Enantioselective synthesis of α-carbon deuterium-labelled l-α-amino acids

In this paper we describe a simple and efficient method for the synthesis of α-carbon deuterium labelled l-α-amino acids via asymmetric alkylation of a benzophenone-derived glycine imine. The key alkylation step employs a chiral quaternary ammonium salt derived from cinchonidine in conjunction with KOD in D2O enabling both side-chain and isotopic label to be incorporated in a single reaction step. Mild acid hydrolysis of the resulting imines then furnishes the labelled amino acid esters in good overall yield and high enantiomeric excess.