene-1,2-diol (79). To a solution of iodide 78 (1.1 g, 2.2 mmol, 1.0 equiv) in 4:1 THF/H2O (22 mL, 0.1 M wrt 78) at rt was added preactivated zinc dust76 (1.4 g, 22 mmol, 10 equiv). The reaction mixture was sonicated at 40–45 °C for 4 h, then cooled to 0 °C and charged with sodium borohydride (0.17 g, 4.4 mmol, 2.0 equiv) in three portions. The resulting suspension was stirred at 0 °C for 2 h, slowly quenched with 1 M NaHSO4 (15 mL), diluted with Et2O (15 mL), warmed to rt, and filtered through Celite . The  filter cake was rinsed with Et2O (3 x 10 mL) and sat. aq NH4Cl (3 x 10 mL). The layers were separated and the aqueous layer extracted with Et2O (3 x 50 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 2:1 → 3:2 → 1:1 hexanes/EtOAc) afforded diol 79 (0.56 g, 78% yield) as a clear, colorless oil. [α] 25 +7.6° (c = 0.66, CH2Cl2); IR (neat) 3419 (br), 3064, D 3031, 2934, 2877, 1497, 1455, 1403, 1351, 1209, 1066, 1028, 998, 931, 870, 736, 699 cm–1; 1 H-NMR (600 MHz, C6D6) δ 7.27 (m, 2H, two of ArH), 7.22 (m, 2H, two of ArH), 7.17–7.12 € (m, 4H, four of ArH), 7.08 (m, 2H, two of ArH), 5.78 (ddd, J = 17.4, 10.4, 7.3 Hz, 1H, C31H), 5.24 (d, J = 17.4 Hz, 1H, one of C32-H), 5.11 (d, J = 10.4 Hz, 1H, one of C32-H), 4.75 (d, J = 11.3 Hz, 1H, one of –OCH2Ph), 4.49 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.43 (d, J = 11.3 Hz, 1H, one of –OCH2Ph), 4.22 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.11 (dd, J = 7.3, 6.4 Hz, 1H, C30-H), 3.76 (dddd, J = 7.6, 5.4, 5.4, 3.4 Hz, 1H, C28-H), 3.55–3.47 (m, J = 11.1,                                                                                                                 (76) Hyldtoft, L.; Madsen, R. J. Am. Chem. Soc. 2000, 122, 8444–8452.   97 7.8, 5.4, 4.8 Hz, 2H, C27-H2), 3.45 (dd, J = 6.4, 3.4 Hz, 1H, C29-H), 2.41 (d, J = 7.6 Hz, 1H, C28-OH), 1.86 (dd, J = 7.8, 4.8 Hz, 1H, C27-OH); 13C-NMR (125 MHz, C6D6) δ 138.9, 138.9, 135.6, 128.6, 128.6, 128.3, 128.1, 127.9, 127.7, 118.9, 82.1, 81.6, 74.8, 71.4, 70.9, 64.3; HRMS (ESI-TOF) m/z calcd for C20H24NaO4 [M+Na]+: 351.15668, found: 351.15697. OBn HO 27 31 27 OBn 31 O OH OBn 79 Me O Me 63 OBn (S)-4-((1S,2R)-1,2-Bis(benzyloxy)but-3-enyl)-2,2-dimethyl-1,3-dioxolane (63). To a solution of diol 79 (2.7 g, 8.1 mmol, 1.0 equiv) in 2:1 acetone/2,2-dimethoxypropane (81 mL, 0.1 M wrt 79) at rt was added PPTS (10 mg, 41 µmol, 0.005 equiv). The reaction mixture was stirred at rt for 10 h, quenched with a small spatula tip full of NaHCO3 (s), stirred vigorously for an additional 15 min, and filtered through Celite . The filter cake was rinsed with EtOAc  (40 mL total), and the filtrate concentrated. Column chromatography (gradient elution, 4% → 6% → 8% EtOAc in hexanes) afforded acetonide 63 (2.7 g, 90% yield) as a clear, colorless oil. [α] 24 –25.3° (c = 2.1, CH2Cl2); IR (neat) 3065, 3031, 2985, 2873, 1497, 1455, 1380, D 1252, 1213, 1070, 1001, 930, 861, 736, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.35–7.26 € (m, 10H, ArH), 5.90 (ddd, J = 17.4, 10.4, 7.0 Hz, 1H, C31-H), 5.33 (d, J = 17.4 Hz, 1H, one of C32-H), 5.31 (d, J = 10.4 Hz, 1H, one of C32-H), 4.79 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.76 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.60 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.34 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.27 (ddd, J = 7.8, 6.4, 6.4 Hz, 1H, C28-H), 3.93 (dd, J = 6.7, 5.1 Hz, 1H, C30-H), 3.82 (dd, J = 8.2, 6.3 Hz, 1H, one of C27-H), 3.65 (dd, J = 8.1, 8.1, 1H, one of C27-H), 3.45 (dd, J = 6.6, 4.8 Hz, 1H, C29-H), 1.40 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3); 13C-NMR (125 MHz, CDCl3) δ 138.6, 138.1, 134.9, 128.3, 128.2, 128.2, 128.1, 128.0, 127.8, 127.6, 127.4, 118.4, 108.7, 81.3, 80.5, 76.8, 74.0, 70.6, 65.9, 26.6, 25.7; HRMS (ESI-TOF) m/z calcd for C23H28NaO4 [M+Na]+: 391.18798, found: 391.18848. 27 OBn 31 27 OBn O 31 O Me O Me 63 OBn O Me O Me 80 H OBn   98 (2S,3R)-2,3-Bis(benzyloxy)-3-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)propanal (80). To a solution of alkene 63 (0.55 g, 1.5 mmol, 1.0 equiv) in 1:1 CH2Cl2/MeOH (30 mL, 0.05 M wrt 63) at –78 °C was added pyridine (1.2 mL, 15 mmol, 10 equiv). The reaction mixture was bubbled with ozone until it turned blue, purged with oxygen until the color faded, quenched dropwise with a solution of triphenylphosphine (0.47 g, 1.8 mmol, 1.2 equiv) in 1:1 CH2Cl2/MeOH (7.4 mL, 0.24 M wrt PPh3), slowly warmed to rt o/n (16 h total stir time), and then diluted with 1 M aq NaHSO4 (40 mL) and brine (5 mL). The layers were separated and the aqueous layer extracted with CH2Cl2 (2 x 20 mL). The combined organic extracts were dried over Na2SO4, filtered and concentrated. A sufficient quantity of crude aldehyde 80 was purified by column chromatography (4:1 hexanes/EtOAc) for characterization. [α] 24 –30.9° D (c = 6.4, CH2Cl2); IR (neat) 3032, 2987, 2936, 2874, 1732 (s), 1498, 1455, 1371, 1255, 1211, 1152 1077, 850, 739, 699 cm–1; 1H-NMR (600 MHz, C6D6) δ 9.70 (d, J = 1.2 Hz, 1H, C31-H), € 7.25 (m, 2H, two of ArH), 7.17–7.05 (m, 8H, eight of ArH), 4.56 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.52 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.50 (d, J = 11.6 Hz, 1H, one of – OCH2Ph), 4.40 (ddd, J = 7.2, 6.7, 5.4 Hz, 1H, C28-H), 4.15 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 3.69 (dd, J = 4.5, 1.3 Hz, 1H, C30-H), 3.69 (dd, J = 8.2, 6.6 Hz, 1H, one of C27-H), 3.61 (dd, J = 8.3, 7.2 Hz, 1H, one of C27-H), 3.45 (dd, J = 5.4, 4.5 Hz, 1H, C29-H), 1.38 (s, 3H, one of CH3), 1.24 (s, 3H, one of CH3); 13C-NMR (125 MHz, C6D6) δ 201.0, 138.5, 137.7, 128.6, 128.5, 128.3, 128.2, 128.2, 127.9, 127.8, 109.7, 83.0, 79.9, 76.3, 73.7, 73.1, 65.8, 26.5, 25.7; HRMS (ESI-TOF) m/z calcd for C22H26NaO5 [M+Na]+: 393.16725, found: 393.16666. 27 OBn O 31 27 OBn OH 31 33a O Me O Me 80 H O Me O Me 64 OBn OBn (1R,2R,3S)-1,2-Bis(benzyloxy)-1-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)hex-5-en-3-ol (64). To a solution of crude aldehyde 80 (theoretical 0.55 g, 1.5 mmol, 1.0 equiv) in CH2Cl2 (30 mL, 0.05 M wrt 80) at 0 °C was added freshly prepared77 MgBr2•OEt2 (1.5 g, 6.0 mmol, 4.0 equiv). The resulting suspension was stirred at 0 °C for 5 min, cooled to –78 °C, and then                                                                                                                 (77) Peterson, S. Studies Toward the Synthesis of Amphidinol 3. Ph.D. Thesis, Harvard University, 2006.   99 charged dropwise with a freshly prepared78 solution of allylmagnesium bromide in Et2O (5.3 mL, 0.42 M, 2.2 mmol, 1.5 equiv). The reaction mixture was stirred at –78 °C for 2.5 h, slowly warmed to –40 °C over 30 min, then briefly warmed to 0 °C and quenched with sat. aq NH4Cl (30 mL). The biphasic mixture was diluted with H2O (5 mL) and CH2Cl2 (30 mL) and warmed to rt. The layers were separated and the aqueous layer extracted with CH2Cl2 (3 x 40 mL). The combined organic extracts were dried over Na2SO4, filtered and concentrated. The residue was analyzed by 1H-NMR spectroscopy to assess reaction diastereoselectivity (d.r. = 89:11). Column chromatography (gradient elution, 16% → 18% → 20% EtOAc in hexanes) afforded homoallylic carbinol 64 (0.35 g, 56% yield, two steps) as a clear, colorless oil. [α] 25 D –18.9° (c = 1.4, CH2Cl2); IR (neat) 3477 (br), 3065, 3031, 2984, 2935, 1641, 1497, 1454, 1371, 1249, 1211, 1068, 916, 858, 736, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.36–7.29 € (m, 8H, eight of ArH), 7.27 (m, 2H, two of ArH), 5.77 (dddd, J = 17.1, 10.3, 7.0, 7.0 Hz, 1H, C33-H), 5.07 (d, J = 10.3 Hz, 1H, one of C33a-H), 5.03 (dd, J = 17.1, 1.5 Hz, 1H, one of C33aH), 4.68 (d, J = 12.4 Hz, 1H, one of –OCH2Ph), 4.66 (d, J = 12.3 Hz, 1H, one of –OCH2Ph), 4.64 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.52 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.44 (ddd, J = 6.7, 6.7, 5.6 Hz, 1H, C28-H), 3.95 (dd, J = 8.1, 6.7 Hz, 1H, one of C27-H), 3.90 (dddd, J = 7.6, 7.0, 5.4, 2.2 Hz, 1H, C31-H), 3.78 (dd, J = 7.8, 7.8 Hz, 1H, one of C27-H), 3.55 (dd, J = 5.3, 5.3 Hz, 1H, C29-H), 3.46 (dd, J = 5.3, 2.2 Hz, 1H, C30-H), 2.60 (d, J = 6.9 Hz, 1H, C28-OH), 2.31 (ddd, J = 14.2, 7.2, 7.0 Hz, 1H, one of C32-H), 2.23 (ddd, J = 14.1, 6.9, 6.3 Hz, 1H, one of C32-H), 1.44 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3); 13C-NMR (125 MHz, CDCl3) δ 138.2, 137.8, 134.9, 128.5, 128.4, 128.3, 128.1, 128.0, 127.7, 117.4, 109.0, 79.5, 77.8, 76.0, 73.9, 73.9, 69.2, 66.0, 39.0, 26.5, 25.6; HRMS (ESI-TOF) m/z calcd for C25H33O5 [M+H]+: 413.2323, found: 413.2330. O 27 OBn OH 31 27 OBn O 31 34a O Me O Me 64 O Me O Me 81 33a OBn OBn                                                                                                                 (78) Benson, R.E.; McKusick, B.C. Org. Synth. 1958, 38, 78–84.   100 (1R,2R,3S)-1,2-Bis(benzyloxy)-1-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)hex-5-en-3-yl acrylate (81). To a solution of homoallylic carbinol 64 (1.6 g, 4.0 mmol, 1.0 equiv) in THF (20 mL, 0.2 M wrt 64) at room temperature was added EtN(iPr)2 (2.1 mL, 12 mmol, 3.0 equiv), DMAP (0.12 g, 0.99 mmol, 0.25 equiv), and a freshly prepared solution of acrylic pivalic anhydride in PhH (6.0 mL, 2.0 M, 12 mmol, 3.0 equiv). The resulting suspension was stirred at room temperature for 7 h, then charged with additional EtN(iPr)2 (2.1 mL, 12 mmol, 3.0 equiv), DMAP (0.12 g, 0.99 mmol, 0.25 equiv), and acrylic pivalic anhydride (6.0 mL, 2.0 M in PhH, 12 mmol, 3.0 equiv). The reaction mixture was stirred for an additional 12 h, quenched with sat. aq NaHCO3 (35 mL), and diluted with Et2O (35 mL) and H2O (5 mL). The layers were separated and the aqueous layer extracted with Et2O (2 x 60 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 6% → 8% → 10% EtOAc in hexanes) afforded acrylate ester 81 (1.48 g, 80% yield) as a clear, colorless oil. [α] 25 –19.3° (c = 1.3, CH2Cl2); D IR (neat) 3066, 3032, 2985, 2892, 1730 (s), 1640, 1497, 1455, 1405, 1371, 1260, 1195, 1064 (br), 987, 919, 853, 808, 736, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.35–7.27 (m, 10H, € ArH), 6.42 (dd, J = 17.3, 1.2 Hz, 1H, one of C34a-H), 6.14 (dd, J = 17.3, 10.4 Hz, 1H, C34-H), 5.83 (dd, J = 10.4, 1.2 Hz, 1H, one of C34a-H), 5.67 (dddd, J = 17.1, 10.1, 7.0, 7.0 Hz, 1H, C33H), 5.32 (ddd, J = 7.3, 5.2, 4.9 Hz, 1H, C31-H), 5.02 (dd, J = 10.1, 1.5 Hz, 1H, one of C33a-H), 4.99 (dd, J = 17.1, 1.5 Hz, 1H, one of C33a-H), 4.74 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.72 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.64 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.58 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.26 (ddd, J = 6.4, 6.4, 6.4 Hz, 1H, C28-H), 3.86 (dd, J = 8.3, 6.5 Hz, 1H, one of C27-H), 3.73 (dd, J = 7.9, 7.6 Hz, 1H, one of C27-H), 3.65 (dd, J = 5.0, 4.8 Hz, 1H, C30-H), 3.51 (dd, J = 5.4, 5.4 Hz, 1H, C29-H), 2.46 (dddd, J = 14.3, 6.6, 5.6, 1.0 Hz, 1H, one of C32-H), 2.32 (ddd, J = 14.6, 7.5, 7.2 Hz, 1H, one of C32-H), 1.43 (s, 3H, one of CH3), 1.34 (s, 3H, one of CH3); 13C-NMR (125 MHz, CDCl3) δ 165.5, 138.2, 137.9, 133.5, 131.1, 128.4, 128.4, 128.3, 128.2, 128.1, 127.8, 127.7, 117.9, 109.0, 78.6, 78.0, 76.4, 74.0, 73.9, 72.5, 65.8, 35.4, 26.5, 25.6; HRMS (ESI-TOF) m/z calcd for C28H34NaO6 [M+Na]+: 489.2248, found: 489.2229.   101 O 27 Cy3P Ru Cl Cl 90 Ph 27 O OBn O 31 35 OBn O 31 PCy3 O Me O Me 81 O Me O Me 65 OBn OBn (S)-6-((1R,2R)-1,2-Bis(benzyloxy)-2-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)ethyl)-5,6dihydro-2H-pyran-2-one (65). To a degassed solution of diene 81 (0.28 g, 0.60 mmol, 1.0 equiv) in PhH (40 mL, 0.015 M wrt 81) at room temperature was added ruthenium catalyst 90 (0.025 g, 0.030 mmol, 0.05 equiv). The reaction mixture was purged with argon for 5 min, stirred at 65 °C for 12 h, then recharged with additional catalyst (0.025 g, 0.030 mmol, 0.05 equiv) at this time and approximately every 7 h twice after (total catalyst 90 added: 0.2 equiv). The reaction mixture was stirred at 65 °C for an additional 12 h, cooled to room temperature, concentrated to half volume, diluted with 2:1 hexanes/EtOAc (50 mL) and filtered through a silica gel plug (4 cm). The filter cake was rinsed with 2:1 hexanes/EtOAc (200 mL), and the filtrate concentrated. Column chromatography (gradient elution, 4:1 → 3:1 → 5:2 hexanes/EtOAc) afforded lactone 65 (0.23 g, 89% yield) as a dark brown oil contaminated with ruthenium-based impurities (<5%). A sufficient quantity of this material was repurified by column chromatography to produce a clear, colorless oil for characterization. [α] 25 –91.0° (c = 1.2, CH2Cl2); IR (neat) 3064, 3031, 2986, 2935, 2881, D 1732 (s), 1498, 1455, 1381, 1248, 1213, 1157, 1116, 1064, 893, 851, 816, 740, 700 cm–1; 1HNMR (600 MHz, CDCl3) δ 7.36–7.28 (m, 10H, ArH), 6.79 (ddd, J = 9.7, 6.3, 2.3 Hz, 1H, C33€ H), 5.97 (ddd, J = 9.7, 2.8, 0.7 Hz, 1H, C34-H), 4.75 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.73 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.71 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.71 (ddd, J = 12.2, 4.2, 3.8 Hz, 1H, C31-H), 4.67 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.39 (ddd, J = 6.9, 6.7, 5.1 Hz, 1H, C28-H), 3.90 (dd, J = 8.2, 6.6 Hz, 1H, one of C27-H), 3.79 (dd, J = 8.2, 7.0 Hz, 1H, one of C27-H), 3.72 (dd, J = 5.3, 5.3 Hz, 1H, C29-H), 3.61 (dd, J = 5.3, 4.2 Hz, 1H, C30-H), 2.51 (dddd, J = 18.3, 12.2, 2.6, 2.5 Hz, 1H, one of C32-H), 2.08 (dddd, J = 18.5, 6.2, 3.8, 0.9 Hz, 1H, one of C32-H), 1.45 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3); 13 C-NMR (125 MHz, CDCl3) δ 163.7, 145.5, 138.1, 137.6, 128.4, 128.4, 128.3, 128.1, 128.0, 127.8, 120.8, 109.2, 79.1, 78.0, 77.8, 76.3, 74.6, 74.2, 65.7, 26.5, 25.8, 25.6; HRMS (ESITOF) m/z calcd for C26H30NaO6 [M+Na]+: 461.1935, found: 461.1937.   102 O 27 O 27 OBn O 31 35 OBn O 31 35 OH OH O Me O Me 65 O Me O Me 82 OBn OBn (3R,4R,6S)-6-((1R,2R)-1,2-Bis(benzyloxy)-2-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)ethyl)3,4-dihydroxytetrahydro-2H-pyran-2-one (82). To a bright yellow suspension of NaIO4 (0.17 g, 0.80 mmol, 1.5 equiv) and CeCl3•7H2O (0.020 g, 0.053 mmol, 0.1 equiv) in deionized H2O (0.53 mL, 1.5 M wrt NaIO4) at 0 °C was added EtOAc (0.66 mL, 1.2 M wrt NaIO4), MeCN (0.80 mL, 1.0 M wrt NaIO4), and an aqueous solution of RuCl3 (27 µL, 0.1 M, 2.7 µmol, 0.005 equiv). The bilayer suspension was stirred at 0 °C for 5 min, then charged slowly dropwise with a solution of unsaturated lactone 65 (0.23 g, 0.53 mmol, 1.0 equiv) in EtOAc (1.1 mL, 0.5 M wrt 65) over 1 min (with 2 x 0.27 mL rinses). The reaction mixture was vigorously stirred at 0 °C for 1.5 h, charged with Na2SO4 (0.53 g), then filtered through Na2SO4 with EtOAc rinses (50 mL total) into a flask containing sat. aq Na2SO3 (10 mL) and brine (10 mL). The layers were separated and the aqueous layer extracted with EtOAc (2 x 50 mL). The combined organic extracts were dried over Na2SO4 with added hexanes (150 mL) and filtered through a silica gel plug (4 cm). The filter cake was rinsed with 1:1 hexanes/EtOAc (300 mL), and the filtrate concentrated and azeotroped with PhH (2 x 5 mL) to afford crude diol 82 (0.21 g, 85% yield) as a solid of mixed white and brown coloration due to contamination with ruthenium-based impurities (<5%). The crude product was analyzed by 1 H-NMR spectroscopy to assess reaction diastereoselectivity (d.r. ≥ 95:05). [α] 24 –12.1° (c = D 1.0, CH2Cl2); IR (neat) 3442 (br), 3064, 3030, 2965, 2934, 1745 (s), 1455, 1371, 1214, 1124, 1062, 854, 741, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.36–7.24 (m, 10H, ArH), 5.03 € (ddd, J = 11.4, 4.1, 2.2 Hz, 1H, C31-H), 4.80 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.78 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.53 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.38 (ddd, J = 6.7, 6.6, 4.5 Hz, 1H, C28-H), 4.29 (m, 1H, C33H), 4.05 (dd, J = 2.9, 1.0 Hz, 1H, C34-H), 3.99 (dd, J = 8.2, 6.6 Hz, 1H, one of C27-H), 3.87 (dd, J = 8.2, 6.9 Hz, 1H, one of C27-H), 3.82 (dd, J = 6.7, 4.5 Hz, 1H, C29-H), 3.57 (dd, J = 6.9, 2.3 Hz, 1H, C30-H), 3.38 (d, J = 1.0 Hz, 1H, C34-OH), 2.69 (dd, J = 2.1, 1.2 Hz, 1H, C33OH), 2.12 (dddd, J = 14.4, 11.4, 2.1, 2.1 Hz, 1H, one of C32-H), 1.99 (ddd, J = 14.5, 4.2, 4.2   103 Hz, 1H, one of C32-H), 1.45 (s, 3H, one of CH3), 1.36 (s, 3H, one of CH3); 13C-NMR (125 MHz, CDCl3) δ 173.7, 138.2, 137.4, 128.5, 128.4, 128.1, 128.1, 127.9, 127.7, 109.1, 80.0, 78.2, 76.9, 76.2, 74.8, 74.7, 70.4, 66.1, 65.5, 29.8, 26.5, 25.6; HRMS (ESI-TOF) m/z calcd for C26H32NaO8 [M+Na]+: 495.1989, found: 495.1999. O 27 O OH 27 OBn O 31 35 OBn O 31 35 O O O Me O Me 82 OH O Me O Me 66 Me Me OBn OBn (3aR,6S,7aR)-6-((1R,2R)-1,2-Bis(benzyloxy)-2-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)ethyl)2,2-dimethyldihydro-3aH-[1,3]dioxolo[4,5-c]pyran-4(6H)-one (66). To a solution of diol 82 (0.75 g, 1.6 mmol, 1.0 equiv) in 2:1 acetone/2,2-dimethoxypropane (32 mL, 0.05 M wrt 82) at rt was added PPTS (40 mg, 0.16 mmol, 0.1 equiv). The reaction mixture was stirred at 30 °C for 15 h, quenched with a large spatula tip full of NaHCO3 (s), stirred vigorously for an additional 15 min, and filtered through Celite . The filter cake was rinsed with EtOAc (40 mL  total), and the filtrate concentrated. Column chromatography (gradient elution, 16% → 18% → 20% EtOAc in hexanes) afforded acetonide 66 (0.63 g, 78% yield) as a white solid. [α] 25 D +6.5° (c = 1.1, CH2Cl2); IR (neat) 3031, 2987, 2936, 1751 (s), 1497, 1456, 1377, 1266, 1211, 1159, 1119, 1061, 919, 852, 738, 700 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.35–7.26 (m, € 10H, ArH), 4.92 (ddd, J = 10.4, 2.2, 2.1 Hz, 1H, C31-H), 4.76 (d, J = 11.4 Hz, 1H, one of – OCH2Ph), 4.74 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.69 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.57 (m, J = 9.7, 2.8 Hz, 1H, C33-H), 4.56 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.53 (dd, J = 6.9, 1.0 Hz, 1H, C34-H), 4.35 (ddd, J = 6.4, 6.3, 4.8 Hz, 1H, C28-H), 3.97 (dd, J = 7.3, 6.4 Hz, 1H, one of C27-H), 3.84 (dd, J = 7.3, 7.3 Hz, 1H, one of C27-H), 3.78 (dd, J = 5.9, 5.0 Hz, 1H, C29-H), 3.61 (dd, J = 6.2, 3.2 Hz, 1H, C30-H), 2.99 (ddd, J = 15.1, 10.3, 3.1 Hz, 1H, one of C32-H), 1.88 (ddd, J = 15.1, 2.1, 1.8 Hz, 1H, one of C32-H), 1.48 (s, 3H, one of CH3), 1.44 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3), 1.33 (s, 3H, one of CH3); 13C-NMR (125 MHz, CDCl3) δ 167.8, 138.1, 137.5, 128.5, 128.4, 128.2, 128.0, 127.9, 127.7, 110.6, 109.0, 80.1, 78.1, 76.1, 74.9, 74.6, 74.5, 72.9, 71.7, 65.5, 30.9, 26.5, 26.0, 25.6, 24.0; HRMS (ESI-TOF) m/z calcd for C29H36KO8 [M+K]+: 551.2042, found: 551.2039.   104 O 27 OBn O 31 35 O O O Me O Me 66 Me Me 27 OBn OH O 31 35 O Me Me OH OBn O BnO Me O Me 83 (2S,3R,4R)-3,4-Bis(benzyloxy)-4-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)-1-((4R,5S)-5(hydroxymethyl)-2,2-dimethyl-1,3-dioxolan-4-yl)butan-2-ol (83). To a solution of lactone 66 (0.64 g, 1.3 mmol, 1.0 equiv) in THF (13 mL, 0.10 M wrt 66) at 0 °C was added H2O (36 µL, 2.0 mmol, 1.6 equiv) and LiBH4 (0.041 g, 1.9 mmol, 1.5 equiv). The reaction mixture was slowly warmed to rt o/n (16 h total stir time), then recooled to 0 °C, quenched with 1 M aq NaOH (15 mL), stirred vigorously at rt for 0.5 h, and diluted with Et2O (15 mL). The layers were separated and the organic layer washed sequentially with H2O and brine (10 mL each). The combined aqueous layers were extracted with Et2O (2 x 15 mL), and the combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 2:1 → 1:1 → 1:2 hexanes/EtOAc + 1% Et3N) afforded diol 83 (0.64 g, quant. yield) as a clear, colorless oil. [α] 23 –10.1° (c = 2.7, CH2Cl2); D IR (neat) 3480 (br), 3064, 3031, 2986, 2935, 2879, 1497, 1456, 1371, 1251, 1216, 1161, 1118, 1065, 892, 862, 737, 700 cm–1; 1H-NMR (600 MHz, C6D6) δ 7.38 (m, 2H, ArH), 7.23– € 7.06 (m, 8H, ArH), 4.77 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.63 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.62 (ddd, J = 7.2, 6.6, 5.0 Hz, 1H, C28-H), 4.44 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.19 (dddd, J = 8.2, 4.2, 4.0, 3.4 Hz, 1H, C31-H), 4.07 (ddd, J = 10.0, 5.9, 4.1 Hz, 1H, C33-H), 3.95–3.90 (m, J = 8.2, 7.3, 6.6 Hz, 2H, C27-H2), 3.90 (m, J = 6.2, 3.1 Hz, 1H, C34-H), 3.82 (dd, J = 5.6, 5.1 Hz, 1H, C29-H), 3.60 (dd, J = 5.8, 3.0 Hz, 1H, C30-H), 3.45–3.38 (m, J = 11.3, 7.2, 6.2, 5.4, 4.7 Hz, 2H, C35-H2), 3.08 (d, J = 4.5 Hz, 1H, C31-OH), 1.98 (ddd, J = 14.1, 9.7, 8.5 Hz, 1H, one of C32-H), 1.94 (dd, J = 7.2, 4.8 Hz, 1H, C35-OH), 1.55 (ddd, J = 14.1, 4.0, 4.0 Hz, 1H, one of C32-H), 1.52 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.33 (s, 3H, one of CH3), 1.19 (s, 3H, one of CH3); 13CNMR (125 MHz, C6D6) δ 139.3, 138.8, 128.6, 128.5, 128.5, 128.2, 128.0, 127.7, 109.1, 108.2, 81.4, 79.1, 78.3, 77.4, 76.0, 74.5, 74.2, 70.0, 66.3, 61.6, 33.3, 28.1, 26.9, 26.0, 25.4; HRMS (ESI-TOF) m/z calcd for C29H41O8 [M+H]+: 517.2796, found: 517.2800.   105 27 OBn OH O 31 35 27 OBn OH O 31 35 O Me Me OH O Me Me OTBDPS O BnO Me O Me 83 O BnO Me O Me 84 (2S,3R,4R)-3,4-Bis(benzyloxy)-1-((4R,5S)-5-((tert-butyldiphenylsilyloxy)methyl)-2,2dimethyl-1,3-dioxolan-4-yl)-4-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)butan-2-ol (84). To a solution of diol 83 (0.60 g, 1.2 mmol, 1.0 equiv) and imidazole (0.12 g, 1.7 mmol, 1.5 equiv) in DMF (5.8 mL, 0.20 M wrt 83) at 0 °C was added tert-butylchlorodiphenylsilane (0.33 mL, 1.3 mmol, 1.1 equiv). The reaction mixture was stirred at 0 °C for 4 h, quenched with sat. aq NaHCO3 (15 mL), and diluted with 1:1 hexanes/Et2O (30 mL) and H2O (5 mL). The layers were separated and the aqueous layer extracted with 1:1 hexanes/Et2O (2 x 30 mL). The combined organic extracts were dried over Na2SO4, filtered and concentrated. Column chromatography (gradient elution, 12% → 16% → 20% EtOAc in hexanes) afforded silyl ether 84 (0.83 g, 95% yield) as a clear, colorless oil. [α] 24 –7.2° (c = 2.8, CH2Cl2); IR (neat) D 3522 (br), 3070, 3030, 2985, 2933, 2859, 1455, 1428, 1380, 1360, 1252, 1216, 1113, 1066, 824, 738 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.71 (m, 5H, ArH), 7.49–7.29 (m, 15H, ArH), € 4.77 (d, J = 12.2 Hz, 1H, one of –OCH2Ph), 4.75 (d, J = 12.3 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.57 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.50 (ddd, J = 6.9, 6.7, 5.7 Hz, 1H, C28-H), 4.23 (ddd, J = 10.8, 6.0, 2.3 Hz, 1H, C33-H), 4.15 (ddd, J = 6.4, 6.3, 6.0 Hz, 1H, C34-H), 4.13 (m, J = 8.1, 3.4 Hz, 1H, C31-H), 3.97 (dd, J = 8.1, 6.6 Hz, 1H, one of C27-H), 3.85 (dd, J = 7.8, 7.8 Hz, 1H, one of C27-H), 3.69 (dd, J = 5.4, 5.4 Hz, 1H, C29-H), 3.66 (dd, J = 10.8, 6.8 Hz, 1H, one of C35-H), 3.63 (dd, J = 10.7, 5.7 Hz, 1H, one of C35-H), 3.49 (dd, J = 5.4, 2.9 Hz, 1H, C30-H), 3.26 (d, J = 3.2 Hz, 1H, C31-OH), 1.87 (ddd, J = 14.2, 10.8, 8.5 Hz, 1H, one of C32-H), 1.69 (ddd, J = 14.1, 3.2, 2.9 Hz, 1H, one of C32H), 1.49 (s, 3H, one of CH3), 1.42 (s, 3H, one of CH3), 1.41 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3), 1.10 (s, 9H, C(CH3)3); 13 C-NMR (125 MHz, CDCl3) δ 138.5, 137.9, 135.6, 135.5, 133.3, 133.1, 129.8, 129.8, 128.4, 128.3, 128.3, 128.0, 127.8, 127.7, 127.7, 127.6, 108.8, 108.4, 80.6, 78.4, 78.0, 76.8, 76.4, 74.1, 74.0, 70.0, 65.9, 62.7, 32.8, 28.0, 26.8, 26.6, 25.7, 25.4, 19.2; HRMS (ESI-TOF) m/z calcd for C45H58NaO8Si [M+Na]+: 777.3793, found: 777.3797.   106 27 OBn OH O 31 35 27 OBn OBn O 31 35 O Me Me OTBDPS O Me Me OTBDPS O BnO Me O Me 84 O BnO Me O Me 61 tert-Butyl(((4S,5R)-2,2-dimethyl-5-((2S,3R,4R)-2,3,4-tris(benzyloxy)-4-((S)-2,2-dimethyl1,3-dioxolan-4-yl)butyl)-1,3-dioxolan-4-yl)methoxy)diphenylsilane (61). To a solution of carbinol 84 (0.83 g, 1.1 mmol, 1.0 equiv) in DMF (5.5 mL, 0.20 M wrt 84) at –20 °C was added sodium hydride (0.13 g, 60 wt% mineral oil dispersion, 3.3 mmol, 3.0 equiv). The suspension was stirred at –20 °C for 15 min, then charged with benzyl bromide (0.20 mL, 1.6 mmol, 1.5 equiv) and tetrabutylammonium iodide (0.041 g, 0.11 mmol, 0.1 equiv). The reaction mixture was stirred at –20 °C for 3 h, briefly warmed to 0 °C, then quenched with sat. aq NH4Cl (15 mL), and diluted with 1:1 hexanes/Et2O (40 mL) and H2O (5 mL). The layers were separated and the aqueous layer extracted with 1:1 hexanes/Et2O (2 x 30 mL). The combined organic extracts were dried over Na2SO4, filtered and concentrated. Column chromatography (gradient elution, 6% → 8% → 10% EtOAc in hexanes) afforded benzyl ether 61 (0.88 g, 95% yield) as a clear, colorless oil. [α] 25 +10.4° (c = 0.94, CH2Cl2); IR D (neat) 3069, 3030, 2985, 2933, 2859, 1496, 1455, 1428, 1370, 1253, 1212, 1109, 1071, 823, 739 cm–1; 1H-NMR (600 MHz, C6D6) δ 7.81–7.79 (m, 4H, ArH), 7.42 (m, J = 7.3 Hz, 2H, € ArH), 7.30 (m, J = 7.2 Hz, 2H, ArH), 7.25 (m, J = 7.2 Hz, 2H, ArH), 7.22–7.04 (m, 15H, ArH), 4.98 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.83 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.70 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.65 (ddd, J = 7.0, 6.7, 6.7 Hz, 1H, C28-H), 4.58 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.54 (d, J = 11.4 Hz, 1H, one of – OCH2Ph), 4.44 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.35 (ddd, J = 10.5, 6.4, 1.8 Hz, 1H, C33-H), 4.23 (ddd, J = 8.8, 3.7, 3.4 Hz, 1H, C31-H), 4.10 (ddd, J = 6.0, 6.0, 5.6 Hz, 1H, C34-H), 3.96 (dd, J = 6.6, 4.2 Hz, 1H, C29-H), 3.91 (dd, J = 7.9, 7.6 Hz, 1H, one of C27-H), 3.86 (m, J = 4.1 Hz, 1H, C30-H), 3.85 (dd, J = 8.2, 6.4 Hz, 1H, one of C27-H), 3.82 (dd, J = 10.8, 6.3 Hz, 1H, one of C35-H), 3.77 (dd, J = 10.7, 5.2 Hz, 1H, one of C35-H), 2.18 (ddd, J = 14.4, 7.1, 1.8 Hz, 1H, one of C32-H), 1.94 (ddd, J = 14.5, 10.7, 3.4 Hz, 1H, one of C32-H), 1.51 (s, 3H, one of CH3), 1.44 (s, 3H, one of CH3), 1.34 (s, 3H, one of CH3), 1.27 (s, 3H, one of CH3), 1.16 (s, 9H, C(CH3)3); 13C-NMR (125 MHz, C6D6) δ 139.7, 139.3, 139.2, 136.1, 136.0, 133.8, 133.7, 130.1, 128.5, 128.5, 128.4, 128.3, 128.1, 127.9, 127.7, 127.7, 109.0, 108.0, 79.7, 79.3, 78.5,   107 78.4, 77.8, 74.1, 74.0, 73.7, 72.0, 66.3, 63.6, 29.6, 28.3, 27.1, 25.9, 25.5, 19.4; HRMS (ESITOF) m/z calcd for C52H64O8Si [M+H]+: 845.4443, found: 845.4456. 27 OBn OBn O 31 35 27 OBn OBn O 31 35 O Me Me OTBDPS O Me Me OH O BnO Me O Me 61 O BnO Me O Me 85 ((4S,5R)-2,2-Dimethyl-5-((2S,3R,4R)-2,3,4-tris(benzyloxy)-4-((S)-2,2-dimethyl-1,3dioxolan-4-yl)butyl)-1,3-dioxolan-4-yl)methanol (85). To a solution of silyl ether 61 (0.88 g, 1.0 mmol, 1.0 equiv) in THF (6.9 mL, 0.15 M wrt 61) at 0 °C was added dropwise a solution of tetrabutylammonium fluoride in THF (1.6 mL, 1.0 M, 1.6 mmol, 1.5 equiv). The reaction mixture was stirred at 0 °C for 8 h, slowly warmed to rt over 6 h, then quenched with sat. aq NaHCO3 (15 mL), and diluted with Et2O (35 mL) and H2O (5 mL). The layers were separated and the aqueous layer extracted with Et2O (2 x 35 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 4:1 → 2:1 hexanes/EtOAc + 1% Et3N) afforded carbinol 85 (0.63 g, quant. yield) as a clear, colorless oil. [α] 24 +6.4° (c = 0.81, CH2Cl2); IR (neat) D 3478 (br), 3063, 3030, 2985, 2935, 2880, 1496, 1454, 1370, 1251, 1213, 1160, 1064, 916, 855, 736 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.36–7.27 (m, 15H, ArH), 4.81 (d, J = 11.9 Hz, € 1H, one of –OCH2Ph), 4.75 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.69 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.65 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.57 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.55 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.23 (ddd, J = 7.2, 6.7, 6.7 Hz, 1H, C28-H), 4.01 (ddd, J = 10.1, 6.3, 2.9 Hz, 1H, C33-H), 3.84 (ddd, J = 6.2, 5.9, 4.2 Hz, 1H, C31H), 3.79 (ddd, J = 6.2, 5.9, 4.2 Hz, 1H, C34-H), 3.59 (dd, J = 6.7, 4.0 Hz, 1H, C29-H), 3.54 (dd, J = 7.9, 7.5 Hz, 1H, one of C27-H), 3.52 (dd, J = 5.9, 4.0 Hz, 1H, C30-H), 3.44 (dd, J = 8.1, 6.4 Hz, 1H, one of C27-H), 3.31 (m, J = 11.3, 7.6, 7.2, 4.5, 4.4 Hz, 2H, C35-H2), 1.74 (dd, J = 7.8, 4.5 Hz, 1H, C35-OH), 1.60 (ddd, J = 14.5, 6.4, 2.9 Hz, 1H, one of C32-H), 1.43 (s, 3H, one of CH3), 1.41 (s, 3H, one of CH3), 1.36 (ddd, J = 14.5, 10.1, 4.1 Hz, 1H, one of C32-H), 1.29 (s, 3H, one of CH3), 1.29 (s, 3H, one of CH3); 13C-NMR (125 MHz, CDCl3) δ 138.6, 138.3, 138.1, 129.0, 128.5, 128.4, 128.4, 128.3, 128.0, 127.8, 127.6, 108.8, 108.0, 77.8, 77.7, 77.7,   108 76.7, 73.8, 73.4, 72.8, 72.2, 65.6, 61.7, 28.6, 28.2, 26.7, 25.5, 25.4; HRMS (ESI-TOF) m/z calcd for C36H46NaO8 [M+Na]+: 629.3085, found: 629.3104. 