A1,3-strain enabled retention of chirality during bis-cyclization of β-ketoamides: total synthesis of (−)-salinosporamide A and (−)-homosalinosporamide A

Abstract

A concise, enantioselective synthesis of the Phase I anticancer agent, (−)-salinosporamide A, is described. The brevity of the described strategy stems from a key bis-cyclization of a β-keto tertiary amide, accomplished on gram scale, which retains optical purity enabled by A^1,3-strain rendering epimerization slow relative to the rate of bis-cyclization. The versatility of the strategy for derivative synthesis is demonstrated by the synthesis of (−)-homosalinosporamide A.