Stereoselective synthesis of N-benzyl (2S,3S,4S)-3-hydroxy-4-methylproline

Abstract

The synthesis of (2S,3S,4S)-N-benzyl-3-hydroxy 4-methyl proline and its stereoisomer (2R,3R,4S)-N-benzyl-3-hydroxy 4-methyl proline has been achieved starting with the conjugate addition of methyl methacrolate and benzylamine. The other key reactions performed in our strategy include enzymatic separation of an α-methyl β-amino alcohol, Sharpless asymmetric dihydroxylation of an α,β-unsaturated δ-amino ester, and intramolecular cyclization of a sulfonate to a pyrrolidine ring system. Two stereoisomers were synthesized from the common α,β-unsaturated δ-amino ester intermediate. This protocol is simple, straightforward, efficient, highly stereoselective, and economically viable.