27 OBn OBn O 31 35 27 OBn OBn O 31 O 35 O Me Me OH O Me Me H O BnO Me O Me 85 O BnO Me O Me 67 (4R,5R)-2,2-Dimethyl-5-((2S,3R,4R)-2,3,4-tris(benzyloxy)-4-((S)-2,2-dimethyl-1,3dioxolan-4-yl)butyl)-1,3-dioxolane-4-carbaldehyde (67). To a solution of carbinol 85 (0.12 g, 0.19 mmol, 1.0 equiv) and EtN(iPr)2 (0.10 mL, 0.58 mmol, 3.0 equiv) in CH2Cl2 (0.55 mL, 0.35 M wrt 85) and DMSO (0.22 mL, 0.88 M wrt 85) at –30 °C was added a solution of SO3•py (0.093 g, 0.58 mmol, 3.0 equiv) in DMSO (0.33 mL, 1.75 M wrt SO3•py). The reaction mixture was stirred between –30 °C and –20 °C for 1.5 h, then quenched with brine (20 mL), Et2O (60 mL) and H2O (2 mL). The layers were separated and the organic layer washed sequentially with 1 M aq NaHSO4 (20 mL), sat. aq NaHCO3 (20 mL), and 1:1 H2O/brine (2 x 20 mL). The organic layer was then dried over Na2SO4 with added hexanes, filtered and concentrated to afford crude aldehyde 67 (0.11 g, 96% yield) as a clear, colorless oil that was used without further purification. [α] 25 +7.4° (c = 0.94, CH2Cl2); IR (neat) 3063, D 3030, 2986, 2934, 1734 (s), 1496, 1454, 1370, 1255, 1216, 1159, 1065, 858, 736, 699 cm–1; 1 H-NMR (600 MHz, CDCl3) δ 9.38 (d, J = 3.2 Hz, 1H, C35-H), 7.35–7.28 (m, 15H, ArH), € 4.80 (d, J = 12.0 Hz, 1H, one of –OCH2Ph), 4.75 (d, J = 12.0 Hz, 1H, one of –OCH2Ph), 4.72 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.62 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.56 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.54 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.24 (ddd, J = 7.2, 6.9, 6.9 Hz, 1H, C28-H), 4.19 (ddd, J = 10.0, 7.3, 2.8 Hz, 1H, C33-H), 3.88 (dd, J = 7.2, 3.4 Hz, 1H, C34-H), 3.86 (ddd, J = 6.2, 6.2, 4.2 Hz, 1H, C31-H), 3.56 (dd, J = 7.0, 3.6 Hz, 1H, C29-H), 3.51 (dd, J = 7.9, 7.8 Hz, 1H, one of C27-H), 3.46 (dd, J = 6.2, 3.6 Hz, 1H, C30-H), 3.42 (dd, J = 8.1, 6.4 Hz, 1H, one of C27-H), 1.75 (ddd, J = 14.6, 6.3, 2.8 Hz, 1H, one of C32H), 1.52 (s, 3H, one of CH3), 1.43 (s, 3H, one of CH3), 1.33 (s, 3H, one of CH3), 1.30 (s, 3H, one of CH3), 1.21 (ddd, J = 14.6, 10.1, 4.2 Hz, 1H, one of C32-H); 13C-NMR (125 MHz, CDCl3) δ 201.7, 138.4, 138.1, 138.0, 128.9, 128.7, 128.4, 128.4, 128.3, 128.3, 128.0, 127.8, 127.8, 110.5, 108.9, 81.7, 77.9, 77.7, 77.4, 76.4, 74.4, 73.7, 73.3, 72.3, 65.6, 29.3, 27.6, 26.7,   109 25.5, 25.3; HRMS (ESI-TOF) m/z calcd for C36H44NaO8 [M+Na]+: 627.2928, found: 627.2914. Synthesis of the C27–C48 Aldehyde 27 OBn OBn O 31 O 35 O H OTES OTBS 39 O Me Me C9H19 O BnO Me O Me 67 13 27 OBn OBn O 31 OH O 35 OTBS 39 O Me Me C9H19 O BnO Me O Me 68 OTES (5S,8R)-5-((S)-((4S,5R)-2,2-Dimethyl-5-((2S,3R,4R)-2,3,4-tris(benzyloxy)-4-((S)-2,2dimethyl-1,3-dioxolan-4-yl)butyl)-1,3-dioxolan-4-yl)(hydroxy)methyl)-3,3-diethyl10,10,11,11-tetramethyl-8-nonyl-4,9-dioxa-3,10-disiladodecan-6-one (68). To a solution of ketone 13 (0.29 g, 0.62 mmol, 2.0 equiv) and EtNMe2 (0.14 mL, 1.2 mmol, 4.0 equiv) in pentane (3.1 mL, 0.2 M wrt 13) at 0 °C was added Cy2BCl (0.14 mL, 0.65 mmol, 2.1 equiv). The enolization mixture was stirred at 0 °C for 20 min, then stirred at rt for 15 h, then cooled to –78 °C and charged slowly dropwise with a solution of aldehyde 67 (0.19 g, 0.31 mmol, 1.0 equiv) in Et2O (0.70 mL, 0.44 M wrt 67) over 1 min (with 0.30 mL rinse). The reaction mixture was stirred at –78 °C for 0.5 h, slowly warmed to –40 °C over 0.5 h, stirred at –40 °C for 4 h, slowly warmed to –25 °C over 2 h, stirred at –25 °C for 9 h, then quenched at 0 °C with aq pH 7 buffer (3 mL), MeOH (3 mL), Et2O (15 mL) and 30% aq H2O2 (1 mL). The biphasic mixture was stirred vigorously at 0 °C for 0.5 h, then at rt for 1 h. The layers were separated and the aqueous layer extracted with Et2O (2 x 15 mL). The combined organic extracts were washed with 10% aq Na2S2O3 (2 x 10 mL) and brine (10 mL), dried over Na2SO4 with added hexanes, filtered and concentrated. The residue was analyzed by 1H-NMR spectroscopy to assess reaction diastereoselectivity (d.r. = 91:09). Column chromatography (gradient elution, 5% → 6% EtOAc in hexanes) afforded aldol adduct 68 (0.26 g, 77% yield) as a clear, colorless oil. [α] 25 +0.2° (c = 1.7, CH2Cl2); IR (neat) 3567 (br), 3065, 3031, 2929, D 2856, 1721 (s), 1497, 1456, 1379, 1253, 1211, 1159, 1074, 836, 776, 733, 699 cm–1; 1H-NMR   € 110 (600 MHz, CDCl3) δ 7.35–7.26 (m, 15H, ArH), 4.82 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.71 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 12.0 Hz, 1H, one of –OCH2Ph), 4.60 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.53 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.23 (dddd, J = 6.2, 6.0, 5.4, 5.4 Hz, 1H, C39-H), 4.18 (ddd, J = 7.0, 6.9, 6.7 Hz, 1H, C28-H), 4.07 (m, J = 8.5, 7.6 Hz, 1H, C33-H), 4.03 (m, J = 7.3 Hz, 1H, C34-H), 3.90 (m, J = 3.4 Hz, 1H, C31-H), 3.88 (d, J = 8.6 Hz, 1H, C36-H), 3.62 (dd, J = 6.7, 4.0 Hz, 1H, C29-H), 3.57 (dd, J = 5.3, 4.1 Hz, 1H, C30-H), 3.53 (dd, J = 7.9, 7.8 Hz, 1H, one of C27-H), 3.42 (dd, J = 7.9, 6.7 Hz, 1H, one of C27-H), 3.37 (dd, J = 8.8, 8.8 Hz, 1H, C35H), 2.92 (dd, J = 18.5, 5.6 Hz, 1H, one of C38-H), 2.65 (dd, J = 18.4, 6.8 Hz, 1H, one of C38H), 2.13 (d, J = 8.9 Hz, 1H, C35-OH), 1.88 (ddd, J = 14.5, 10.4, 3.2 Hz, 1H, one of C32-H), 1.74 (ddd, J = 14.5, 7.0, 1.8 Hz, 1H, one of C32-H), 1.53 (m, J = 5.0 Hz, 1H, one of C40-H), 1.43 (s, 3H, one of CH3), 1.42–1.37 (m, 1H, one of C40-H), 1.40 (s, 3H, one of CH3), 1.36– 1.23 (m, 14H, C41–47-H2), 1.27 (s, 3H, one of CH3), 1.26 (s, 3H, one of CH3), 0.97 (t, J = 8.0 Hz, 9H, –SiCH2CH3), 0.88 (s, 9H, C(CH3)3), 0.88 (t, J = 7.2 Hz, 3H, C48-H3), 0.64 (q, J = 7.9 Hz, 6H, –SiCH2CH3), 0.09 (s, 3H, one of SiCH3), 0.06 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 210.1, 138.8, 138.4, 138.2, 129.0, 128.3, 128.3, 128.3, 128.2, 127.9, 127.7, 127.5, 108.7, 107.6, 78.7, 78.3, 77.8, 77.6, 76.9, 74.8, 73.8, 73.6, 72.9, 71.9, 71.1, 67.6, 65.5, 45.8, 37.5, 31.9, 29.7, 29.6, 29.6, 29.3, 26.8, 26.7, 25.9, 25.5, 25.0, 24.3, 22.7, 18.0, 14.1, 6.7, 4.7, –4.5, –4.7; HRMS (ESI-TOF) m/z calcd for C61H98NaO11Si2 [M+Na]+: 1085.6540, found: 1085.6487. OBn OBn O 31 OH O 35 OTBS 27 39 27 OBn OBn O 31 O 35 TES O OTES OTBS 39 O Me Me C9H19 HO C9H19 O BnO Me O Me 68 OTES HO BnO Me O Me 69 (5R,8S,9S)-9-((4R,5R)-2,2-Dimethyl-5-((2S,3R,4R,5S)-2,3,4-tris(benzyloxy)-5,6dihydroxyhexyl)-1,3-dioxolan-4-yl)-11,11-diethyl-2,2,3,3-tetramethyl-5-nonyl-8((triethylsilyl)oxy)-4,10-dioxa-3,11-disilatridecan-7-one (69). To a solution of carbinol 68 (0.25 g, 0.24 mmol, 1.0 equiv) and 2,6-lutidine (0.16 mL, 1.4 mmol, 6.0 equiv) in CH2Cl2 (2.4 mL, 0.1 M wrt 68) at 0 °C was added TESOTf (0.11 mL, 0.47 mmol, 2.0 equiv). The reaction mixture was stirred at 0 °C for 3 h, charged with TMSOTf (85 µL, 0.47 mmol, 2.0 equiv),   111 stirred at 0 °C for an additional 3 h, then quenched with 1 M aq H2SO4 (8 mL) and Et2O (8 mL). The biphasic mixture was stirred vigorously at 0 °C for 0.5 h, then diluted with H2SO4 (10 mL) and Et2O (30 mL), and the layers were separated. The organic layer was washed sequentially with sat. aq NaHCO3 and brine (10 mL each), dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 4:1 → 3:1 hexanes/EtOAc) afforded diol 69 (0.24 g, 88% yield) as a clear, colorless oil. [α] 26 +18.8° (c D = 1.4, CH2Cl2); IR (neat) 3440 (br), 3065, 3032, 2955, 2929, 2878, 1712 (s), 1456, 1378, 1250, 1220, 1100, 1061, 837, 775, 732, 699 cm–1; 1H-NMR (600 MHz, C6D6) δ 7.40 (m, J = 7.9, 0.9 Hz, 2H, ArH), 7.35 (m, J = 7.9, 0.9 Hz, 2H, ArH), 7.23–7.07 (m, 11H, ArH), 4.76 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.74 (d, J = 12.3 Hz, 1H, one of –OCH2Ph), 4.68 (ddd, J = 11.9, 5.1, 2.8 Hz, 1H, C33-H), 4.62 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.58 (m, J = 5.9, 5.9 Hz, 1H, C39-H), 4.56 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.52 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.49 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.30 (dd, J = 9.2, 5.1 Hz, 1H, C34H), 4.18 (ddd, J = 8.9, 4.5, 2.9 Hz, 1H, C31-H), 4.13 (dd, J = 9.2, 2.1 Hz, 1H, C35-H), 4.08 (dd, J = 7.2, 2.8 Hz, 1H, C30-H), 4.03 (d, J = 2.1 Hz, 1H, C36-H), 4.02 (dd, J = 7.2, 4.0 Hz, 1H, C29-H), 3.97 (m, J = 4.5, 4.2 Hz, 1H, C28-H), 3.71 (m, J = 10.8, 5.6 Hz, 1H, one of C27-H), 3.67 (m, 1H, one of C27-H), 3.26 (dd, J = 19.5, 6.0 Hz, 1H, one of C38-H), 3.19 (dd, J = 19.5, 6.0 Hz, 1H, one of C38-H), 2.89 (d, J = 5.1 Hz, 1H, C28-OH), 2.16 (ddd, J = 12.6, 12.3, 4.5 Hz, 1H, one of C32-H), 2.06 (ddd, J = 12.7, 9.1, 2.8 Hz, 1H, one of C32-H), 1.78 (m, J = 5.6 Hz, 1H, C27-OH), 1.76 (m, 1H, one of C40-H), 1.69 (m, 1H, one of C40-H), 1.60–1.51 (m, 2H, C41H2), 1.43 (s, 3H, one of CH3), 1.42–1.23 (m, 12H, C42–47-H2), 1.28 (s, 3H, one of CH3), 1.16 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 1.03 (s, 9H, C(CH3)3), 0.96 (t, J = 8.0 Hz, 9H, –SiCH2CH3), 0.92–0.80 (m, J = 8.1 Hz, 6H, –SiCH2CH3), 0.91 (t, J = 6.7 Hz, 3H, C48-H3), 0.62–0.52 (m, J = 8.1, 7.9 Hz, 6H, –SiCH2CH3), 0.22 (s, 3H, one of SiCH3), 0.21 (s, 3H, one of SiCH3); 13CNMR (125 MHz, C6D6) δ 211.6, 139.2, 139.0, 138.9, 128.6, 128.5, 128.5, 128.4, 128.3, 128.3, 128.1, 127.9, 127.6, 108.2, 79.5, 79.4, 79.3, 79.0, 76.4, 75.9, 74.7, 74.4, 74.3, 72.2, 72.0, 67.7, 64.1, 49.1, 38.5, 30.6, 30.3, 30.1, 30.0, 29.8, 28.8, 26.1, 26.1, 25.6, 23.1, 18.3, 14.3, 7.3, 7.1, 5.7, 5.0, –4.2, –4.4; HRMS (ESI-TOF) m/z calcd for C64H108NaO11Si3 [M+Na]+: 1159.7092, found: 1159.7053.   112 27 OBn OBn O 31 O 35 TES O OTES OTBS 27 39 OBn OBn O 31 O 35 TES O OTES OTBS 39 HO C9H19 AcO C9H19 HO BnO Me O Me 69 HO BnO Me O Me 86 (2S,3R,4R,5S)-3,4,5-Tris(benzyloxy)-6-((4R,5R)-5-((5S,6S,9R)-3,3-diethyl-11,11,12,12tetramethyl-9-nonyl-7-oxo-6-((triethylsilyl)oxy)-4,10-dioxa-3,11-disilatridecan-5-yl)-2,2dimethyl-1,3-dioxolan-4-yl)-2-hydroxyhexyl acetate (86). To a solution of diol 69 (0.22 g, 0.19 mmol, 1.0 equiv) and 2,4,6-collidine (51 µL, 0.38 mmol, 2.0 equiv) in CH2Cl2 (0.96 mL, 0.2 M wrt 69) at –78 °C was added acetyl chloride (18 µL, 0.25 mmol, 1.3 equiv). The reaction mixture was stirred at –78 °C for 2 h, slowly warmed to 0 °C over 2 h, then quenched at 0 °C with 1 M aq H2SO4 (1 mL) and Et2O (1 mL). The biphasic mixture was stirred vigorously while warming to rt over 5 min, then diluted with H2SO4 (10 mL) and Et2O (40 mL), and the layers were separated. The organic layer was washed with 1:1 sat. aq NaHCO3/brine (15 mL), dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 12% → 14% → 16% EtOAc in hexanes) afforded acetate ester 86 (0.22 g, 98% yield) as a clear, colorless oil. [α] 26 +16.6° (c = 2.7, CH2Cl2); IR D (neat) 3467 (br), 3064, 3032, 2930, 1743 (s), 1717 (s), 1458, 1375, 1247, 1096, 1062, 981, 838, 733, 700 cm–1; 1H-NMR (600 MHz, C6D6) δ 7.38 (m, J = 7.5 Hz, 2H, ArH), 7.36 (m, J = 7.3 Hz, 2H, ArH), 7.22–7.06 (m, 11H, ArH), 4.74 (d, J = 10.8 Hz, 1H, one of –OCH2Ph), 4.74 (d, J = 12.4 Hz, 1H, one of –OCH2Ph), 4.67 (ddd, J = 12.0, 5.1, 2.8 Hz, 1H, C33-H), 4.64 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.60 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.56 (m, J = 5.9, 5.7, 5.6 Hz, 1H, C39-H), 4.52 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 4.48 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.36 (dd, J = 11.1, 6.9 Hz, 1H, one of C27-H), 4.29 (dd, J = 9.0, 4.8 Hz, 1H, C34-H), 4.28 (dd, J = 11.3, 5.9 Hz, 1H, one of C27-H), 4.19 (m, J = 7.3, 7.0, 2.8 Hz, 1H, C28-H), 4.17 (m, J = 8.8, 4.5 Hz, 1H, C31-H), 4.13 (dd, J = 9.4, 1.9 Hz, 1H, C35-H), 4.11 (dd, J = 9.1, 2.6 Hz, 1H, C30-H), 4.03 (dd, J = 7.6, 2.6 Hz, 1H, C29-H), 4.02 (d, J = 1.9 Hz, 1H, C36-H), 3.24 (dd, J = 19.5, 6.0 Hz, 1H, one of C38-H), 3.23 (dd, J = 19.5, 5.9 Hz, 1H, one of C38-H), 2.75 (d, J = 7.3 Hz, 1H, C28-OH), 2.18 (ddd, J = 12.6, 12.2, 4.5 Hz, 1H, one of C32-H), 2.08 (ddd, J = 12.7, 8.8, 2.5 Hz, 1H, one of C32-H), 1.74 (m, 1H, one of C40-H), 1.68 (m, 1H, one of C40-H), 1.62 (s, 3H, COCH3), 1.60–1.50 (m, 2H, C41-H2), 1.42 (s, 3H, one of   113 CH3), 1.40–1.24 (m, 12H, C42–47-H2), 1.28 (s, 3H, one of CH3), 1.16 (t, J = 7.9 Hz, 9H, – SiCH2CH3), 1.02 (s, 9H, C(CH3)3), 0.95 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.93–0.79 (m, J = 7.9 Hz, 6H, –SiCH2CH3), 0.90 (t, J = 6.8 Hz, 3H, C48-H3), 0.60–0.53 (m, J = 8.1, 7.8 Hz, 6H, –SiCH2CH3), 0.21 (s, 3H, one of SiCH3), 0.20 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, C6D6) δ 211.6, 170.2, 139.2, 138.8, 138.7, 128.6, 128.5, 128.5, 128.4, 128.3, 127.9, 127.6, 127.5, 108.2, 79.5, 79.3, 79.3, 79.1, 76.5, 75.9, 74.9, 74.4, 74.4, 71.9, 69.9, 67.7, 66.0, 49.1, 38.4, 32.3, 30.4, 30.3, 30.1, 30.0, 29.8, 28.8, 26.1, 26.0, 25.6, 23.1, 20.4, 18.3, 14.3, 7.3, 7.1, 5.7, 5.0, –4.2, –4.4; HRMS (ESI-TOF) m/z calcd for C66H110NaO12Si3 [M+Na]+: 1201.7197, found: 1201.7193. OBn OBn O 31 27 O 35 TES O OTES OTBS 39 27 OBn OBn O O 35 TES O OTES OTBS 39 AcO C9H19 HO BnO Me O Me 86 31 AcO TBSO BnO Me O Me C9H19 70 (2S,3S,4R,5S)-3,4,5-Tris(benzyloxy)-2-((tert-butyldimethylsilyl)oxy)-6-((4R,5R)-5((5S,6S,9R)-3,3-diethyl-11,11,12,12-tetramethyl-9-nonyl-7-oxo-6-((triethylsilyl)oxy)-4,10dioxa-3,11-disilatridecan-5-yl)-2,2-dimethyl-1,3-dioxolan-4-yl)hexyl acetate (70). To a solution of carbinol 86 (0.22 g, 0.19 mmol, 1.0 equiv) and 2,6-lutidine (88 µL, 0.75 mmol, 4.0 equiv) in CH2Cl2 (0.94 mL, 0.2 M wrt 86) at 0 °C was added TBSOTf (86 µL, 0.38 mmol, 2.0 equiv). The reaction mixture was stirred at 0 °C for 4 h, slowly warmed to rt over 4 h, stirred at rt for 2 h, then quenched at 0 °C with sat. aq NaHCO3 (2 mL) and Et2O (1 mL). The biphasic mixture was stirred vigorously while warming to rt over 5 min, then diluted with H2O (10 mL) and Et2O (40 mL), and the layers were separated. The organic layer was washed sequentially with 1 M aq NaHSO4 and 1:1 sat. aq NaHCO3/brine (15 mL each), dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 2% → 3% → 4% EtOAc in hexanes) afforded acetate ester 70 (0.18 g, 74% yield) as a clear, colorless oil. [α] 26 +10.4° (c = 2.8, CH2Cl2); IR (neat) 3066, 3032, 2930, 2857, 1745 D (s), 1714 (s), 1456, 1369, 1251, 1101, 1055, 1008, 979, 836, 777, 732, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.35–7.15 (m, 15H, ArH), 4.77 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.66 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.62 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.59 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.56 (d, J = 11.3 Hz, 1H, one of –OCH2Ph), 4.45 (d, J   114 = 11.6 Hz, 1H, one of –OCH2Ph), 4.28 (dd, J = 11.3, 3.7 Hz, 1H, one of C27-H), 4.24 (ddd, J = 7.0, 6.7, 6.0 Hz, 1H, C33-H), 4.20 (dddd, J = 6.0, 5.9, 5.6, 5.4 Hz, 1H, C39-H), 4.10 (dd, J = 11.3, 6.9 Hz, 1H, one of C27-H), 3.92 (m, J = 3.7 Hz, 1H, C28-H), 3.92 (m, J = 4.8 Hz, 1H, C31-H), 3.91 (dd, J = 5.1, 3.8 Hz, 1H, C29-H), 3.84 (dd, J = 5.1, 5.0 Hz, 1H, C30-H), 3.82 (dd, J = 8.9, 5.1 Hz, 1H, C34-H), 3.76 (dd, J = 9.1, 1.9 Hz, 1H, C35-H), 3.65 (d, J = 1.9 Hz, 1H, C36-H), 2.86 (dd, J = 19.6, 6.6 Hz, 1H, one of C38-H), 2.81 (dd, J = 19.6, 5.4 Hz, 1H, one of C38-H), 1.89 (m, 1H, one of C32-H), 1.89 (s, 3H, COCH3), 1.79 (m, J = 7.0, 6.0 Hz, 1H, one of C32-H), 1.46–1.20 (m, 16H, C40–47-H2), 1.39 (s, 3H, one of CH3), 1.24 (s, 3H, one of CH3), 0.95 (t, J = 8.0 Hz, 9H, –SiCH2CH3), 0.86 (t, J = 7.2 Hz, 3H, C48-H3), 0.86 (s, 9H, one of C(CH3)3), 0.84 (s, 9H, one of C(CH3)3), 0.83 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.68–0.55 (m, J = 7.9, 7.8, 7.5 Hz, 6H, –SiCH2CH3), 0.48–0.40 (m, J = 8.1, 7.9 Hz, 6H, –SiCH2CH3), 0.06 (s, 3H, one of SiCH3), 0.01 (s, 3H, one of SiCH3), –0.02 (s, 3H, one of SiCH3), –0.02 (s, 3H, one of SiCH3); 13C-NMR (100 MHz, CDCl3) δ 212.0, 170.7, 138.8, 138.6, 138.4, 128.3, 128.2, 128.2, 128.1, 127.7, 127.5, 127.4, 127.3, 107.6, 78.7, 78.6, 78.5, 77.3, 76.1, 75.3, 73.9, 73.9, 73.9, 71.3, 71.3, 67.3, 66.6, 48.7, 37.9, 31.9, 30.4, 29.8, 29.6, 29.6, 29.3, 28.7, 25.9, 25.9, 25.8, 25.2, 22.7, 20.9, 18.1, 18.0, 14.1, 6.9, 6.8, 5.1, 4.5, –4.5, –4.5, –4.5, –4.7; HRMS (ESITOF) m/z calcd for C72H124NaO12Si4 [M+Na]+: 1315.8062, found: 1315.8075. OBn OBn O O 35 27 TES O OTES OTBS 39 27 OBn OBn O O 35 TES O OTES OTBS 39 31 AcO TBSO BnO Me O Me C9H19 31 HO TBSO BnO Me O Me C9H19 70 87 (5R,8S,9S)-9-((4R,5R)-2,2-Dimethyl-5-((2S,3R,4S,5S)-2,3,4-tris(benzyloxy)-5-((tertbutyldimethylsilyl)oxy)-6-hydroxyhexyl)-1,3-dioxolan-4-yl)-11,11-diethyl-2,2,3,3tetramethyl-5-nonyl-8-((triethylsilyl)oxy)-4,10-dioxa-3,11-disilatridecan-7-one (87). To a solution of acetate ester 70 (0.14 g, 0.11 mmol, 1.0 equiv) in CH2Cl2 (2.2 mL, 0.05 M wrt 70) at –78 °C was added dropwise a solution of DIBALH in PhMe (0.15 mL, 1.0 M, 0.15 mmol, 1.4 equiv). The reaction mixture was stirred at –78 °C for 15 min, then quenched sequentially at –78 °C with EtOAc (0.15 mL), sat. aq Rochelle’s salt (5 mL), and CH2Cl2 (2 mL). The biphasic mixture was stirred vigorously at rt for 2 h, then diluted with H2O (10 mL) and CH2Cl2 (30 mL). The layers were separated and the aqueous layer extracted with CH2Cl2 (2 x   115 30 mL). The combined organic extracts were dried over Na2SO4, filtered and concentrated. Column chromatography (gradient elution, 3% → 4% → 5% EtOAc in hexanes) afforded carbinol 87 (0.12 g, 84% yield) as a clear, colorless oil. [α] 25 +19.6° (c = 1.8, CH2Cl2); IR D (neat) 3510 (br), 3065, 3031, 2930, 2857, 1711 (s), 1461, 1408, 1378, 1252, 1219, 1098, 1061, 1008, 836, 776, 732, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.32–7.20 (m, 15H, ArH), 4.80 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.66 (m, 2H, –OCH2Ph), 4.63 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.56 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.50 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.28 (ddd, J = 11.1, 5.0, 3.1 Hz, 1H, C33-H), 4.22 (dddd, J = 6.0, 5.7, 5.6, 5.4 Hz, 1H, C39-H), 3.98 (ddd, J = 4.1, 4.0, 3.5 Hz, 1H, C31-H), 3.92 (dd, J = 4.4, 4.0 Hz, 1H, C30-H), 3.91 (dd, J = 6.0, 5.0 Hz, 1H, C29-H), 3.84 (m, J = 5.3, 5.0 Hz, 1H, C28-H), 3.84 (dd, J = 8.8, 5.0 Hz, 1H, C34-H), 3.77 (dd, J = 8.9, 1.9 Hz, 1H, C35-H), 3.69 (ddd, J = 11.3, 8.2, 3.1 Hz, 1H, one of C27-H), 3.67 (d, J = 1.9 Hz, 1H, C36-H), 3.56 (ddd, J = 11.4, 5.1, 4.7 Hz, 1H, one of C27-H), 2.89 (dd, J = 19.6, 6.7 Hz, 1H, one of C38-H), 2.82 (dd, J = 19.6, 5.3 Hz, 1H, one of C38-H), 1.78 (dd, J = 8.1, 4.7 Hz, 1H, C27-OH), 1.75 (ddd, J = 13.0, 11.1, 4.2 Hz, 1H, one of C32-H), 1.71 (m, J = 13.0, 2.8 Hz, 1H, one of C32-H), 1.48–1.22 (m, 16H, C40– 47 -H2), 1.42 (s, 3H, one of CH3), 1.26 (s, 3H, one of CH3), 0.97 (t, J = 7.9 Hz, 9H, – SiCH2CH3), 0.89 (s, 9H, one of C(CH3)3), 0.88 (t, 3H, C48-H3), 0.87 (s, 9H, one of C(CH3)3), 0.84 (t, J = 8.0 Hz, 9H, –SiCH2CH3), 0.70–0.57 (m, J = 7.8, 7.5, 7.3 Hz, 6H, –SiCH2CH3), 0.43 (q, J = 7.9 Hz, 6H, –SiCH2CH3), 0.08 (s, 3H, one of SiCH3), 0.04 (s, 3H, one of SiCH3), 0.01 (s, 3H, one of SiCH3), –0.01 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 211.9, 138.8, 138.6, 138.3, 128.4, 128.2, 128.2, 128.2, 128.0, 127.5, 127.4, 127.4, 127.3, 107.7, 78.8, 78.6, 78.5, 77.5, 76.1, 75.3, 74.1, 73.9, 73.5, 73.3, 71.4, 67.3, 64.2, 48.7, 37.9, 31.9, 30.4, 29.8, 29.6, 29.6, 29.3, 28.7, 26.0, 25.9, 25.9, 25.2, 22.7, 18.1, 18.0, 14.1, 6.9, 6.8, 5.3, 5.1, 5.0, 4.5, –4.5, –4.5, –4.7, –4.7; HRMS (ESI-TOF) m/z calcd for C70H122NaO11Si4 [M+Na]+: 1273.7956, found: 1273.7948. OBn OBn O O 35 TES O OTES OTBS 39 O 27 OBn OBn O O 35 TES O OTES OTBS 39 31 HO TBSO BnO Me O Me C9H19 31 H 27 TBSO BnO Me O Me C9H19 87 71   116 (2R,3S,4R,5S)-3,4,5-Tris(benzyloxy)-2-((tert-butyldimethylsilyl)oxy)-6-((4R,5R)-5((5S,6S,9R)-3,3-diethyl-11,11,12,12-tetramethyl-9-nonyl-7-oxo-6-((triethylsilyl)oxy)-4,10dioxa-3,11-disilatridecan-5-yl)-2,2-dimethyl-1,3-dioxolan-4-yl)hexanal (71). To a solution of carbinol 87 (0.24 g, 0.19 mmol, 1.0 equiv) and EtN(iPr)2 (0.10 mL, 0.58 mmol, 3.0 equiv) in CH2Cl2 (0.55 mL, 0.35 M wrt 87) and DMSO (0.11 mL, 1.8 M wrt 87) at –30 °C was added a solution of SO3•py (0.092 g, 0.58 mmol, 3.0 equiv) in DMSO (0.44 mL, 1.3 M wrt SO3•py). The reaction mixture was stirred between –30 °C and –20 °C for 1.5 h, quenched with brine (15 mL), then diluted with Et2O (40 mL) and H2O (1 mL). The layers were separated and the organic layer washed sequentially with 1 M aq NaHSO4 (15 mL), sat. aq NaHCO3 (15 mL), and 1:1 H2O/brine (2 x 15 mL). The organic layer was then dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 1% → 1.5% → 2% EtOAc in hexanes) afforded aldehyde 71 (0.23 g, 95% yield) as a clear, colorless oil. [α] 26 +11.9° (c = 2.2, CH2Cl2); IR (neat) 3066, 3031, 2927, 2872, 1731 D (s), 1714 (s), 1455, 1416, 1380, 1252, 1220, 1143, 1097, 1061, 1026, 979, 950, 894, 837, 777, 729, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 9.74 (s, 1H, C27-H), 7.33–7.18 (m, 15H, ArH), 4.68 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.63 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.61 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.47 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.46 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 4.32 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.25 (dddd, J = 5.7, 5.7, 5.7, 5.7 Hz, 1H, C39-H), 4.22 (ddd, J = 11.4, 5.0, 2.1 Hz, 1H, C33-H), 4.08 (dd, J = 5.9, 3.7 Hz, 1H, C29-H), 3.97 (d, J = 5.7 Hz, 1H, C28-H), 3.88 (dd, J = 5.6, 3.7 Hz, 1H, C30-H), 3.84 (dd, J = 9.1, 5.1 Hz, 1H, C34-H), 3.79 (m, 1H, C31-H), 3.78 (dd, J = 9.1, 2.0 Hz, 1H, C35H), 3.70 (d, J = 2.1 Hz, 1H, C36-H), 2.90 (dd, J = 19.6, 6.4 Hz, 1H, one of C38-H), 2.85 (dd, J = 19.6, 5.6 Hz, 1H, one of C38-H), 1.87 (ddd, J = 13.9, 3.7, 1.6 Hz, 1H, one of C32-H), 1.75 (ddd, J = 13.8, 11.9, 5.0 Hz, 1H, one of C32-H), 1.48–1.27 (m, 16H, C40–47-H2), 1.41 (s, 3H, one of CH3), 1.27 (s, 3H, one of CH3), 0.97 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.89 (t, J = 7.0 Hz, 3H, C48-H3), 0.88 (s, 9H, one of C(CH3)3), 0.88 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.88 (s, 9H, one of C(CH3)3), 0.71–0.59 (m, J = 8.1, 7.9, 7.8 Hz, 6H, –SiCH2CH3), 0.43 (q, J = 7.9 Hz, 6H, –SiCH2CH3), 0.09 (s, 3H, one of SiCH3), 0.06 (s, 3H, one of SiCH3), 0.02 (s, 3H, one of SiCH3), –0.10 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 211.9, 200.6, 138.7, 138.0, 137.7, 128.7, 128.6, 128.4, 128.3, 128.2, 128.0, 127.7, 127.5, 127.4, 107.6, 80.9, 78.8, 78.4, 77.0, 76.9, 76.7, 75.3, 74.9, 73.7, 73.7, 72.1, 67.3, 48.7, 37.9, 31.9, 31.0, 29.8, 29.6,   117 29.6, 29.3, 28.6, 26.1, 25.9, 25.8, 25.2, 22.7, 18.3, 18.0, 14.1, 6.9, 6.8, 5.1, 4.5, –4.5, –4.6, – 4.7, –5.5; HRMS (ESI-TOF) m/z calcd for C70H120NaO11Si4 [M+Na]+: 1271.7800, found: 1271.7846. Synthesis of the Aflastatin A C3–C48 Degradation Products Magnesium bromide diethyl etherate (MgBr2•OEt2).79 Magnesium turnings (99.98%) (2.3 g, 95 mmol, 1.0 equiv) were added to a two-necked round-bottomed flask, equipped with a reflux condenser and a magnetic stir bar. Diethyl ether (150 mL) was added, followed by a small amount of 1,2-dibromoethane. After refluxing was initiated by external heating, the remaining 1,2-dibromoethane (8.2 mL, 95 mmol, 1.0 equiv) was added portion-wise such that a moderate reflux was maintained. After completion of the reaction, excess diethyl ether was removed under a stream of nitrogen, yielding a white paste. The surface of the paste was broken with a spatula and the residue further dried with a stream of nitrogen. This process was repeated until a white solid was obtained. The compound was stored under argon at room temperature. Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS O Me O OBn OBn O O 35 TES O OTBS 39 Me Me O Me TBS Me Me 72 Me Me 31 H 27 TBSO BnO Me O Me C9H19 OTES 71 Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 73 TBSO BnO Me O Me OTES (5R,8S,9S)-9-((4R,5R)-2,2-Dimethyl-5-((2S,3R,4S,5S,6S,8R,10R)-2,3,4-tris(benzyloxy)-11((4R,5S,6S)-6-((S)-1-((4S,6R)-6-((S)-1-((4R,5R,6R)-6-((2S,3R,4R,6R,8S)-3,9bis(benzyloxy)-4-((tert-butyldimethylsilyl)oxy)-6,8-dimethylnonan-2-yl)-2,2,5-trimethyl1,3-dioxan-4-yl)ethyl)-2,2-dimethyl-1,3-dioxan-4-yl)ethyl)-2,2,5-trimethyl-1,3-dioxan-4yl)-5-((tert-butyldimethylsilyl)oxy)-6,8-dihydroxy-10-((triisopropylsilyl)oxy)undecyl)-1,3                                                                                                                 (79) Harwood, L.M.; Manage, A.C.; Robin, S.; Hopes, S.F.G.; Watkin, D.J.; Williams, C.E. Synlett 1993, 777– 780.   118 dioxolan-4-yl)-11,11-diethyl-2,2,3,3-tetramethyl-5-nonyl-8-((triethylsilyl)oxy)-4,10-dioxa3,11-disilatridecan-7-one (73). To a solution of aldehyde 71 (0.23 g, 0.18 mmol, 1.0 equiv) and ketone 72 (0.24 g, 0.20 mmol, 1.1 equiv) in CH2Cl2 (1.3 mL, 0.14 M wrt 71) at –5 °C was added freshly prepared MgBr2•OEt2 (0.38 g, 1.5 mmol, 8.0 equiv). The resulting suspension was stirred at –5 °C for 10 min, then charged dropwise with 1,2,2,6,6-pentamethylpiperidine (83 µL, 0.46 mmol, 2.5 equiv). The reaction mixture was stirred at –5 °C for 7 min, then rapidly quenched with pre-chilled sat. aq NaHCO3 (3 mL). The biphasic mixture was stirred vigorously at rt for 10 min, then diluted with Et2O (30 mL), H2O (10 mL) and sat. aq NaHCO3 (15 mL). The layers were separated and the aqueous layer extracted with CH2Cl2 (2 x 30 mL). The combined organic extracts were washed sequentially with sat. aq NH4Cl (2 x 20 mL) and brine (15 mL), dried over Na2SO4, filtered, concentrated and azeotroped with PhH (2 x 2 mL) to afford crude aldol adduct 88 as a clear, pale yellow oil that was used without further purification. To a solution of crude aldol adduct 88 (theoretical 0.44 g, 0.18 mmol, 1.0 equiv) in 4:1 THF/MeOH (1.8 mL, 0.1 M wrt 88) at –78 °C was added dropwise a solution of diethylmethoxyborane in THF (0.20 mL, 1.0 M, 0.20 mmol, 1.1 equiv). The reaction mixture was stirred at –78 °C for 2.5 h, then charged with sodium borohydride (21 mg, 0.55 mmol, 3.0 equiv) in one portion. The reaction mixture was slowly warmed to –55 °C over 0.5 h, stirred at –55 °C for 20 h, quenched with a pre-mixed mixture of 1 M aq NaOH (1 mL) and 30% aq H2O2 (0.4 mL), then diluted with 4:1 THF/MeOH (1 mL). The heterogeneous mixture was stirred vigorously at 0 °C for 1.5 h, then diluted with Et2O (30 mL) and aq pH 7 buffer (3 mL). The layers were separated and the aqueous layer extracted with Et2O (2 x 30 mL). The combined organic extracts were washed with 10% aq Na2S2O3 (2 x 10 mL) and brine (10 mL), dried over Na2SO4 with added hexanes, filtered and concentrated. The residue was analyzed by 1H-NMR spectroscopy to assess reaction diastereoselectivity (d.r. ≥ 95:05). Column chromatography (gradient elution, 6% → 6.5% EtOAc in hexanes) afforded diol 73 (0.31 g, 70% yield, two steps) as a white foam. [α] 25 +1.0° (c = 1.2, CH2Cl2); IR (neat) 3498 (br), D 3068, 3036, 2932, 2864, 1712, 1459, 1380, 1253, 1202, 1175, 1098, 1008, 982, 837, 775, 733, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.34–7.21 (m, 25H, ArH), 4.73 (d, J = 12.0 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.9 Hz, 1H, one   119 of –OCH2Ph), 4.66 (m, 2H, –OCH2Ph), 4.61 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.52 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.49 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.45 (m, 2H, – OCH2Ph), 4.28 (ddd, J = 11.6, 7.0, 2.5 Hz, 1H, C33-H), 4.25 (m, J = 7.0, 6.0 Hz, 1H), 4.22 (m, 1H), 4.21 (m, J = 5.1, 5.1 Hz, 1H, C39-H), 4.18–4.16 (m, 2H), 4.03–3.98 (m, 2H), 3.98–3.92 (m, 3H), 3.91 (m, 1H, C31-H), 3.88 (m, 1H, C8-H), 3.82 (dd, J = 8.9, 4.9 Hz, 1H, C34-H), 3.79 (dd, J = 8.9, 1.9 Hz, 1H, C35-H), 3.69 (m, 1H), 3.66 (d, J = 1.9 Hz, 1H, C36-H), 3.60 (m, J = 1.6 Hz, 1H), 3.59 (m, J = 9.8 Hz, 1H), 3.54 (m, J = 7.2, 2.8 Hz, 2H), 3.40 (dd, J = 6.2, 2.6 Hz, 1H, C9-H), 3.33 (dd, J = 9.1, 5.3 Hz, 1H, one of C3-H), 3.14 (dd, J = 9.1, 7.4 Hz, 1H, one of C3-H), 2.88 (dd, J = 19.6, 6.6 Hz, 1H, one of C38-H), 2.83 (dd, J = 19.5, 5.4 Hz, 1H, one of C38-H), 2.39 (m, J = 6.8, 6.6, 2.5 Hz, 1H, C10-H), 1.94–1.80 (m, 4H), 1.80–1.57 (m, 8H), 1.52 (m, J = 1.9 Hz, 1H), 1.48–1.20 (m, 16H, C40–47-H2), 1.48–1.20 (m, 5H), 1.44 (s, 3H, one of CH3), 1.39 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3), 1.31 (s, 3H, one of CH3), 1.24 (s, 3H, one of CH3), 1.16 (ddd, J = 13.3, 8.0, 5.6 Hz, 1H), 1.07 (m, 18H, –SiCH(CH3)2), 1.07 (m, 3H, – SiCH(CH3)2), 1.04 (ddd, J = 13.3, 6.3, 2.2 Hz, 1H), 0.99–0.97 (m, J = 6.9 Hz, 6H, two of – CH(CH3)), 0.96 (t, J = 8.0 Hz, 9H, –SiCH2CH3), 0.92–0.81 (m, 12H, four of –CH(CH3)), 0.88 (s, 9H, one of C(CH3)3), 0.88 (t, J = 7.1 Hz, 3H, C48-H3), 0.86 (s, 9H, one of C(CH3)3), 0.84 (s, 9H, one of C(CH3)3), 0.83 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.73 (d, J = 6.9 Hz, 3H, one of –CH(CH3)), 0.70–0.58 (m, J = 7.9, 7.8 Hz, 6H, –SiCH2CH3), 0.43 (q, J = 8.0 Hz, 6H, – SiCH2CH3), 0.07 (s, 3H, one of SiCH3), 0.03 (s, 3H, one of SiCH3), 0.03 (s, 3H, one of SiCH3), 0.01 (s, 3H, one of SiCH3), –0.03 (s, 3H, one of SiCH3), –0.13 (s, 3H, one of SiCH3); 13 C-NMR (125 MHz, CDCl3) δ 211.8, 139.8, 138.8, 138.8, 137.9, 137.7, 128.5, 128.4, 128.3, 128.3, 128.2, 128.1, 128.0, 127.8, 127.4, 127.4, 127.4, 127.3, 127.3, 127.0, 107.5, 98.3, 98.3, 97.2, 80.9, 79.6, 78.9, 78.5, 77.2, 75.9, 75.9, 75.8, 75.5, 75.0, 74.8, 74.0, 73.6, 73.3, 73.0, 72.8, 72.8, 72.5, 71.5, 71.5, 71.0, 69.9, 69.7, 68.2, 67.3, 67.2, 48.7, 45.1, 42.5, 40.8, 40.7, 39.2, 39.1, 38.6, 37.9, 32.7, 32.4, 31.9, 31.9, 31.3, 30.6, 30.4, 30.1, 30.0, 29.8, 29.6, 29.6, 29.3, 28.6, 27.1, 27.0, 26.0, 26.0, 25.9, 25.8, 25.2, 22.7, 20.7, 20.1, 19.8, 19.3, 18.2, 18.2, 18.2, 18.0, 18.0, 14.1, 12.7, 11.0, 9.5, 9.0, 8.9, 6.9, 6.8, 5.1, 4.6, 4.5, –3.7, –3.8, –4.2, –4.4, – 4.5, –4.7; HRMS (ESI-TOF) m/z calcd for C139H242NaO22Si6 [M+Na]+: 2454.6326, found: 2454.6361.   