Total Synthesis of (−)-Salinosporamide A

A concise and stereoselective total synthesis of (−)-salinosporamide A (1), a potent inhibitor of the 20S proteasome that is in clinical development as an anticancer drug candidate, has been accomplished in 14 steps with 19% overall yield from 4-pentenoic acid. Our synthesis features a stereoselective alkylation utilizing a chiral auxiliary, formation of a pyrrolidine unit, and oxidation of the pyrrolidine to a γ-lactam. To demonstrate the scalability of our synthesis, (−)-salinosporamide A has been synthesized on a gram scale.