Munro, Thomas A.Ho, Douglas M.Cohen, Bruce2014-02-242012Munro, Thomas A., Douglas M. Ho, and Bruce Michael Cohen. 2012. Salvinorin B meth­oxy­methyl ether. Acta Crystallographica Section E: Structure Reports Online 68(Pt 11): o3225-o3226.1600-5368http://nrs.harvard.edu/urn-3:HUL.InstRepos:11738405The title compound [MOM-SalB; systematic name: methyl (2S,4aR,6aR,7R,9S,10aS,10bR)-2-(3-fur­yl)-9-meth­oxy­meth­oxy-6a,10b-dimethyl-4,10-dioxo-2,4a,5,6,7,8,9,10a-octa­hydro-1H-benzo[f]isochromene-7-carboxyl­ate], \(C_{23}H_{30}O_8\), is a deriv­ative of the κ-opioid salvinorin A with enhanced potency, selectivity, and duration of action. Superimposition of their crystal structures reveals, surprisingly, that the terminal C and O atoms of the MOM group overlap with the corresponding atoms in salvinorin A, which are separated by an additional bond. This counter-intuitive isosterism is possible because the MOM ether adopts the 'classic anomeric' conformation (gauche–gauche), tracing a helix around the planar acetate of salvinorin A. This overlap is not seen in the recently reported structure of the tetra­hydro­pyranyl ether, which is less potent. The classic anomeric conformation is strongly favoured in alk­oxy­methyl ethers, but not in substituted acetals, which may contribute to their reduced potency. This structure may prove useful in evaluating models of the activated \(\kappa\)-opioid receptor.en-USJournal Article2014-02-2410.1107/S1600536812043449