120 Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 73 TBSO BnO Me O Me OTES OH HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH OH 39 Me Me OH Me Me Me Me Me 74 OH OBn H O C9H19 (2S,3R,4R,5S,6S,8S,10R,12R,13S,14R,15S,16S,18R,19S,20R,21R,22R,23S,24R,25R,27R,29 S)-2,3,4,24,30-Pentakis(benzyloxy)-13,15,19,21,23,27,29-heptamethyl-1((2R,3S,4S,5S,6S)-3,4,5,6-tetrahydroxy-6-((R)-2-hydroxyundecyl)tetrahydro-2H-pyran-2yl)triacontan-5,6,8,10,12,14,16,18,20,22,25-undecaol (74). To a solution of ketone 73 (70 mg, 29 µmol, 1.0 equiv) in 1:1 CH3CN/CH2Cl2 (1 mL, 0.03 M wrt 73) at 0 °C was added dropwise a solution of fluorosilicic acid (H2SiF6) in H2O (~60 µL, 20–25 wt. %). The reaction mixture was stirred at 0 °C for 0.5 h, then warmed to rt and stirred for 12 h, carefully quenched with two small spatula tips full of NaHCO3 (s), stirred vigorously for an additional 1 h, and filtered through Celite . The filter cake was rinsed with 1:1 EtOAc/CH3OH (20 mL  total), and the filtrate concentrated. Pipette column chromatography (gradient elution, 2.5% → 3% → 3.5% CH3OH in CH2Cl2) afforded lactol 74 (0.034 g, 58% yield) as a clear, colorless oil. [α] 24 –9.0° (c = 0.61, CH3OH); IR (neat) 3377 (br), 3062, 3032, 2926, 2855, D 1455, 1383, 1327, 1274, 1209, 1155, 1094, 1068, 1030, 970, 850, 736, 699 cm–1; 1H-NMR (600 MHz, CD3OD) δ 7.46–7.20 (m, 25H, ArH), 4.88 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.84 (d, J = 10.7 Hz, 1H, one of –OCH2Ph), 4.77 (d, J = 11.3 Hz, 1H, one of –OCH2Ph), 4.71 (d, J = 10.5 Hz, 1H, one of –OCH2Ph), 4.67 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.60 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.50 (d, J = 11.4 Hz, 2H, two of –OCH2Ph), 4.45 (m, 2H, two of –OCH2Ph), 4.32 (m, J = 8.8 Hz, 1H), 4.08–4.00 (m, 4H), 3.99–3.95 (m, 3H), 3.97 (m, 1H, C31-H), 3.91 (m, J = 9.1, 1.2 Hz, 1H), 3.88–3.83 (m, 2H), 3.86 (m, 1H, C33-H), 3.84 (dd, J = 9.5, 3.2 Hz, 1H, C35-H), 3.80 (m, J = 8.6, 2.1 Hz, 1H), 3.65 (m, J = 9.4, 1.9 Hz, 1H), 3.65 (d, J = 3.4 Hz, 1H, C36-H), 3.47 (dd, J = 9.5, 9.4 Hz, 1H, C34-H), 3.34 (dd, J = 9.2, 5.3 Hz,   121 1H, one of C3-H), 3.32 (m, J = 4.4, 1.8 Hz, 1H), 3.23 (dd, J = 9.2, 6.6 Hz, 1H, one of C3-H), 3.20 (m, J = 9.4 Hz, 1H), 2.54 (ddd, J = 10.0, 10.0, 2.4 Hz, 1H, one of C32-H), 2.25 (m, J = 7.0, 6.6, 6.3 Hz, 1H, C10-H), 2.03 (dd, J = 14.5, 2.0 Hz, 1H, one of C38-H), 2.01–1.97 (m, 1H), 1.99 (ddd, J = 10.0, 7.2, 7.1 Hz, 1H, one of C32-H), 1.83 (m, J = 6.6, 6.2 Hz, 1H, one of C4H), 1.82–1.73 (m, 4H), 1.69–1.38 (m, 14H), 1.58 (dd, J = 14.4, 10.8 Hz, 1H, one of C38-H), 1.34–1.23 (m, 14H, C41–47-H2), 0.95–0.92 (m, J = 7.0, 6.9 Hz, 15H, five of –CH(CH3)), 0.88 (t, J = 7.0 Hz, 3H, C48-H3), 0.81 (d, J = 7.0 Hz, 3H, one of –CH(CH3)), 0.74 (d, J = 6.9 Hz, 3H, one of –CH(CH3)); 13C-NMR (125 MHz, CD3OD) δ 140.5, 140.2, 140.0, 140.0, 139.5, 130.0, 129.4, 129.4, 129.3, 129.3, 129.2, 128.9, 128.8, 128.7, 128.5, 128.5, 128.4, 99.9, 84.6, 81.7, 81.5, 80.0, 78.9, 77.0, 76.7, 76.7, 76.1, 76.1, 75.9, 75.6, 74.7, 74.3, 74.0, 74.0, 74.0, 73.2, 72.5, 71.8, 71.8, 71.4, 70.7, 70.5, 69.8, 68.7, 45.5, 43.0, 43.0, 43.0, 42.6, 42.6, 42.1, 40.1, 40.0, 39.7, 39.2, 37.2, 36.7, 33.1, 32.1, 32.1, 31.0, 30.9, 30.9, 30.6, 28.7, 26.8, 23.8, 21.3, 18.9, 14.5, 13.7, 11.5, 9.5, 6.5, 6.2; HRMS (ESI-TOF) m/z calcd for C88H136NaO22 [M+Na]+: 1567.9415, found: 1567.9435. OH HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH OH 39 Me Me OH Me Me Me Me Me 74 OH OBn H O C9H19 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH OH 39 Me Me OH Me Me Me Me Me 1 OH OH H O C9H19 (2S,4R,6R,7R,8S,9R,10R,11R,12S,13R,15S,16S,17R,18S,19R,21R,23S,25S,26S,27R,28R,29 S)-2,4,8,10,12,16,18-Heptamethyl-30-((2R,3S,4S,5S,6S)-3,4,5,6-tetrahydroxy-6-((R)-2hydroxyundecyl)tetrahydro-2H-pyran-2-yl)triacontane1,6,7,9,11,13,15,17,19,21,23,25,26,27,28,29-hexadecaol (1). To a solution of pentabenzyl ether 74 (12 mg, 7.7 µmol, 1.0 equiv) in 6:1 dioxane/H2O (0.31 mL, 25 mM wrt 74) at rt was added palladium black (~10 mg). The reaction mixture was purged with hydrogen for 1 min, stirred vigorously for 12 h, then recharged with additional catalyst at this time and   122 approximately every 12 h thrice after (total palladium black added: ~50 mg). The reaction mixture was stirred at rt for 20 h, then filtered through Celite . The filter cake was rinsed with  1:1 THF/CH3OH (15 mL total), and the filtrate concentrated. Reversed-phase C18 column chromatography (gradient elution, 5% → 100% CH3CN in H2O; eluted 50% → 70%) afforded aflastatin A C3–C48 degradation lactol 1 (4.5 mg, 53% yield) as a white solid. [α] 25 +7.2° (c D = 0.29, 3:1 CH3OH/THF); IR (neat) 3319 (br), 2923, 2858, 1571, 1452, 1321, 1277, 1158, 1092, 973, 848 cm–1; 1H-NMR (600 MHz, C5D5N) δ 7.00 (d, J = 4.5 Hz, 1H, C35-OH), 6.81 (d, J = 5.0 Hz, 1H, C34-OH), 6.69 (d, J = 4.7 Hz, 1H, C27-OH), 6.52 (d, J = 6.7 Hz, 1H, C27OH), 6.47 (br s, 1H, one of –OH), 6.43–6.39 (m, 2H, two of –OH), 6.35–6.31 (m, 2H, two of –OH), 6.30–6.21 (m, 5H, five of –OH), 6.10–6.05 (m, 3H, three of –OH), 5.98–5.92 (m, 3H, three of –OH), 5.87 (dd, J = 5.3, 5.3 Hz, 1H, C3-OH), 5.03 (m, J = 5.4 Hz, 1H, C29-H), 4.97 (m, J = 6.7 Hz, 1H, C31-H), 4.85 (ddd, J = 9.8, 9.7, 2.9 Hz, 1H, C33-H), 4.76 (dd, J = 9.4, 3.2 Hz, 1H, C35-H), 4.72 (m, 1H, C39-H), 4.68 (m, J = 8.8, 8.2 Hz, 1H, C27-H), 4.62 (m, 1H, C25H), 4.61 (m, 1H, C17-H), 4.58 (dd, J = 5.6, 1.8 Hz, 1H, C30-H), 4.51–4.46 (m, 2H, C15-H and C23-H), 4.48 (d, J = 3.1 Hz, 1H, C36-H), 4.43 (m, J = 8.8, 3.7 Hz, 1H, C21-H), 4.38 (dd, J = 9.4, 9.4 Hz, 1H, C34-H), 4.32 (m, 1H, C11-H), 4.30 (m, 1H, C28-H), 4.29 (m, 1H, C8-H), 4.12 (m, J = 8.9 Hz, 1H, C13-H), 4.06 (m, J = 9.7 Hz, 1H, C19-H), 4.00 (dd, J = 4.7, 4.1 Hz, 1H, C9H), 3.80 (m, J = 10.4, 4.8 Hz, 1H, one of C3-H), 3.61 (m, J = 10.4, 6.7 Hz, 1H, one of C3-H), 3.21 (ddd, J = 13.6, 7.2, 2.8 Hz, 1H, one of C32-H), 2.73 (m, J = 13.3 Hz, 1H, one of C38-H), 2.60 (m, J = 12.9 Hz, 1H, one of C26-H), 2.56 (ddd, J = 13.8, 10.1, 6.4 Hz, 1H, one of C32-H), 2.31 (m, J = 6.4 Hz, 1H, C10-H), 2.21 (m, J = 9.4, 6.7, 5.7 Hz, 1H, C18-H), 2.16 (m, 1H, one of C26-H), 2.15 (m, 1H, C6-H), 2.14 (dd, J = 14.4, 10.6 Hz, 1H, one of C38-H), 2.08 (m, 1H, C12H), 2.08–2.01 (m, 4H, one of C16-H, one of C22-H, and C24-H2), 1.99 (m, 1H, C4-H), 1.96 (m, 1H, one of C16-H), 1.95 (m, 1H, C14-H), 1.87 (m, 1H, C20-H), 1.86 (m, 1H, one of C22-H), 1.83 (m, J = 6.9, 5.4 Hz, 1H, one of C7-H), 1.77 (m, J = 7.6, 6.0 Hz, 1H, one of C5-H), 1.74 (m, J = 8.1, 5.9 Hz, 1H, one of C7-H), 1.65 (m, 1H, one of C40-H), 1.57–1.44 (m, 2H, one of C40-H, and one of C41-H), 1.35 (m, 1H, one of C41-H), 1.31–1.10 (m, 10H, C42–46-H2), 1.27 (d, J = 6.9 Hz, 3H, C51-H3), 1.24 (d, J = 7.0 Hz, 3H, C53-H3), 1.22 (m, 2H, C47-H2), 1.20 (d, J = 7.0 Hz, 3H, C55-H3), 1.10 (d, J = 6.7 Hz, 3H, C49-H3), 1.06 (d, J = 6.6 Hz, 3H, C50-H3), 1.05 (m, 1H, one of C5-H), 0.97 (d, J = 6.9 Hz, 3H, C54-H3), 0.83 (t, J = 7.1 Hz, 3H, C48-H3), 0.80   123 (d, J = 6.7 Hz, 3H, C52-H3); 13C-NMR (125 MHz, C5D5N) δ 100.1 (C37), 81.6 (C13), 78.9 (C11), 78.8 (C19), 78.0 (C9), 77.1 (C15), 76.3 (C21), 76.1 (C28), 75.1 (C36), 74.2 (C30), 74.0 (C17), 73.3 (C34), 72.9 (C35), 72.3 (C27), 71.7 (C33), 71.4 (C29), 71.3 (C25), 71.0 (C31), 70.7 (C23), 69.5 (C8), 69.0 (C39), 67.3 (C3), 45.7 (C16), 42.8 (C38), 42.7 (C18), 42.7 (C22), 42.4 (C7), 42.1 (C26), 41.6 (C5), 39.6 (C40), 39.5 (C20), 39.5 (C14), 38.8 (C12), 38.1 (C10), 37.4 (C32), 37.0 (C24), 34.0 (C4), 32.1 (C46), 30.1 (C44), 29.9 (C43), 29.8 (C42), 29.6 (C45), 27.9 (C6), 25.9 (C41), 22.9 (C47), 21.7 (C50), 18.7 (C49), 14.3 (C48), 13.2 (C52), 11.7 (C54), 8.3 (C51), 6.4 (C53), 6.1 (C55); HRMS (ESI-TOF) m/z calcd for C53H106NaO22 [M+Na]+: 1117.7068, found: 1117.7111. OH HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH OH 39 Me Me OH Me Me Me Me Me 74 OH OBn H O C9H19 OH HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH OMe 39 Me Me OH Me Me Me Me Me 89 OH OBn H O C9H19 (2S,3R,4R,5S,6S,8S,10R,12R,13S,14R,15S,16S,18R,19S,20R,21R,22R,23S,24R,25R,27R,29 S)-2,3,4,24,30-Pentakis(benzyloxy)-13,15,19,21,23,27,29-heptamethyl-1((2R,3S,4S,5S,6S)-3,4,5-trihydroxy-6-((R)-2-hydroxyundecyl)-6-methoxytetrahydro-2Hpyran-2-yl)triacontan-5,6,8,10,12,14,16,18,20,22,25-undecaol (89). To a solution of lactol 74 (34 mg, 22 µmol, 1.0 equiv) in CH3OH (1.1 mL, 20 mM wrt 74) at rt was added Dowex® 50WX8 hydrogen form ion-exchange resin (0.22 g, 10 mg/µmol 74, 200–400 mesh). The reaction mixture was stirred at 30 °C for 2 d, then filtered through Celite . The filter cake was  rinsed with 1:1 CH2Cl2/CH3OH (15 mL total), and the filtrate concentrated. Pipette column chromatography (gradient elution, 4.5% → 5% → 6% CH3OH in CH2Cl2) afforded lactol methyl ether 89 (0.013 g, 39% yield) as a clear, colorless oil. [α] 25 +0.30° (c = 0.67, D CH3OH); IR (neat) 3379 (br), 3036, 2926, 2854, 1454, 1384, 1331, 1207, 1105, 1066, 976, 847, 735, 698 cm–1; 1H-NMR (600 MHz, CD3OD) δ 7.43–7.21 (m, 25H, ArH), 4.85 (d, J =   124 11.0 Hz, 1H, one of –OCH2Ph), 4.79 (d, J = 10.8 Hz, 1H, one of –OCH2Ph), 4.75 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 4.74 (d, J = 10.8 Hz, 1H, one of –OCH2Ph), 4.66 (d, J = 11.3 Hz, 1H, one of –OCH2Ph), 4.60 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.55 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.49 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.45 (m, 2H, two of – OCH2Ph), 4.25 (m, J = 7.9 Hz, 1H), 4.06 (m, J = 4.4, 4.1, 3.5 Hz, 1H), 4.02 (m, J = 4.8, 3.5 Hz, 1H), 4.01 (m, J = 2.6 Hz, 1H), 3.99–3.94 (m, J = 8.3, 6.9, 4.2 Hz, 3H), 3.97 (m, 1H, C31H), 3.91 (m, 1H), 3.90 (d, J = 3.7 Hz, 1H, C36-H), 3.88–3.84 (m, J = 6.3, 2.5 Hz, 2H), 3.79 (m, J = 2.1 Hz, 1H), 3.78 (dd, J = 9.5, 3.7 Hz, 1H, C35-H), 3.69 (m, J = 6.6, 1.8 Hz, 1H), 3.65 (m, J = 9.6, 1.8 Hz, 1H), 3.48 (dd, J = 9.5, 9.4 Hz, 1H, C34-H), 3.42 (ddd, J = 9.2, 9.2, 2.2 Hz, 1H, C33-H), 3.35 (m, J = 8.2, 1.4 Hz, 1H), 3.33 (dd, J = 9.2, 4.0 Hz, 1H, one of C3-H), 3.31 (m, 1H), 3.23 (dd, J = 9.2, 6.6 Hz, 1H, one of C3-H), 3.07 (s, 3H, –OCH3), 2.57 (m, J = 12.1, 8.5 Hz, 1H, one of C32-H), 2.25 (m, J = 7.0, 6.9, 6.7 Hz, 1H, C10-H), 1.97 (ddd, J = 14.4, 4.7, 2.6 Hz, 1H), 1.93 (ddd, J = 14.1, 9.2, 3.7 Hz, 1H, one of C32-H), 1.90–1.73 (m, 6H), 1.84 (m, 1H, one of C4-H), 1.71–1.39 (m, 14H), 1.38–1.24 (m, 14H, C41–47-H2), 0.95–0.92 (m, J = 7.2 Hz, 15H, five of –CH(CH3)), 0.89 (t, J = 7.0 Hz, 3H, C48-H3), 0.81 (d, J = 6.9 Hz, 3H, one of –CH(CH3)), 0.74 (d, J = 6.7 Hz, 3H, one of –CH(CH3)); 13C-NMR (125 MHz, CD3OD) δ 140.5, 140.1, 140.0, 140.0, 139.7, 129.7, 129.4, 129.3, 129.3, 129.3, 129.2, 129.2, 129.0, 128.7, 128.7, 128.6, 128.5, 128.5, 128.5, 103.4, 84.6, 82.1, 81.7, 80.2, 78.8, 77.0, 77.0, 76.7, 76.2, 76.0, 76.0, 75.6, 75.4, 74.3, 74.0, 74.0, 72.9, 72.5, 72.2, 72.1, 71.9, 71.8, 70.8, 70.5, 68.8, 68.1, 48.5, 45.3, 43.0, 43.0, 43.0, 42.6, 42.0, 40.2, 40.0, 39.7, 39.2, 39.0, 37.2, 36.8, 33.1, 32.4, 32.1, 30.8, 30.8, 30.7, 30.5, 28.7, 26.6, 23.7, 21.3, 18.9, 14.5, 13.7, 11.5, 9.5, 6.5, 6.2; HRMS (ESI-TOF) m/z calcd for C89H138NaO22 [M+Na]+: 1581.9572, found: 1581.9502. OH HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 35 OH OH OMe 39 Me Me OH Me Me Me Me Me 89 OH OBn H O C9H19 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH OMe 39 Me Me OH Me Me Me Me Me 46a OH OH H O C9H19   125 (2S,4R,6R,7R,8S,9R,10R,11R,12S,13R,15S,16S,17R,18S,19R,21R,23S,25S,26S,27R,28R,29 S)-2,4,8,10,12,16,18-Heptamethyl-30-((2R,3S,4S,5S,6S)-3,4,5-trihydroxy-6-((R)-2hydroxyundecyl)-6-methoxytetrahydro-2H-pyran-2-yl)triacontane1,6,7,9,11,13,15,17,19,21,23,25,26,27,28,29-hexadecaol (46a). To a solution of pentabenzyl ether 89 (13 mg, 8.3 µmol, 1.0 equiv) in 6:1 dioxane/H2O (0.33 mL, 25 mM wrt 89) at rt was added palladium black (~10 mg). The reaction mixture was purged with hydrogen for 1 min, stirred vigorously for 12 h, then recharged with additional catalyst at this time and approximately every 12 h thrice after (total palladium black added: ~50 mg). The reaction mixture was stirred at rt for 20 h, then filtered through Celite . The filter cake was rinsed with  1:1 THF/CH3OH (15 mL total), and the filtrate concentrated. Reversed-phase C18 column chromatography (gradient elution, 30% → 90% CH3CN in H2O; eluted 45% → 60%) afforded aflastatin A C3–C48 degradation lactol methyl ether 46a (6.8 mg, 74% yield) as a white solid. [α] 24 +14.0° (c = 0.65, CH3OH); IR (neat) 3353 (br), 2925, 2858, 1444, 1382, 1318, 1209, D 1108, 1034, 968, 848 cm–1; 1H-NMR (600 MHz, C5D5N) δ 6.89 (d, J = 3.5 Hz, 1H, one of – OH), 6.63 (d, J = 4.4 Hz, 1H, one of –OH), 6.49 (d, J = 3.5 Hz, 1H, C39-OH), 6.46 (br s, 1H, one of –OH), 6.41 (br s, 1H, one of –OH), 6.38 (d, J = 4.7 Hz, 1H, one of –OH), 6.31–6.23 (m, 4H, four of –OH), 6.20 (d, J = 6.9 Hz, 1H, C35-OH), 6.12 (d, J = 4.5 Hz, 1H, C31-OH), 6.11–6.04 (m, 4H, four of –OH), 5.99 (d, J = 4.4 Hz, 1H, C29-OH), 5.96–5.92 (m, 2H, two of –OH), 5.87 (dd, J = 5.3, 5.0 Hz, 1H, C3-OH), 4.96 (m, J = 3.8 Hz, 1H, C29-H), 4.93 (m, J = 2.3 Hz, 1H, C31-H), 4.67 (d, J = 3.7 Hz, 1H, C36-H), 4.67 (m, J = 3.2 Hz, 1H, C27-H), 4.64 (m, 1H, C25-H), 4.62 (m, J = 8.2 Hz, 1H, C17-H), 4.56 (dd, J = 9.1, 3.5 Hz, 1H, C35-H), 4.52–4.46 (m, J = 2.8 Hz, 3H, C15-H, C23-H and C30-H), 4.42 (m, J = 6.7 Hz, 1H, C21-H), 4.34 (m, J = 7.0 Hz, 1H, C28-H), 4.32 (dd, J = 9.5, 9.4 Hz, 1H, C34-H), 4.31 (m, J = 8.6 Hz, 1H, C11-H), 4.28 (m, 1H, C8-H), 4.23 (ddd, J = 9.3, 9.1, 2.5 Hz, 1H, C33-H), 4.19 (m, J = 5.9, 5.7, 4.6 Hz, 1H, C39-H), 4.12 (m, J = 8.5 Hz, 1H, C13-H), 4.05 (m, J = 9.8 Hz, 1H, C19-H), 4.00 (m, J = 4.4, 4.0 Hz, 1H, C9-H), 3.80 (ddd, J = 10.2, 5.1, 4.6 Hz, 1H, one of C3-H), 3.61 (ddd, J = 10.1, 6.7, 5.2 Hz, 1H, one of C3-H), 3.35 (s, 3H, C56-H3), 3.17 (ddd, J = 14.1, 6.4, 2.5 Hz, 1H, one of C32-H), 2.60 (m, J = 14.1 Hz, 1H, one of C26-H), 2.49 (ddd, J = 14.1, 8.5, 6.4 Hz, 1H, one of C32-H), 2.45 (dd, J = 15.3, 9.3 Hz, 1H, one of C38-H), 2.30 (m, J = 6.5 Hz, 1H, C10-H), 2.21 (m, 1H, C18-H), 2.20 (m, J = 14.9 Hz, 1H, one of C38-H), 2.17 (m, 1H, one of C26-H), 2.15 (m,   126 J = 6.9 Hz, 1H, C6-H), 2.08 (m, 1H, C12-H), 2.07–2.00 (m, 3H, one of C16-H, one of C22-H, and one of C24-H), 2.00–1.92 (m, 4H, C4-H, C14-H, one of C16-H, and one of C24-H), 1.87 (m, 1H, C20-H), 1.85 (m, 1H, one of C22-H), 1.83 (m, J = 6.7, 5.1 Hz, 1H, one of C7-H), 1.77 (m, J = 7.5, 6.3 Hz, 1H, one of C5-H), 1.75 (m, J = 7.9, 6.0 Hz, 1H, one of C7-H), 1.67 (m, 1H, one of C40-H), 1.63–1.53 (m, 2H, one of C40-H, and one of C41-H), 1.47 (m, 1H, one of C41-H), 1.32–1.14 (m, 10H, C42–46-H2), 1.28 (d, J = 6.9 Hz, 3H, C51-H3), 1.24 (d, J = 6.9 Hz, 3H, C53H3), 1.22 (m, 2H, C47-H2), 1.19 (d, J = 6.9 Hz, 3H, C55-H3), 1.10 (d, J = 6.7 Hz, 3H, C49-H3), 1.06 (d, J = 6.7 Hz, 3H, C50-H3), 1.04 (m, 1H, one of C5-H), 0.97 (d, J = 6.7 Hz, 3H, C54-H3), 0.83 (t, J = 7.0 Hz, 3H, C48-H3), 0.80 (d, J = 6.9 Hz, 3H, C52-H3); 13 C-NMR (125 MHz, C5D5N) δ 103.3 (C37), 81.6 (C13), 78.9 (C11), 78.9 (C19), 78.0 (C9), 77.1 (C15), 76.3 (C21), 76.3 (C28), 75.5 (C30), 74.0 (C17), 73.1 (C36), 72.8 (C33), 72.6 (C35), 72.4 (C34), 72.2 (C27), 71.5 (C29), 71.1 (C25), 70.9 (C31), 70.9 (C23), 69.5 (C8), 67.3 (C3), 66.9 (C39), 47.8 (C56), 45.8 (C16), 42.8 (C18), 42.8 (C22), 42.4 (C7), 42.1 (C26), 41.6 (C5), 39.5 (C20), 39.5 (C14), 39.4 (C38), 39.4 (C40), 38.8 (C12), 38.1 (C10), 37.6 (C32), 37.0 (C24), 34.0 (C4), 32.1 (C46), 30.0 (C44), 30.0 (C43), 29.8 (C42), 29.5 (C45), 27.9 (C6), 26.0 (C41), 22.9 (C47), 21.7 (C50), 18.7 (C49), 14.3 (C48), 13.2 (C52), 11.7 (C54), 8.3 (C51), 6.4 (C53), 6.1 (C55); HRMS (ESI-TOF) m/z calcd for C54H108NaO22 [M+Na]+: 1131.7225, found: 1131.7209. OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH OMe 39 Me Me OH Me Me Me Me Me 46a OH OH H O C9H19 OH HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 35 OH OH OCD3 39 Me Me OH Me Me Me Me Me 46b OH OH H O C9H19 (2S,4R,6R,7R,8S,9R,10R,11R,12S,13R,15S,16S,17R,18S,19R,21R,23S,25S,26S,27R,28R,29 S)-2,4,8,10,12,16,18-Heptamethyl-30-((2R,3S,4S,5S,6S)-3,4,5-trihydroxy-6-((R)-2hydroxyundecyl)-6-(2H3)methoxytetrahydro-2H-pyran-2-yl)triacontane-   127 1,6,7,9,11,13,15,17,19,21,23,25,26,27,28,29-hexadecaol (46b). To a solution of lactol methyl ether 46a (6.8 mg, 6.1 µmol, 1.0 equiv) in CD3OD (1.5 mL, 4.0 mM wrt 46a) at rt was added Dowex® 50WX8 hydrogen form ion-exchange resin (~1 mg, 200–400 mesh). The reaction mixture stood at rt for 18 h, then was filtered through Celite . The filter cake was rinsed with  1:1 CH2Cl2/CH3OH (15 mL total), and the filtrate concentrated. Reversed-phase C18 column chromatography (gradient elution, 5% → 100% CH3CN in H2O; eluted 50% → 65%) afforded aflastatin A C3–C48 degradation lactol trideuteriomethyl ether 46b (5.4 mg, 79% yield) as a white solid. [α] 24 +12.6° (c = 0.34, CH3OH); IR (neat) 3331 (br), 2922, 2857, 1457, 1437, D 1314, 1159, 1107, 1061, 969, 848 cm–1; 1H-NMR (600 MHz, C5D5N) δ 6.90 (br s, 1H, one of –OH), 6.63 (br s, 1H, one of –OH), 6.49 (br s, 1H, one of –OH), 6.45 (br s, 1H, one of –OH), 6.41 (br s, 1H, one of –OH), 6.37 (br s, 1H, one of –OH), 6.30–6.21 (m, 4H, four of –OH), 6.19 (br s, 1H, one of –OH), 6.11 (br s, 1H, one of –OH), 6.10–6.02 (m, 4H, four of – OH), 5.96 (br s, 1H, one of –OH), 5.95–5.91 (m, 2H, two of –OH), 5.90 (br s, 1H, one of – OH), 4.97 (m, J = 2.5 Hz, 1H, C29-H), 4.92 (m, J = 2.6 Hz, 1H, C31-H), 4.67 (d, J = 3.7 Hz, 1H, C36-H), 4.67 (m, 1H, C27-H), 4.64 (m, J = 4.2, 3.7 Hz, 1H, C25-H), 4.62 (m, J = 7.0 Hz, 1H, C17-H), 4.57 (dd, J = 9.1, 3.5 Hz, 1H, C35-H), 4.52–4.45 (m, 3H, C15-H, C23-H and C30-H), 4.42 (m, J = 8.6 Hz, 1H, C21-H), 4.34 (m, J = 8.3 Hz, 1H, C28-H), 4.31 (dd, J = 9.2, 9.1 Hz, 1H, C34-H), 4.31 (m, 1H, C11-H), 4.28 (m, J = 4.1, 4.0 Hz, 1H, C8-H), 4.23 (m, J = 10.8, 5.1 Hz, 1H, C33-H), 4.18 (m, J = 10.7, 5.9 Hz, 1H, C39-H), 4.11 (m, J = 8.7 Hz, 1H, C13-H), 4.05 (m, J = 9.5 Hz, 1H, C19-H), 4.00 (m, J = 4.4, 4.1 Hz, 1H, C9-H), 3.79 (m, J = 10.3, 4.8 Hz, 1H, one of C3-H), 3.60 (m, J = 10.4, 6.7 Hz, 1H, one of C3-H), 3.17 (ddd, J = 11.4, 3.4, 2.8 Hz, 1H, one of C32-H), 2.59 (m, J = 13.8 Hz, 1H, one of C26-H), 2.49 (ddd, J = 14.0, 7.5, 6.4 Hz, 1H, one of C32-H), 2.44 (dd, J = 15.2, 9.4 Hz, 1H, one of C38-H), 2.30 (m, J = 6.1 Hz, 1H, C10-H), 2.21 (m, 1H, C18-H), 2.20 (m, J = 15.2 Hz, 1H, one of C38-H), 2.16 (m, 1H, one of C26-H), 2.14 (m, J = 7.2 Hz, 1H, C6-H), 2.08 (m, 1H, C12-H), 2.07–2.00 (m, 3H, one of C16-H, one of C22-H, and one of C24-H), 2.00–1.92 (m, 4H, C4-H, C14-H, one of C16-H, and one of C24-H), 1.87 (m, 1H, C20-H), 1.85 (m, 1H, one of C22-H), 1.83 (m, J = 6.7, 5.4 Hz, 1H, one of C7-H), 1.76 (m, J = 7.6, 6.0 Hz, 1H, one of C5-H), 1.74 (m, J = 7.9, 7.2, 6.4 Hz, 1H, one of C7-H), 1.67 (m, 1H, one of C40-H), 1.62–1.53 (m, 2H, one of C40-H, and one of C41-H), 1.47 (m, 1H, one of C41-H), 1.32–1.13 (m, 10H, C42–46-H2), 1.28 (d, J = 7.0 Hz, 3H, C51-H3), 1.23   128 (d, J = 6.7 Hz, 3H, C53-H3), 1.22 (m, 2H, C47-H2), 1.19 (d, J = 6.9 Hz, 3H, C55-H3), 1.10 (d, J = 6.7 Hz, 3H, C49-H3), 1.06 (d, J = 6.6 Hz, 3H, C50-H3), 1.04 (m, 1H, one of C5-H), 0.97 (d, J = 6.7 Hz, 3H, C54-H3), 0.83 (t, J = 7.1 Hz, 3H, C48-H3), 0.80 (d, J = 6.9 Hz, 3H, C52-H3); 13CNMR (125 MHz, C5D5N) δ 103.2 (C37), 81.6 (C13), 78.8 (C11), 78.7 (C19), 77.9 (C9), 77.1 (C15), 76.2 (C21), 76.2 (C28), 75.4 (C30), 73.9 (C17), 73.0 (C36), 72.7 (C33), 72.6 (C35), 72.3 (C34), 72.2 (C27), 71.5 (C29), 71.1 (C25), 70.9 (C31), 70.8 (C23), 69.5 (C8), 67.2 (C3), 66.9 (C39), 45.7 (C16), 42.7 (C18), 42.7 (C22), 42.3 (C7), 42.1 (C26), 41.6 (C5), 39.5 (C20), 39.5 (C14), 39.3 (C38), 39.3 (C40), 38.8 (C12), 38.1 (C10), 37.5 (C32), 36.9 (C24), 34.0 (C4), 32.0 (C46), 30.0 (C44), 29.9 (C43), 29.8 (C42), 29.5 (C45), 27.8 (C6), 26.0 (C41), 22.9 (C47), 21.6 (C50), 18.6 (C49), 14.2 (C48), 13.2 (C52), 11.6 (C54), 8.3 (C51), 6.4 (C53), 6.1 (C55); HRMS (ESI-TOF) m/z calcd for C54H105D3NaO22 [M+Na]+: 1134.7413, found: 1134.7407. Stereochemical Proof by Mosher’s Ester Analysis Homoallylic alcohol 64 27 OBn OH 31 O Me O Me 64 H C(CH3)2 C27-H2 C28-H C29-H C30-H PhCH2O PhCH2O C32-H C33-H C34-H δS (ppm) 1.42 1.34 3.69 3.58 4.29 3.42 3.63 4.59 4.53 4.68 4.65 2.57 2.24 5.62 5.00 4.97 OBn δR (ppm) 1.39 1.30 3.59 3.53 4.11 3.29 3.60 4.59 4.51 4.48 4.45 2.61 2.37 5.71 5.07 5.01 Δδ = δS – δR +0.03 +0.04 +0.10 +0.05 +0.18 +0.13 +0.03 0.00 +0.02 +0.20 +0.20 –0.04 –0.13 –0.09 –0.07 –0.04 L2 L3     129 Chapter 4 Synthesis of Aflastatin A I. Installation of the Tetramic Acid Our asymmetric syntheses of the aflastatin A (AsA) C3–C48 degradation fragments allowed us to confirm the stereochemical revision of AsA. Having achieved this objective, we finally turned our attention to the synthesis of the natural product itself. Unlike its C3–C48 degradation fragments, AsA is capped by a D-alanine-based tetramic acid moiety. 1 We therefore focused on developing a method for its installation. Our first retrosynthesis plan for AsA (1) involved disconnection at C2–C3 to produce tetramic acid derivative 2 and C3–C48 aldehyde fragment 3 (Scheme 4.1).2 We planned to install the tetramic acid by Wittig or Horner-Wadsworth-Emmons reaction as late in the synthesis as possible because we expected the C5’ stereocenter to be readily epimerizable.1b (1) (2) For reviews of tetramic acid natural products, see: (a) Schobert, R.; Schlenk, A. Bioorg. Med. Chem. 2008, 16, 4203–4221; (b) Royles, B.J.L. Chem. Rev. 1995, 95, 1981–2001. Young, J.M. Studies Toward the Synthesis of Aflastatin A. Ph.D. Thesis, Harvard University, 2008. 130 Scheme 4.1. Retrosynthesis plan for aflastatin A (1). OH O Me N Me 2' OH 2 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 35 OH OH 39 O Me Me Me OH Me Me Me 1 Me Me OH OH H O OH C9H19 olefination O O 2' OR OR OR OR OR 7 11 15 Me N Me 5' OH O 2 P OEt OEt Me O C9H19 H 3 Me 19 Me OR O 39 Me OR Me Me Me RO 23 Me OR OR OR OR OR OR OR OR 35 31 27 2 OR OR OR OR 3 Precedent for this transformation was borne out of the syntheses of streptolydigin and the tirandamycins by the laboratories of Boeckman, 3 DeShong, 4 and Schlessinger. 5 In a separate yet closely related example, Rosen and coworkers made disubstituted (E) alkene 6 by addition of the potassium dianion of chiral tetramic acid phosphonate 4 to unsaturated aldehyde 5 (eq 1).6 Fortunately, additions to aliphatic aldehydes under the same conditions were also known.5a However, the reaction of 2-methylated phosphonates such as 2 to produce trisubstituted (E) alkenes warranted investigation, so we embarked upon its synthesis. O 2' Me N Me 5' OH O P OEt 2 OEt O 4 O H Me 5 t-BuOK (2.1 equiv.) THF, 0 °C O 2' OH 2 3 Me N Me (1) Me 6 5' O (3) (a) Boeckman, R.K., Jr.; Thomas, A.J. J. Org. Chem. 1982, 47, 2823–2824; (b) Boeckman, R.K., Jr.; Starrett, J.E., Jr.; Nickell, D.G.; Sum, P.-E. J. Am. Chem. Soc. 1986, 108, 5549–5559; (c) Boeckman, R.K., Jr.; Potenza, J.C.; Enholm, E.J. J. Org. Chem. 1987, 52, 469–472. (a) DeShong, P.; Ramesh, S.; Elango, V.; Perez, J.J. J. Am. Chem. Soc. 1985, 107, 5219–5224; (b) Shimshock, S.J.; Waltermire, R.E.; DeShong, P. J. Am. Chem. Soc. 1991, 113, 8791–8796. (a) Schlessinger, R.H.; Bebernitz, G.R. J. Org. Chem. 1985, 50, 1344–1346; (b) Schlessinger, R.H.; Bebernitz, G.R.; Lin, P. J. Am. Chem. Soc. 1985, 107, 1777–1778; (c) Schlessinger, R.H.; Graves, D.D. Tetrahedron Lett. 1987, 28, 4385–4388. Rosen, T.; Fernandes, P.B.; Marovich, M.A.; Shen, L.; Mao, J.; Pernet, A.G. J. Med. Chem. 1989, 32, 1062–1069. (4) (5) (6) 131 The synthesis of tetramic acid phosphonate 27 began with the preparation of N-methylD-alanine ethyl ester (9) in five steps from D-alanine (Scheme 4.2).8 Reductive opening of oxazolidinone 7 9 was followed by ethylation of the nascent carboxylate to produce Nmethylated alanine derivative 8. Deprotection provided N-methyl amino ester 9 as a dilute solution in dichloromethane for immediate use since it was prone to self-dimerization. Scheme 4.2. Synthesis of N-methyl-D-alanine ethyl ester (9). Me O O D-Ala Me a,b O 5' Me c,d 42% EtO O 8 5' Me Cbz e EtO O 9 5' 5' NH3 94% N Cbz 7 O N Me NH Me Reagents and conditions: (a) CbzCl, Na2CO3, dioxane, H2O, 0 °C to rt; (b) HO(CH2O)nH, CSA, PhMe, 90 °C, 94% (2 steps); (c) Et3SiH, TFA, CH2Cl2, 84%; (d) EtI, K2CO3, DMF, rt to 50 °C, 51%; (e) H2, Pd/C, CH2Cl2, rt. The synthesis of tetramic acid phosphonate 2 was then completed in five steps from 2,2,6-trimethyl-4H-1,3-dioxin-4-one (10) (Scheme 4.3).2,8 Methylation, phosphination, and oxidative workup provided phosphonate 1110 in moderate overall yield. Cycloelimination of dioxinone 11 and capture of ethanethiol by the resultant acylketene intermediate11 afforded βketothioester 1212 in excellent yield. Amide bond formation13 and modified Lacey-Dieckmann cyclization14 of β-ketoamide 13 produced tetramic acid phosphonate 2 in good overall yield. (7) (8) (9) The syntheses of tetramic acid phosphonate 2 and model tetramic acid 15 (vide infra) were performed as a collaboration between Dr. Joseph M. Young and David A. Thaisrivongs. Thaisrivongs, D.A. Synthesis of the C5'–C2 and C36–C48 Subunits of Aflastatin A. A.B. Thesis, Harvard University, 2007. Aurelio, L.; Box, J.S.; Brownlee, R.T.C.; Hughes, A.B.; Sleebs, M.M. J. Org. Chem. 2003, 68, 2652–2667. (10) (a) Boeckman, R.K., Jr.; Kamenecka, T.M.; Nelson, S.G.; Pruitt, J.R.; Barta, T.E. Tetrahedron Lett. 1991, 32, 2581–2584; (b) Boeckman, R.K., Jr.; Barta, T.E.; Nelson, S.G. Tetrahedron Lett. 1991, 32, 4091–4094; (c) Roush, W.R.; Brown, B.B. J. Org. Chem. 1993, 58, 2162–2172. (11) (a) Clemens, R.J.; Hyatt, J.A. J. Org. Chem. 1985, 50, 2431–2435; (b) Sakaki, J.; Kobayashi, S.; Sato, M.; Kaneko, C. Chem. Pharm. Bull. 1990, 38, 2262–2264. (12) (a) Hayashi, Y.; Narasaka, K. Chem. Lett. 1998, 313–314; (b) Hayashi, Y.; Kanayama, J.; Yamaguchi, J.; Shoji, M. J. Org. Chem. 2002, 67, 9443–9448. (13) Kim, H.-O.; Olsen, R.K.; Choi, O.-S. J. Org. Chem. 1987, 52, 4531–4536. (14) (a) Lacey, R.N.; J. Chem. Soc. 1954, 850–854; (b) Bloomer, J.L.; Kappler, F.E. J. Chem. Soc., Perkin Trans. I 1976, 1485–1491. 132 Scheme 4.3. Synthesis of tetramic acid phosphonate 2. Me Me O O 10 Me EtO O 9 d 5' Me Me a,b Me 35% O 11 Me 12 84% EtO O 5' O 1 O O 1 O P OEt OEt Me c 95% EtS O O 1 12 O P OEt OEt Me O O 1 NH Me N Me 13 O P OEt OEt Me e 98% O 3' Me N Me 4' OH O 2 P OEt OEt Me O 2 Reagents and conditions: (a) LDA, MeI, THF, –78 °C to 0 °C, 60%; (b) LiHMDS, (EtO)2PCl, rt; aq H2O2, PhH, 0 °C, 59%; (c) EtSH, PhMe, 111 °C, 95%; (d) CuI, Et3N, CH2Cl2, rt, 84% (2 steps from 8); (e) Cs2CO3, THF, rt, 98%. Our attempted addition of the potassium dianion of chiral tetramic acid phosphonate 2 to piperonal (14) resulted in decomposition (eq 2).2,8 Several other bases were then screened (NaH/nBuLi, LDA, and Ba(OH)2), but resulted in little to no reactivity, even at elevated temperatures. We attributed the lack of reactivity to the reduced kinetic acidity of phosphonate 2. Deprotonation of the H2 proton is attenuated by minimization of allylic strain between the C2 stereocenter and tetramic acid ring. O 2' Me N Me 5' OH O 2 P OEt OEt Me O 2 O H 3 O O 14 t-BuOK, NaH/nBuLi, LDA, or Ba(OH)2 no reactivity or decomposition O 2' OH 2 3 Me N Me O (2) O 5' O Me 15 Although desirable, one-step installation of the tetramic acid was infeasible. As an alternative, Ley and coworkers reported a reliable three-step procedure for installing tetramic acids via olefination, amide bond formation, and cyclization.15 Accordingly, addition of the sodium dianion of thioester phosphonate 12 to piperonal (14) produced the desired trisubstituted (E)-alkene 16 in very good yield and excellent E:Z selectivity (Scheme 4.4). (15) (a) Ley, S.V.; Smith, S.C.; Woodward, P.R. Tetrahedron Lett. 1988, 29, 5829–5832; (b) Ley, S.V.; Smith, S.C.; Woodward, P.R. Tetrahedron 1992, 48, 1145–1174; (c) Burke, L.T.; Dixon, D.J.; Ley, S.V.; Rodríguez, F. Org. Lett. 2000, 2, 3611–3613. 133 Addition13 of amine 9 to thioester 16 was followed by modified Lacey-Dieckmann cyclization15b of β-ketoamide 17 to complete the synthesis of model tetramic acid 157 in good overall yield. Scheme 4.4. Synthesis of model tetramic acid 15. O EtS O 1 O P OEt OEt Me a 83% E : Z > 99:01 EtS O O 2 3 Me O O EtO O 9 O 3' 5' b 81% Me 16 NH Me 12 Me EtO O 5' O O 1 OH 4' N Me O Me O c 83% 3 Me N Me O O Me 15 O 17 Reagents and conditions: (a) piperonal (14), NaH, THF, 0 °C to rt, 83%, E : Z > 99:01; (b) CuI, Et3N, CH2Cl2, rt, 81%; (c) nBu4NF, THF, rt, 83%. We then attempted to subject more elaborate model aldehydes 18 and 1916 to this reaction sequence. 17 Unfortunately, addition of various metal dianions of thioester phosphonate 12 to these aldehydes resulted in epimerization of the C4 methyl stereocenter (eq 3). Throughout our screen of strong bases, aldehyde epimerization was accompanied by variable levels of conversion and E:Z selectivity. Although mild deprotonation of phosphonate 12 by Ba(OH)218 curtailed epimerization, we only observed trace amounts of desired product. From these experiments we determined that phosphonates requiring double deprotonation for reactivity were incompatible with aldehydes bearing epimerizable αstereocenters, and therefore would not be appropriate for our synthesis of AsA. (16) Precursors to model aldehydes 18 and 19 were previously synthesized by Dr. Joseph M. Young. See: Ref. 2. (17) Application of the Ley protocol to model aldehydes 18 and 19 was attempted by the author in collaboration with Dr. Egmont Kattnig. (18) (a) Alvarez Ibarra, C.; Arias, S.; Fernández, M.J.; Sinisterra, J.V. J. Chem. Soc., Perkin Trans. II 1989, 503–508; (b) Paterson, I.; Yeung, K.