A concise and straightforward total synthesis of (±)-salinosporamide A, based on a biosynthesis model

Abstract

A 14-step total synthesis of (±)-salinosporamide A (1), a potent inhibitor of the 20S proteasome isolated from the marine bacterium Salinospora tropica, is described. The synthesis is based on a diastereoselective intramolecular aldolisation of a substituted β-keto amide intermediate, i.e.13, derived from a β-keto acid, viz.21, and an α-amino malonate, leading to the pyrrolidinone ring 24 in the natural product. This synthetic approach closely mimics the origin of the pyrrolidinone ring in salinosporamide A in vivo. Another key feature of the total synthesis is a regioselective reduction of the malonate derivative 31 to the key aldehyde intermediate 32, using Super-hydride.