Highly Diastereoselective Synthesis of Cyclic α‐Aminophosphonic and α‐Aminophosphinic Acids from Glycyl‐l‐Proline 2,5‐Diketopiperazine

Abstract

This paper describes the first diastereoselective synthesis of cyclic α‐aminophosphonic and α‐amino phosphonic acids from glycyl‐l‐proline 2,5‐diketopiperazine (S)‐6 prepared according to the usual peptide coupling procedures. The highlights of this contribution is the chemoselective reduction of the carbamate‐imide activated carbonyl group in the N‐Boc 2,5‐diketopiperazine (S)‐11 to generate the unstable hemiaminals (1R,8aS)‐12 and (1S,8aS)‐13, followed by the highly diastereoselective nucleophilic addition of trimethyl phosphite or dimethyl phenylphosphonite to the chiral carbenium ion (S)‐5. Acid hydrolysis of the phosphonate and phosphinate functionalities with simultaneous cleavage of the tert‐butyl carbamate protecting group led to the target compounds. The high diastereoselectivity in the nucleophilic addition of trivalent phosphorus to the chiral carbenium ion (S)‐5 is in agreement with our precedent reports.