-S.; Smaill, J.B. Synlett 1993, 774–776. 134 O EtS O 1 O P OEt OEt Me O H 4 7 R NaH, NaH/nBuLi, KHMDS, LiHMDS, Ba(OH)2, LDA/HMPA no reactivity or epimerization O 2' OH 2 3 4 7 Me Me Me N Me R 5' 12 aldehydes: O H 3 7 18 or 19 Me Me TESO O 11 O Me Me Me Me Me (3) 20 or 21 O 15 O OR H 3 7 RO O 11 O O 15 Me Me OR Me 18, R = TBS Me Me Me Me OR Me Me Me OMe N Me 19, R = TBS Ultimately, we found recourse in a three-step procedure developed by Boeckman, Jones and their respective coworkers.19 Although the overall transformations are similar to Ley's protocol15 (Scheme 4.5), olefination occurs under milder conditions and requires single deprotonation of dioxenone phosphonate 11.10b,20 Subsequently, amide formation occurs not by addition of an amine to a thioester, but rather by cycloelimination of dioxinone 24 and capture of amine 9 by the resultant acylketene intermediate to produce common β-ketoamide 23.21 Both strategies then generate the highly polar and readily epimerizable tetramic acid 25 in a final cyclization step. Scheme 4.5. Ley and Boeckman procedures for tetramic acid installation. O Ley: EtS 12 Me Me O Boeckman: O 11 O 1 O 1 O P OEt OEt Me base (2 equiv.); RCHO olefination base (1 equiv.); RCHO O EtS O O 2 3 amine 9, CuI R Me EtO O 5' O O 1 Me 22 Me Me amide formation amine 9, heat R Me 24 N Me R Me 23 cyclization O 3' OH 4' O P OEt OEt Me O O 2 3 3 Me N Me R O 25 Me (19) (a) Boeckman, R.K., Jr.; Weidner, C.H.; Perni, R.B.; Napier, J.J. J. Am. Chem. Soc. 1989, 111, 8036–8037; (b) Jones, R.C.F.; Tankard, M. J. Chem. Soc., Perkin Trans. I 1991, 240–241. (20) (a) Boeckman, R.K., Jr.; Shao, P.; Wrobleski, S.T.; Boehmler, D.J.; Heintzelman, G.R.; Barbosa, A.J. J. Am. Chem. Soc. 2006, 128, 10572–10588; (b) Yoshinari, T.; Ohmori, K.; Schrems, M.G.; Pfaltz, A.; Suzuki, K. Angew. Chem., Int. Ed. 2010, 49, 881–885. (21) Sato, M.; Ogasawara, H.; Komatsu, S.; Kato, T. Chem. Pharm. Bull. 1984, 32, 3848–3856. 135 For the cycloelimination step, Jones and Tankard demonstrated that the reactant amino esters could be generated in situ from their corresponding hydrochloride salts.19b As such, we took this opportunity to synthesize a more stable form of amino ester 9, namely its hydrochloride salt 9•HCl, 22 in three steps from N-Cbz-D-alanine (26) (Scheme 4.6). Methylation,23 ethyl ester formation,8 and reductive removal of the Cbz protecting group under anhydrous acidic conditions produced the hydrochloride salt of N-methyl-D-alanine ethyl ester (9•HCl) in excellent overall yield. Scheme 4.6. Synthesis of N-Me-D-Ala-OEt•HCl (9•HCl). Me HO O 26 a 5' Me HO O 27 5' Me Cbz b 91% EtO O 28 5' Me Cbz c quant. EtO O 5' Cl NHCbz 91%, Ref. 23 N Me N Me NH2 Me 9•HCl Reagents and conditions: (a) MeI, NaH, THF, 0 °C to rt, 91%, Ref. 23a; (b) EtI, K2CO3, DMF, 0 °C to rt, 91%; (e) H2, Pd/C, AcCl, EtOH, rt, quant. With both dioxinone phosphonate 11 (Scheme 4.3) and ammonium salt 9•HCl in hand, we applied Boeckman's protocol19 to the synthesis of model tetramic acid 32 (Scheme 4.7).24 Addition of the lithium anion of phosphonate 11 to model aldehyde 19 in the presence of HMPA10b,20 produced trisubstituted (E)-alkene 29 as a single isomer in excellent yield and without epimerization of the C4 methyl stereocenter. Next, cycloelimination19b of dioxinone 29 in the presence of ammonium salt 9•HCl and molecular sieves (and the absence of exogenous base) led to the formation of β-ketoamide 30 in very good yield. Then, LaceyDieckmann cyclization14 was induced by potassium trimethylsilanolate, rather than potassium (22) The synthesis of the corresponding methyl ester was achieved by Dr. Egmont Kattnig. The synthesis of ammonium salt 9•HCl represents the culminative work of David A. Thaisrivongs, Dr. Peter H. Fuller, and the author. (23) (a) Trouche, N.; Wieckowski, S.; Sun, W.; Chaloin, O.; Hoebeke, J.; Fournel, S.; Guichard, G. J. Am. Chem. Soc. 2007, 129, 13480–13492; (b) Stodulski, M.; Mlynarski, J. Tetrahedron: Asymmetry 2008, 19, 970–975. (24) The synthesis of tetramic acid 31 was first performed by Dr. Egmont Kattnig, and then modified by Dr. Peter H. Fuller. The synthesis of tetramate salt 32•Et2NH was performed in collaboration with Dr. Fuller. 136 tert-butoxide,14b to cleanly produce tetramic acid 31 in good yield. As before, removal of the acetonide and silyl protecting groups was achieved with hexafluorosilicic acid,25 proceeded with concomitant lactonization, and ultimately furnished model 3-acyltetramic acid 32. Importantly, both the cyclization and deprotection steps proceeded without appreciable epimerization of the C5' stereocenter. Scheme 4.7. Synthesis of model tetramic acid 32. 11 O H 3 7 Me Me RO O 11 Me Me O 15 Me Me 3 2 7 11 15 O Me Me OR Me Me Me N Me OMe a O 95% E : Z > 95:05 O O RO O O O OMe N Me Me Me Me OR Me Me Me 19, R = TBS 29, R = TBS Me Me Me EtO O 5' Cl 29 b 82% Me EtO O Me Me 5' O O 1 3 7 RO O 11 O O 15 NH2 Me N Me Me Me Me OR Me Me Me OMe N Me c 79% 9•HCl O 3' 30, R = TBS OH RO 7 3 O 11 O O 15 Me N Me 4' O Me Me Me OR Me Me Me N Me OMe O d O 2' OH 1 2 3 7 OH O 11 15 Me Me 32, R = TBS Me N 5' Me O Me Me e Me 32 OH Me Me 32•Et2NH Reagents and conditions: (a) phosphonate 11, LDA, THF, –78 °C to 0 °C; HMPA, –78 °C; aldehyde 19, –78 °C to rt, 95%, E:Z > 95:05; (b) 4 Å MS, PhMe, 110 °C, 82%; (c) KOTMS, TMSOH, THF, 0 °C, 79%; (d) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt; (e) Et2NH, MeOH, rt. After completing the synthesis of model tetramic acid 32, we compared its NMR spectroscopic data to that reported by the isolation group for AsA.26 Acknowledging the obvious stereochemical and structural differences in the C8–C9 diol and C10–C15 (25) (a) Pilcher, A.S.; Hill, D.K.; Shimshock, S.J.; Waltermire, R.E.; DeShong, P. J. Org. Chem. 1992, 57, 2492–2495; (b) Pilcher, A.S.; Shimshock, S.J. J. Org. Chem. 1993, 58, 5130–5134. (26) (a) Sakuda, S.; Ono, M.; Furihata, K.; Nakayama, J.; Suzuki, A.; Isogai, A. J. Am. Chem. Soc. 1996, 118, 7855–7856; (b) Ono, M.; Sakuda, S.; Suzuki, A.; Isogai, A. J. Antibiotics 1997, 50, 111–118; (c) Ono, M.; Suzuki, A.; Isogai, A.; Sakuda, S. Production Aflastatin A from Streptomyces sp., A Pharmaceutical Composition and Methods of Use. U.S. Patent 5,773,263, June 30, 1998. 137 polypropionate regions, respectively, we were still disappointed by the general disagreement of data sets in the seemingly removed N1'–C6'/C1–C3 enoyltetramate region. Additionally, we observed significant line broadening of resonances in the carbon NMR spectrum of model tetramic acid 32 due to rotameric and tautomeric equilibria.27 At this point in time we realized that the isolation group purified AsA under basic conditions, and reported spectral data corresponding not to the free tetramic acid but its corresponding diethylamine salt.26b,c Unfortunately, conversion of model tetramic acid 32 to diethylammonium tetramate 32•Et2NH did not completely resolve chemical shift discrepancies in the C1–C3 enoyl region. To resolve this issue, we undertook the synthesis of AsA tetramic acid degradation fragment 38 (Scheme 4.8).28 Parikh-Doering oxidation29 of C3 carbinol 3330 and reaction10b,20 of resultant aldehyde 34 with dioxinone phosphonate 11 provided trisubstituted (E)-alkene 35 as a single isomer in good yield over two steps. Cycloelimination19b of dioxinone 35 in the presence of ammonium salt 9•HCl led to the formation of β-ketoamide 36 in excellent yield. Modified Lacey-Dieckmann cyclization14 was followed by silyl group removal25 to furnish degradation fragment 38. The free tetramic acid was then converted to its corresponding diethylamine salt 38•Et2NH. Comparison of our NMR spectroscopic data for diethylammonium tetramate 38•Et2NH to that reported by the isolation group for the naturally derived tetramic acid (27) (a) Yamaguchi, T.; Saito, K.; Tsujimoto, T.; Yuki, H. Bull. Chem. Soc. Jpn. 1976, 49, 1161–1162; (b) Saito, K.; Yamaguchi, T. Bull. Chem. Soc. Jpn. 1978, 51, 651–652; (c) Saito, K.; Yamaguchi, T. J. Chem. Soc., Perkin Trans. II 1979, 1605–1609; (d) Steyn, P.S.; Wessels, P.L. Tetrahedron Lett. 1978, 19, 4707–4710; (d) Nolte, M.J.; Steyn, P.S.; Wessels, P.L. J. Chem. Soc., Perkin Trans. I 1980, 1057–1065; (e) Steyn, P.S.; Wessels, P.L. S. Afr. J. Chem. 1980, 33, 120; (f) Jeong, Y.-C.; Moloney, M.G. J. Org. Chem. 2011, 76, 1342–1354 and references therein. (28) The synthesis of degradation fragment 38•Et2NH was performed by the author. (29) Parikh, J.R.; Doering, W.v.E. J. Am. Chem. Soc. 1967, 89, 5505–5507. (30) A precursor to carbinol 33 was previously synthesized by Dr. Joseph M. Young. See: Ch. 2. 138 degradation fragment 3826a,b revealed a spectroscopic match save those resonances corresponding to the diethylammonium cation. Since naturally derived degradation fragment 38 was also purified under basic conditions, we concluded that the data tabulated by the isolation group for naturally derived AsA tetramic acid degradation fragment 38 should in fact be attributed to its derivative diethylammonium tetramate salt 38•Et2NH. Scheme 4.8. Synthesis of degradation fragments 38 and 38•Et2NH. Me Me O HO 3 7 O 7 O 2 OR a H 3 OR 11 b O 74%, 2 steps 3 7 OR Me Me Me Me Me Me Me 33, R = TBDPS Me EtO O 5' 34, R = TBDPS Me EtO O 5' 35, R = TBDPS O O 1 5 Cl 35 c 97% NH2 Me N Me 36 OTBDPS Me d Me Me 9•HCl O 3' OH 4' 3 7 OR f O 2' O Et2NH2 3 7 OH Me N Me O Me e Me Me Me N Me 5' O Me Me Me 37, R = TBDPS 38, R = H 38•Et2NH Reagents and conditions: (a) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C; (b) phosphonate 11, LDA, THF, –78 °C to 0 °C; HMPA, –78 °C; aldehyde 34, –78 °C to rt, E:Z > 95:05. 74% (2 steps); (c) 4 Å MS, PhMe, 110 °C, 97%; (d) KOTMS, TMSOH, THF, 0 °C; (e) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt; (f) Et2NH, MeOH, rt. In the end, our synthesis of tetramate 38•Et2NH and its spectroscopic match to naturally derived tetramic acid degradation fragment 38 confirmed the absolute stereochemical assignment of the C5' stereocenter.31 When taken together with our syntheses of the AsA C3–C48 degradation fragments, we confirmed both the revised stereochemical assignment and full absolute configuration of AsA.32 (31) Ikeda, H.; Matsumori, N.; Ono, M.; Suzuki, A.; Isogai, A.; Nagasawa, H.; Sakuda, S. J. Org. Chem. 2000, 65, 438–444. (32) Sakuda, S.; Matsumori, N.; Furihata, K.; Nagasawa, H. Tetrahedron Lett. 2007, 48, 2527–2531. 139 II. Revised Synthesis of the C27–C48 Aldehyde Having found a suitable method for installing the tetramic acid moiety, we embarked upon the synthesis of AsA (1) and its diethylamine salt. Our final retrosynthesis plan33 for AsA (1) involved disconnections at C2–C3 and C3'–C4' to produce C3–C48 aldehyde 39, as well as two tetramic acid precursors: the hydrochloride salt of N-methyl-D-alanine ethyl ester (9•HCl), and dioxinone phosphonate 11 (Scheme 4.9). In turn, we envisioned aldehyde 39 to arise from the diastereoselective aldol addition of C3–C26 ketone 40 to C27–C48 aldehyde 41.33 We took this opportunity to revise the original synthesis of C27–C48 aldehyde 41 in order to reduce the number of protecting group manipulation steps.34 Scheme 4.9. Retrosynthesis plan for aflastatin A (1). OH O 3' OH 2 4' 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 35 OH OH 39 Me N Me O Me Me Me OH Me Me Me 1 Me Me OH OH H O OH C9H19 tetramic acid installation Me EtO O 5' O H 3 7 OR OR OR OR OR 11 15 Cl O Me Me O O 1 Me 19 NH2 Me 9•HCl 11 O P OEt OEt Me C9H19 Me OR O 39 Me OR Me Me Me RO 23 Me OR OR OR OR OR OR OR OR 35 31 27 26 OR OR OR OR 39 chelate-controlled aldol addition Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' O 23 O Me OBn OBn O 31 OR" O 35 OTBS 39 Me Me OR Me Me Me Me Me H 27 TBSO BnO C9H19 Me O Me OR" 41, R" = TES 40, R = TBS, R' = TIPS Our synthesis of C27–C48 aldehyde 41 began with the preparation of C27–C31 (33) Kattnig, E. An Aldol Approach Toward Aflastatin A – Synthesis of the C3–C48 Polyol. Postdoctoral Report, Harvard University, 2011. (34) The revised synthesis of C27–C48 aldehyde 41 was performed by the author. 140 aldehyde 46 from dibenzylglucopyranoside 4235 in five steps (Scheme 4.10). Iodination36 and silylation produced pyranoside 43 in excellent overall yield. Zinc-mediated fragmentation37 and in situ reduction produced enol 44, which in turn was silylated and oxidatively cleaved, ultimately furnishing C27–C31 aldehyde 45 in 86% overall yield. Scheme 4.10. Synthesis of C27–C31 aldehyde 45. H HO 31 O 27 OMe OH H a,b 97% I 31 O 27 OMe OTBS c 88% BnO 31 d,e 92% BnO TESO 27 TBSO BnO 45 O 31 BnO OBn 42 BnO OBn 43 HO 27 TBSO BnO 44 H Reagents and conditions: (a) PPh3, I2, imidazole, PhMe, MeCN, rt, 97%; (b) TBSCl, imidazole, CH2Cl2, 0 °C to rt, quant.; (c) Zn, THF, H2O, ))), 45 °C; NaBH4, 0 °C, 88%; (d) TESCl, imidazole, CH2Cl2, 0 °C to rt, 98%; (e) O3, py, CH2Cl2, MeOH, –78 °C; PPh3, –78 °C to rt, 94%. Our synthesis of C27–C48 aldehyde 41 continued with the stereoselective allylation of syn α,β-bisalkoxy aldehyde 45 (Scheme 4.11). Although both α- and β-oxygen substituents were available for chelation,38 the rate of reaction of allylmagnesium bromide with the fivemembered chelate39 was significantly faster, 40 producing homoallylic alcohol 46 in 95% yield as a single diastereomer (d.r. ≥ 95:05). Acryloylation41 of the nascent C31 carbinol, and ring- (35) Français, A.; Urban, D.; Beau, J.-M. Angew. Chem., Int. Ed. 2007, 46, 8662–8665. (36) (a) Garegg, P.J.; Samuellson, B. J. Chem. Soc., Perkin Trans. I. 1980, 2866–2869; (b) Garegg, P.J.; Johansson, R.; Ortega, C.; Samuellson, B. J. Chem. Soc., Perkin Trans. I. 1982, 681–683. (37) Skaanderup, P.R.; Hyldtoft, L.; Madsen, R. Monatsh. Chem. 2002, 133, 467–472. (38) The possibility of bicyclic chelates involving the aldehyde carbonyl and both oxygen substituents cannot be ruled out. See: (a) Charette, A.B.; Mellon C.; Rouillard, L.; Malenfant, E. Pure Appl. Chem. 1992, 64, 1925–1931; (b) Charette, A.B.; Mellon C.; Rouillard, L.; Malenfant, E. Synlett 1993, 81–82. (39) (a) Cram, D.J.; Abd Elhafez, F.A. J. Am. Chem. Soc. 1952, 74, 5828–5835; (b) Cram, D.J.; Kopecky, K.R. J. Am. Chem. Soc. 1959, 81, 2748–2755; (c) Cram, D.J.; Leitereg, T.H. J. Am. Chem. Soc. 1968, 90, 4019– 4026. (40) For examples that suggest five-membered magnesium chelates react much faster than six-membered chelates, see: (a) Frye, S.V.; Eliel, E.L.; Cloux, R. J. Am. Chem. Soc. 1987, 109, 1862–1863; (b) Williams, D.R.; Klingler, F.D. Tetrahedron Lett. 1987, 28, 869–872; (c) Keck, G.E.; Andrus, M.B.; Romer, D.R. J. Org. Chem. 1991, 56, 417–420; (d) Burgess, K.; Chaplin, D.A. Tetrahedron Lett. 1992, 33, 6077–6080. (41) Tanaka, A.; Suzuki, H.; Yamashita, K. Agric. Biol. Chem. 1989, 53, 2253–2256. 141 closing metathesis42 of the intermediate diene then furnished unsaturated lactone 47. Scheme 4.11. Synthesis of C27–C35 aldehyde 52. BnO TESO 27 TBSO BnO 45 O OBn O TESO 27 TBSO BnO O OBn O MOPO 27 TBSO BnO 49 OBn OBn O MOPO 27 TBSO BnO 51 31 35 31 35 31 34 O 31 a H 92%, dr ≥ 95:05 OBn OH 32 b,c 68% TESO 27 TBSO BnO 46 31 O d dr ≥ 95:05 OBn O HO 27 TBSO BnO 31 34 OH OH e 65%, 2 steps 33 33 47 O O 48 OBn OH O MOPO 27 TBSO BnO 50 i,j OTBDPS 87% OBn OBn O MOPO 27 TBSO BnO 52 31 31 35 Me Me f 91% g,h OH 85% Me O Me O 35 H Me O Me Me O Me Reagents and conditions: (a) MgBr2•OEt2, allylMgBr, CH2Cl2, Et2O, PhMe, –78 °C, 92%, dr ≥ 95:05; (b) acrylic pivalic anhydride, EtN(iPr)2, DMAP, THF, PhH, rt, 98%; (c) (Ph3P)2Cl2Ru=CHPh, PhH, 65 °C, 69%; (d) RuCl3, CeCl3•7H2O, NaIO4, EtOAc, MeCN, H2O, 0 °C, dr ≥ 95:05; (e) Me2C(OMe)2, PPTS, acetone, 35 °C, 65% (2 steps); (f) LiBH4, H2O, THF, 0 °C to rt, 91%; (g) TBDPSCl, imidazole, DMF, 0 °C, 92%; (h) BnBr, NaH, nBu4NI, DMF, –20 °C to –5 °C, 92%; (i) nBu4NF, AcOH, THF, rt, 93%; (j) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C, 94%. Stereoselective dihydroxylation 43 , 44 proceeded with concomitant removal of the primary TES ether to give triol 48 as a single diastereomer. Acetonide formation and protection of the C27 carbinol as its 2-methoxy-2-propyl (MOP) ether45 produced lactone 49 in good yield over two steps. Reduction to diol 50, selective protection of the primary carbinol, (42) Schwab, P.; France, M.B.; Ziller, J.W.; Grubbs, R.H. Angew. Chem. 1995, 107, 2179–2181; Angew. Chem., Int. Ed. 1995, 34, 2039–2041. (43) (a) Plietker, B.; Niggemann, M. J. Org. Chem. 2005, 70, 2402–2405; (b) Plietker, B. Synthesis 2005, 2453– 2472. (44) For examples of the diastereoselective dihydroxylation of related α,β-unsaturated δ-lactones using Upjohn conditions (OsO4, NMO), see: (a) Ghosh, A.K.; Kim, J.-H. Tetrahedron Lett. 2003, 44, 3967–3969; (b) Ramachandran, P.V.; Prabhudas, B.; Chandra, J.S.; Reddy, M.V.R. J. Org. Chem. 2004, 69, 6294–6304; (c) Bhaket, P.; Stauffer, C.S.; Datta, A. J. Org. Chem. 2004, 69, 8594–8601. (45) For one of the earliest examples of using a 2-methoxy-2-propyl (MOP) ether as a carbinol protecting group, see: Kluge, A.F.; Untch, K.G.; Fried, J.H. J. Am. Chem. Soc. 1972, 94, 7827–7832. 142 and benzylation yielded disilyl ether 51. Selective removal of the TBDPS ether and oxidation29 of the resultant carbinol ultimately provided C27–C35 aldehyde 52 in 10 steps and 32% overall yield from aldehyde 45. With a more efficient route to aldehyde 52 in hand, the synthesis of the C27–C48 fragment 41 was nearly complete. Addition46 of the corresponding (E) enolate of ketone 53 to aldehyde 52 produced the desired anti-Felkin product 54 in moderate yield and good diastereoselection (Scheme 4.12). Silylation of the C35 carbinol and selective cleavage of the primary MOP ether were then accomplished in one pot. Oxidation29 of the resultant C27 carbinol completed the synthesis of C27–C48 aldehyde 41 in good overall yield and 21 linear steps from methyl α-D-(+)-glucopyranoside. Scheme 4.12. Synthesis of C27–C48 aldehyde 41. OBn OBn O MOPO 27 TBSO BnO 52 OBn OBn O MOPO 27 TBSO BnO 31 31 O 35 O H OTES OTBS 39 a 57%, dr = 85:15 C9H19 53 Me O Me OH O 36 35 OTBS b,c 39 O 79% OBn OBn O 31 OR O 35 OTBS 39 C9H19 Me O Me OTES 54 H 27 TBSO BnO C9H19 Me O Me OR 41, R = TES Reagents and conditions: (a) ketone 53, Cy2BCl, Me2NEt, pentane, 0 °C to rt; aldehyde 52, Et2O, –78 °C to – 25 °C, dr = 85:15, 57%; (b) TESOTf, 2,6-lutidine, CH2Cl2, 0 °C; aq H2SO4, 83%; (c) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C, 95%. III. Completion of the Synthesis of Aflastatin A47 Having completed the syntheses of both the C3–C26 and C27–C48 fragments, we ventured forward with the synthesis of C3–C48 aldehyde 58 (Scheme 4.13). Satisfyingly, chelate-controlled addition of ketone 40 to aldehyde 41 under our soft enolization conditions33 (46) (a) Glorius, F. Development of α-Oxygenated Aldol Methodology and Progress Towards the Synthesis of Aflastatin A. Postdoctoral Report, Harvard University, 2001; (b) Evans, D.A.; Glorius, F.; Burch, J.D. Org. Lett. 2005, 7, 3331–3335. (47) The synthesis of AsA 1 and its diethylamine salt 1•Et2NH was performed by the author. 143 delivered the desired β-hydroxy ketone with excellent diastereoselection. We immediately reduced the aldol adduct48 under Prasad's conditions49, to afford 1,3-syn diol 55 as a single diastereomer in good overall yield. Both steps were completely chemoselective and eliminated the need to mask the C37 carbonyl. Scheme 4.13. Synthesis of C3–C48 aldehydes 58. Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' O 23 O Me OBn OBn O 31 OR" O 35 OTBS 39 Me Me OR Me Me Me Me Me a,b H 27 TBSO BnO 70%, dr = 95:05 C9H19 Me O Me OR" 41, R" = TES 40, R = TBS, R' = TIPS Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' OH OH OBn OBn O 26 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me c RO BnO 93% Me O Me OR" 55, R = TBS, R' = TIPS, R" = TES Me Me OR'" O HO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' OR'" OR'" OH OR'" O 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me f RO R'"O Me O Me d,e OR" 56, R'" = H 57, R'" = TMS OR" O 35 R = TBS, R' = TIPS, R" = TES Me Me O H 3 7 87% Me Me O 15 Me Me O 19 OR'" O 11 O O O OR' OR'" OR'" OH OR'" O 23 27 31 OR 39 C9H19 Me Me OR Me Me Me Me Me RO R'"O Me O Me OR" 58, R = TBS, R' = TIPS, R" = TES, R'" = TMS Reagents and conditions: (a) MgBr2•OEt2, PMP, CH2Cl2, –5 °C, d.r. = 95:05; (b) Et2BOMe, NaBH4, THF, MeOH, –78 °C to –55 °C; aq H2O2, aq NaOH, MeOH, 0 °C, dr ≥ 95:05, 70% (2 steps); (c) H2, Pd black, THF, dioxane, H2O, rt, 93%; (d) TMSCl, py, CH2Cl2, 0 °C to rt; (e) PPTS, CH2Cl2, iPrOH, 0 °C; Et3N, 87% (2 steps); (f) SO3•Py, EtN(iPr)2, DMSO, CH2Cl2, –30 °C to –20 °C. Our synthesis of C3–C48 aldehyde 58 continued with the hydrogenolysis of pentabenzyl ether 55 to produce heptaol 56. We removed all the benzyl protecting groups in (48) We observed that the intermediate aldol adduct is subject to retro-aldolization on silica gel. For higher overall yields of diol 55, we performed the aldol addition and reduction in tandem before purification. (49) Chen, K.-M.; Hardtmann, G.E.; Prasad, K.; Repič, O; Shapiro, M.J. Tetrahedron Lett. 1987, 28, 155–158. 144 advance of installing the tetramic acid because hydrogenation of the C2–C3 alkene of enoyltetramic acids under similar conditions (H2/Pd) was known.50 Persilylation of heptaol 56 was then attempted and produced an inseparable yet inconsequential mixture of hexakistrimethylsilyl ethers. We believe persilylation of the C27–C31 pentaol was incomplete, unselective, and potentially complicated by 1,2-silyl migration of the C28 TBS ether.51,52 Unfortunately, this mixture of differentially silylated material complicated spectral analyses and persisted until global deprotection. Nevertheless, the C3 carbinol was selectively desilylated and oxidized29,53 to afford a mixture of C3–C48 aldehydes best represented by structure 58. With C3–C48 aldehydes 58 in hand, we installed the tetramic acid moiety according to Boeckman's three-step method.19 Addition of the lithium anion of dioxinone phosphonate 11 to aldehydes 58 in the presence of HMPA10b,20 provided trisubstituted (E) alkenes 59 in moderate yield over two steps (Scheme 4.14). Cycloelimination19b of dioxinones 59 in the presence of ammonium salt 9•HCl led to the formation of β-ketoamides 60 in good yield. (50) (a) Jones, R.C.F.; Pillainayagam, T.A. Synlett 2004, 2815–2817; (b) Schlenk, A.; Diestel, R.; Sasse, F.; Schobert, R. Chem. Eur. J. 2010, 16, 2599–2604. (51) Mulzer, J.; Schöllhorn, B. Angew. Chem., Int. Ed. 1990, 29, 431–432. (52) We believe regioisomers are formed in this step due to the inconsequential 1,2-migration of the tertbutyldimethylsilyl (TBS) group(s) at C28 and/or (less likely) C8. (53) Selective oxidation of the C3 carbinol may also be achieved with TEMPO as catalytic oxidant, but we observed that aldehydes 58 were more prone to decomposition during workup. See: De Luca, L.; Giacomelli, G.; Porcheddu, A. Org. Lett. 2001, 3, 3041–3043. 145 Scheme 4.14. Synthesis of β-ketoamides 60. Me Me O O 11 O 1 Me Me O P OEt OEt Me RO C9H19 39 Me Me O 15 O H 3 7 OR' O 11 O O Me 19 Me O R"O 35 Me OR Me Me Me Me O O Me Me 58, R = TBS, R' = TMS, R" = TES O R'O HO R'O R'O 23 31 27 OTIPS OR" O Me Me Me EtO O 5' Me Me OR' OR Me Me O 15 a 3 Cl O O O 2 59%, 2 steps, Me Me E : Z > 95:05 OR' O O 7 11 O Me 19 NH2 Me Me RO C9H19 39 Me Me OR Me Me Me Me O O Me Me 59, R = TBS, R' = TMS, R" = TES 9•HCl O R"O 35 O R'O HO R'O R'O 23 31 27 OTIPS OR" O b Me EtO O 5' Me Me 69% OR' OR Me Me OR' O O Me Me O 15 O O 3 7 O Me 19 N Me RO 11 Me Me Me OR Me Me Me Me O O Me Me 60, R = TBS, R' = TMS, R" = TES O R"O 35 O R'O HO R'O R'O 23 31 27 C9H19 39 OTIPS OR" O Me Me OR' OR Reagents and conditions: (a) phosphonate 11, LDA, THF, –78 °C to 0 °C; HMPA, –78 °C; aldehydes 58, –78 °C to rt, E:Z > 95:05, 59% (2 steps); (b) 4 Å MS, PhMe, 110 °C, 69%. Modified Lacey-Dieckmann cyclization14 of β-ketoamides 60 was then induced by potassium trimethylsilanolate and produced tetramic acids 61 without appreciable elimination of the C39 silyl ether (Scheme 4.15). Removal of the acetonide and silyl protecting groups25 converged the isomer mixture of tetramic acids and completed the synthesis of AsA (1). The free tetramic acid was converted to its corresponding diethylammonium salt 1•Et2NH upon purification. Spectroscopic data for diethylammonium tetramate 1•Et2NH was identical in all respects (1H-NMR, 13C-NMR, IR, HRMS) to those reported by the isolation group for the 146 naturally derived AsA salt.26 The optical rotation of the synthetic material ([α] 26 –2.8° (c = D 0.55, DMSO)) was also in agreement with that reported for the naturally derived sample ([α] 19 –2.6° (c = 0.545, DMSO)). D Scheme 4.15. Synthesis of the diethylamine salt of AsA (1•Et2NH). Me Me O a 60 Me N Me RO C9H19 39 4' 3' Me Me O 15 OH 3 7 OR' O 11 O O Me 19 O Me Me Me OR Me Me Me Me O O Me Me 61, R = TBS, R' = TMS, R" = TES O R"O 35 O R'O HO R'O R'O 23 31 27 OTIPS OR" O Me Me OR' OR b Et2NH2 O Me N Me 2' 36%, 2 steps OH OH OH 39 O 3 7 HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 35 O Me Me Me OH Me Me Me Me Me 1•Et2NH OH OH H O OH C9H19 Reagents and conditions: (a) KOTMS, TMSOH, THF, 0 °C; (b) aq H2SiF6, MeCN, CH2Cl2, 0 °C to rt; Et2NH, MeOH, H2O, rt (purification), 36% (2 steps). Herein we have described the asymmetric synthesis of aflastatin A (1) in 32 linear steps and 0.69% overall yield from methacrolein, and in 91 total steps from commercially available starting materials. Our synthesis features several complex diastereoselective fragment couplings, including an anti-Felkin-selective α-oxygenated aldol reaction, two tritylcatalyzed Felkin-selective aldol additions, and two chelate-controlled/soft enolization-based aldol couplings. We hope our work involving oxygenated enolates, trityl catalysis, and soft enolization with magnesium clearly demonstrates the reliability of these methods in complex settings, as well as their potential applicability to the large-scale production of chiral building blocks for stereoselective organic synthesis. 147 IV. Graphical Summary of the Total Synthesis of Aflastatin A Synthesis of the C3–C26 Ketone Synthesis of C8–C15 Aldehyde 75 O Ph 62 OBn O Ph 93% 66 OBn O Ph 67 9 9 9 O H 11 O N O 63 86%, dr > 95:05 OH O Ph 64 OH O 9 O N O Me Bn Me Bn 87% Me N Me OMe 99% Ph 65 9 Me N Me OMe O H 13 O N O 8 OBn OH O O dr > 95:05 Ph 69 11 O 15 O N O Me Me Me Bn 68 Me Me Me Bn 75%, 2 steps OBn OR O 8 OBn OR OH O 8 O N O 59% Ph O 15 O N O Ph 11 15 11 Me Me Me Bn Me Me Me Bn 71, R = TES 80% 70, R = TES OBn OR OH O 8 OBn OH OH O N Me OMe 8 Ph 11 15 Ph 73 11 15 Me Me Me Me Me Me 91%, 2 steps OMe N Me 72, R = TES Me Me OBn O H O 9 Me Me O N Me OMe 92% Ph OBn O 9 O 13 O 13 O OMe N Me Me Me 75 Me Me Me 74 Me 148 Synthesis of C3–C15 Aldehyde 9354,55 O EtO 3 EtO Ref. 54 Me 77 96% ee, dr = 98:02 3 O 7 O OEt Me 80 O OEt 6 4 EtO Ref. 55 7 MgBr OEt Me 79 O 78 76 O EtO 4 O 6 OEt Me 78%, 2 steps, dr > 95:05 EtO 4 O H O Me H 6 O OEt 4 O Me 70%, 3 steps H OH 6 Me Me 82 Me Me 83 Me 84 81 7 7 BnO 3 7 OH 75%, 3 steps BnO 3 HO Me 87 Me 3 O Me 86 Me Me Me 4 H I 6 Me 88 85% Me Me 85 Me Me Me OBn O O 13 O N Me OMe BnO 86%, dr > 95:05 3 7 OBn O 11 O O 15 BnO 3 7 I H O 9 Me 89 Me Me Me 90 Me Me Me OH Me Me 91 Me OMe N Me 97% Me Me O 15 Me Me OBn O BnO 3 7 11 O OBn O H 97% BnO 3 7 11 O O 15 Me Me OR Me Me Me Me Me OR Me Me Me OMe N Me 93, R = TBS 92, R = TBS (54) Dunn, T.B. Synthesis of the C21–C40 Fragment of Azaspiracid-1. Ph.D. Thesis, Harvard University, 2005 and references cited therein. (55) (a) Ref. 54; (b) Rambaud, M.; Bakasse, M.; Duguay, G.; Villieras, J. Synthesis 1988, 564–566. 149 Synthesis of C16–C26 Enolsilane 11356 O 19 O H 21 O N O 88%, dr > 95:05 95 OH O 19 O N O 98% TBSO 19 O N Me Bn O O Me 94 Me Bn Me 96 Me Bn Me 97 84%, dr = 95:05 O O 21 17 TBSO O 21 O N Me OMe 74%, 3 steps H 17 OR O 21 TBSO N Me OMe HO 17 O 21 Me 77% TBSO Me Me Me Me Me 99 N Me OMe Me 18 Me OTBS 101 100, R = TBS TBSO HO 21 98 TBSO HO HO 21 17 O 21 17 O O 25 17 O 25 H OMe 87%, dr > 95:05 Me OMe Me Me dr > 95:05, 84%, 2 steps Me Me 105 Me 106 102 TBSO RO RO 21 25 OR OR 25 17 R 17 TBSO RO RO 21 O 25 OMe OMe Me Me 104, R = TMS Ref. 56, 2 steps O Me 103 Me Me TMSO 17 108, R = TMS Me Me 107, R = TMS 76%, 3 steps OH OH OH 21 25 25 O OMe 17 17 OH OH OR 21 25 Me Me Me 91% Me 109 Me Me 110, R = TIPS 93% Me Me OR 25 Me Me OR 25 17 O O 21 O Me 99% Me 17 O O 21 O O 21 OR 25 Me Me Me 113, R = TIPS Me Me 86% Me 112, R = TIPS Me Me 111, R = TIPS (56) (a) Chan, T.-H.; Brownbridge, P. J. Chem. Soc., Chem. Commun. 1979, 578–579; (b) Brownbridge, P.; Chan, T.-H.; Brook, M.A.; Kang, G.J. Can. J. Chem. 1983, 61, 688–693. 