High-Affinity Alkynyl Bisubstrate Inhibitors of Nicotinamide N-Methyltransferase (NNMT)

Abstract

Nicotinamide N-methyltransferase (NNMT) is a metabolic enzyme responsible for the methylation of nicotinamide (NAM) using cofactor S-adenosylmethionine (SAM). NNMT overexpression has been linked to diabetes, obesity, and a variety of cancers. Successful development of potent and selective NNMT inhibitors could further reveal the role of NNMT in various diseases, potentially enabling new treatments for metabolic disorders and several cancers. In this work, structure-based rational design led to the development of potent and selective alkynyl bisubstrate inhibitors of NNMT. The reported nicotinamide-SAM conjugate (named NS1) features an alkyne as a key design element that closely mimics the linear, 180° transition state geometry found in the NNMT-catalyzed SAM → NAM methyl transfer reaction. NS1 was synthesized as a single enantiomer and diastereomer in 14 steps and found to be a high-affinity, subnanomolar NNMT inhibitor. An X-ray co-crystal structure and structure-activity relationship (SAR) study revealed the unique ability of an alkynyl linker to span the methyl transfer tunnel of NNMT with ideal shape complementarity. The compounds reported in this work represent the most potent and selective NNMT inhibitors reported to date. The rational design principle described herein could potentially be extended to other methyltransferase enzymes.