Stereoselective synthesis of stable isotope-labeled L-α-amino acids: enantioselective synthesis of 13C-, 15N-labeled L-proline using Oppolzer's glycine template

We have developed a stereoselective route to the synthesis of stable isotope-labeled L-proline. Alkylation of (2R)-N-{N′-[bis(methylthio)methylidine]-glycyl}bornane-10,2-sultam with 3-chloro-iodopropane yielded (2R)-N-{(2′S)-2′-{[Bis(methylthio)methylidine]amino}-5-chloropentan-1-oyl}bornane-10,2-sultam. Cyclization to the imino acid occurred during the sequential removal of the α-amino protecting group and the chiral auxiliary.