150 Synthesis of C3–C26 Ketone 40 Me Me 93, R = TBS BnO 3 7 Me Me O 15 OBn O 11 O TMSO H dr > 95:05 O 19 O OR' 23 Me Me Me OR Me Me Me Me Me 113, R' = TIPS 114, R = TBS R' = TIPS R" = TMS BnO 3 7 Me Me OBn O 11 Me Me OH OR" O 15 19 O O OR' 23 Me Me Me OR Me Me Me Me Me 84%, 2 steps 115, R = TBS R' = TIPS BnO 3 7 Me Me OBn O 11 Me Me OH O 15 O O 19 O OR' 23 Me Me Me OR Me Me Me Me Me 87%, dr > 95:05 116, R = TBS R' = TIPS BnO 3 7 Me Me OBn O 11 Me Me OH OH O 15 19 O O OR' 23 Me Me Me OR Me Me Me Me 85% Me 117, R = TBS R' = TIPS BnO 3 7 Me Me OBn O 11 Me Me O 15 Me Me O 19 O O O OR' 23 Me Me Me OR Me Me Me Me 81% Me 40, R = TBS R' = TIPS BnO 3 7 Me Me OBn O 11 Me Me O 15 Me Me O 19 O O O OR' O 23 Me Me Me OR Me Me Me Me Me 151 Synthesis of the C27–C48 Aldehyde Synthesis of C36–C48 Ketone 53 37 OH OAc 118 39 OH 39 OTBS 39 C9H19 119 72%, ≥ 90% ee C9H19 90% 121 C9H19 73%, dr ~ 1:1 120 O OTBS 39 OH OTBS 39 OH OTBS 39 C9H19 OTES 99% C9H19 53 OTES 90% C9H19 123 OH 122 Synthesis of C27–C31 Aldehyde 45 H HO 31 O 27 OMe OH quant. H TMSO 31 O 27 OMe Ph H O 31 O 27 OMe OH HO OH 124 TMSO OTMS OTMS 125 O 126 OBn 82%, two steps OMe 27 H I 31 O 27 OMe OTBS quant. H I 31 O H HO 97% 31 O 27 OMe OH BnO 43 OBn 88% BnO BnO OBn 127 BnO OH BnO OBn 42 BnO O 31 31 31 HO 27 TBSO BnO 44 98% TESO 27 TBSO BnO 128 94% TESO 27 TBSO BnO 45 H 152 Synthesis of C27–C48 Aldehyde 41 BnO O 92%, dr ≥ 95:05 O Cl 129 O OBn O HO 27 TBSO BnO 31 35 OBn OH TESO 27 TBSO BnO O Ref. 41 O t-Bu O 31 31 H TESO 27 TBSO BnO 45 46 O 35 O t-Bu HO 35 130 131 98% O OBn O 35 OH OH dr ≥ 95:05 OBn O TESO 27 TBSO BnO 47 O O O 49 31 35 69% 48 TESO 27 TBSO BnO 31 132 65%, 2 steps OBn O MOPO 27 TBSO BnO 31 OBn OH O Me Me 91% MOPO 27 TBSO BnO 50 31 35 35 OH Me O Me 92% OBn OH O OBn OBn O MOPO 27 TBSO BnO 93% 31 35 OTBDPS 92% Me O Me 51 MOPO 27 TBSO BnO 133 OBn OBn O O 31 35 OTBDPS Me O Me OBn OBn O MOPO 27 TBSO BnO 134 31 35 O OTBS 39 OH 94% Me O Me MOPO 27 TBSO BnO 52 31 35 H Me O Me 57%, dr = 85:15 C9H19 53 OTES OBn OBn O HO 27 TBSO BnO 31 OR O 35 OTBS 39 OBn OBn O 83% MOPO 27 TBSO BnO 54 31 OH O 35 OTBS 39 C9H19 C9H19 Me O Me 95% OR 135, R = TES Me O Me OTES O OBn OBn O 31 OR O 35 OTBS 39 H 27 TBSO BnO C9H19 Me O Me OR 41, R = TES 153 Alternative Synthesis of the C27–C48 Aldehyde Synthesis of C27–C35 Aldehyde 15657,58 O O 35 O OH Ref. 57, 2 steps MeO 35 O OH 84% MeO 35 OTBDPS 87% NH3 L-serine OH 136 O OH 137 O O Me 35 OTBDPS OPMB MeO 79% N Me 35 OTBDPS OPMB MeO 78% N Me 35 OTBDPS OH 140 O O HO 27 139 27 138 O H O 31 O N O 70%, dr > 95:05 143 OH Ref. 58, 2 steps O Me O Me 142 TESO 27 BnO Bn OH OH 141 TESO 27 O 31 O 27 OH O O 84% O Me O BnO Me 144 TESO HO 27 31 O N O O Me O BnO Me 93% 31 OH 92% O Me O BnO Me 145 N 146 Bn Bn TESO 27 O 31 O H Me OTBDPS OPMB 35 O OTBDPS OPMB 35 O Me O Me 147 OBn 72%, dr = 97:03 O Me O Me 149 31 OBn 148 27 31 35 OTBDPS OPMB 86%, dr = 93:07 35 OTBDPS OPMB OH OH OH 27 TESO HO HO 68% O Me O Me 31 O Me O Me OBn 151 OH OH O OBn 150 OBn OBn O 83% 27 27 31 35 O Me O BnO Me OTBDPS 88% O Me O BnO Me 31 35 OTBDPS 95% H O PMP H O PMP 152 OBn OBn O 27 153 OBn OBn O 27 27 31 35 O 35 OBn OBn O OH quant. O Me O BnO Me 31 35 O Me O BnO Me 31 H 96% O Me O BnO Me OR Me O Me Me O Me Me O Me 156 155 154, R = TBDPS (57) Hirth, G.; Walther, W. Helv. Chim. Acta 1985, 68, 1863–1871. (58) Hubschwerlen, C.; Specklin, J.-L.; Higelin, J. Org. Synth. 1995, 72, 1–5. 154 Synthesis of C27–C48 Aldehyde 41 27 OBn OBn O 31 O 35 O H OTES 53 OTBS 27 39 OBn OBn O 31 OH O 35 OTBS 39 O Me O BnO Me 157 C9H19 Me O Me 77%, dr = 91:09 O Me O BnO Me 158 C9H19 Me O Me OTES 88% OBn OBn O AcO 27 31 OR O 35 OTBS 39 OBn OBn O HO 98% 27 31 OR O 35 OTBS 39 C9H19 C9H19 HO BnO Me O Me OR HO BnO Me O Me OR 160, R = TES 74% 159, R = TES OBn OBn O AcO 27 TBSO BnO 31 OR O 35 OTBS 39 OBn OBn O 84% HO 27 TBSO BnO 31 OR O 35 OTBS 39 C9H19 C9H19 Me O Me OR Me O Me OR 161, R = TES 162, R = TES 95% O OBn OBn O 31 OR O 35 OTBS 39 H 27 TBSO BnO C9H19 Me O Me OR 41, R = TES 155 Synthesis of Aflastatin A Synthesis of C3–C48 Aldehydes 58 Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' O 23 O Me OBn OBn O 31 OR" O 35 OTBS 39 Me Me OR Me Me Me Me Me H 27 TBSO BnO C9H19 Me O Me OR" 41, R" = TES 40, R = TBS, R' = TIPS Me Me OBn O BnO 3 7 11 dr = 95:05 Me Me O 15 Me Me O 19 O O O OR' O 23 OH OBn OBn O 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me RO BnO dr ≥ 95:05, 70%, 2 steps Me O Me OR" 163, R = TBS, R' = TIPS, R" = TES Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' OH OH OBn OBn O 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me 93% RO BnO Me O Me OR" 55, R = TBS, R' = TIPS, R" = TES Me Me OH O HO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' OH OH OH OH O 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me RO HO Me O Me OR" 56, R = TBS, R' = TIPS, R" = TES Me Me OR'" O R'"O 3 7 11 Me Me O 15 Me Me O 19 O O O OR' OR'" OR'" OH OR'" O 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me 87%, 2 steps RO R'"O Me O Me OR" 164, R = TBS, R' = TIPS, R" = TES, R'" = TMS Me Me OR'" O HO 3 7 11 Me Me O 15 Me Me O 19 O O O OR' OR'" OR'" OH OR'" O 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me RO R'"O Me O Me OR" 57, R = TBS, R' = TIPS, R" = TES, R'" = TMS Me Me O H 3 7 Me Me O 15 Me Me O 19 OR'" O 11 O O O OR' OR'" OR'" OH OR'" O 23 27 31 OR" O 35 OR 39 C9H19 Me Me OR Me Me Me Me Me RO R'"O Me O Me OR" 58, R = TBS, R' = TIPS, R" = TES, R'" = TMS 156 Syntheses of Dioxinone Phosphonate 11 and Ammonium Salt 9•HCl Me Me O O 10 Me HO O 26 5' Me Me O Me 60% O 165 Me HO 5' Me Me O 59% O 11 Me O 1 O 1 O 1 Me O P OEt OEt Me Me NHCbz 91%, Ref. 23 O 27 N Me Cbz 91% EtO O 5' N Me Cbz quant. EtO O Cl 5' NH2 Me 28 9•HCl Synthesis of β-Ketoamides 60 Me Me O O 11 O 1 Me Me O P OEt OEt Me RO C9H19 39 Me Me O 15 O H 3 7 OR' O 11 O O Me 19 Me O R"O 35 Me OR Me Me Me Me O O Me Me 58, R = TBS, R' = TMS, R" = TES O R'O HO R'O R'O 23 31 27 OTIPS OR" O Me Me OR' OR 59%, 2 steps, E : Z > 95:05 Me Me Me EtO O 5' Me Me 3 7 Me Me O 15 Cl O O O OR' O 11 O O Me 19 NH2 Me Me RO C9H19 39 Me Me OR Me Me Me Me O O Me Me 59, R = TBS, R' = TMS, R" = TES 9•HCl O R"O 35 O R'O HO R'O R'O 23 31 27 OTIPS OR" O Me Me 69% OR' OR Me Me OR' O O Me Me O 15 Me EtO O 5' O O 3 7 O Me 19 N Me RO 11 Me Me Me OR Me Me Me Me O O Me Me 60, R = TBS, R' = TMS, R" = TES O R"O 35 O R'O HO R'O R'O 23 31 27 C9H19 39 OTIPS OR" O Me Me OR' OR 157 Synthesis of Aflastatin A (1) and its Diethylamine Salt (1•Et2NH) Me Me Me EtO O 5' Me Me O 15 O O 3 7 OR' O 11 O O Me 19 N Me RO Me Me Me OR Me Me Me Me O O Me Me 60, R = TBS, R' = TMS, R" = TES O R"O 35 O R'O HO R'O R'O 23 31 27 C9H19 39 OTIPS OR" O Me Me OR' OR Me Me O Me N Me RO C9H19 39 2' Me Me O 15 OH 3 7 OR' O 11 O O Me 19 O Me Me Me OR Me Me Me Me O O Me Me 61, R = TBS, R' = TMS, R" = TES O R"O 35 O R'O HO R'O R'O 23 31 27 OTIPS OR" O Me Me OR' OR 36%, 2 steps Et2NH2 O Me N Me 2' OH HO HO HO HO HO HO HO HO HO HO HO HO HO 7 11 15 19 23 27 31 35 O 3 OH OH 39 O Me Me Me OH Me Me Me Me Me 1•Et2NH OH OH H O OH C9H19 158 IV. Experimental Section Spectroscopic Data for Tetramic Acid Degradation Fragment 38•Et2NH O 2' O Et2NH2 3 7 OH Me N Me 5' O Me Me Me 38•Et2NH Diethylammonium (1Z,2E,4S,6R)-1-((R)-1,5-dimethyl-2,4-dioxopyrrolidin-3-ylidene)-8- hydroxy-2,4,6-trimethyloct-2-en-1-olate (38•Et2NH). White solid; 1H-NMR (600 MHz, CD3OD) δ 5.69 (d, J = 9.8 Hz, 1H, C3-H), 3.59 (ddd, J = 10.8, 6.6, 6.6 Hz, 1H, one of C8-H2), 3.54 (ddd, J = 11.0, 6.7, 6.6 Hz, 1H, one of C8-H2), 3.46 (q, J = 6.7 Hz, 1H, C5'-H), 3.02 (q, J = 7.3 Hz, 4H, NCH2CH3), 2.85 (s, 3H, C7'-H3), 2.66–2.63 (m, 1H, C4-H), 1.83 (d, J = 1.2 Hz, 3H, C9-H3), 1.71–1.68 (m, 1H, C6-H), 1.50–1.46 (m, J = 6.7, 6.6 Hz, 1H, one of C7-H2), 1.38– 1.31 (m, J = 7.0, 6.7 Hz, 2H, one of C5-H2, and one of C7-H2), 1.27 (t, J = 7.3 Hz, 6H, NCH2CH3), 1.26 (d, J = 7.3 Hz, 3H, C6'-H3), 1.12 (ddd, J = 13.3, 9.1, 4.4 Hz, 1H, one of C5H2), 0.99 (d, J = 6.6 Hz, 3H, C10-H3), 0.90 (d, J = 6.6 Hz, 3H, C11-H3); 13C-NMR (125 MHz, CD3OD) δ 196.0 (C4'), 195.7 (C1), 175.8 (C2'), 143.2 (C3), 137.0 (C2), 101.0 (C3'), 61.8 (C5'), 60.9 (C8), 46.2 (C5), 43.4 (NCH2CH3), 41.8 (C7), 31.7 (C4), 28.3 (C6), 26.9 (C7'), 21.1 (C10), 20.4 (C11), 16.3 (C6'), 13.6 (C9), 11.6 (NCH2CH3); HRMS (ESI-TOF) m/z calcd for C17H28NO4 [M+H]+: 310.2013, found: 310.2015. Synthesis of the C27–C35 Aldehyde H HO 31 O OMe 27 H I 31 O OMe 27 BnO OBn 42 OH BnO OBn 127 OH (2S,3R,4R,5S,6S)-4,5-Bis(benzyloxy)-6-(iodomethyl)-2-methoxytetrahydro-2H-pyran-3-ol (127). To a solution of diol 42 (9.8 g, 26 mmol, 1.0 equiv), imidazole (5.4 g, 79 mmol, 3.0 equiv), and triphenylphosphine (10.7 g, 40.7 mmol, 1.55 equiv) in 2:1 PhMe/MeCN (131 mL, 0.2 M wrt 42) at rt was added iodine (10 g, 39 mmol, 1.5 equiv) in three portions. The reaction mixture was stirred at rt for 3 h, quenched with brine (100 mL), and then diluted with H2O (10 mL) and Et2O (50 mL). The layers were separated and the aqueous layer extracted   159 with Et2O (3 x 100 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 5:1 → 4:1 → 3:1 hexanes/EtOAc) afforded iodide 127 (12.3 g, 97% yield) as a white solid. [α] 25 +95.4° (c D = 2.3, CH2Cl2); IR (neat) 3424 (br), 3029, 2924, 1497, 1453, 1399, 1361, 1325, 1214, 1192, 1140, 1087, 1046, 733, 696 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.39–7.30 (m, 10H, ArH), € 4.95 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 4.94 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.84 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.78 (d, J = 3.8 Hz, 1H, C27-H), 4.72 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 3.80 (dd, J = 9.2, 8.9 Hz, 1H, C29-H), 3.71 (ddd, J = 8.8, 8.6, 3.8 Hz, 1H, C28-H), 3.51 (dd, J = 10.5, 2.6 Hz, 1H, one of C32-H), 3.48 (ddd, J = 9.1, 6.4, 2.6 Hz, 1H, C31-H), 3.48 (s, 3H, –OCH3), 3.36 (dd, J = 9.2, 8.9 Hz, 1H, C30-H), 3.32 (dd, J = 10.5, 6.3 Hz, 1H, one of C32-H), 2.16 (d, J = 8.6 Hz, 1H, C28-OH); 13C-NMR (125 MHz, CDCl3) δ 138.4, 137.9, 128.5, 128.5, 127.9, 127.9, 127.8, 99.3, 82.8, 81.2, 75.4, 75.3, 73.1, 69.7, 55.5, 7.3; HRMS (ESI-TOF) m/z calcd for C21H25INaO5 [M+Na]+: 507.06389, found: 507.06416. H I 31 O 27 OMe OH H I 31 O 27 OMe OTBS BnO OBn 127 BnO OBn 43 (((2S,3R,4S,5S,6S)-4,5-Bis(benzyloxy)-6-(iodomethyl)-2-methoxytetrahydro-2H-pyran-3yl)oxy)(tert-butyl)dimethylsilane (43). To a solution of carbinol 127 (12.3 g, 25.3 mmol, 1.0 equiv) and imidazole (3.5 g, 51 mmol, 2.0 equiv) in CH2Cl2 (25 mL, 1.0 M wrt 127) at 0 °C was added tert-butylchlorodimethylsilane (5.7 g, 38 mmol, 1.5 equiv). The reaction mixture was stirred at 0 °C for 2 h, slowly warmed to rt over 2 h, stirred at rt for 8 h, quenched at 0 °C with brine (40 mL), and diluted with Et2O (150 mL) and H2O (20 mL). The layers were separated and the organic layer washed with 1:1 H2O/brine (2 x 50 mL), dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 3% → 4% → 5% EtOAc in hexanes) afforded silyl ether 43 (15.2 g, quant. yield) as a clear, colorless oil. [α] 23 +56.1° (c = 2.9, CH2Cl2); IR (neat) 3064, 3032, 2929, 2857, 1455, 1360, D 1254, 1196, 1151, 1090, 1051, 1000, 862, 838, 778, 735, 698 cm–1; 1H-NMR (600 MHz, C6D6) δ 7.32 (m, 2H, ArH), 7.20–7.05 (m, 8H, ArH), 4.95 (d, J = 11.6 Hz, 1H, one of – OCH2Ph), 4.85 (d, J = 11.3 Hz, 1H, one of –OCH2Ph), 4.74 (d, J = 11.6 Hz, 1H, one of –   160 OCH2Ph), 4.57 (m, 1H, C27-H), 4.56 (d, J = 11.3 Hz, 1H, one of –OCH2Ph), 4.03 (ddd, J = 9.1, 9.1, 2.2 Hz, 1H, C29-H), 3.77 (ddd, J = 9.4, 3.6, 1.8 Hz, 1H, C28-H), 3.47 (ddd, J = 6.6, 2.3, 1.6 Hz, 1H, C31-H), 3.33 (dd, J = 9.2, 1.6 Hz, 1H, C30-H), 3.30 (dd, J = 10.5, 2.5 Hz, 1H, one of C32-H), 3.20 (s, 3H, –OCH3), 3.12 (dd, J = 10.6, 6.5 Hz, 1H, one of C32-H), 0.93 (s, 9H, C(CH3)3), 0.03 (s, 3H, one of SiCH3), –0.02 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, C6D6) δ 139.4, 138.8, 128.5, 128.5, 128.4, 127.9, 127.8, 127.5, 127.5, 100.5, 82.5, 82.1, 75.5, 75.2, 74.6, 70.0, 55.3, 25.9, 18.2, 8.0, –4.5, –4.6; HRMS (ESI-TOF) m/z calcd for C27H39INaO5Si [M+Na]+: 621.15036, found: 621.14896. H I 31 O 27 OMe OTBS HO 27 TBSO OBn 31 BnO OBn 43 OBn 44 (2S,3S,4R)-3,4-Bis(benzyloxy)-2-((tert-butyldimethylsilyl)oxy)hex-5-en-1-ol (44). To a solution of iodide 43 (3.7 g, 6.2 mmol, 1.0 equiv) in 9:1 THF/H2O (77 mL, 0.08 M wrt 43) at rt was added preactivated zinc dust59 (4.0 g, 62 mmol, 10 equiv). The reaction mixture was sonicated at 40–45 °C for 3 h, then cooled to 0 °C and charged with sodium borohydride (0.77 g, 20 mmol, 3.3 equiv) in six portions over 1 h. The resulting suspension was stirred at 0 °C for an additional 15 min, slowly quenched with 1 M NaHSO4 (40 mL), diluted with Et2O (40 mL), warmed to rt, and filtered through Celite . The filter cake was rinsed with Et2O (3 x 50  mL) and sat. aq NH4Cl (3 x 50 mL). The layers were separated and the aqueous layer extracted with Et2O (3 x 150 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 6% → 7% → 8% → 9% EtOAc in hexanes) afforded carbinol 44 (2.4 g, 88% yield) as a clear, colorless oil. [α] 23 –12.1° (c = 1.1, CH2Cl2); IR (neat) 3466 (br), 3072, 3032, 2931, 2861, D 1461, 1396, 1361, 1253, 1209, 1055, 928, 834, 776, 735, 697 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.36–7.28 (m, 10H, two of ArH), 5.94 (ddd, J = 17.4, 10.4, 7.3 Hz, 1H, C31-H), 5.31 (dd, J = 17.4, 0.8 Hz, 1H, one of C32-H), 5.29 (dd, J = 10.5, 0.8 Hz, 1H, one of C32-H), 4.71 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.64 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.38 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.09 (ddd, J =                                                                                                                 (59) Hyldtoft, L.; Madsen, R. J. Am. Chem. Soc. 2000, 122, 8444–8452.   161 7.3, 3.8, 0.7 Hz, 1H, C30-H), 3.76 (ddd, J = 5.7, 4.8, 4.5 Hz, 1H, C28-H), 3.67 (ddd, J = 11.7, 5.7, 5.2 Hz, 1H, one of C27-H), 3.59 (ddd, J = 11.7, 7.5, 4.2 Hz, 1H, one of C27-H), 3.52 (dd, J = 5.9, 3.9 Hz, 1H, C29-H), 2.37 (dd, J = 7.3, 5.8 Hz, 1H, C27-OH), 0.88 (s, 9H, C(CH3)3), 0.05 (s, 3H, one of SiCH3), 0.01 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 138.3, 137.9, 135.7, 128.3, 128.3, 128.1, 128.1, 127.6, 118.1, 82.6, 79.3, 74.3, 72.6, 70.6, 64.0, 25.8, 18.0, –4.7, –4.7; HRMS (ESI-TOF) m/z calcd for C26H38NaO4Si [M+Na]+: 465.24316, found: 465.24360. OBn HO 27 TBSO 44 31 OBn TESO 27 TBSO 31 OBn OBn 128 (S)-5-((1S,2R)-1,2-Bis(benzyloxy)but-3-en-1-yl)-8,8-diethyl-2,2,3,3-tetramethyl-4,7-dioxa3,8-disiladecane (128). To a solution of carbinol 44 (6.0 g, 14 mmol, 1.0 equiv) and imidazole (1.4 g, 20 mmol, 1.5 equiv) in CH2Cl2 (14 mL, 1.0 M wrt 44) at 0 °C was added chlorotriethylsilane (2.7 mL, 16 mmol, 1.2 equiv). The reaction mixture was stirred at 0 °C for 2 h, slowly warmed to rt over 2 h, stirred at rt for 7 h, quenched at 0 °C with sat. aq NH4Cl (50 mL), and diluted with 1:1 hexanes/Et2O (150 mL) and H2O (10 mL). The layers were separated and the organic layer washed sequentially with sat. aq NH4Cl and 1:1 H2O/brine (50 mL each), dried over Na2SO4, filtered and concentrated. Column chromatography (gradient elution, 2% → 2.5% → 3% EtOAc in hexanes) afforded silyl ether 128 (7.4 g, 98% yield) as a clear, colorless oil. [α] 24 –12.9° (c = 2.3, CH2Cl2); IR (neat) 3066, 3031, 2955, 2934, 2877, D 1455, 1251, 1087, 1005, 961, 928, 836, 808, 777, 731, 697 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.37–7.27 (m, 10H, two of ArH), 5.92 (ddd, J = 17.3, 10.4, 7.6 Hz, 1H, C31-H), 5.30 (dd, J = 17.4, 0.8 Hz, 1H, one of C32-H), 5.27 (m, J = 10.4 Hz, 1H, one of C32-H), 4.77 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.63 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.38 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.13 (dd, J = 7.5, 5.0 Hz, 1H, C30-H), 3.86 (ddd, J = 6.7, 4.4, 4.0 Hz, 1H, C28-H), 3.79 (dd, J = 10.4, 3.8 Hz, 1H, one of C27-H), 3.60 (dd, J = 10.4, 6.7 Hz, 1H, one of C27-H), 3.49 (dd, J = 4.7, 4.7 Hz, 1H, C29-H), 0.95 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.87 (s, 9H, C(CH3)3), 0.58 (q, J = 7.9 Hz, 6H, – SiCH2CH3), 0.05 (s, 3H, one of SiCH3), –0.01 (s, 3H, one of SiCH3); 13C-NMR (125 MHz,   162 CDCl3) δ 138.9, 138.4, 136.4, 128.2, 128.1, 128.1, 128.1, 127.4, 127.4, 117.8, 82.3, 79.9, 74.2, 74.2, 70.7, 64.3, 25.9, 18.1, 6.8, 4.4 –4.1, –4.9; HRMS (ESI-TOF) m/z calcd for C32H52NaO4Si2 [M+Na]+: 579.32963, found: 579.33115. OBn TESO 27 TBSO 31 OBn O TESO 27 TBSO 45 31 H OBn 128 OBn (2S,3S,4S)-2,3-Bis(benzyloxy)-4-((tert-butyldimethylsilyl)oxy)-5((triethylsilyl)oxy)pentanal (45). To a solution of alkene 128 (7.4 g, 13 mmol, 1.0 equiv) in 1:1 CH2Cl2/MeOH (0.27 L, 0.05 M wrt 128) at –78 °C was added pyridine (11 mL, 0.13 mol, 10 equiv). The reaction mixture was bubbled with ozone until it turned blue, purged with oxygen until the color faded, quenched dropwise with a solution of triphenylphosphine (4.2 g, 16 mmol, 1.2 equiv) in 1:1 CH2Cl2/MeOH (66 mL, 0.24 M wrt PPh3), slowly warmed to rt over 1.5 h, stirred at rt for 9 h, concentrated, and azeotroped with PhH (2 x 50 mL). Column chromatography (gradient elution, 2% → 3% → 4% EtOAc in hexanes) afforded aldehyde 45 (6.9 g, 94% yield) as a clear, colorless oil. [α] 21 –25.6° (c = 3.0, CH2Cl2); IR (neat) 3065, D 3032, 2954, 2933, 2878, 1733 (s), 1456, 1362, 1252, 1121, 1088, 1006, 959, 837, 779, 734, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 9.68 (d, J = 1.8 Hz, 1H, C31-H), 7.36–7.28 (m, 10H, ArH), 4.72 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.65 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.63 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.55 (d, J = 11.8 Hz, 1H, one of – OCH2Ph), 4.09 (dd, J = 4.7, 1.2 Hz, 1H, C30-H), 3.91 (ddd, J = 6.5, 5.3, 3.5 Hz, 1H, C28-H), 3.83 (dd, J = 10.6, 3.5 Hz, 1H, one of C27-H), 3.81 (dd, J = 5.3, 4.7 Hz, 1H, C29-H), 3.67 (dd, J = 10.6, 6.5 Hz, 1H, one of C27-H), 0.96 (t, J = 8.2 Hz, 9H, –SiCH2CH3), 0.86 (s, 9H, C(CH3)3), 0.59 (q, J = 8.2 Hz, 6H, –SiCH2CH3), 0.04 (s, 3H, one of SiCH3), –0.01 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 202.0, 137.8, 137.2, 128.4, 128.33, 128.27, 128.1, 128.0, 127.8, 83.4, 80.1, 73.9, 73.25, 73.18, 63.6, 25.8, 18.0, 6.8, 4.3, –4.5, –5.0; HRMS (ESITOF) m/z calcd for C31H50KO5Si2 [M+K]+: 597.28284, found: 597.28060.   163 OBn O TESO 27 TBSO 45 31 OBn OH H TESO 27 TBSO 46 31 33a OBn OBn (4S,5R,6S,7S)-5,6-Bis(benzyloxy)-7-((tert-butyldimethylsilyl)oxy)-8-((triethylsilyl)oxy)oct1-en-4-ol (46). To a solution of aldehyde 45 (6.9 g, 12 mmol, 1.0 equiv) in CH2Cl2 (0.25 L, 0.05 M wrt 45) at 0 °C was added a freshly prepared solution of MgBr2•OEt2 in 2:1 Et2O/PhMe (74 mL, 0.67 M, 50 mmol, 4.0 equiv). The reaction mixture was stirred at 0 °C for 5 min, cooled to –78 °C, and then charged dropwise with a freshly prepared60 solution of allylmagnesium bromide in Et2O (44 mL, 0.42 M, 19 mmol, 1.5 equiv). The reaction mixture was stirred at –78 °C for 2 h, charged with additional allylmagnesium bromide (15 mL, 0.42 M in Et2O, 6.2 mmol, 0.5 equiv), stirred at –78 °C for an additional 1.5 h, then briefly warmed to 0 °C and quenched with sat. aq NH4Cl (100 mL). The biphasic mixture was diluted with H2O (50 mL) and CH2Cl2 (50 mL) and warmed to rt. The layers were separated and the aqueous layer extracted with CH2Cl2 (2 x 150 mL). The combined organic extracts were dried over Na2SO4, filtered and concentrated. The residue was analyzed by 1H-NMR spectroscopy to assess reaction diastereoselectivity (d.r. ≥ 95:05). Column chromatography (gradient elution, 3% → 4% → 5% EtOAc in hexanes) afforded homoallylic carbinol 46 (6.9 g, 92% yield) as a clear, colorless oil. [α] 22 –11.8° (c = 1.4, CH2Cl2); IR (neat) 3452 (br), 3067, D 3032, 2955, 2879, 1459, 1412, 1362, 1252, 1093, 1006, 917, 837, 808, 777, 733, 698 cm–1; 1 H-NMR (600 MHz, C6D6) δ 7.32 (m, J = 7.6 Hz, 2H, two of ArH), 7.28 (m, J = 7.6 Hz, 2H, two of ArH), 7.16–7.13 (m, 4H, four of ArH), 7.10–7.05 (m, J = 7.6, 7.1 Hz, 2H, two of ArH), 5.94 (dddd, J = 17.0, 10.6, 7.7, 6.5 Hz, 1H, C33-H), 5.07 (ddd, J = 15.9, 1.8, 1.1 Hz, 1H, one of C33a-H), 5.05 (d, J = 10.5 Hz, 1H, one of C33a-H), 4.88 (d, J = 11.2 Hz, 1H, one of –OCH2Ph), 4.73 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.58 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.14 (ddd, J = 7.0, 4.1, 4.1 Hz, 1H, C28-H), 4.04 (dd, J = 10.3, 4.1 Hz, 1H, one of C27-H), 4.02 (dddd, J = 8.2, 6.5, 5.9, 2.3 Hz, 1H, C31-H), 4.00 (dd, J = 7.3, 4.1 Hz, 1H, C29-H), 3.84 (dd, J = 10.3, 7.1 Hz, 1H, one of C27H), 3.78 (dd, J = 7.3, 2.3 Hz, 1H, C30-H), 2.44 (ddddd, J = 14.1, 6.5, 6.5, 1.8, 1.2 Hz, 1H, one                                                                                                                 (60) Benson, R.E.; McKusick, B.C. Org. Synth. 1958, 38, 78–84.   164 of C32-H), 2.36 (ddddd, J = 14.1, 7.7, 6.4, 1.2, 1.2 Hz, 1H, one of C32-H), 2.24 (d, J = 8.8 Hz, 1H, C28-OH), 1.03 (s, 9H, C(CH3)3), 1.00 (t, J = 8.2 Hz, 9H, –SiCH2CH3), 0.60 (q, J = 8.2 Hz, 6H, –SiCH2CH3), 0.20 (s, 3H, one of SiCH3), 0.13 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, C6D6) δ 139.3, 139.2, 135.9, 128.5, 128.3, 128.1, 127.9, 127.7, 117.1, 81.2, 80.8, 75.1, 74.8, 74.5, 71.2, 64.6, 39.7, 26.2, 18.5, 7.1, 4.8, –3.8, –4.5; HRMS (ESI-TOF) m/z calcd for C34H56NaO5Si2 [M+Na]+: 623.35585, found: 623.35554. O 34a OBn OH TESO 27 TBSO 46 31 OBn O TESO 27 TBSO 31 33a OBn OBn 132 (4S,5R,6S,7S)-5,6-Bis(benzyloxy)-7-((tert-butyldimethylsilyl)oxy)-8-((triethylsilyl)oxy)oct1-en-4-yl acrylate (132). To a solution of homoallylic carbinol 46 (1.2 g, 2.0 mmol, 1.0 equiv) in THF (9.8 mL, 0.2 M wrt 46) at room temperature was added EtN(iPr)2 (1.4 mL, 7.8 mmol, 4.0 equiv), DMAP (60 mg, 0.49 mmol, 0.25 equiv), and a freshly prepared solution of acrylic pivalic anhydride in PhH (2.9 mL, 2.0 M, 5.9 mmol, 3.0 equiv). The resulting suspension was stirred at room temperature for 12 h, then charged with additional EtN(iPr)2 (1.4 mL, 7.8 mmol, 4.0 equiv), DMAP (60 mg, 0.49 mmol, 0.25 equiv), and acrylic pivalic anhydride (2.9 mL, 2.0 M, 5.9 mmol, 3.0 equiv). The reaction mixture was stirred for an additional 9 h, quenched with sat. aq NaHCO3 (20 mL), and diluted with 1:1 hexanes/Et2O (80 mL) and H2O (5 mL). The layers were separated and the aqueous layer extracted with 1:1 hexanes/Et2O (2 x 75 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 1% → 1.5% EtOAc in hexanes) afforded acrylate ester 132 (1.3 g, 98% yield) as a clear, colorless oil. [α] 22 D –17.4° (c = 2.3, CH2Cl2); IR (neat) 3066, 3032, 2954, 2880, 1726 (s), 1638, 1460, 1406, 1359, 1295, 1260, 1190, 1089, 1008, 921, 837, 807, 777, 734, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.37–7.26 (m, 10H, ArH), 6.41 (dd, J = 17.3, 1.5 Hz, 1H, one of C34a-H), 6.16 (dd, J = 17.3, 10.2 Hz, 1H, C34-H), 5.81 (dd, J = 10.2, 1.5 Hz, 1H, one of C34a-H), 5.67 (dddd, J = 17.0, 10.0, 7.7, 7.0 Hz, 1H, C33-H), 5.25 (ddd, J = 7.1, 5.3, 4.1 Hz, 1H, C31-H), 5.00 (m, J = 1.2 Hz, 2H, C33a-H2), 4.79 (d, J = 11.2 Hz, 1H, one of –OCH2Ph), 4.75 (d, J = 11.7 Hz, 1H,   165 one of –OCH2Ph), 4.72 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.67 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 3.92 (dd, J = 5.9, 4.1 Hz, 1H, C30-H), 3.90 (ddd, J = 6.5, 5.3, 3.5 Hz, 1H, C28H), 3.77 (dd, J = 10.0, 5.3 Hz, 1H, one of C27-H), 3.72 (dd, J = 5.9, 3.5 Hz, 1H, C29-H), 3.55 (dd, J = 10.0, 6.5 Hz, 1H, one of C27-H), 2.41–2.33 (m, J = 14.1, 7.6, 7.1, 7.0, 5.3, 1.1 Hz, 2H, C32-H2), 0.91 (s, 9H, C(CH3)3), 0.90 (t, J = 8.2 Hz, 9H, –SiCH2CH3), 0.52 (q, J = 8.2 Hz, 6H, –SiCH2CH3), 0.11 (s, 3H, one of SiCH3), 0.09 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 165.6, 138.7, 138.4, 133.7, 130.8, 128.5, 128.3, 128.2, 127.9, 127.54, 127.47, 117.8, 78.7, 78.3, 74.6, 73.8, 73.3, 72.9, 63.7, 35.6, 26.0, 18.2, 6.8, 4.3, –3.9, –4.7; HRMS (ESITOF) m/z calcd for C37H59O6Si2 [M+H]+: 655.3845, found: 655.3819. Cy3P O OBn O TESO 27 TBSO 31 Cl Ru Cl PCy3 166 Ph O OBn O TESO 27 TBSO 47 31 35 OBn 132 OBn (S)-6-((1R,2S,3S)-1,2-Bis(benzyloxy)-3-((tert-butyldimethylsilyl)oxy)-4((triethylsilyl)oxy)butyl)-5,6-dihydro-2H-pyran-2-one (47). To a degassed solution of diene 132 (1.3 g, 1.9 mmol, 1.0 equiv) in PhH (0.13 L, 0.015 M wrt 132) at room temperature was added ruthenium catalyst 166 (79 mg, 96 µmol, 0.05 equiv). The reaction mixture was purged with argon for 5 min, stirred at 65 °C for 8 h, then recharged with additional catalyst (79 mg, 96 µmol, 0.05 equiv) at this time and approximately every 12 h thrice after (total catalyst 166 added: 0.25 equiv). The reaction mixture was stirred at 65 °C for an additional 8 h, cooled to room temperature, concentrated to half volume, diluted with 9:1 hexanes/EtOAc (0.13 L) and filtered through a silica gel plug (4 cm). The filter cake was rinsed with 9:1 hexanes/EtOAc (0.5 L), and the filtrate concentrated. Column chromatography (gradient elution, 9:1 → 8:1 → 7:1 hexanes/EtOAc) afforded lactone 47 (0.83 g, 69% yield) as a pale brown oil contaminated with ruthenium-based impurities (<5%). A sufficient quantity of this material was repurified by column chromatography to produce a clear, colorless oil for characterization. [α] 22 –59.8° D (c = 2.3, CH2Cl2); IR (neat) 3064, 3032, 2954, 2885, 1733 (s), 1496, 1460, 1384, 1248, 1089, 957, 837, 813, 778, 738, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.36–7.26 (m, 10H, ArH), 6.71 (ddd, J = 9.4, 6.4, 2.3 Hz, 1H, C33-H), 5.95 (dd, J = 9.4, 2.3 Hz, 1H, C34-H), 4.81 (d, J =   166 11.7 Hz, 1H, one of –OCH2Ph), 4.77 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.71 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.70 (ddd, J = 12.9, 4.1, 4.1 Hz, 1H, C31-H), 4.68 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 3.97 (ddd, J = 5.9, 4.1, 3.6 Hz, 1H, C28-H), 3.86 (dd, J = 5.9, 4.1 Hz, 1H, C29-H), 3.84 (dd, J = 5.9, 4.1 Hz, 1H, C30-H), 3.74 (dd, J = 10.6, 3.5 Hz, 1H, one of C27H), 3.64 (dd, J = 10.6, 5.9 Hz, 1H, one of C27-H), 2.39 (dddd, J = 18.2, 12.9, 2.4, 2.3 Hz, 1H, one of C32-H), 1.82 (ddd, J = 18.2, 6.5, 4.1 Hz, 1H, one of C32-H), 0.94 (t, J = 8.0 Hz, 9H, – SiCH2CH3), 0.89 (s, 9H, C(CH3)3), 0.57 (q, J = 8.0 Hz, 6H, –SiCH2CH3), 0.08 (s, 3H, one of SiCH3), 0.05 (s, 3H, one of SiCH3); 13 C-NMR (125 MHz, CDCl3) δ 163.8, 145.2, 138.3, 138.2, 128.4, 128.3, 128.2, 127.7, 127.6, 121.0, 78.6, 78.4, 78.2, 75.0, 73.7, 73.5, 64.1, 25.9, 25.8, 18.1, 6.8, 4.3, –4.3, –4.7; HRMS (ESI-TOF) m/z calcd for C35H55O6Si2 [M+H]+: 627.3532, found: 627.3526. O OBn O TESO 27 TBSO 47 31 35 O OBn O HO 27 TBSO 48 31 35 OH OH OBn OBn (3R,4R,6S)-6-((1R,2S,3S)-1,2-Bis(benzyloxy)-3-((tert-butyldimethylsilyl)oxy)-4hydroxybutyl)-3,4-dihydroxytetrahydro-2H-pyran-2-one (48). To a bright yellow suspension of NaIO4 (0.76 g, 3.5 mmol, 1.5 equiv) and CeCl3•7H2O (88 mg, 0.24 mmol, 0.1 equiv) in deionized H2O (1.1 mL, 3⅓ M wrt NaIO4) at 0 °C was added EtOAc (3.0 mL, 1.2 M wrt NaIO4), MeCN (3.5 mL, 1.0 M wrt NaIO4), and an aqueous solution of RuCl3 (0.12 mL, 0.1 M, 12 µmol, 0.005 equiv). The bilayer suspension was stirred at 0 °C for 2 min, then charged slowly dropwise with a solution of unsaturated lactone 47 (1.5 g, 2.4 mmol, 1.0 equiv) in EtOAc (3.0 mL, 0.5 M overall wrt 47) over 1 min (with 1.0 mL and 0.7 mL rinses). The reaction mixture was vigorously stirred at 0 °C for 40 min, charged with Na2SO4 (2.4 g), then filtered through Na2SO4 with EtOAc rinses (0.3 L total) into a separatory funnel containing sat. aq Na2SO3 (50 mL) and 1:1 H2O/brine (100 mL). The layers were separated and the aqueous layer extracted with EtOAc (4 x 0.1 L). The combined organic extracts were dried over Na2SO4 with added hexanes (0.18 L) and filtered through a silica gel plug (4 cm). The filter cake was rinsed with 4:1 hexanes/EtOAc (0.25 L), then 1:2 hexanes/EtOAc (1 L), and the latter filtrate concentrated to afford crude triol 48 as a pale yellow solid contaminated   167 with aldehyde byproduct (~9%). [α] 24 –0.06° (c = 2.3, CH2Cl2); IR (neat) 3444 (br), 3065, D 3032, 2954, 2930, 2883, 2858, 1735 (s), 1497, 1455, 1390, 1362, 1253, 1200, 1115, 1048, 938, 837, 779, 735, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.35–7.28 (m, 10H, ArH), 5.07 € (ddd, J = 11.7, 4.1, 1.7 Hz, 1H, C31-H), 4.94 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.77 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.67 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.58 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.26 (m, 1H, C33-H), 4.03 (m, J = 2.9 Hz, 1H, C34-H), 3.99 (dd, J = 8.2, 4.1 Hz, 1H, C29-H), 3.92 (ddd, J = 4.7, 4.1, 4.1 Hz, 1H, C28-H), 3.77 (ddd, J = 11.1, 7.6, 3.5 Hz, 1H, one of C27-H), 3.73 (dd, J = 8.2, 1.7 Hz, 1H, C30-H), 3.71 (ddd, J = 11.1, 4.7, 4.7 Hz, 1H, one of C27-H), 3.40 (s, 1H, C34-OH), 2.64 (s, 1H, C33-OH), 2.10 (dd, J = 7.6, 4.7 Hz, 1H, C27-OH), 2.08 (dddd, J = 14.1, 11.7, 2.4, 2.3 Hz, 1H, one of C32-H), 1.90 (ddd, J = 14.0, 4.1, 4.1 Hz, 1H, one of C32-H), 0.88 (s, 9H, C(CH3)3), 0.06 (s, 6H, Si(CH3)2); 13 C-NMR (125 MHz, CDCl3) δ 173.7, 138.1, 137.9, 128.4, 128.1, 128.0, 127.8, 127.7, 79.8, 79.4, 76.9, 75.3, 74.4, 72.1, 70.5, 66.1, 63.1, 30.0, 25.8, 18.0, –4.8, –4.9; HRMS (ESI-TOF) m/z calcd for C29H42NaO8Si [M+Na]+: 569.2541, found: 569.2558. O OBn O HO 27 TBSO 48 31 35 O OH OH MOPO 27 TBSO 49 OBn O 31 35 O O Me Me OBn OBn (3aR,6S,7aR)-6-((1R,2S,3S)-1,2-Bis(benzyloxy)-3-((tert-butyldimethylsilyl)oxy)-4-((2methoxypropan-2-yl)oxy)butyl)-2,2-dimethyldihydro-3aH-[1,3]dioxolo[4,5-c]pyran4(6H)-one (49). To a solution of crude triol 48 (theoretical 1.3 g, 2.4 mmol, 1.0 equiv) in 2:1 acetone/2,2-dimethoxypropane (47 mL, 0.05 M wrt 48) at rt was added PPTS (59 mg, 0.24 mmol, 0.1 equiv). The reaction mixture was stirred at 35 °C for 12 h, quenched with NaHCO3 (s) (~0.1 g), stirred vigorously for an additional 30 min at rt, and filtered through Celite . The  filter cake was rinsed with EtOAc (75 mL total), and the filtrate concentrated. Column chromatography (gradient elution, 18% → 20% → 25% EtOAc in hexanes) afforded acetonide 49 (1.0 g, 65% yield, two steps) as a clear, colorless oil. [α] 24 +2.2° (c = 2.1, D CH2Cl2); IR (neat) 3062, 3030, 2988, 2934, 2893, 2858, 1751 (s), 1459, 1377, 1261, 1211, 1156, 1114, 1077, 1049, 930, 834, 779, 738, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.35–   168 7.26 (m, 10H, ArH), 4.92 (ddd, J = 10.6, 2.9, 2.4 Hz, 1H, C31-H), 4.87 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.74 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.63 (d, J = 11.2 Hz, 1H, one of –OCH2Ph), 4.55 (ddd, J = 7.0, 4.1, 3.5 Hz, 1H, C33-H), 4.50 (d, J = 7.1 Hz, 1H, C34-H), 4.01 (ddd, J = 6.4, 4.1, 3.5 Hz, 1H, C28-H), 3.92 (dd, J = 7.1, 4.1 Hz, 1H, C29-H), 3.80 (dd, J = 7.1, 2.9 Hz, 1H, C30-H), 3.60 (dd, J = 10.0, 3.5 Hz, 1H, one of C27-H), 3.50 (dd, J = 10.0, 6.5 Hz, 1H, one of C27-H), 3.18 (s, 3H, –OCH3), 2.01 (ddd, J = 14.6, 10.5, 4.1 Hz, 1H, one of C32-H), 1.75 (ddd, J = 14.7, 2.9, 2.4 Hz, 1H, one of C32-H), 1.46 (s, 3H, one of CH3), 1.32 (s, 3H, one of CH3), 1.31 (s, 6H, two of CH3), 0.89 (s, 9H, C(CH3)3), 0.09 (s, 3H, one of Si(CH3)2), 0.05 (s, 3H, one of Si(CH3)2); 13C-NMR (125 MHz, CDCl3) δ 167.9, 138.4, 138.0, 128.4, 128.3, 128.2, 127.8, 127.7, 127.6, 110.4, 99.9, 80.0, 79.3, 75.2, 74.8, 74.0, 72.8, 72.1, 71.5, 62.0, 48.6, 30.4, 26.1, 26.0, 24.42, 24.40, 23.8, 18.3, –4.3, –4.8; HRMS (ESI-TOF) m/z calcd for C36H54NaO9Si [M+Na]+: 681.3429, found: 681.3412. O OBn O MOPO 27 TBSO 49 31 35 O O Me Me OBn OH O 31 MOPO 27 TBSO BnO Me O Me 35 OH OBn 50 (2S,3R,4S,5S)-3,4-Bis(benzyloxy)-5-((tert-butyldimethylsilyl)oxy)-1-((4R,5S)-5(hydroxymethyl)-2,2-dimethyl-1,3-dioxolan-4-yl)-6-((2-methoxypropan-2-yl)oxy)hexan2-ol (50). To a solution of lactone 49 (1.0 g, 1.5 mmol, 1.0 equiv) in THF (15 mL, 0.10 M wrt 49) at 0 °C was added H2O (44 µL, 2.5 mmol, 1.6 equiv) and LiBH4 (50 mg, 1.1 mmol, 1.5 equiv). The reaction mixture was slowly warmed to rt o/n (12 h total stir time), then recooled to 0 °C, quenched with 1 M aq NaOH (15 mL), stirred vigorously at rt for 1 h, and diluted with Et2O (75 mL). The layers were separated and the organic layer washed sequentially with H2O and brine (10 mL each). The combined aqueous layers were extracted with Et2O (3 x 50 mL), and the combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 5:2 → 2:1 → 3:2 hexanes/EtOAc + 1% Et3N) afforded diol 50 (0.92 g, 91% yield) as a clear, colorless oil. [α] 23 D –7.8° (c = 2.3, CH2Cl2); IR (neat) 3456 (br), 3060, 3029, 2987, 2934, 2883, 1460, 1374, €   169 1252, 1215, 1078, 1051, 835, 778, 738, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.37–7.26 (m, 10H, ArH), 4.84 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.75 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.62 (d, J = 11.2 Hz, 1H, one of – OCH2Ph), 4.14 (ddd, J = 9.3, 5.9, 4.7 Hz, 1H, C33-H), 4.03 (ddd, J = 7.1, 5.9, 4.7 Hz, 1H, C34H), 4.02 (ddd, J = 7.6, 4.1, 3.5 Hz, 1H, C28-H), 3.98 (dddd, J = 8.8, 4.7, 4.1, 2.9 Hz, 1H, C31H), 3.82 (dd, J = 7.1, 4.1 Hz, 1H, C29-H), 3.63 (dd, J = 10.0, 3.0 Hz, 1H, one of C27-H), 3.62 (dd, J = 7.6, 2.9 Hz, 1H, C30-H), 3.47 (ddd, J = 11.2, 7.1, 4.1 Hz, 1H, one of C35-H), 3.44 (dd, J = 10.0, 7.6 Hz, 1H, one of C27-H), 3.42 (ddd, J = 11.2, 7.6, 4.7 Hz, 1H, one of C35-H), 3.17 (s, 3H, –OCH3), 3.07 (d, J = 4.7 Hz, 1H, C31-OH), 1.90 (dd, J = 7.6, 4.1 Hz, 1H, C35-OH), 1.78 (ddd, J = 14.0, 9.4, 8.8 Hz, 1H, one of C32-H), 1.49 (ddd, J = 14.1, 4.2, 4.1 Hz, 1H, one of C32-H), 1.44 (s, 3H, one of CH3), 1.32 (s, 3H, one of CH3), 1.31 (s, 3H, one of CH3), 1.30 (s, 3H, one of CH3), 0.89 (s, 9H, C(CH3)3), 0.09 (s, 3H, one of Si(CH3)2), 0.04 (s, 3H, one of Si(CH3)2); 13C-NMR (125 MHz, CDCl3) δ 138.6, 138.4, 128.5, 128.31, 128.30, 128.0, 127.7, 127.6, 108.3, 99.9, 80.4, 80.0, 77.8, 75.6, 74.7, 73.9, 72.4, 69.8, 62.0, 61.5, 48.4, 32.3, 28.1, 25.9, 25.4, 24.4, 24.4, 18.2, –4.3, –4.8; HRMS (ESI-TOF) m/z calcd for C36H58NaO9Si [M+Na]+: 685.3742, found: 685.3736. OBn OH O 31 MOPO 27 TBSO BnO Me O Me 35 OBn OH O OH 31 MOPO 27 TBSO BnO Me O Me 35 OTBDPS 50 133 (2S,3R,4S,5S)-3,4-Bis(benzyloxy)-5-((tert-butyldimethylsilyl)oxy)-1-((4R,5S)-5-(((tertbutyldiphenylsilyl)oxy)methyl)-2,2-dimethyl-1,3-dioxolan-4-yl)-6-((2-methoxypropan-2yl)oxy)hexan-2-ol (133). To a solution of diol 50 (1.7 g, 2.6 mmol, 1.0 equiv) and imidazole (0.26 g, 3.8 mmol, 1.5 equiv) in DMF (13 mL, 0.20 M wrt 50) at 0 °C was added tertbutylchlorodiphenylsilane (0.80 mL, 3.1 mmol, 1.2 equiv). The reaction mixture was stirred at 0 °C for 6 h, quenched with sat. aq NaHCO3 (25 mL), and diluted with 1:1 hexanes/Et2O (0.1 L) and H2O (15 mL). The layers were separated and the aqueous layer extracted with 1:1 hexanes/Et2O (3 x 75 mL). The combined organic extracts were dried over Na2SO4, filtered and concentrated. Column chromatography (gradient elution, 9% → 10% → 12% EtOAc in hexanes) afforded silyl ether 133 (2.1 g, 92% yield) as a clear, colorless oil. [α] 23 +0.21° (c = D   170 2.9, CH2Cl2); IR (neat) 3543 (br), 3062, 3031, 2990, 2932, 2888, 2857, 1468, 1430, 1370, 1251, 1214, 1112, 1082, 1056, 831, 777, 737, 701 cm–1; 1H-NMR (600 MHz, C6D6) δ 7.78– 7.72 (m, J = 3.5 Hz, 4H, ArH), 7.31 (m, J = 7.0, 5.3 Hz, 4H, ArH), 7.21–7.18 (m, J = 6.5, 4.1 Hz, 6H, ArH), 7.11 (m, J = 7.0, 1.2 Hz, 4H, ArH), 7.04 (m, J = 7.6, 1.2 Hz, 2H, ArH), 4.88 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.74 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.66 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.39 (dddd, J = 11.4, 4.7, 4.7, 2.9 Hz, 1H, C31-H), 4.34 (ddd, J = 7.6, 3.5, 3.5 Hz, 1H, C34-H), 4.20 (ddd, J = 8.2, 5.9, 2.3 Hz, 1H, C33-H), 4.19–4.14 (m, J = 7.0, 5.9, 2.9 Hz, 2H, C28-H and C29-H), 3.97 (dd, J = 10.0, 3.5 Hz, 1H, one of C35-H), 3.89 (dd, J = 7.0, 2.9 Hz, 1H, C30-H), 3.81 (dd, J = 10.6, 5.9 Hz, 1H, one of C27-H), 3.78 (dd, J = 11.1, 7.0 Hz, 1H, one of C27-H), 3.73 (dd, J = 10.0, 7.6 Hz, 1H, one of C35-H), 3.17 (d, J = 4.7 Hz, 1H, C31-OH), 3.14 (s, 3H, –OCH3), 2.13 (ddd, J = 14.1, 11.2, 8.2 Hz, 1H, one of C32-H), 1.95 (ddd, J = 14.1, 4.7, 2.3 Hz, 1H, one of C32-H), 1.34 (s, 3H, one of CH3), 1.31 (s, 3H, one of CH3), 1.29 (s, 3H, one of CH3), 1.21 (s, 3H, one of CH3), 1.13 (s, 9H, C(CH3)3), 1.08 (s, 9H, C(CH3)3), 0.24 (s, 3H, one of Si(CH3)2), 0.21 (s, 3H, one of Si(CH3)2); 13C-NMR (125 MHz, C6D6) δ 139.5, 139.4, 136.0, 135.9, 133.8, 133.7, 130.1, 130.0, 128.5, 128.3, 128.14, 128.12, 128.09, 128.06, 127.9, 127.61, 127.59, 108.5, 100.1, 80.9, 80.5, 78.5, 77.0, 74.7, 74.4, 73.4, 70.9, 63.2, 62.9, 48.3, 33.2, 28.1, 27.1, 26.3, 25.6, 24.7, 24.6, 19.4, 18.6, –3.8, –4.4; HRMS (ESI-TOF) m/z calcd for C52H76NaO9Si2 [M+Na]+: 923.4920, found: 923.4888. OBn OH O 31 MOPO 27 TBSO BnO Me O Me 35 OBn OBn O OTBDPS 31 MOPO 27 TBSO BnO Me O Me 35 OTBDPS 133 51 (S)-3,3,8,8,9,9-Hexamethyl-6-((1S,2R,3S)-1,2,3-tris(benzyloxy)-4-((4R,5S)-5-(((tertbutyldiphenylsilyl)oxy)methyl)-2,2-dimethyl-1,3-dioxolan-4-yl)butyl)-2,4,7-trioxa-8siladecane (51). To a solution of carbinol 133 (2.1 g, 2.3 mmol, 1.0 equiv) in DMF (12 mL, 0.20 M wrt 133) at –20 °C was added sodium hydride (0.28 g, 60 wt% mineral oil dispersion, 7.0 mmol, 3.0 equiv). The suspension was stirred at –20 °C for 15 min, then charged with benzyl bromide (0.42 mL, 3.5 mmol, 1.5 equiv) and tetrabutylammonium iodide (86 mg, 0.23 mmol, 0.1 equiv). The reaction mixture was stirred between –20 °C and –5 °C for 6 h, briefly   171 warmed to 0 °C, then quenched with sat. aq NaHCO3 (50 mL), and diluted with 1:1 hexanes/Et2O (0.15 L) and H2O (50 mL). The layers were separated and the aqueous layer extracted with 1:1 hexanes/Et2O (3 x 0.1 L). The combined organic extracts were dried over Na2SO4, filtered and concentrated. Column chromatography (gradient elution, 6% → 8% → 9% EtOAc in hexanes) afforded benzyl ether 51 (2.1 g, 92% yield) as a clear, colorless oil. [α] 25 –0.42° (c = 2.0, CH2Cl2); IR (neat) 3069, 3031, 2988, 2933, 2890, 2858, 1456, 1429, D 1378, 1252, 1213, 1110, 1082, 1052, 832, 778, 736, 700 cm–1; 1H-NMR (600 MHz, C6D6) € δ 7.83–7.79 (m, 4H, ArH), 7.38 (m, J = 7.0 Hz, 2H, ArH), 7.33 (m, J = 7.1 Hz, 2H, ArH), 7.22–7.17 (m, 8H, ArH), 7.16–7.02 (m, 15H, ArH), 4.81 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.79 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.75 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.68 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.67 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.57 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.41 (ddd, J = 10.5, 5.8, 2.4 Hz, 1H, C33-H), 4.30 (ddd, J = 7.6, 4.1, 3.5 Hz, 1H, C28-H), 4.19 (ddd, J = 8.2, 4.1, 4.1 Hz, 1H, C31-H), 4.17–4.13 (m, J = 4.7, 4.1, 4.1 Hz, 2H, C29-H and C30-H), 4.08 (ddd, J = 5.9, 5.8, 5.3 Hz, 1H, C34-H), 4.01 (dd, J = 10.0, 3.6 Hz, 1H, one of C27-H), 3.85 (dd, J = 10.6, 5.9 Hz, 1H, one of C35-H), 3.79 (dd, J = 10.5, 5.3 Hz, 1H, one of C35-H), 3.67 (dd, J = 10.0, 7.6 Hz, 1H, one of C27-H), 3.08 (s, 3H, –OCH3), 2.36 (ddd, J = 14.1, 8.2, 2.4 Hz, 1H, one of C32-H), 2.18 (ddd, J = 14.1, 10.5, 3.5 Hz, 1H, one of C32-H), 1.46 (s, 3H, one of CH3), 1.28 (s, 3H, one of CH3), 1.26 (s, 6H, two of CH3), 1.16 (s, 9H, C(CH3)3), 1.07 (s, 9H, C(CH3)3), 0.25 (s, 3H, one of Si(CH3)2), 0.21 (s, 3H, one of Si(CH3)2); 13C-NMR (125 MHz, C6D6) δ 139.5, 139.41, 139.38, 136.1, 136.0, 133.9, 133.8, 130.0, 128.5, 128.4, 128.3, 128.07, 128.06, 127.91, 127.86, 127.59, 127.56, 108.0, 100.0, 79.9, 78.7, 78.6, 76.8, 74.3, 74.0, 73.9, 73.1, 71.9, 63.6, 63.4, 48.3, 30.7, 28.4, 27.1, 26.4, 25.6, 24.62, 24.60, 19.5, 18.6, –3.7, –4.2; HRMS (ESI-TOF) m/z calcd for C59H82NaO9Si2 [M+Na]+: 1013.5390, found: 1013.5355. OBn OBn O 31 MOPO 27 TBSO BnO Me O Me 35 OBn OBn O OTBDPS 31 MOPO 27 TBSO BnO Me O Me 35 OH 51 134 ((4S,5R)-2,2-Dimethyl-5-((2S,3R,4S,5S)-2,3,4-tris(benzyloxy)-5-((tertbutyldimethylsilyl)oxy)-6-((2-methoxypropan-2-yl)oxy)hexyl)-1,3-dioxolan-4-yl)methanol   172 (134). To a solution of silyl ether 51 (0.70 g, 0.70 mmol, 1.0 equiv) in THF (14 mL, 0.05 M wrt 51) at rt was added dropwise a pre-mixed solution of glacial acetic acid (40 µL, 0.70 mmol, 1.0 equiv) and tetrabutylammonium fluoride in THF (0.77 mL, 1.0 M, 0.77 mmol, 1.1 equiv). The reaction mixture was stirred at rt for 15 h, quenched with sat. aq NaHCO3 (15 mL), and diluted with 1:1 hexanes/Et2O (40 mL) and H2O (5 mL). The layers were separated and the aqueous layer extracted with 1:1 hexanes/Et2O (3 x 30 mL). The combined organic extracts were dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 20% → 22% → 24% EtOAc in hexanes + 1% Et3N) afforded carbinol 134 (0.49 g, 93%) as a clear, colorless oil. [α] 22 –12.5° (c = 1.8, CH2Cl2); D IR (neat) 3468 (br), 3063, 3032, 2988, 2934, 2886, 2858, 1497, 1458, 1378, 1252, 1214, 1082, 1051, 964, 835, 778, 735, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.38–7.27 (m, 15H, ArH), 4.74 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.71 (d, J = 12.4 Hz, 1H, one of – OCH2Ph), 4.69 (d, J = 11.2 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 11.7 Hz, 1H, one of – OCH2Ph), 4.61 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.56 (d, J = 11.1 Hz, 1H, one of – OCH2Ph), 4.06 (ddd, J = 7.6, 4.7, 3.6 Hz, 1H, C28-H), 3.95 (ddd, J = 9.4, 5.9, 4.1 Hz, 1H, C33H), 3.90 (dd, J = 4.7, 4.1 Hz, 1H, C30-H), 3.84 (dd, J = 4.6, 4.2 Hz, 1H, C29-H), 3.76 (m, J = 5.9, 5.8 Hz, 1H, C31-H), 3.73 (m, J = 7.0, 4.1 Hz, 1H, C34-H), 3.71 (dd, J = 10.0, 3.6 Hz, 1H, one of C27-H), 3.39 (dd, J = 10.0, 7.6 Hz, 1H, one of C27-H), 3.38 (m, J = 12.0, 7.1 Hz, 1H, one of C35-H), 3.32 (br m, J = 10.5 Hz, 1H, one of C35-H), 3.13 (s, 3H, –OCH3), 1.81 (ddd, J = 14.1, 5.9, 4.1 Hz, 1H, one of C32-H), 1.76 (br s, 1H, C35-OH), 1.71 (ddd, J = 14.1, 9.4, 5.8 Hz, 1H, one of C32-H), 1.43 (s, 3H, one of CH3), 1.29 (s, 3H, one of CH3), 1.25 (s, 6H, two of CH3), 0.92 (s, 9H, C(CH3)3), 0.10 (s, 3H, one of Si(CH3)2), 0.06 (s, 3H, one of Si(CH3)2); 13CNMR (125 MHz, CDCl3) δ 138.6, 138.41, 138.39, 128.5, 128.3, 128.2, 128.0, 127.9, 127.6, 127.54, 127.53, 107.9, 99.8, 78.8, 77.7, 77.5, 76.3, 74.0, 73.8, 73.3, 72.2, 72.0, 62.8, 61.6, 48.3, 30.0, 28.2, 26.0, 25.3, 24.39, 24.37, 18.2, –4.1, –4.6; HRMS (ESI-TOF) m/z calcd for C43H68NO9Si [M+NH4]+: 770.46579, found: 770.46677. OBn OBn O 31 MOPO 27 TBSO BnO Me O Me 35 OBn OBn O OH 31 MOPO 27 TBSO BnO Me O Me O 35 H 134 52   173 (4R,5R)-2,2-Dimethyl-5-((2S,3R,4S,5S)-2,3,4-tris(benzyloxy)-5-((tertbutyldimethylsilyl)oxy)-6-((2-methoxypropan-2-yl)oxy)hexyl)-1,3-dioxolane-4carbaldehyde (52). To a solution of carbinol 134 (0.12 g, 0.16 mmol, 1.0 equiv) and EtN(iPr)2 (83 µL, 0.48 mmol, 3.0 equiv) in CH2Cl2 (0.46 mL, 0.35 M wrt 134) and DMSO (80 µL, 2.0 M wrt 134) at –30 °C was added a solution of SO3•py (76 mg, 0.48 mmol, 3.0 equiv) in DMSO (0.37 mL, 1.3 M wrt SO3•py). The reaction mixture was stirred between –30 °C and –20 °C for 1 h, then quenched with brine (8 mL), Et2O (40 mL) and H2O (2 mL). The layers were separated and the organic layer washed sequentially with 1 M aq NaHSO4 (10 mL), sat. aq NaHCO3 (10 mL), and 1:1 H2O/brine (2 x 10 mL). The organic layer was then dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 15% → 20% EtOAc in hexanes) afforded aldehyde 52 (0.11 g, 94% yield) as a clear, colorless oil. [α] 24 –12.0° (c = 2.6, CH2Cl2); IR (neat) 3067, 3031, 2989, 2934, 2887, 2857, D 1734 (s), 1497, 1458, 1378, 1253, 1214, 1157, 1081, 1052, 963, 834, 778, 735, 699 cm–1; 1HNMR (600 MHz, CDCl3) δ 9.42 (d, J = 3.0 Hz, 1H, C35-H), 7.39–7.27 (m, 15H, ArH), 4.74 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.73 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.68 (d, J = 10.0 Hz, 1H, one of –OCH2Ph), 4.66 (d, J = 11.2 Hz, 1H, one of –OCH2Ph), 4.62 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.54 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.18 (ddd, J = 8.8, 7.0, 4.1 Hz, 1H, C33-H), 4.07 (ddd, J = 7.7, 4.7, 3.0 Hz, 1H, C28-H), 3.88 (dd, J = 5.3, 3.5 Hz, 1H, C30-H), 3.81 (ddd, J = 5.9, 5.9, 5.3 Hz, 1H, C31-H), 3.78 (dd, J = 4.7, 3.5 Hz, 1H, C29H), 3.74 (dd, J = 7.0, 2.9 Hz, 1H, C34-H), 3.73 (dd, J = 9.9, 2.9 Hz, 1H, one of C27-H), 3.38 (dd, J = 10.0, 7.6 Hz, 1H, one of C27-H), 3.14 (s, 3H, –OCH3), 1.94 (ddd, J = 14.1, 5.9, 4.1 Hz, 1H, one of C32-H), 1.21 (ddd, J = 14.7, 8.8, 5.9 Hz, 1H, one of C32-H), 1.54 (s, 3H, one of CH3), 1.30 (s, 3H, one of CH3), 1.28 (s, 3H, one of CH3), 1.26 (s, 3H, one of CH3), 0.92 (s, 9H, C(CH3)3), 0.11 (s, 3H, one of Si(CH3)2), 0.06 (s, 3H, one of Si(CH3)2); 13C-NMR (125 MHz, CDCl3) δ 201.6, 138.5, 138.3, 138.2, 128.5, 128.3, 128.2, 128.10, 128.08, 127.62, 127.60, 127.56, 110.2, 99.8, 81.7, 78.6, 77.3, 75.51, 75.46, 73.7, 73.2, 72.2, 71.8, 62.9, 48.3, 30.9, 27.6, 26.0, 25.2, 24.4 (2C), 18.1, –4.2, –4.6; HRMS (ESI-TOF) m/z calcd for C43H62NaO9Si [M+Na]+: 773.4055, found: 773.4047.   174 Synthesis of the C27–C48 Aldehyde OBn OBn O 31 MOPO 27 TBSO BnO Me O Me O 35 O H OTES OTBS 39 C9H19 52 53 OBn OBn O 31 MOPO 27 TBSO BnO Me O Me OH O 35 OTBS 39 C9H19 OTES 54 (5S,8R)-5-((S)-((4S,5R)-2,2-Dimethyl-5-((2S,3R,4S,5S)-2,3,4-tris(benzyloxy)-5-((tertbutyldimethylsilyl)oxy)-6-((2-methoxypropan-2-yl)oxy)hexyl)-1,3-dioxolan-4yl)(hydroxy)methyl)-3,3-diethyl-10,10,11,11-tetramethyl-8-nonyl-4,9-dioxa-3,10disiladodecan-6-one (54). To a solution of ketone 53 (0.12 g, 0.27 mmol, 2.1 equiv) and EtNMe2 (58 µL, 0.53 mmol, 4.2 equiv) in pentane (1.3 mL, 0.2 M wrt 53) at 0 °C was added Cy2BCl (61 µL, 0.28 mmol, 2.2 equiv). The enolization mixture was stirred at 0 °C for 20 min, then stirred at rt for 16 h, then cooled to –78 °C and charged slowly dropwise with a solution of aldehyde 52 (0.11 g, 0.15 mmol, 1.0 equiv) in Et2O (0.24 mL, 0.3 M wrt 52) over 1 min (with 0.20 mL rinse). The reaction mixture was stirred at –78 °C for 45 min, slowly warmed to –40 °C over 0.5 h, stirred at –40 °C for 4 h, slowly warmed to –25 °C over 2 h, stirred at –25 °C for 10 h, then quenched at 0 °C with aq pH 7 buffer (3 mL), MeOH (3 mL), Et2O (30 mL) and 30% aq H2O2 (1 mL). The biphasic mixture was stirred vigorously at 0 °C for 1 h, then at rt for 1 h. The layers were separated and the aqueous layer extracted with Et2O (2 x 30 mL). The combined organic extracts were washed with 10% aq Na2S2O3 (2 x 15 mL) and brine (15 mL), dried over Na2SO4 with added hexanes, filtered and concentrated. The residue was analyzed by 1H-NMR spectroscopy to assess reaction diastereoselectivity (d.r. = 85:15). Column chromatography (gradient elution, 3% → 4% → 5% EtOAc in hexanes) afforded aldol adduct 54 (0.10 g, 57% yield) as a clear, colorless oil. [α] 23 –7.6° (c = 2.3, D CH2Cl2); IR (neat) 3558 (br), 3064, 3031, 2954, 2929, 2856, 1721 (s), 1497, 1467, 1379, 1253, 1212, 1086, 1052, 1004, 967, 835, 776, 732, 697 cm–1; 1H-NMR (600 MHz, C6D6) δ 7.41 (m, J = 8.2 Hz, 2H, two of ArH), 7.39 (m, J = 7.7 Hz, 2H, two of ArH), 7.36 (m, J =   175 7.6 Hz, 2H, two of ArH), 7.24–7.18 (m, 6H, six of ArH), 7.13–7.09 (m, 3H, three of ArH), 4.82 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.79 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.78 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.73 (d, J = 11.8 Hz, 1H, one of –OCH2Ph), 4.65 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.58 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.54 (dddd, J = 6.5, 5.9, 5.3, 5.2 Hz, 1H, C39-H), 4.49 (ddd, J = 10.0, 7.1, 2.9 Hz, 1H, C33-H), 4.31 (m, J = 7.0 Hz, 1H, C34-H), 4.30 (ddd, J = 7.6, 3.5, 3.0 Hz, 1H, C28-H), 4.25 (d, J = 8.2 Hz, 1H, C36-H), 4.15–4.13 (m, J = 6.5, 5.3, 4.7 Hz, 2H, C30-H and C31-H), 4.10 (dd, J = 4.7, 3.5 Hz, 1H, C29H), 4.01 (dd, J = 9.9, 3.0 Hz, 1H, one of C27-H), 3.85 (dd, J = 8.8, 8.2 Hz, 1H, C35-H), 3.66 (dd, J = 10.0, 7.6 Hz, 1H, one of C27-H), 3.21 (dd, J = 18.2, 5.3 Hz, 1H, one of C38-H), 3.08 (s, 3H, –OCH3), 2.89 (dd, J = 18.2, 6.5 Hz, 1H, one of C38-H), 2.53 (d, J = 8.8 Hz, 1H, C35OH), 2.50 (ddd, J = 14.1, 10.0, 4.1 Hz, 1H, one of C32-H), 2.36 (ddd, J = 14.1, 6.5, 2.9 Hz, 1H, one of C32-H), 1.82–1.76 (m, J = 13.5, 5.9, 4.7 Hz, 1H, one of C40-H), 1.65–1.60 (m, J = 13.5, 5.9, 5.3 Hz, 1H, one of C40-H), 1.57–1.45 (m, 2H, C41-H2), 1.38 (s, 3H, one of CH3), 1.37–1.22 (m, 12H, C42–47-H2), 1.263 (s, 3H, one of CH3), 1.257 (s, 3H, one of CH3), 1.22 (s, 3H, one of CH3), 1.07 (s, 9H, C(CH3)3), 1.02 (s, 9H, C(CH3)3), 1.01 (t, J = 7.9 Hz, 9H, – SiCH2CH3), 0.90 (t, J = 7.1 Hz, 3H, C48-H3), 0.67 (q, J = 7.8 Hz, 6H, –SiCH2CH3), 0.25 (s, 3H, one of SiCH3), 0.22 (s, 3H, one of SiCH3), 0.20 (s, 3H, one of SiCH3), 0.18 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, C6D6) δ 209.2, 139.3 (3C), 128.6, 128.5, 128.4, 128.3, 128.1, 128.0, 127.9, 127.7, 127.64, 127.59, 107.9, 100.0, 79.8, 79.4, 78.7, 76.9, 75.7, 74.5, 74.1, 73.9, 72.9, 72.1, 72.0, 68.3, 63.4, 48.2, 46.4, 38.0, 32.3, 31.1, 30.2, 30.1, 30.0, 29.7, 27.0, 26.4, 26.2, 25.5, 24.62, 24.60, 24.56, 23.1, 18.5, 18.3, 14.3, 7.0, 5.1, –3.8, –4.20, –4.21, –4.5; HRMS (ESI-TOF) m/z calcd for C68H120NaO12Si3 [M+NH4]+: 1226.81128, found: 1226.81179. OBn OBn O 31 MOPO 27 TBSO BnO Me O Me OH O 35 OTBS 39 OBn OBn O 31 HO 27 TBSO BnO Me O Me O 35 TES O OTBS 39 C9H19 C9H19 OTES OTES 54 135 (5R,8S,9S)-9-((4R,5R)-2,2-Dimethyl-5-((2S,3R,4S,5S)-2,3,4-tris(benzyloxy)-5-((tertbutyldimethylsilyl)oxy)-6-hydroxyhexyl)-1,3-dioxolan-4-yl)-11,11-diethyl-2,2,3,3tetramethyl-5-nonyl-8-((triethylsilyl)oxy)-4,10-dioxa-3,11-disilatridecan-7-one (135). To a solution of carbinol 54 (0.10 g, 83 µmol, 1.0 equiv) and 2,6-lutidine (39 µL, 0.33 mmol, 4.0   176 equiv) in CH2Cl2 (0.41 mL, 0.2 M wrt 54) at 0 °C was added TESOTf (28 µL, 0.12 mmol, 1.5 equiv). The reaction mixture was stirred between 0 °C and 10 °C for 3 h, charged with additional TESOTf (19 µL, 83 µmol, 1.0 equiv), stirred between 0 °C and 10 °C for 1 h, then quenched with 1 M aq H2SO4 (1 mL) and Et2O (2 mL). The biphasic mixture was stirred vigorously at 0 °C for 1 h, then diluted with H2SO4 (6 mL) and Et2O (40 mL), and the layers were separated. The organic layer was washed sequentially with sat. aq NaHCO3 and brine (6 mL each), dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 3% → 4% EtOAc in hexanes) afforded diol 135 (86 mg, 83% yield) as a clear, colorless oil. [α] 25 +19.6° (c = 1.8, CH2Cl2); IR (neat) 3510 (br), 3065, D 3031, 2930, 2857, 1711 (s), 1461, 1408, 1378, 1252, 1219, 1098, 1061, 1008, 836, 776, 732, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.32–7.20 (m, 15H, ArH), 4.80 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.66 (m, 2H, –OCH2Ph), 4.63 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.56 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.50 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.28 (ddd, J = 11.1, 5.0, 3.1 Hz, 1H, C33-H), 4.22 (dddd, J = 6.0, 5.7, 5.6, 5.4 Hz, 1H, C39-H), 3.98 (ddd, J = 4.1, 4.0, 3.5 Hz, 1H, C31-H), 3.92 (dd, J = 4.4, 4.0 Hz, 1H, C30-H), 3.91 (dd, J = 6.0, 5.0 Hz, 1H, C29-H), 3.84 (m, J = 5.3, 5.0 Hz, 1H, C28-H), 3.84 (dd, J = 8.8, 5.0 Hz, 1H, C34-H), 3.77 (dd, J = 8.9, 1.9 Hz, 1H, C35-H), 3.69 (ddd, J = 11.3, 8.2, 3.1 Hz, 1H, one of C27-H), 3.67 (d, J = 1.9 Hz, 1H, C36-H), 3.56 (ddd, J = 11.4, 5.1, 4.7 Hz, 1H, one of C27-H), 2.89 (dd, J = 19.6, 6.7 Hz, 1H, one of C38-H), 2.82 (dd, J = 19.6, 5.3 Hz, 1H, one of C38-H), 1.78 (dd, J = 8.1, 4.7 Hz, 1H, C27-OH), 1.75 (ddd, J = 13.0, 11.1, 4.2 Hz, 1H, one of C32-H), 1.71 (m, J = 13.0, 2.8 Hz, 1H, one of C32-H), 1.48–1.22 (m, 16H, C40–47-H2), 1.42 (s, 3H, one of CH3), 1.26 (s, 3H, one of CH3), 0.97 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.89 (s, 9H, one of C(CH3)3), 0.88 (t, 3H, C48-H3), 0.87 (s, 9H, one of C(CH3)3), 0.84 (t, J = 8.0 Hz, 9H, –SiCH2CH3), 0.70–0.57 (m, J = 7.8, 7.5, 7.3 Hz, 6H, –SiCH2CH3), 0.43 (q, J = 7.9 Hz, 6H, –SiCH2CH3), 0.08 (s, 3H, one of SiCH3), 0.04 (s, 3H, one of SiCH3), 0.01 (s, 3H, one of SiCH3), –0.01 (s, 3H, one of SiCH3); 13 C-NMR (125 MHz, CDCl3) δ 211.9, 138.8, 138.6, 138.3, 128.4, 128.2, 128.2, 128.2, 128.0, 127.5, 127.4, 127.4, 127.3, 107.7, 78.8, 78.6, 78.5, 77.5, 76.1, 75.3, 74.1, 73.9, 73.5, 73.3, 71.4, 67.3, 64.2, 48.7, 37.9, 31.9, 30.4, 29.8, 29.6, 29.6, 29.3, 28.7, 26.0, 25.9, 25.9, 25.2, 22.7, 18.1, 18.0, 14.1, 6.9, 6.8, 5.3, 5.1, 5.0, 4.5, –4.5, –4.5, –4.7, –4.7; HRMS (ESI-TOF) m/z calcd for C70H122NaO11Si4 [M+Na]+: 1273.7956, found: 1273.7948.   177 27 OBn OBn O O 35 TES O OTES OTBS 39 O OBn OBn O O 35 TES O OTES OTBS 39 31 HO TBSO BnO Me O Me C9H19 31 H 27 TBSO BnO Me O Me C9H19 135 41 (2R,3S,4R,5S)-3,4,5-Tris(benzyloxy)-2-((tert-butyldimethylsilyl)oxy)-6-((4R,5R)-5((5S,6S,9R)-3,3-diethyl-11,11,12,12-tetramethyl-9-nonyl-7-oxo-6-((triethylsilyl)oxy)-4,10dioxa-3,11-disilatridecan-5-yl)-2,2-dimethyl-1,3-dioxolan-4-yl)hexanal (41). To a solution of carbinol 135 (0.24 g, 0.19 mmol, 1.0 equiv) and EtN(iPr)2 (0.10 mL, 0.58 mmol, 3.0 equiv) in CH2Cl2 (0.55 mL, 0.35 M wrt 135) and DMSO (0.11 mL, 1.8 M wrt 135) at –30 °C was added a solution of SO3•py (0.092 g, 0.58 mmol, 3.0 equiv) in DMSO (0.44 mL, 1.3 M wrt SO3•py). The reaction mixture was stirred between –30 °C and –20 °C for 1.5 h, quenched with brine (15 mL), then diluted with Et2O (40 mL) and H2O (1 mL). The layers were separated and the organic layer washed sequentially with 1 M aq NaHSO4 (15 mL), sat. aq NaHCO3 (15 mL), and 1:1 H2O/brine (2 x 15 mL). The organic layer was then dried over Na2SO4 with added hexanes, filtered and concentrated. Column chromatography (gradient elution, 1% → 1.5% → 2% EtOAc in hexanes) afforded aldehyde 41 (0.23 g, 95% yield) as a clear, colorless oil. [α] 26 +11.9° (c = 2.2, CH2Cl2); IR (neat) 3066, 3031, 2927, 2872, 1731 D (s), 1714 (s), 1455, 1416, 1380, 1252, 1220, 1143, 1097, 1061, 1026, 979, 950, 894, 837, 777, 729, 699 cm–1; 1H-NMR (600 MHz, CDCl3) δ 9.74 (s, 1H, C27-H), 7.33–7.18 (m, 15H, ArH), 4.68 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.63 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.61 (d, J = 11.6 Hz, 1H, one of –OCH2Ph), 4.47 (d, J = 11.4 Hz, 1H, one of –OCH2Ph), 4.46 (d, J = 11.0 Hz, 1H, one of –OCH2Ph), 4.32 (d, J = 11.1 Hz, 1H, one of –OCH2Ph), 4.25 (dddd, J = 5.7, 5.7, 5.7, 5.7 Hz, 1H, C39-H), 4.22 (ddd, J = 11.4, 5.0, 2.1 Hz, 1H, C33-H), 4.08 (dd, J = 5.9, 3.7 Hz, 1H, C29-H), 3.97 (d, J = 5.7 Hz, 1H, C28-H), 3.88 (dd, J = 5.6, 3.7 Hz, 1H, C30-H), 3.84 (dd, J = 9.1, 5.1 Hz, 1H, C34-H), 3.79 (m, 1H, C31-H), 3.78 (dd, J = 9.1, 2.0 Hz, 1H, C35H), 3.70 (d, J = 2.1 Hz, 1H, C36-H), 2.90 (dd, J = 19.6, 6.4 Hz, 1H, one of C38-H), 2.85 (dd, J = 19.6, 5.6 Hz, 1H, one of C38-H), 1.87 (ddd, J = 13.9, 3.7, 1.6 Hz, 1H, one of C32-H), 1.75 (ddd, J = 13.8, 11.9, 5.0 Hz, 1H, one of C32-H), 1.48–1.27 (m, 16H, C40–47-H2), 1.41 (s, 3H, one of CH3), 1.27 (s, 3H, one of CH3), 0.97 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.89 (t, J = 7.0 Hz, 3H, C48-H3), 0.88 (s, 9H, one of C(CH3)3), 0.88 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.88 (s,   178 9H, one of C(CH3)3), 0.71–0.59 (m, J = 8.1, 7.9, 7.8 Hz, 6H, –SiCH2CH3), 0.43 (q, J = 7.9 Hz, 6H, –SiCH2CH3), 0.09 (s, 3H, one of SiCH3), 0.06 (s, 3H, one of SiCH3), 0.02 (s, 3H, one of SiCH3), –0.10 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 211.9, 200.6, 138.7, 138.0, 137.7, 128.7, 128.6, 128.4, 128.3, 128.2, 128.0, 127.7, 127.5, 127.4, 107.6, 80.9, 78.8, 78.4, 77.0, 76.9, 76.7, 75.3, 74.9, 73.7, 73.7, 72.1, 67.3, 48.7, 37.9, 31.9, 31.0, 29.8, 29.6, 29.6, 29.3, 28.6, 26.1, 25.9, 25.8, 25.2, 22.7, 18.3, 18.0, 14.1, 6.9, 6.8, 5.1, 4.5, –4.5, –4.6, – 4.7, –5.5; HRMS (ESI-TOF) m/z calcd for C70H120NaO11Si4 [M+Na]+: 1271.7800, found: 1271.7846. Synthesis of Aflastatin A Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS O Me O OBn OBn O O 35 TES O OTBS 39 Me Me O Me TBS Me Me 40 Me Me 31 H 27 TBSO BnO Me O Me C9H19 OTES 41 Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 55 TBSO BnO Me O Me OTES (5R,8S,9S)-9-((4R,5R)-2,2-Dimethyl-5-((2S,3R,4S,5S,6S,8R,10R)-2,3,4-tris(benzyloxy)-11((4R,5S,6S)-6-((S)-1-((4S,6R)-6-((S)-1-((4R,5R,6R)-6-((2S,3R,4R,6R,8S)-3,9bis(benzyloxy)-4-((tert-butyldimethylsilyl)oxy)-6,8-dimethylnonan-2-yl)-2,2,5-trimethyl1,3-dioxan-4-yl)ethyl)-2,2-dimethyl-1,3-dioxan-4-yl)ethyl)-2,2,5-trimethyl-1,3-dioxan-4yl)-5-((tert-butyldimethylsilyl)oxy)-6,8-dihydroxy-10-((triisopropylsilyl)oxy)undecyl)-1,3dioxolan-4-yl)-11,11-diethyl-2,2,3,3-tetramethyl-5-nonyl-8-((triethylsilyl)oxy)-4,10-dioxa3,11-disilatridecan-7-one (55). To a solution of aldehyde 41 (0.23 g, 0.18 mmol, 1.0 equiv) and ketone 40 (0.24 g, 0.20 mmol, 1.1 equiv) in CH2Cl2 (1.3 mL, 0.14 M wrt 41) at –5 °C was added freshly prepared MgBr2•OEt2 (0.38 g, 1.5 mmol, 8.0 equiv). The resulting suspension was stirred at –5 °C for 10 min, then charged dropwise with 1,2,2,6,6-pentamethylpiperidine (83 µL, 0.46 mmol, 2.5 equiv). The reaction mixture was stirred at –5 °C for 7 min, then   179 rapidly quenched with pre-chilled sat. aq NaHCO3 (3 mL). The biphasic mixture was stirred vigorously at rt for 10 min, then diluted with Et2O (30 mL), H2O (10 mL) and sat. aq NaHCO3 (15 mL). The layers were separated and the aqueous layer extracted with CH2Cl2 (2 x 30 mL). The combined organic extracts were washed sequentially with sat. aq NH4Cl (2 x 20 mL) and brine (15 mL), dried over Na2SO4, filtered, concentrated and azeotroped with PhH (2 x 2 mL) to afford crude aldol adduct 163 as a clear, pale yellow oil that was used without further purification. To a solution of crude aldol adduct 163 (theoretical 0.44 g, 0.18 mmol, 1.0 equiv) in 4:1 THF/MeOH (1.8 mL, 0.1 M wrt 163) at –78 °C was added dropwise a solution of diethylmethoxyborane in THF (0.20 mL, 1.0 M, 0.20 mmol, 1.1 equiv). The reaction mixture was stirred at –78 °C for 2.5 h, then charged with sodium borohydride (21 mg, 0.55 mmol, 3.0 equiv) in one portion. The reaction mixture was slowly warmed to –55 °C over 0.5 h, stirred at –55 °C for 20 h, quenched with a pre-mixed mixture of 1 M aq NaOH (1 mL) and 30% aq H2O2 (0.4 mL), then diluted with 4:1 THF/MeOH (1 mL). The heterogeneous mixture was stirred vigorously at 0 °C for 1.5 h, then diluted with Et2O (30 mL) and aq pH 7 buffer (3 mL). The layers were separated and the aqueous layer extracted with Et2O (2 x 30 mL). The combined organic extracts were washed with 10% aq Na2S2O3 (2 x 10 mL) and brine (10 mL), dried over Na2SO4 with added hexanes, filtered and concentrated. The residue was analyzed by 1H-NMR spectroscopy to assess reaction diastereoselectivity (d.r. ≥ 95:05). Column chromatography (gradient elution, 6% → 6.5% EtOAc in hexanes) afforded diol 55 (0.31 g, 70% yield, two steps) as a white foam. [α] 25 +1.0° (c = 1.2, CH2Cl2); IR (neat) 3498 (br), D 3068, 3036, 2932, 2864, 1712, 1459, 1380, 1253, 1202, 1175, 1098, 1008, 982, 837, 775, 733, 698 cm–1; 1H-NMR (600 MHz, CDCl3) δ 7.34–7.21 (m, 25H, ArH), 4.73 (d, J = 12.0 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.70 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.66 (m, 2H, –OCH2Ph), 4.61 (d, J = 11.7 Hz, 1H, one of –OCH2Ph), 4.52 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.49 (d, J = 11.9 Hz, 1H, one of –OCH2Ph), 4.45 (m, 2H, – OCH2Ph), 4.28 (ddd, J = 11.6, 7.0, 2.5 Hz, 1H, C33-H), 4.25 (m, J = 7.0, 6.0 Hz, 1H), 4.22 (m, 1H), 4.21 (m, J = 5.1, 5.1 Hz, 1H, C39-H), 4.18–4.16 (m, 2H), 4.03–3.98 (m, 2H), 3.98–3.92 (m, 3H), 3.91 (m, 1H, C31-H), 3.88 (m, 1H, C8-H), 3.82 (dd, J = 8.9, 4.9 Hz, 1H, C34-H), 3.79 (dd, J = 8.9, 1.9 Hz, 1H, C35-H), 3.69 (m, 1H), 3.66 (d, J = 1.9 Hz, 1H, C36-H), 3.60 (m, J =   180 1.6 Hz, 1H), 3.59 (m, J = 9.8 Hz, 1H), 3.54 (m, J = 7.2, 2.8 Hz, 2H), 3.40 (dd, J = 6.2, 2.6 Hz, 1H, C9-H), 3.33 (dd, J = 9.1, 5.3 Hz, 1H, one of C3-H), 3.14 (dd, J = 9.1, 7.4 Hz, 1H, one of C3-H), 2.88 (dd, J = 19.6, 6.6 Hz, 1H, one of C38-H), 2.83 (dd, J = 19.5, 5.4 Hz, 1H, one of C38-H), 2.39 (m, J = 6.8, 6.6, 2.5 Hz, 1H, C10-H), 1.94–1.80 (m, 4H), 1.80–1.57 (m, 8H), 1.52 (m, J = 1.9 Hz, 1H), 1.48–1.20 (m, 16H, C40–47-H2), 1.48–1.20 (m, 5H), 1.44 (s, 3H, one of CH3), 1.39 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3), 1.31 (s, 3H, one of CH3), 1.24 (s, 3H, one of CH3), 1.16 (ddd, J = 13.3, 8.0, 5.6 Hz, 1H), 1.07 (m, 18H, –SiCH(CH3)2), 1.07 (m, 3H, – SiCH(CH3)2), 1.04 (ddd, J = 13.3, 6.3, 2.2 Hz, 1H), 0.99–0.97 (m, J = 6.9 Hz, 6H, two of – CH(CH3)), 0.96 (t, J = 8.0 Hz, 9H, –SiCH2CH3), 0.92–0.81 (m, 12H, four of –CH(CH3)), 0.88 (s, 9H, one of C(CH3)3), 0.88 (t, J = 7.1 Hz, 3H, C48-H3), 0.86 (s, 9H, one of C(CH3)3), 0.84 (s, 9H, one of C(CH3)3), 0.83 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.73 (d, J = 6.9 Hz, 3H, one of –CH(CH3)), 0.70–0.58 (m, J = 7.9, 7.8 Hz, 6H, –SiCH2CH3), 0.43 (q, J = 8.0 Hz, 6H, – SiCH2CH3), 0.07 (s, 3H, one of SiCH3), 0.03 (s, 3H, one of SiCH3), 0.03 (s, 3H, one of SiCH3), 0.01 (s, 3H, one of SiCH3), –0.03 (s, 3H, one of SiCH3), –0.13 (s, 3H, one of SiCH3); 13 C-NMR (125 MHz, CDCl3) δ 211.8, 139.8, 138.8, 138.8, 137.9, 137.7, 128.5, 128.4, 128.3, 128.3, 128.2, 128.1, 128.0, 127.8, 127.4, 127.4, 127.4, 127.3, 127.3, 127.0, 107.5, 98.3, 98.3, 97.2, 80.9, 79.6, 78.9, 78.5, 77.2, 75.9, 75.9, 75.8, 75.5, 75.0, 74.8, 74.0, 73.6, 73.3, 73.0, 72.8, 72.8, 72.5, 71.5, 71.5, 71.0, 69.9, 69.7, 68.2, 67.3, 67.2, 48.7, 45.1, 42.5, 40.8, 40.7, 39.2, 39.1, 38.6, 37.9, 32.7, 32.4, 31.9, 31.9, 31.3, 30.6, 30.4, 30.1, 30.0, 29.8, 29.6, 29.6, 29.3, 28.6, 27.1, 27.0, 26.0, 26.0, 25.9, 25.8, 25.2, 22.7, 20.7, 20.1, 19.8, 19.3, 18.2, 18.2, 18.2, 18.0, 18.0, 14.1, 12.7, 11.0, 9.5, 9.0, 8.9, 6.9, 6.8, 5.1, 4.6, 4.5, –3.7, –3.8, –4.2, –4.4, – 4.5, –4.7; HRMS (ESI-TOF) m/z calcd for C139H242NaO22Si6 [M+Na]+: 2454.6326, found: 2454.6361.   181 Me Me OBn O BnO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 55 TBSO BnO Me O Me OTES Me Me OH O HO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OH OH O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 56 TBSO HO Me O Me OTES (5R,8S,9S)-9-((4R,5R)-5-((2S,3R,4S,5S,6S,8R,10R)-5-((tert-Butyldimethylsilyl)oxy)-11((4R,5S,6S)-6-((S)-1-((4S,6R)-6-((S)-1-((4R,5S,6S)-6-((2R,3R,4R,6R,8S)-4-((tertbutyldimethylsilyl)oxy)-3,9-dihydroxy-6,8-dimethylnonan-2-yl)-2,2,5-trimethyl-1,3dioxan-4-yl)ethyl)-2,2-dimethyl-1,3-dioxan-4-yl)ethyl)-2,2,5-trimethyl-1,3-dioxan-4-yl)2,3,4,6,8-pentahydroxy-10-((triisopropylsilyl)oxy)undecyl)-2,2-dimethyl-1,3-dioxolan-4yl)-11,11-diethyl-2,2,3,3-tetramethyl-5-nonyl-8-((triethylsilyl)oxy)-4,10-dioxa-3,11disilatridecan-7-one (56). To a solution of pentabenzyl ether 55 (0.11 g, 45 µmol, 1.0 equiv) in THF (0.30 mL, 0.15 M wrt 55) and 6:1 dioxane/H2O (0.15 mL, 0.30 M wrt 55) at rt was added palladium black (~10 mg). The reaction mixture was purged with hydrogen for 1 min, stirred vigorously for 6 h, then recharged with additional catalyst at this time and approximately every 6 h thrice after (total palladium black added: ~50 mg). The reaction mixture was stirred at rt for 6 h, then filtered through Celite . The filter cake was rinsed with  THF (35 mL total), and the filtrate concentrated. Column chromatography (gradient elution, 1% → 1.5% EtOH in CH2Cl2) afforded heptaol 56 (84 mg, 93% yield) as a clear, colorless glass. [α] 23 –5.1° (c = 2.1, CH2Cl2); IR (neat) 3448 (br), 2932, 2864, 1716, 1462, 1380, 1254, D 1201, 1096, 1057, 1007, 981, 885, 837, 776, 743, 678 cm–1; 1H-NMR (500 MHz, CDCl3) δ 4.44 (m, 1H), 4.36 (m, J = 11.7, 4.9 Hz, 1H), 4.25 (m, J = 5.4, 4.4 Hz, 1H), 4.21 (m, J = 5.9, 5.4 Hz, 1H, C39-H), 4.17–4.11 (m, 3H), 4.11–3.94 (m, 4H), 3.94–3.83 (m, 4H), 3.78–3.64 (m, 6H), 3.64–3.55 (m, 3H), 3.49 (dd, J = 10.5, 5.1 Hz, 1H), 3.42–3.37 (m, J = 9.8, 8.3 Hz, 2H, C3-H2), 3.22 (m, J = 3.9 Hz, 1H), 2.92 (dd, J = 19.5, 5.4 Hz, 1H, one of C38-H), 2.81 (dd, J = 19.5, 5.9 Hz, 1H, one of C38-H), 2.08 (m, J = 9.8 Hz, 1H, C3-OH), 1.93–1.81 (m, 6H), 1.79–   182 1.68 (m, 5H), 1.65 (m, J = 7.3, 7.3 Hz, 1H), 1.62–1.47 (m, 6H), 1.47 (s, 3H, one of CH3), 1.45–1.22 (m, 16H, C40–47-H2), 1.43 (s, 3H, one of CH3), 1.38 (s, 3H, one of CH3), 1.36 (m, 1H), 1.36 (m, 1H, one of C5-H), 1.36 (s, 3H, one of CH3), 1.34 (s, 3H, one of CH3), 1.34 (s, 3H, one of CH3), 1.27 (s, 3H, one of CH3), 1.25 (s, 3H, one of CH3), 1.07 (m, 21H, – SiCH(CH3)2, and –SiCH(CH3)2), 1.03 (d, J = 6.8 Hz, 3H, one of –CH(CH3)), 0.98 (m, 1H, one of C5-H), 0.95 (t, J = 7.8 Hz, 18H, –SiCH2CH3), 0.95 (d, J = 7.8 Hz, 3H, one of –CH(CH3)), 0.92 (d, J = 6.3 Hz, 3H, one of –CH(CH3)), 0.92 (d, J = 6.3 Hz, 3H, one of –CH(CH3)), 0.89 (s, 18H, two of C(CH3)3), 0.87 (t, 3H, C48-H3), 0.86 (d, 3H, one of –CH(CH3)), 0.86 (s, 9H, one of C(CH3)3), 0.80 (d, J = 6.8 Hz, 3H, one of –CH(CH3)), 0.67 (d, J = 5.9 Hz, 3H, one of – CH(CH3)), 0.70–0.58 (m, J = 7.8, 7.3 Hz, 12H, –SiCH2CH3), 0.11 (s, 9H, three of SiCH3), 0.10 (s, 3H, one of SiCH3), 0.06 (s, 3H, one of SiCH3), 0.02 (s, 3H, one of SiCH3); 13C-NMR (125 MHz, CDCl3) δ 212.0, 108.1, 98.4, 98.2, 97.1, 79.1, 78.4, 75.8, 75.8, 75.0, 74.8, 74.7, 74.5, 73.5, 73.4, 73.3, 72.4, 71.3, 70.8, 70.5, 69.9, 69.5, 68.5, 68.2, 68.2, 67.2, 48.4, 43.9, 41.9, 41.9, 41.2, 40.0, 39.9, 39.2, 38.5, 37.8, 36.3, 33.3, 33.1, 32.9, 31.9, 31.8, 30.3, 30.0, 29.8, 29.7, 29.6, 29.5, 29.3, 28.4, 26.8, 25.9, 25.8, 25.8, 25.8, 25.1, 22.6, 20.8, 20.1, 19.7, 19.2, 18.1, 18.0, 18.0, 18.0, 17.1, 14.1, 12.7, 10.9, 9.3, 9.2, 9.1, 6.8, 6.8, 5.1, 4.7, 4.7, –3.4, – 4.2, –4.4, –4.6, –4.6, –4.7; HRMS (ESI-TOF) m/z calcd for C104H213O22Si6 [M+H]+: 1982.41586, found: 1982.41308. Me Me OH O HO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OH OH O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 56 R = TMS TBSO HO Me O Me OTES Me Me OR O HO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 57 TBSO RO Me O Me OTES Primary carbinols 57. To a solution of heptaol 56 (0.10 g, 51 µmol, 1.0 equiv) and pyridine (58 µL, 0.72 mmol, 14 equiv) in CH2Cl2 (0.86 mL, 60 mM wrt 56) at 0 °C was added chlorotrimethylsilane (65 µL, 0.51 mmol, 10 equiv). The reaction mixture was stirred at 0 °C   183 for 2 h, slowly warmed to rt over 2 h, stirred at rt for 2 d, quenched at 0 °C with H2O (1 mL), and diluted with Et2O (3 mL). The layers were separated and the aqueous layer extracted with 9:1 hexanes/EtOAc (5 x 2 mL). The combined organic extracts were filtered through a silica gel plug (4 cm), and the filter cake rinsed with 9:1 hexanes/EtOAc (50 mL). The filtrate was concentrated, then azeotroped with PhH (3 x 5 mL) to afford a crude mixture of regioisomeric hexakistrimethylsilyl ethers 164 as a clear, colorless oil that was used without further purification. To a solution of crude trimethylsilyl ethers 164 (theoretical 0.13 g, 51 µmol, 1.0 equiv) in 4:1 CH2Cl2/iPrOH (1.3 mL, 0.04 M wrt 164) at 0 °C was added PPTS (0.13 mg, 0.51 µmol, 0.01 equiv). The reaction mixture was stirred at 0 °C for 2 h, quenched with Et3N (0.1 mL), stirred while warming to rt over 5 min, and filtered through a silica gel plug (4 cm). The filter cake was rinsed with 9:1 hexanes/EtOAc (50 mL), and the filtrate concentrated. Column chromatography (gradient elution, 3% → 3.5% → 4% EtOAc in hexanes) afforded a mixture of primary carbinols 57 (0.10 g, 87% yield, two steps) as a white foam. [α] 23 –7.8° (c = 2.6, D CH2Cl2); IR (neat) 3509 (br), 2955, 1718, 1463, 1379, 1252, 1201, 1094, 1056, 978, 840, 775, 746, 679 cm–1; partial list of resonances: 1H-NMR (600 MHz, CDCl3) δ 4.23–4.15 (m, J = 11.2, 2.9 Hz, 2H), 4.21 (m, J = 5.9, 5.8, 5.3 Hz, 1H, C39-H), 4.18–4.15 (m, J = 11.2, 2.9 Hz, 2H), 3.89 (m, 1H), 3.84–3.76 (m, 3H), 3.75–3.65 (m, 4H), 3.63 (dd, J = 4.7, 3.5 Hz, 1H), 3.58–3.48 (m, 7H), 3.34 (ddd, J = 10.6, 7.0, 4.1 Hz, 1H), 2.91–2.83 (m, J = 6.5, 5.3 Hz, 2H, C38-H2), 2.70 (d, J = 8.3 Hz, 1H, CH-OH), 2.17–2.15 (m, 1H), 1.43 (s, 3H, one of CH3), 1.41 (s, 3H, one of CH3), 1.38 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3), 1.34 (s, 3H, one of CH3), 1.28 (s, 3H, one of CH3), 1.21 (s, 3H, one of CH3), 1.06 (m, 21H, –SiCH(CH3)2, 0.962 (t, J = 7.9 Hz, 9H, –SiCH2CH3), 0.958 (t, J = 7.9 Hz, 9H, – SiCH2CH3), 0.91 (s, 9H, one of C(CH3)3), 0.89 (d, J = 7.0 Hz, 3H, one of –CH(CH3)), 0.89 (s, 9H, one of C(CH3)3), 0.87 (d, J = 7.1 Hz, 3H, one of –CH(CH3)), 0.87 (d, J = 7.0 Hz, 3H, one of –CH(CH3)), 0.86 (d, 3H, one of –CH(CH3)), 0.86 (s, 9H, one of C(CH3)3), 0.85 (d, J = 7.1 Hz, 3H, one of –CH(CH3)), 0.78 (d, J = 7.0 Hz, 3H, one of –CH(CH3)), 0.70 (d, J = 7.0 Hz, 3H, one of –CH(CH3)), 0.70–0.58 (m, 12H, –SiCH2CH3), 0.15 (s, 9H, one of –Si(CH3)3), 0.14 (s, 9H, one of –Si(CH3)3), 0.11 (s, 9H, one of –Si(CH3)3), 0.10 (s, 9H, one of –Si(CH3)3), 0.08 (s, 9H, one of –Si(CH3)3); 13C-NMR (125 MHz, CDCl3) δ 211.8, 106.9, 98.5, 98.2, 97.2, 78.4,   184 78.3, 77.6, 77.3, 77.0, 76.2, 76.0, 75.1, 73.5, 73.2, 73.1, 72.5, 71.5, 70.6, 70.4, 68.1 (3C), 67.4, 67.3, 66.8, 48.9, 46.0, 41.8 (2C), 40.2, 39.6, 39.3, 38.6, 37.9, 34.8, 33.0, 31.9, 31.83, 31.80, 30.4, 30.1, 30.0, 29.8, 29.63, 29.59, 29.3, 28.8, 27.1, 26.1, 26.0, 25.9, 25.8, 25.2, 22.7, 20.9, 20.2, 20.0, 19.4, 18.4, 18.34, 18.30, 18.1, 18.0, 17.7, 14.1, 12.9, 11.1, 9.5, 8.9, 6.9, 5.2, 4.7, 1.35, 1.34, 0.95, 0.91, 0.78, –3.5 (2C), –4.0, –4.6, –4.7, –4.8; HRMS (ESI-TOF) m/z calcd for C119H252NaO22Si11 [M+Na]+: 2364.58752, found: 2364.59544. Me Me OR O HO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me 57 R = TMS TBSO RO Me O Me OTES Me Me 2' Me Me 3 7 Me Me O 15 Me Me O 19 O 3' O OR O 11 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O C9H19 Me Me Me O Me TBS Me Me Me Me 59 TBSO RO Me O Me OTES Dioxinones 59. To a solution of carbinols 57 (73 mg, 30 µmol, 1.0 equiv) and EtN(iPr)2 (16 µL, 91 µmol, 3.0 equiv) in CH2Cl2 (0.43 mL, 0.07 M wrt 57) and DMSO (0.10 mL, 0.3 M wrt 57) at –30 °C was added a solution of SO3•py (14 mg, 91 µmol, 3.0 equiv) in DMSO (0.30 mL, 0.3 M wrt SO3•py). The reaction mixture was stirred between –30 °C and –20 °C for 1.5 h, charged with an additional solution of SO3•py (14 mg, 91 µmol, 3.0 equiv) in DMSO (0.10 mL, 0.9 M wrt SO3•py), stirred for an additional 3 h, quenched with brine (8 mL), then diluted with Et2O (40 mL) and H2O (1 mL). The layers were separated and the organic layer washed sequentially with 1 M aq NaHSO4 (8 mL), sat. aq NaHCO3 (8 mL), and 1:1 H2O/brine (2 x 8 mL). The organic layer was then dried over Na2SO4 with added hexanes, filtered and concentrated. Benzene was added during concentration to prevent decomposition. Column chromatography (gradient elution, 2% → 3% EtOAc in hexanes) afforded a mixture of aldehydes 58 as a clear, colorless oil that was slightly wet with benzene. To a solution of dioxinone phosphonate 11 (27 mg, 91 µmol, 3.0 equiv) in THF (0.45 mL, 0.2 M wrt 11) at –78 °C was added a freshly prepared solution of LDA in THF (0.18 mL, 0.5 M,   185 91 µmol, 3.0 equiv). The reaction mixture was slowly warmed to 0 °C over 1.5 h, stirred at 0 °C for 30 min, then recooled to –78 °C and charged with HMPA (0.10 mL, 0.3 M wrt 58). The reaction mixture was stirred at –78 °C for 45 min, charged with a solution of aldehydes 58 (theoretical 73 mg, 30 µmol, 1.0 equiv) in THF (0.15 mL, 0.20 M wrt 58), slowly warmed to 0 °C over 3 h, stirred at 0 °C for 3 h, quenched with brine (1 mL), then diluted with Et2O (3 mL) and H2O (0.2 mL). The biphasic mixture was directly filtered through a silica gel plug (4 cm), the filter cake rinsed with 9:1 hexanes/EtOAc (50 mL), and the filtrate concentrated. Column chromatography (gradient elution, 3% → 3.5% → 4% EtOAc in hexanes) afforded a mixture of dioxinones 59 (44 mg, 59% yield, two steps) as a white foam. [α] 22 +2.5° (c = 2.2, D CH2Cl2); IR (neat) 3506 (br), 2956, 2877, 1736, 1639, 1597, 1462, 1378, 1252, 1202, 1096, 1058, 1010, 978, 839, 776, 746, 678 cm–1; partial list of resonances: 1H-NMR (600 MHz, CDCl3) δ 6.14 (d, J = 10.0 Hz, 1H, C3-H), 5.40 (s, 1H, C3'-H), 4.21–4.15 (m, 2H), 4.20 (m, J = 5.9, 5.8, 5.3 Hz, 1H, C39-H), 4.12–4.06 (m, 2H), 3.92–3.87 (m, 1H), 3.86–3.75 (m, 3H), 3.69–3.65 (m, 4H), 3.59–3.44 (m, 7H), 2.91–2.83 (m, 2H, C38-H2), 2.70 (d, J = 8.2 Hz, 1H, CH-OH), 2.70–2.66 (m, 1H, C4-H), 2.17–2.11 (m, 1H), 1.82 (s, 3H, C2-CH3), 1.70 (s, 6H, two of CH3), 1.43 (s, 3H, one of CH3), 1.41 (s, 3H, one of CH3), 1.37 (s, 3H, one of CH3), 1.36 (s, 3H, one of CH3), 1.35 (s, 3H, one of CH3), 1.33 (s, 3H, one of CH3), 1.27 (s, 3H, one of CH3), 1.21 (s, 3H, one of CH3), 1.05 (m, 21H, –SiCH(CH3)2, 0.99 (d, J = 6.4 Hz, 3H, –C4(CH3)), 0.97 (d, 3H, one of –CH(CH3)), 0.96 (t, J = 7.9 Hz, 18H, –SiCH2CH3), 0.90 (s, 9H, one of C(CH3)3), 0.87 (d, J = 7.1 Hz, 3H, one of –CH(CH3)), 0.86 (s, 9H, one of C(CH3)3), 0.85 (s, 9H, one of C(CH3)3), 0.84 (d, J = 7.1 Hz, 3H, one of –CH(CH3)), 0.82 (d, J = 7.1 Hz, 3H, one of –CH(CH3)), 0.78 (d, J = 7.1 Hz, 3H, one of –CH(CH3)), 0.69 (d, J = 6.4 Hz, 3H, one of – CH(CH3)), 0.70–0.58 (m, 12H, –SiCH2CH3), 0.15 (s, 9H, one of –Si(CH3)3), 0.14 (s, 9H, one of –Si(CH3)3), 0.11 (s, 9H, one of –Si(CH3)3), 0.08 (s, 18H, two of –Si(CH3)3); 13C-NMR (125 MHz, CDCl3) δ 211.9, 165.8, 162.4, 143.5, 125.7, 106.9, 105.9, 98.5, 98.2, 97.2, 91.4, 78.4, 78.3, 77.6, 77.5, 77.0, 76.8, 76.1, 76.0, 75.1, 73.5, 73.1, 73.0, 72.4, 71.5, 70.6, 70.4, 68.1, 67.4, 67.3, 66.8, 48.8, 46.0, 45.3, 40.7, 40.2, 39.6, 39.3, 38.6, 37.9, 36.6, 32.8, 31.9, 31.8, 31.7, 30.6, 30.4, 30.1, 30.0, 29.8, 29.63, 29.59, 29.3, 28.8, 28.4, 27.6, 26.9, 26.2, 26.1, 26.0, 25.9, 25.8, 25.7, 25.4, 25.2, 24.7, 24.6, 23.3, 22.7, 21.2, 20.3, 20.2, 20.0, 19.4, 18.4, 18.34, 18.30, 18.2, 18.02, 18.00, 14.1, 12.9, 12.3, 11.1, 9.5, 8.9, 8.8, 6.9, 5.2, 4.7, 1.39, 1.35, 0.94,   186 0.76 (2C), –3.5 (2C), –4.1, –4.6, –4.7, –4.8; HRMS (ESI-TOF) m/z calcd for C127H264NO24Si11 [M+NH4]+: 2495.69248, found: 2495.68105. Me Me 2' Me Me 3 7 Me Me O 15 Me Me O 19 O 3' O OR O 11 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O C9H19 Me Me Me O Me TBS Me Me Me Me 59 R = TMS TBSO RO Me O Me OTES Me Me Me EtO 4' Me Me O 15 Me Me O 19 O O 3 7 OR O 11 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O N 2' Me C9H19 Me Me Me O Me TBS Me Me Me Me 60 TBSO RO Me O Me OTES β-Ketoamides 60. A mixture of dioxinones 59 (12 mg, 4.7 µmol, 1.0 equiv), aminium chloride 9•HCl (13 mg, 75 µmol, 16 equiv), and 4 Å molecular sieves (25 mg, 1:1 mass ratio wrt 59 + 9•HCl) was azeotroped with 1:1 CH2Cl2/PhH (3 x 1 mL) in a 0.5 dram vial. The reaction vessel was charged with PhMe (94 µL, 50 mM wrt 59), sealed with Teflon tape and parafilm, then heated to 110 °C for 7 h. The reaction mixture was cooled to rt, diluted with 9:1 CH2Cl2/MeOH (0.5 mL), and filtered through a silica gel plug (4 cm). The filter cake was rinsed with 9:1 CH2Cl2/MeOH (30 mL), and the filtrate concentrated. Column chromatography (gradient elution, 0.5% → 0.75% → 1% EtOAc in hexanes) afforded a mixture of β-ketoamides 60 (8.5 mg, 69% yield) as a clear, colorless oil. These β-ketoamides 60 existed as a complex mixture of rotamers and tautomers. partial list of resonances: 1HNMR (600 MHz, CDCl3) δ 6.57–6.28 (3 x d, J = 10.0 Hz, 1H, C3-H), 2.95–2.84 (3 x s, 3H, NCH3), 2.91–2.83 (m, 2H, C38-H2), 2.75–2.68 (m, 1H, C4-H), 2.70 (d, J = 8.2 Hz, 1H, CH-OH), 1.82 (s, 3H, C2-CH3); 13C-NMR (125 MHz, CDCl3) δ 211.9, 195.1, 171.7, 168.0, 150.8, 135.2, 106.9, 98.5, 98.2, 97.2.   187 Me Me Me EtO 4' Me Me O 15 Me Me O 19 O O 3 7 OR O 11 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O N 2' Me C9H19 Me Me Me O Me TBS Me Me Me Me 60 TBSO RO Me O Me OTES R = TMS OH HO HO HO HO HO HO HO HO HO HO HO HO HO 7 11 15 19 23 27 31 35 Et2NH2 O Me N Me 2' O 3 OH OH 39 O Me Me Me OH Me Me Me Me Me 1•Et2NH OH OH H O OH C9H19 Aflastatin A diethylamine salt (1•Et2NH). To a solution of β-ketoamides 60 (19 mg, 7.4 µmol, 1.0 equiv) in 1:1 THF/TMSOH (0.37 mL, 0.02 M wrt 60) at 0 °C was added KOTMS (2.3 mg, 16 µmol, 2.2 equiv). The reaction mixture was stirred at 0 °C for 2.5 h, charged with additional KOTMS (9.5 mg, 74 µmol, 10 equiv), then stirred for an additional 45 min. The reaction mixture was quenched at 0 °C with AcOH (8 µL, 15 µmol, 20 equiv), warmed to rt and stirred for 30 min, diluted with 19:1 CH2Cl2/CH3OH (1 mL), and filtered through a silica gel plug (4 cm). The filter cake was rinsed with 19:1 CH2Cl2/CH3OH (30 mL), and the filtrate concentrated to afford a mixture of tetramic acids 61 as a pale reddish orange solid. To a solution of tetramic acids 61 (theoretical 19 mg, 7.4 µmol, 1.0 equiv) in 3:2 CH2Cl2/ CH3CN (0.5 mL, 15 mM wrt 61) at 0 °C was added dropwise a solution of fluorosilicic acid (H2SiF6) in H2O (~60 µL, 20–25 wt. %). The reaction mixture was diluted with CH3CN (0.4 mL), then immediately warmed to rt and stirred for 1 d. The reaction mixture was quenched with TMSOMe (0.5 mL), stirred for 15 min, then filtered through Celite , and the filter cake  rinsed with 4:1 CH2Cl2/CH3OH (100 mL total). The filtrate was concentrated, triturated with THF (5 x 0.3 mL), and azeotroped with 1% Et2NH in CH3OH (3 x 5 mL). Purification by reversed-phase HPLC (gradient elution, 65% → 80% CH3OH in H2O + 0.5% Et2NH, 20 min runtime) on a C18 column (Capcell Pak C18 UG, 5 µm, 120 Å, 250 mm x 10 mm) and lyophilization afforded the diethylamine salt of aflastatin A (1•Et2NH) (3.6 mg, 36% yield, two steps) as a white solid. [α] 26 –2.80° (c = 0.55, DMSO); IR (neat) 3321 (br), 2924, 2853, D 1600, 1450, 1379, 1314, 1209, 1154, 1065, 968, 843 cm–1; 1H-NMR (600 MHz, DMSO-d6) δ 6.13 (br s, 1H, C37-OH), 5.42 (d, J = 9.9 Hz, 1H, C3-H), 5.28 (br s, 1H, C25-OH), 5.27 (br s,   188 1H, C13-OH), 5.19 (br s, 1H, C11-OH), 5.02 (br s, 1H, C8-OH), 4.85 (br s, 1H, C39-OH), 4.80 (br s, 1H, C15-OH), 4.79 (br s, 1H, C23-OH), 4.75 (br s, 1H, C21-OH), 4.72 (br s, 1H, C17-OH), 4.71 (br s, 1H, C27-OH), 4.64 (br s, 1H, C34-OH), 4.62 (br s, 1H, C28-OH), 4.60 (br s, 1H, C19OH), 4.49 (br s, 1H, C36-OH), 4.42 (br s, 1H, C9-OH), 4.40 (br s, 1H, C35-OH), 4.17 (br s, 2H, C30-OH and C31-OH), 4.15 (br s, 1H, C29-OH), 3.90 (m, 1H, C17-H), 3.87 (m, 1H, C25-H), 3.86 (m, 2H, C15-H and C39-H), 3.85 (m, 2H, C29-H and C31-H), 3.79 (m, 1H, C21-H), 3.76 (m, 1H, C23-H), 3.69 (m, J = 7.6 Hz, 1H, C13-H), 3.68 (m, 1H, C11-H), 3.64 (m, J = 7.6 Hz, 1H, C8-H), 3.62 (m, J = 7.0 Hz, 2H, C27-H and C33-H), 3.56 (m, J = 7.1 Hz, 1H, C35-H), 3.44 (m, 2H, C19H and C30-H), 3.39 (m, 1H, C36-H), 3.26 (m, 2H, C9-H and C28-H), 3.24 (q, J = 6.4 Hz, 1H, C5'-H), 3.17 (dd, J = 9.4, 9.4 Hz, 1H, C34-H), 2.70 (s, 3H, C7'-H3), 2.53 (m, 1H, C4-H), 2.05 (m, J = 10.6, 7.1 Hz, 1H, one of C32-H), 1.88 (m, 1H, C6-H), 1.83 (m, 1H, one of C26-H), 1.82 (m, J = 12.9 Hz, 1H, one of C38-H), 1.81 (m, 1H, C10-H), 1.69 (s, 3H, C49-H3), 1.66 (m, 1H, C14-H), 1.65 (m, 1H, C18-H), 1.61 (m, J = 8.2, 7.6 Hz, 2H, C12-H, and one of C16-H), 1.56 (m, 1H, one of C24-H), 1.55–1.50 (m, 3H, C20-H and C22-H2), 1.46 (m, 1H, one of C32-H), 1.41 (dd, J = 14.1, 10.5 Hz, 1H, one of C38-H), 1.40 (m, 1H, one of C24-H), 1.33 (m, 2H, one of C5H, and one of C26-H), 1.30 (m, 3H, one of C16-H, and C40-H2), 1.28–1.18 (m, 14H, C41–47-H2), 1.25 (m, 2H, C7-H2), 1.12 (d, J = 7.0 Hz, 3H, C6'-H3), 0.94 (m, 1H, one of C5-H), 0.88 (d, J = 6.4 Hz, 3H, C50-H3), 0.85–0.83 (m, 9H, C48-H3, C52-H3, and C51-H3), 0.81 (d, J = 6.5 Hz, 3H, C54-H3), 0.78 (d, J = 6.4 Hz, 3H, C56-H3), 0.68 (d, J = 7.0 Hz, 3H, C55-H3), 0.64 (d, J = 6.5 Hz, 3H, C53-H3); 13C-NMR (125 MHz, DMSO-d6) δ 193.3 (C4'), 191.8 (C1), 173.5 (C2'), 138.8 (C3), 135.0 (C2), 98.4 (C37), 98.2 (C3'), 79.0 (C13), 76.2 (C19), 75.8 (C11), 74.9 (C9), 74.5 (C15), 74.3 (C28), 73.5 (C21), 73.0 (C36), 72.4 (C30), 71.2 (C34), 70.7 (C35), 70.2 (C17), 70.1 (C33), 69.7 (C27), 69.3 (C29), 68.6 (2C, C25 and C31), 67.9 (C23), 67.5 (C39), 67.2 (C8), 59.4 (C5'), 44.7 (C5), 44.5 (C24), 42.7 (C7), 41.8 (C18, C22 or C38), 41.7 (C18, C22 or C38), 41.6 (C18, C22 or C38), 41.0 (C26), 38.25 (C12, C14, C20 or C40), 38.21 (C12, C14, C20 or C40), 38.1 (C12, C14, C20 or C40), 38.0 (C12, C14, C20 or C40), 37.1 (C10), 35.8 (C32), 34.8 (C16), 31.3 (C46), 29.8 (C4), 29.2 (C42), 29.1 (C43 or C44), 29.0 (C43 or C44), 28.7 (C45), 26.3 (C7'), 26.2 (C6), 24.9 (C41), 22.1 (C47), 21.4 (C50), 20.7 (C51), 15.9 (C6'), 14.0 (C48), 13.4 (C49), 12.8 (C53), 10.5 (C55), 8.7 (C52), 6.4 (C54), 5.8 (C56); HRMS (ESITOF) m/z calcd for C62H115NNaO24 [M+Na]+: 1280.77012, found: 1280.77464.   189 Stereochemical Proof by Mosher’s Ester Analysis Homoallylic alcohol 46 OBn OH TESO 27 TBSO 46 H C27-H2 C28-H C29-H C30-H PhCH2O PhCH2O TBS TES δS (ppm) 3.73 3.53 4.02 3.63 3.91 4.71 4.61 4.66 4.61 0.90 0.09 0.08 0.87 0.48 2.42 2.22 5.59 4.96 4.90 δR (ppm) 3.70 3.52 3.96 3.60 3.91 4.65 4.49 4.56 4.56 0.90 0.09 0.08 0.88 0.50 2.47 2.31 5.68 5.03 4.98 Δδ = δS – δR +0.03 +0.01 +0.06 +0.03 0.00 +0.06 +0.12 +0.10 +0.05 0.00 0.00 0.00 –0.01 –0.02 –0.05 –0.09 –0.09 –0.07 –0.08 31 OBn L2 C32-H C33-H C34-H L3   190 Appendix 1 Spectral Data Comparisons General Key to Tables a Spectra of naturally derived aflastatin A (AsA) C3–C48 degradation polyol ("1a") were acquired in pyridine-d5 at 150 MHz (13C-NMR) or 600 MHz (1H-NMR): H. Ikeda, N. Matsumori, M. Ono, A. Suzuki, A. Isogai, H. Nagasawa, S. Sakuda, J. Org. Chem. 2000, 65, 438–444. Spectra of synthetic aflastatin A (AsA) C3–C48 degradation polyol (1a), AsA C3–C48 degradation lactol methyl ethers 1b and 1c, model C27–C48 lactols 2a/2d–2h, and model C27–C48 lactol methyl ethers 2b and 2c were acquired in pyridine-d5 at 125 MHz (13C-NMR) or 600 MHz (1HNMR). These values were corrected from those reported in 2000: S. Sakuda, N. Matsumori, K. Furihata, H. Nagasawa, Tetrahedron Lett. 2007, 48, 2527–2531. Spectra of naturally derived blasticidin A (BcA) C3–C47 degradation polyol (3a) were acquired in pyridine-d5 at 125 MHz (13C-NMR) or 500 MHz (1H-NMR): S. Sakuda, H. Ikeda, T. Nakamura, R. Kawachi, T. Kondo, M. Ono, M. Sakurada, H. Inagaki, R. Ito, H. Nagasawa, J. Antibiotics 2000, 53, 1378–1384. Atoms for BcA degradation polyol 3a and BcA degradation lactol methyl ether 3b have been renumbered so that they correlate to AsA polyol 2. Only data for the structurally homologous lactol region is shown. b c e g Spectra of naturally derived aflastatin A (AsA) diethylamine salt (4•Et2NH) were acquired in DMSOd6 at 125 MHz (13C-NMR) or 500 MHz (1H-NMR): (a) Sakuda, S.; Ono, M.; Furihata, K.; Nakayama, J.; Suzuki, A.; Isogai, A. J. Am. Chem. Soc. 1996, 118, 7855–7856; (b) Ono, M.; Sakuda, S.; Ikeda, H.; Furihata, K.; Nakayama, J.; Suzuki, A.; Isogai, A. J. Antibiotics 1998, 51, 1019–1028. Spectra of synthetic aflastatin A (AsA) diethylamine salt (4•Et2NH) were acquired in DMSO-d6 at 125 MHz (13C-NMR) or 600 MHz (1H-NMR). h   191 Table 1. Contrast Between 13C-NMR Data for Naturally Derived and Synthetic Aflastatin A (AsA) C3–C48 Degradation Polyols 1a.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 |Δδ| ≥ ±1 ppm AsA # 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 d Natural “1a”a 67.2 34.0 41.6 27.8 42.3 69.5 77.9 38.1 78.8 38.8 81.6 39.3 77.1 45.7 73.9 42.7 78.8 39.5 76.2 42.7 70.8 36.9 71.1c 42.1 72.2c Synthetic 1ab 67.3 34.0 41.6 27.9 42.4 69.5 78.0 38.1 78.9 38.8 81.6 39.5 77.1 45.7 74.0 42.7 78.8 39.5 76.3 42.7 70.7 37.0 71.3 42.1 72.3 AsA # 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Natural “1a”a 76.2c 71.5 75.4 70.9 37.5 72.8 72.3 72.6 71.5 103.2 39.3 66.9 39.3 26.0 29.8 30.0 30.0 29.5 32.0 22.9 14.2 18.6 21.7 8.3 13.2 6.4 11.6 6.1 Synthetic 1ab 76.1 71.4 74.2 71.0 37.4 71.7 73.3 72.9 75.1 100.1 42.8 69.0 39.6 25.9 29.8 29.9 30.1 29.6 32.1 22.9 14.3 18.7 21.7 8.3 13.2 6.4 11.7 6.1 Tabulated values in grey are |Δδ| ≥ ±1 ppm.   192 Table 2. Contrast Between 1H-NMR Data for Naturally Derived and Synthetic Aflastatin A (AsA) C3–C48 Degradation Polyols 1a.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 |Δδ| ≥ ±0.1 ppm AsA # 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 d Natural “1a”a 3.80 3.61 1.98 1.78 1.04 2.14 1.84 1.75 4.29 4.00 2.31 4.32 2.08 4.12 1.97 4.49 2.04 1.95 4.61 2.19 4.05 1.86 4.42 2.04 1.86 4.49 2.05 1.98 4.67 2.59 2.14 4.67c Synthetic 1ab 3.80 3.61 1.99 1.77 1.05 2.15 1.83 1.74 4.29 4.00 2.31 4.32 2.08 4.12 1.95 4.48 2.04 1.96 4.61 2.21 4.06 1.87 4.43 2.04 1.86 4.48 2.03 2.03 4.62 2.60 2.16 4.68 AsA # 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Natural “1a”a 4.34c 4.96 4.49 4.92 3.17 2.49 4.24 4.32 4.56 4.64 2.45 2.19 4.18 1.67 1.59 1.59 1.48 1.25 1.19 1.19 1.19 1.19 1.23 0.83 1.10 1.07 1.28 0.81 1.23 0.97 1.19 Synthetic 1ab 4.30 5.03 4.58 4.97 3.21 2.56 4.85 4.38 4.76 4.48 2.14 2.73 4.72 1.65 1.51 1.51 1.35 1.16 1.16 1.16 1.16 1.16 1.22 0.83 1.10 1.06 1.27 0.80 1.24 0.97 1.20 Tabulated values in grey are |Δδ| ≥ ±0.1 ppm.   193 Table 3. Contrast Between NMR Data for Naturally Derived and Synthetic Aflastatin A (AsA) C3–C48 Degradation Polyols 1a, and Model C27–C48 Lactol 2a.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me Me OH Me Me Me Me Me OH OH OH OH 39 OH OH H O C9H19 C27–C48 Model Lactol 2a HO HO HO HO 27 31 35 13C-NMR: 1H-NMR: |Δδ| ≥ ±1 ppm |Δδ| ≥ ±0.1 ppm OH OH H O C9H19 AsA # 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 d Natural “1a” 72.2c 76.2c 71.5 75.4 70.9 37.5 72.8 72.3 72.6 71.5 103.2 39.3 66.9 39.3 26.0 29.8 30.0 30.0 29.5 32.0 22.9 14.2 a C-NMR Synthetic 1ab 72.3 76.1 71.4 74.2 71.0 37.4 71.7 73.3 72.9 75.1 100.1 42.8 69.0 39.6 25.9 29.8 29.9 30.1 29.6 32.1 22.9 14.3 13 Model 2a 64.6 72.9 73.5 73.7 71.6 37.5 71.6 73.8 72.9 75.2 100.2 42.6 69.0 39.6 25.8 29.8 29.9 30.1 29.6 32.1 22.9 14.3 b Natural “1a” 4.67c 4.34c 4.96 4.49 4.92 3.17 2.49 4.24 4.32 4.56 4.64 2.45 2.19 4.18 1.67 1.59 1.59 1.48 1.25 1.19 1.19 1.19 1.19 1.23 0.83 a H-NMR Synthetic 1ab 4.68 4.30 5.03 4.58 4.97 3.21 2.56 4.85 4.38 4.76 4.48 2.14 2.73 4.72 1.65 1.51 1.51 1.35 1.16 1.16 1.16 1.16 1.16 1.22 0.83 1 Model 2ab 4.33 4.61 4.72 4.61 5.00 3.22 2.58 4.89 4.41 4.79 4.50 2.15 2.75 4.76 1.64 1.53 1.51 1.36 1.14 1.14 1.14 1.14 1.14 1.21 0.83 With respect to synthetic 1a, tabulated values in grey are |Δδ| ≥ ±1 ppm (13C-NMR) or |Δδ| ≥ ±0.1 ppm (1H-NMR).   194 Table 4. Contrast Between 13C-NMR Data for Naturally Derived Aflastatin A (AsA) C3–C48 Degradation Polyol 1a, and Model C27–C48 Lactols 2a/2d–2h.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me HO HO HO HO 27 31 Me OH 35 OH Me OH OH OH 39 Me Me Me Me OH OH OH OH 39 OH OH H O C9H19 OH HO HO HO HO 27 31 35 HO HO HO HO 27 31 35 OH OH OH 39 OH OH H O C9H19 OH OH H O C9H19 OH OH H O C9H19 AsA Model Lactol 2a OH HO HO HO HO 27 31 35 epi-C39 Lactol 2d OH HO HO HO HO 27 31 epi-C33–C37 Lactol 2e OH HO HO HO HO 27 31 OH OH OH 39 35 OH OH OH 39 35 OH OH OH 39 OH OH H O C9H19 OH OH H O C9H19 OH OH H O C9H19 epi-C34,C36 Lactol 2f epi-C35,C36 Lactol 2g epi-C36 Lactol 2h AsA # 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 d Natural “1a”a 72.2c 76.2c 71.5 75.4 70.9 37.5 72.8 72.3 72.6 71.5 103.2 39.3 66.9 39.3 26.0 29.8 30.0 30.0 29.5 32.0 22.9 14.2 Model 2ab 64.6 72.9 73.5 73.7 71.6 37.5 71.6 73.8 72.9 75.2 100.2 42.6 69.0 39.6 25.8 29.8 29.9 30.1 29.6 32.1 22.9 14.3 Model 2db 64.6 74.1 73.3 74.8 72.4 37.3 72.9 72.9 73.1 74.2 100.3 45.3 67.6 39.1 26.2 29.8 30.0 30.0 29.6 32.1 22.9 14.3 Model 2eb 64.6 73.2 74.0 73.3 69.9 38.5 71.1 73.0 76.1 74.0 100.2 44.8 67.9 39.0 26.2 29.8 30.0 30.0 29.6 32.1 22.9 14.3 Model 2fb 64.5 73.9 74.2 73.5 70.6 35.7 69.3 72.1 72.5 74.3 100.1 43.8 68.2 39.2 25.8 29.8 29.9 30.0 29.5 32.0 22.9 14.2 Model 2gb 64.6 74.0 73.5 74.0 71.6 37.2 67.3 73.1 74.4 71.8 100.8 45.7 67.8 38.9 26.0 29.8 29.9 30.1 29.6 32.1 22.9 14.3 Model 2hb 64.5 73.6 75.8 73.8 71.5 37.6 70.7 77.1 73.1 77.8 99.8 43.8 68.3 39.2 25.8 29.8 29.9 30.1 29.5 32.0 22.9 14.2 With respect to naturally derived "1a", tabulated values in grey are |Δδ| ≥ ±1 ppm.   195 Table 5. Contrast Between 1H-NMR Data for Naturally Derived Aflastatin A (AsA) C3–C48 Degradation Polyol 1a, and Model C27–C48 Lactols 2a/2d–2h.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me HO HO HO HO 27 31 Me OH 35 OH Me OH OH OH 39 Me Me Me Me OH OH OH OH 39 OH OH H O C9H19 OH HO HO HO HO 27 31 35 HO HO HO HO 27 31 35 OH OH OH 39 OH OH H O C9H19 OH OH H O C9H19 OH OH H O C9H19 AsA Model Lactol 2a OH HO HO HO HO 27 31 35 epi-C39 Lactol 2d OH HO HO HO HO 27 31 epi-C33–C37 Lactol 2e OH HO HO HO HO 27 31 OH OH OH 39 35 OH OH OH 39 35 OH OH OH 39 OH OH H O C9H19 OH OH H O C9H19 OH OH H O C9H19 epi-C34,C36 Lactol 2f epi-C35,C36 Lactol 2g epi-C36 Lactol 2h AsA # 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 d Natural “1a”a 4.67c 4.34c 4.96 4.49 4.92 3.17 2.49 4.24 4.32 4.56 4.64 2.45 2.19 4.18 1.67 1.59 1.59 1.48 1.25 1.19 1.19 1.19 1.19 1.23 0.83 Model 2ab 4.33 4.61 4.72 4.61 5.00 3.22 2.58 4.89 4.41 4.79 4.50 2.15 2.75 4.76 1.64 1.53 1.51 1.36 1.14 1.14 1.14 1.14 1.14 1.21 0.83 Model 2db 4.31 4.54 4.56 4.43 4.83 3.07 2.53 4.87 4.42 4.88 4.59 2.48 2.62 4.59 1.75 1.60 1.60 1.46 1.15 1.15 1.15 1.15 1.15 1.19 0.82 Model 2eb 4.32 4.55 4.64 4.91 4.90 3.11 2.32 5.04 4.38 4.30 4.58 2.38 2.70 4.55 1.74 1.60 1.60 1.44 1.15 1.15 1.15 1.15 1.15 1.19 0.82 Model 2fb 4.32 4.59 4.48 4.68 4.85 2.96 2.69 5.07 4.44 4.56 4.38 2.64 2.04 4.69 1.62 1.48 1.48 1.33 1.15 1.15 1.15 1.15 1.15 1.20 0.82 Model 2gb 4.32 4.59 4.67 4.52 4.92 3.09 2.51 4.91 3.86 4.70 3.91 2.45 2.16 4.58 1.67 1.54 1.54 1.42 1.16 1.16 1.16 1.16 1.16 1.20 0.82 Model 2hb 4.32 4.58 4.70 4.58 4.95 3.21 2.51 4.90 3.94 4.59 3.91 2.67 2.06 4.69 1.63 1.50 1.50 1.38 1.14 1.14 1.14 1.14 1.14 1.20 0.82 With respect to naturally derived "2", tabulated values in grey are |Δδ| ≥ ±0.1 ppm.   196 Table 6. Contrast Between NMR Data for Naturally Derived Aflastatin A (AsA) C3–C48 Degradation Polyol 1a, and Model C27–C48 Lactol Methyl Ethers 2b and 2c.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me Me OH Me Me Me Me OH Me OH OH OR 39 OH OH HO HO HO HO 27 31 H O C9H19 C27–C48 Model Lactol Methyl Ether 2b, R = CH3 C27–C48 Model Lactol Trideuteriomethyl Ether 2c, R = CD3 OH 35 HO HO HO HO 27 31 35 OH OH OR 39 OH OH 13C-NMR: 13 H O C9H19 OH OH 1H-NMR: H O C9H19 |Δδ| ≥ ±0.5 ppm |Δδ| ≥ ±0.05 ppm AsA # 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 –OMe d Natural “1a” 72.2c 76.2c 71.5 75.4 70.9 37.5 72.8 72.3 72.6 71.5 103.2 39.3 66.9 39.3 26.0 29.8 30.0 30.0 29.5 32.0 22.9 14.2 n/a a C-NMR Model 2bb 64.7 73.9 73.6 74.3 71.3 37.5 72.8 72.4 72.7 73.1 103.3 39.4 67.0 39.4 26.0 29.8 30.0 30.0 29.5 32.1 22.9 14.2 47.9 Model 2c 64.6 73.9 73.6 74.3 71.3 37.5 72.8 72.4 72.6 73.1 103.3 39.4 66.9 39.4 26.0 29.8 30.0 30.0 29.5 32.1 22.9 14.2 n/a b Natural “1a” 4.67c 4.34c 4.96 4.49 4.92 3.17 2.49 4.24 4.32 4.56 4.64 2.45 2.19 4.18 1.67 1.59 1.59 1.48 1.25 1.19 1.19 1.19 1.19 1.23 0.83 n/a a H-NMR Model 2bb 4.35 4.65 4.68 4.52 4.94 3.20 2.50 4.26 4.33 4.58 4.68 2.46 2.23 4.19 1.68 1.60 1.60 1.48 1.23 1.17 1.17 1.17 1.17 1.21 0.82 3.37 1 Model 2cb 4.35 4.65 4.68 4.52 4.94 3.20 2.50 4.26 4.33 4.58 4.68 2.46 2.22 4.19 1.68 1.60 1.58 1.48 1.23 1.17 1.17 1.17 1.17 1.21 0.82 n/a With respect to naturally derived "2", tabulated values in grey are |Δδ| ≥ ±0.5 ppm (13C-NMR) or |Δδ| ≥ ±0.05 ppm (1H-NMR).   197 Table 7. Comparison of 13C-NMR Data for Aflastatin A (AsA) C3–C48 Degradation Polyols 1a and Blasticidin A (BcA) Degradation Polyol 3a.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 Blasticidin A (BcA) Degradation Polyol (3a) HO HO HO HO HO HO HO HO HO HO HO HO HO Me Me OH Me Me 19 23 27 31 OH 35 OH OH OH 39 Me OH OH H O C10H21 AsA # 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 d Natural “1a”a 67.2 34.0 41.6 27.8 42.3 69.5 77.9 38.1 78.8 38.8 81.6 39.3 77.1 45.7 73.9 42.7 78.8 39.5 76.2 42.7 70.8 36.9 71.1c 42.1 72.2c Natural 3af Synthetic 1ab 67.3 34.0 41.6 27.9 42.4 69.5 78.0 38.1 78.9 38.8 81.6 39.5 77.1 45.7 74.0 42.7 78.8 39.5 76.3 42.7 70.7 37.0 71.3 42.1 72.3 AsA # 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Natural “1a”a 76.2c 71.5 75.4 70.9 37.5 72.8 72.3 72.6 71.5 103.2 39.3 66.9 39.3 26.0 29.8 30.0 30.0 29.5 32.0 22.9 14.2 18.6 21.7 8.3 13.2 6.4 11.6 6.1 Natural 3af 76.1 71.3 74.2 70.7 37.5 71.7 73.4 72.9 75.1 100.1 42.9 69.1 39.6 25.9 Synthetic 1ab 76.1 71.4 74.2 71.0 37.4 71.7 73.3 72.9 75.1 100.1 42.8 69.0 39.6 25.9 29.8 29.9 30.1 29.6 32.1 22.9 14.3 18.7 21.7 8.3 13.2 6.4 11.7 6.1 70.8 45.7 70.7 45.7 71.3 42.2 72.2 Tabulated values in grey are |Δδ| ≤ ±0.3 ppm.   198 Table 8. Comparison of 1H-NMR Data for Aflastatin A (AsA) C3–C48 Degradation Polyols 1a and Blasticidin A (BcA) Degradation Polyol 3a.d Aflastatin A (AsA) C3–C48 Degradation Polyol (1a) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OH 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 Blasticidin A (BcA) Degradation Polyol (3a) HO HO HO HO HO HO HO HO HO HO HO HO HO Me Me OH Me Me 19 23 27 31 OH 35 OH OH OH 39 Me OH OH H O C10H21 AsA # 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 d Natural “1a”a 3.80 3.61 1.98 1.78 1.04 2.14 1.84 1.75 4.29 4.00 2.31 4.32 2.08 4.12 1.97 4.49 2.04 1.95 4.61 2.19 4.05 1.86 4.42 2.04 1.86 4.49 2.05 1.98 4.67 2.59 2.14 4.67c Natural 3af 4.48 1.89 1.89 4.52 2.02 2.02 4.62 2.60 2.15 4.66 Synthetic 1ab 3.80 3.61 1.99 1.77 1.05 2.15 1.83 1.74 4.29 4.00 2.31 4.32 2.08 4.12 1.95 4.48 2.04 1.96 4.61 2.21 4.06 1.87 4.43 2.04 1.86 4.48 2.03 2.03 4.62 2.60 2.16 4.68 AsA # 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Natural “1a”a 4.34c 4.96 4.49 4.92 3.17 2.49 4.24 4.32 4.56 4.64 2.45 2.19 4.18 1.67 1.59 1.59 1.48 1.25 1.19 1.19 1.19 1.19 1.23 0.83 1.10 1.07 1.28 0.81 1.23 0.97 1.19 Natural 3af 4.30 5.03 4.57 4.98 3.21 2.55 4.85 4.39 4.76 4.48 2.14 2.74 4.72 1.66 1.52 1.54 1.54 1.18 1.18 Synthetic 1ab 4.30 5.03 4.58 4.97 3.21 2.56 4.85 4.38 4.76 4.48 2.14 2.73 4.72 1.65 1.51 1.51 1.35 1.16 1.16 1.16 1.16 1.16 1.22 0.83 1.10 1.06 1.27 0.80 1.24 0.97 1.20 Tabulated values in grey are |Δδ| ≤ ±0.03 ppm.   199 Table 9. Comparison of 13C-NMR Data for Naturally Derived Aflastatin A (AsA) C3–C48 Degradation Polyol 1a, Blasticidin (BcA) Degradation Lactol Methyl Ether 3b, and Aflastatin A (AsA) C3–C48 Degradation Lactol Methyl Ethers 1b and 1c.d Aflastatin A (AsA) C3–C48 Degradation Polyols HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OR 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 Lactol 1a, R = H Lactol Methyl Ether 1b, R = Me Lactol Trideuteriomethyl Ether 1c, R = CD3 Blasticidin A (BcA) Degradation Lactol Methyl Ether (3b) HO HO HO HO HO HO HO HO HO HO HO HO HO Me Me OH Me Me 19 23 27 31 OH 35 OH OH OMe 39 Me OH OH H O C10H21 AsA # 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Natural “1a”a 67.2 34.0 41.6 27.8 42.3 69.5 77.9 38.1 78.8 38.8 81.6 39.3 77.1 45.7 73.9 42.7 78.8 39.5 76.2 42.7 70.8 36.9 73.1f 42.1 72.2c 76.2c Natural 3be Synthetic 1bb 67.3 34.0 41.6 27.9 42.4 69.5 78.0 38.1 78.9 38.8 81.6 39.5 77.1 45.8 74.0 42.8 78.9 39.5 76.3 42.8 70.9 37.0 Synthetic 1cb 67.2 34.0 41.6 27.8 42.3 69.5 77.9 38.1 78.8 38.8 81.6 39.5 77.1 45.7 73.9 42.7 78.7 39.5 76.2 42.7 70.8 36.9 71.1 42.1 72.2 76.2 71.2 42.1 72.2 76.2 71.1 42.1 72.2 76.3   200 Table 9 (Continued). Comparison of 13C-NMR Data for Naturally Derived Aflastatin A (AsA) C3–C48 Degradation Polyol 1a, Blasticidin (BcA) Degradation Lactol Methyl Ether 3b, and Aflastatin A (AsA) C3–C48 Degradation Lactol Methyl Ethers 1b and 1c.d AsA # 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 Natural “1a”a 71.5 75.4 70.9 37.5 72.8 72.3 72.6 71.5f 103.2 39.3 66.9 39.3 26.0 29.8 30.0 30.0 29.5 32.0 22.9 14.2 18.6 21.7 8.3 13.2 6.4 11.6 6.1 n/a Natural 3be 71.5 75.4 70.8 37.6 72.8 72.4 72.6 73.1 103.3 39.4 66.9 39.4 Synthetic 1bb 71.5 75.5 70.9 37.6 72.8 72.4 72.6 73.1 103.3 39.4 66.9 39.4 26.0 29.8 30.0 30.0 29.5 32.1 22.9 14.3 18.7 21.7 8.3 13.2 6.4 11.7 6.1 47.8 Synthetic 1cb 71.5 75.4 70.9 37.5 72.7 72.3 72.6 73.0 103.2 39.3 66.9 39.3 26.0 29.8 29.9 30.0 29.5 32.0 22.9 14.2 18.6 21.6 8.3 13.2 6.4 11.6 6.1 n/a 47.8 d f All tabulated values (except those shaded in grey) are |Δδ| ≤ ±0.2 ppm. Values shaded in grey correspond to those originally reported in 2000. In 2007, the chemical shift of C25 was revised from 73.1 ppm to 71.1 ppm. However, we believe the chemical shift of 71.5 ppm originally reported for C36 should instead be revised to 71.1 ppm. Then, the data for these two atoms should be switched. We noted a similar switch of NMR data for C27 and C28 in the 2007 paper (see note c).   201 Table 10. Comparison of 1H-NMR Data for Naturally Derived Aflastatin A (AsA) C3–C48 Degradation Polyol 1a, Blasticidin (BcA) Degradation Lactol Methyl Ether 3b, and Aflastatin A (AsA) C3–C48 Degradation Lactol Methyl Ethers 1b and 1c.d Aflastatin A (AsA) C3–C48 Degradation Polyols HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OR 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 Lactol 1a, R = H Lactol Methyl Ether 1b, R = Me Lactol Trideuteriomethyl Ether 1c, R = CD3 Blasticidin A (BcA) Degradation Lactol Methyl Ether (3b) HO HO HO HO HO HO HO HO HO HO HO HO HO Me Me OH Me Me 19 23 27 31 OH 35 OH OH OMe 39 Me OH OH H O C10H21 AsA # 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Natural “1a”a 3.80 3.61 1.98 1.78 1.04 2.14 1.84 1.75 4.29 4.00 2.31 4.32 2.08 4.12 1.97 4.49 2.04 1.95 4.61 2.19 4.05 1.86 4.42 2.04 1.86 4.49 2.05 1.98 4.67f 2.59 2.14 4.67c 4.34c Natural 3be 4.63 2.16 2.16 4.68 4.33 Synthetic 1bb 3.80 3.61 1.98 1.77 1.04 2.15 1.83 1.75 4.28 4.00 2.30 4.31 2.08 4.12 1.96 4.50 2.04 1.96 4.62 2.21 4.05 1.87 4.42 2.04 1.85 4.50 2.04 1.98 4.64 2.60 2.17 4.67 4.34 Synthetic 1cb 3.79 3.60 1.98 1.76 1.04 2.14 1.83 1.74 4.28 4.00 2.30 4.31 2.08 4.11 1.96 4.49 2.03 1.96 4.62 2.21 4.05 1.87 4.42 2.03 1.85 4.49 2.03 1.98 4.64 2.59 2.16 4.67 4.34   202 Table 10 (Continued). Comparison of 1H-NMR Data for Naturally Derived Aflastatin A (AsA) C3–C48 Degradation Polyol 1a, Blasticidin (BcA) Degradation Lactol Methyl Ether 3b, and Aflastatin A (AsA) C3–C48 Degradation Lactol Methyl Ethers 1b and 1c.d AsA # 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 Natural “1a”a 4.96 4.49 4.92 3.17 2.49 4.24 4.32 4.56 4.64f 2.45 2.19 4.18 1.67 1.59 1.59 1.48 1.25 1.19 1.19 1.19 1.19 1.23 0.83 1.10 1.07 1.28 0.81 1.23 0.97 1.19 n/a Natural 3be 4.97 4.50 4.93 3.18 2.49 4.21 4.31 4.56 4.66 2.44 2.22 4.18 1.68 1.58 Synthetic 1bb 4.96 4.50 4.93 3.17 2.49 4.23 4.32 4.56 4.67 2.45 2.20 4.19 1.67 1.59 1.59 1.47 1.24 1.19 1.19 1.19 1.19 1.22 0.83 1.10 1.06 1.28 0.80 1.24 0.97 1.19 3.35 Synthetic 1cb 4.97 4.49 4.92 3.17 2.49 4.23 4.31 4.57 4.67 2.44 2.20 4.18 1.67 1.58 1.60 1.47 1.24 1.18 1.18 1.18 1.18 1.22 0.83 1.10 1.06 1.28 0.80 1.23 0.97 1.19 n/a 3.35 d f All tabulated values are |Δδ| ≤ ±0.03 ppm. As with the 13C-NMR data (see Table S9), we believe that the resonances assigned to H25 and H36 (shaded in grey) should be switched. We noted a similar switch of NMR data for H27 and H28 in the 2007 paper (see note c).   203 Table 11. Comparison of 13C-NMR Data for Naturally Derived and Synthetic Aflastatin A (AsA) Diethylamine Salt 4•Et2NH. O Me N Me 2' O Et2NH2 3 7 Aflastatin A (AsA) Diethylamine Salt (4•Et2NH) HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 OH 35 OH OH 39 O Me Me Me OH Me Me Me Me Me OH OH H O OH C9H19 AsA # 1 2 3 4 5 6 7 8 8-OH 9 9-OH 10 11 11-OH 12 13 13-OH 14 15 15-OH 16 17 17-OH 18 19 19-OH 20 21 21-OH 22 23 23-OH 24 25 25-OH 26 27 27-OH 28 28-OH 29 Nat. 4•Et2NHg 191.5 135.2 139.3 29.9 44.8 26.1 42.8 67.2 75.0 37.1 75.8 38.1 78.9 38.1 74.5 34.9 70.4 41.6 76.2 38.1 73.5 41.6 67.9 44.5 68.6 41.0 69.7 74.3 69.4 Syn. 4•Et2NHh 191.8 135.0 138.8 29.8 44.7 26.2 42.7 67.2 74.9 37.1 75.8 38.0 79.0 38.1 74.5 34.8 70.2 41.7 76.2 38.2 73.5 41.6 67.9 44.5 68.6 41.0 69.7 74.3 69.3 AsA # 29-OH 30 30-OH 31 31-OH 32 33 34 34-OH 35 35-OH 36 36-OH 37 37-OH 38 39 39-OH 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 2' 3' 4' 5' 6' 7' Nat. 4•Et2NHg 72.5 68.6 35.8 70.2 71.2 70.7 73.0 98.4 41.6 67.5 38.1 24.9 29.2 29.0 29.0 28.7 31.3 22.1 13.9 13.3 21.5 20.8 8.7 12.8 6.4 10.6 5.8 173.4 98.1 192.6 59.4 15.9 26.3 Syn. 4•Et2NHh 72.4 68.6 35.8 70.1 71.2 70.7 73.0 98.4 41.8 67.5 38.2 24.9 29.2 29.0 29.1 28.7 31.3 22.1 14.0 13.4 21.4 20.7 8.7 12.8 6.4 10.5 5.8 173.5 98.2 193.3 59.4 15.9 26.3   204 Table 12. Comparison of 1H-NMR Data for Naturally Derived and Synthetic Aflastatin A (AsA) Diethylamine Salt 4•Et2NH. O Me N Me 2' O Et2NH2 3 7 Aflastatin A (AsA) Diethylamine Salt (4•Et2NH) HO HO HO HO HO HO HO HO HO HO HO HO HO 11 15 19 23 27 31 OH 35 OH OH 39 O Me Me Me OH Me Me Me Me Me OH OH H O OH C9H19 AsA # 1 2 3 4 5 6 7 8 8-OH 9 9-OH 10 11 11-OH 12 13 13-OH 14 15 15-OH 16 17 17-OH 18 19 19-OH 20 21 21-OH 22 23 23-OH 24 25 25-OH 26 27 27-OH 28 28-OH 29 Nat. 4•Et2NHg Syn. 4•Et2NHh 5.45 2.54 1.34, 0.93 1.90 1.26 3.64 n/a 3.26 n/a 1.81 3.71 5.20 1.62 3.67 5.26 1.67 3.85 4.79 1.60, 1.30 3.91 4.71 1.65 3.46 4.57 1.53 3.81 4.76 1.53 3.79 4.73 1.55, 1.39 3.87 5.24 1.85, 1.35 3.63 4.66 3.25 4.59 3.82 5.42 2.53 1.33, 0.94 1.88 1.25 3.64 5.02 3.26 4.42 1.81 3.68 5.19 1.61 3.69 5.27 1.66 3.86 4.80 1.61, 1.30 3.90 4.72 1.65 3.44 4.60 1.53 3.79 4.75 1.53 3.76 4.79 1.56, 1.40 3.87 5.28 1.83, 1.33 3.62 4.71 3.26 4.62 3.85 AsA # 29-OH 30 30-OH 31 31-OH 32 33 34 34-OH 35 35-OH 36 36-OH 37 37-OH 38 39 39-OH 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 2' 3' 4' 5' 6' 7' Nat. 4•Et2NHg 4.12 3.45 4.17 3.83 4.12 2.06, 1.48 3.62 3.18 n/a 3.56 n/a 3.41 4.45 6.11 1.82, 1.42 3.89 4.75 1.30 1.23 1.23 1.23 1.23 1.23 1.23 1.23 0.84 1.67 0.88 0.85 0.84 0.64 0.81 0.68 0.79 Syn. 4•Et2NHh 4.15 3.44 4.17 3.85 4.17 2.05, 1.46 3.62 3.17 4.64 3.56 4.40 3.39 4.49 6.13 1.82, 1.41 3.86 4.85 1.30 1.23 1.23 1.23 1.23 1.23 1.23 1.23 0.84 1.69 0.88 0.85 0.84 0.64 0.81 0.68 0.78 3.20 1.11 2.68 3.24 1.12 2.70   205 Appendix 2 1 H- and 13C-NMR Spectra   206 Chapter 3 Compound 78. H I 31 O 27 OMe OH BnO OBn 78 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 H I 31 O 27 OMe OH BnO OBn 78 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   207 Compound 79. OBn HO 27 31 OH OBn 79 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01 OBn HO 27 31 OH OBn 79 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   208 Compound 63. OBn 27 31 O Me O Me OBn 63 (600 MHz, CDCl3) ppm0 8 78 67 56 45 34 23 12 01 27 OBn 31 O Me O Me OBn 63 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   209 Compound 80. OBn O 31 27 O Me O Me H OBn 80 (600 MHz, C6D6) ppm0 1011 910 89 78 67 56 45 34 23 12 01 27 OBn O 31 O Me O Me H OBn 80 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   210 Compound 64. 27 OBn OH 31 33a O Me O Me OBn 64 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 27 OBn OH 31 33a O Me O Me OBn 64 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   211 Compound 81. O 27 OBn O 31 34a O Me O Me 33a OBn 81 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O 27 OBn O 31 34a O Me O Me 33a OBn 81 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   212 Compound 65. O 27 OBn O 31 35 O Me O Me OBn 65 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O 27 OBn O 31 35 O Me O Me OBn 65 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   213 Compound 82. O 27 OBn O 31 35 OH OH O Me O Me OBn 82 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O 27 OBn O 31 35 OH OH O Me O Me OBn 82 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   214 Compound 66. O 27 OBn O 31 35 O O O Me O Me Me Me OBn 66 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O 27 OBn O 31 35 O O O Me O Me Me Me OBn 66 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   215 Compound 83. OBn OH O 31 35 27 O Me Me OH O BnO Me O Me 83 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01 27 OBn OH O 31 35 O Me Me OH O BnO Me O Me 83 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   216 Compound 84. OBn OH O 31 35 27 O Me Me OTBDPS O BnO Me O Me 84 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 27 OBn OH O 31 35 O Me Me OTBDPS O BnO Me O Me 84 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   217 Compound 61.   27 OBn OBn O 31 35 O Me Me OTBDPS O BnO Me O Me 61 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01     27 OBn OBn O 31 35 O Me Me OTBDPS O BnO Me O Me 61 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050         218 Compound 85.   27 OBn OBn O 31 35 O Me Me OH O BnO Me O Me 85 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01     27 OBn OBn O 31 35 O Me Me OH O BnO Me O Me 85 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050         219 Compound 67.   27 OBn OBn O 31 O 35 O Me Me H O BnO Me O Me 67 (600 MHz, CDCl3) ppm0 10 910 89 78 67 56 45 34 23 12 01     27 OBn OBn O 31 O 35 O Me Me H O BnO Me O Me 67 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050         220 Compound 68.   27 OBn OBn O 31 OH O 35 OTBS 39 O Me Me C9H19 O BnO Me O Me OTES 68 (600 MHz, CDCl3)   ppm0 89 78 67 56 45 34 23 12 01   27 OBn OBn O 31 OH O 35 OTBS 39 O Me Me C9H19 O BnO Me O Me OTES 68 (125 MHz, CDCl3)   ppm0 200   150200 100150 50100 050     221 Compound 69.   27 OBn OBn O 31 O 35 TES O OTBS 39 HO C9H19 HO BnO Me O Me OTES 69 (600 MHz, C6D6)   ppm0 89 78 67 56 45 34 23 12 01   27 OBn OBn O 31 O 35 TES O OTBS 39 HO C9H19 HO BnO Me O Me OTES 69 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050     222 Compound 86. TES O 27 OBn OBn O 31 O 35 OTBS 39 AcO C9H19 HO BnO Me O Me OTES 86 (600 MHz, C6D6)   ppm0 89 78 67 56 45 34 23 12 01   27 OBn OBn O 31 O 35 TES O OTBS 39 AcO C9H19 HO BnO Me O Me OTES 86 (125 MHz, C6D6)   ppm0 200   150200 100150 50100 050     223 Compound 70.   27 OBn OBn O O 35 TES O OTBS 39 31 AcO TBSO BnO Me O Me C9H19 OTES 70 (600 MHz, CDCl3)   ppm0 89 78 67 56 45 34 23 12 01   27 OBn OBn O O 35 TES O OTBS 39 31 AcO TBSO BnO Me O Me C9H19 OTES 70 (100 MHz, CDCl3)   ppm0 200   150200 100150 50100 050     224 Compound 87.   27 OBn OBn O O 35 TES O OTBS 39 31 HO TBSO BnO Me O Me C9H19 OTES 87 (600 MHz, CDCl3)   ppm0 89 78 67 56 45 34 23 12 01   27 OBn OBn O O 35 TES O OTBS 39 31 HO TBSO BnO Me O Me C9H19 OTES 87 (125 MHz, CDCl3)   ppm0 200   150200 100150 50100 050     225 Compound 71.   O OBn OBn O O 35 TES O OTBS 39 31 H 27 TBSO BnO Me O Me C9H19 OTES 71 (600 MHz, CDCl3)   ppm0 89 78 67 56 45 34 23 12 01   O OBn OBn O O 35 TES O OTBS 39 31 H 27 TBSO BnO Me O Me C9H19 OTES 71 (125 MHz, CDCl3)   ppm0 200   150200 100150 50100 050     226 Compound 73.  73 (600 MHz, CDCl3) BnO 3 7 Me Me OBn O 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me TBSO BnO Me O Me OTES   ppm0 89 78 67 56 45 34 23 12 01   73 (125 MHz, CDCl3) Me Me OBn O O Me Me O 15 Me Me O 19 O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 BnO 3 7 11 C9H19 Me Me O Me TBS Me Me Me Me TBSO BnO Me O Me OTES   ppm0 200   150200 100150 50100 050     227 Compound 74.   74 (600 MHz, CD3OD) HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 OH 35 OH OH 39 Me Me OH Me Me Me Me Me OH OBn H O OH C9H19   ppm0 89 78 67 56 45 34 23 12 01   74 (125 MHz, CD3OD) HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 OH 35 OH OH 39 Me Me OH Me Me Me Me Me OH OBn H O OH C9H19   ppm0 200   150200 100150 50100 050     228 Compound 1.     1 (600 MHz, C5D5N) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH 39 Me Me OH Me Me Me Me Me OH OH H O OH C9H19 H2O PhH MeCN X   ppm0 9 89 78 67 56 45 34 23 12 01   1 (125 MHz, C5D5N) HO HO HO HO HO HO HO HO HO HO HO HO HO OH 35 OH OH 39 HO 3 7 11 15 19 23 27 31 Me Me OH Me Me Me Me Me OH OH H O OH C9H19 X   ppm0 200   150200 100150 50100 050     229 Compound 89.     89 (600 MHz, CD3OD) HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 OH 35 OH OH 39 Me Me OH Me Me Me Me Me OH OBn H O OMe C9H19   ppm0 89 78 67 56 45 34 23 12 01   89 (125 MHz, CD3OD) HO BnO HO HO HO HO HO HO HO HO HO BnO BnO BnO 3 7 11 15 19 23 27 31 OH 35 OH OH 39 Me Me OH Me Me Me Me Me OH OBn H O OMe C9H19   ppm0 200   150200 100150 50100 050     230 Compound 46a.    46a (600 MHz, C5D5N) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OMe 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 PhH H2 O   ppm0 9 89 78 67 56 45 34 23 12 01   46a (125 MHz, C5D5N) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OMe 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 PhH   ppm0 200   150200 100150 50100 050     231 Compound 46b.    46b (600 MHz, C5D5N) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OCD3 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 H2O   ppm0 9 89 78 67 56 45 34 23 12 01   46b (125 MHz, C5D5N) HO HO HO HO HO HO HO HO HO HO HO HO HO HO 3 7 11 15 19 23 27 31 OH 35 OH OH OCD3 39 Me Me OH Me Me Me Me Me OH OH H O C9H19 X   ppm0 200   150200 100150 50100 050     232 Comparison of the 1H-NMR Spectrum Reported for 1a to Our Spectra for 46ab and 46b. Sakuda "1" (600 MHz, C5D5N) Evans 46a (600 MHz, C5D5N) PhH → H2 O ppm1 89 78 67 56 45 34 23 12 Evans 46b (600 MHz, C5D5N) H2 O ppm1 89 78 67 56 45 34 23 12 a Reproduced from: H. Ikeda, N. Matsumori, M. Ono, A. Suzuki, A. Isogai, H. Nagasawa, S. Sakuda, J. Org. Chem. 2000, 65, 438–444. b Arrow (→) points at resonance corresponding to the methyl group (C56-H3) of lactol methyl ether 46a.   233 Comparison of the 13C-NMR Spectrum Reported for 1a to Our Spectra for 46ab and 46b. Sakuda "1" (150 MHz, C5D5N) Evans 46a (125 MHz, C5D5N) PhH → ppm0 100150 50100 050 Evans 46b (125 MHz, C5D5N) X ppm0 100150 50100 050 a Reproduced from: H. Ikeda, N. Matsumori, M. Ono, A. Suzuki, A. Isogai, H. Nagasawa, S. Sakuda, J. Org. Chem. 2000, 65, 438–444. Arrow (→) points at resonance corresponding to the methyl group (C-56) of lactol methyl ether 46a. b   234 Chapter 4 Compound 38•Et2NH. O 2' O Et2NH2 3 7 OH Me N Me 5' O Me Me Me 38•Et2NH (600 MHz, CD3OD) ppm0 89 78 67 56 45 34 23 12 01 O 2' O Et2NH2 3 7 OH Me N Me 5' O Me Me Me 38•Et2NH (125 MHz, CD3OD) ppm0 200 150200 100150 50100 050   235 Compound 127. H I 31 O 27 OMe OH BnO OBn 127 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 H I 31 O 27 OMe OH BnO OBn 127 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   236 Compound 43. H I 31 O 27 OMe OTBS BnO OBn 43 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01 H I 31 O OMe 27 BnO OBn OTBS 43 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   237 Compound 44. OBn HO 27 TBSO BnO 44 (600 MHz, CDCl3) 31 ppm0 89 78 67 56 45 34 23 12 01 OBn HO 27 TBSO BnO 31 44 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   238 Compound 128. OBn TESO 27 TBSO BnO 128 (600 MHz, CDCl3) 31 ppm0 89 78 67 56 45 34 23 12 01 OBn TESO 27 TBSO BnO 31 128 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   239 Compound 45. OBn O TESO 27 TBSO BnO 31 H 45 (600 MHz, CDCl3) ppm0 10 910 89 78 67 56 45 34 23 12 01 OBn O TESO 27 TBSO BnO 31 H 45 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   240 Compound 46. OBn OH TESO 27 TBSO BnO 31 46 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01 OBn OH TESO 27 TBSO BnO 31 46 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   241 Compound 132. O OBn O TESO 27 TBSO BnO 31 132 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O OBn O TESO 27 TBSO BnO 31 132 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   242 Compound 47. O OBn O TESO 27 TBSO BnO 31 35 47 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O OBn O TESO 27 TBSO BnO 31 35 47 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   243 Compound 48. O OBn O TESO 27 TBSO BnO 31 35 OH OH 48 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O OBn O TESO 27 TBSO BnO 31 35 OH OH 48 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   244 Compound 49. O OBn O MOPO 27 TBSO BnO 31 35 O O Me Me 49 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 O OBn O MOPO 27 TBSO BnO 31 35 O O Me Me 49 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   245 Compound 50. OBn OH O 31 MOPO 27 TBSO BnO Me O Me 35 OH 50 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 OBn OH O 31 MOPO 27 TBSO BnO Me O Me 35 OH 50 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   246 Compound 133. OBn OH O 31 MOPO 27 TBSO BnO Me O Me 35 OTBDPS 133 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01 OBn OH O 31 MOPO 27 TBSO BnO Me O Me 35 OTBDPS 133 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   247 Compound 51. OBn OBn O 31 MOPO 27 TBSO BnO Me O Me 35 OTBDPS 51 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01 OBn OBn O 31 MOPO 27 TBSO BnO Me O Me 35 OTBDPS 51 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   248 Compound 134. OBn OBn O 31 MOPO 27 TBSO BnO Me O Me 35 OH 134 (600 MHz, CDCl3) ppm0 89 78 67 56 45 34 23 12 01 OBn OBn O 31 MOPO 27 TBSO BnO Me O Me 35 OH 134 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   249 Compound 52. OBn OBn O 31 MOPO 27 TBSO BnO Me O Me O 35 H 52 (600 MHz, CDCl3) ppm0 910 89 78 67 56 45 34 23 12 01 OBn OBn O 31 MOPO 27 TBSO BnO Me O Me O 35 H 52 (125 MHz, CDCl3) ppm0 200 150200 100150 50100 050   250 Compound 54. OBn OBn O 31 MOPO 27 TBSO BnO Me O Me OH O 35 OTBS 39 C9H19 OTES 54 (600 MHz, C6D6) ppm0 89 78 67 56 45 34 23 12 01 OBn OBn O 31 MOPO 27 TBSO BnO Me O Me OH O 35 OTBS 39 C9H19 OTES 54 (125 MHz, C6D6) ppm0 200 150200 100150 50100 050   251 Compound 135.   27 OBn OBn O O 35 TES O OTBS 39 31 HO TBSO BnO Me O Me C9H19 OTES 135 (600 MHz, CDCl3)   ppm0 89 78 67 56 45 34 23 12 01   27 OBn OBn O O 35 TES O OTBS 39 31 HO TBSO BnO Me O Me C9H19 OTES 135 (125 MHz, CDCl3)   ppm0 200   150200 100150 50100 050     252 Compound 41.   O OBn OBn O O 35 TES O OTBS 39 31 H 27 TBSO BnO Me O Me C9H19 OTES 41 (600 MHz, CDCl3)   ppm0 89 78 67 56 45 34 23 12 01   O OBn OBn O O 35 TES O OTBS 39 31 H 27 TBSO BnO Me O Me C9H19 OTES 41 (125 MHz, CDCl3)   ppm0 200   150200 100150 50100 050     253 Compound 55.  55 (600 MHz, CDCl3) BnO 3 7 Me Me OBn O 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me TBSO BnO Me O Me OTES   ppm0 89 78 67 56 45 34 23 12 01   55 (125 MHz, CDCl3) Me Me OBn O O Me Me O 15 Me Me O 19 O O O 23 TIPS OH OH OBn OBn O 27 31 O 35 TES O OTBS 39 BnO 3 7 11 C9H19 Me Me O Me TBS Me Me Me Me TBSO BnO Me O Me OTES   ppm0 200   150200 100150 50100 050     254 Compound 56. 56 (500 MHz, CDCl3) Me Me OH O HO 3 7 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OH OH OH OH O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me TBSO HO Me O Me OTES ppm0 89 78 67 56 45 34 23 12 01 56 (125 MHz, CDCl3) Me Me OH O O Me Me O 15 Me Me O 19 O O O 23 TIPS OH OH OH OH O 27 31 O 35 TES O OTBS 39 HO 3 7 11 C9H19 Me Me O Me TBS Me Me Me Me TBSO HO Me O Me OTES ppm0 200 150200 100150 50100 050   255 Compound 57. 57, R = TMS (600 MHz, CDCl3) HO 3 7 Me Me OR O 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me TBSO RO Me O Me OTES ppm0 89 78 67 56 45 34 23 12 01 57, R = TMS (125 MHz, CDCl3) HO 3 7 Me Me OR O 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 C9H19 Me Me O Me TBS Me Me Me Me TBSO RO Me O Me OTES ppm0 200 150200 100150 50100 050   256 Compound 59. Me Me O 2' O 3' 59, R = TMS (600 MHz, CDCl3) 3 7 Me Me OR O 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O C9H19 Me Me Me O Me TBS Me Me Me Me TBSO RO Me O Me OTES ppm0 89 78 67 56 45 34 23 12 01 Me Me O 2' O 3' 59, R = TMS (125 MHz, CDCl3) 3 7 Me Me OR O 11 Me Me O 15 Me Me O 19 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O C9H19 Me Me Me O Me TBS Me Me Me Me TBSO RO Me O Me OTES ppm0 200 150200 100150 50100 050   257 Compound 60. 60, R = TMS (600 MHz, CDCl3) Me EtO 4' Me Me OR O 7 11 Me Me O 15 Me Me O 19 O O 3 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O N 2' Me C9H19 Me Me Me O Me TBS Me Me Me Me TBSO RO Me O Me OTES ppm0 89 78 67 56 45 34 23 12 01 60, R = TMS (125 MHz, CDCl3) Me EtO 4' Me Me OR O 7 11 Me Me O 15 Me Me O 19 O 2' O 3 O O O O 23 TIPS OR OR OH OR O 27 31 O 35 TES O OTBS 39 O N Me C9H19 Me Me Me O Me TBS Me Me Me Me TBSO RO Me O Me OTES ppm0 200 150200 100150 50100 050   258 Compound 1•Et2NH. 1•Et2NH (600 MHz, DMSO-d6) O Me N Me 2' OH HO HO HO HO HO HO HO HO HO HO HO HO HO 35 O 3 Et2NH2 7 OH OH 39 11 15 19 23 27 31 O Me Me Me OH Me Me Me Me Me OH OH H O OH C9H19 ppm0 8 78 67 56 45 34 23 12 01 1•Et2NH (125 MHz, DMSO-d6) O Me N Me 2' OH HO HO HO HO HO HO HO HO HO HO HO HO HO 35 O 3 Et2NH2 7 OH OH 39 11 15 19 23 27 31 O Me Me Me OH Me Me Me Me Me OH OH H O OH C9H19 ppm0 200 150200 100150 50100 050   259 Comparison of the 1H-NMR Spectrum Reported for 1•Et2NHa to Our Spectrum. Sakuda 1•Et2NH (500 MHz, DMSO-d6) Evans 1•Et2NH (500 MHz, DMSO-d6) ppm0.5 6.57.0 6.06.5 5.56.0 5.05.5 4.55.0 4.04.5 3.54.0 3.03.5 2.53.0 2.02.5 1.52.0 1.01.5 0.51.0 a Reproduced from: (a) Ono, M.; Sakuda, S.; Suzuki, A.; Isogai, A. J. Antibiotics 1997, 50, 111–118; (b) Ono, M.; Suzuki, A.; Isogai, A.; Sakuda, S. Production Aflastatin A from Streptomyces sp., A Pharmaceutical Composition and Methods of Use. U.S. Patent 5,773,263, June 30, 1998.   260 Comparison of the 13C-NMR Spectrum Reported for 1•Et2NHa to Our Spectrum. Sakuda 1•Et2NH (125 MHz, DMSO-d6) Evans 1•Et2NH (125 MHz, DMSO-d6) ppm0200 150200 100150 50100 050 a Reproduced from: (a) Ono, M.; Sakuda, S.; Suzuki, A.; Isogai, A. J. Antibiotics 1997, 50, 111–118; (b) Ono, M.; Suzuki, A.; Isogai, A.; Sakuda, S. Production Aflastatin A from Streptomyces sp., A Pharmaceutical Composition and Methods of Use. U.S. Patent 5,773,263, June 30, 1998.   261 Comparison of the IR Spectrum Reported for 1•Et2NHa to Our Spectrum. Sakuda 1•Et2NH (KBr) Evans 1•Et2NH (NaCl) a Reproduced from: (a) Ono, M.; Sakuda, S.; Suzuki, A.; Isogai, A. J. Antibiotics 1997, 50, 111–118; (b) Ono, M.; Suzuki, A.; Isogai, A.; Sakuda, S. Production Aflastatin A from Streptomyces sp., A Pharmaceutical Composition and Methods of Use. U.S. Patent 5,773,263, June 30, 1998.   262