Methods for the synthesis of L-lactyl-L-valine-1-14C

The preparation of L-lactyl-L-valine from L-lactic acid and L-valine, by methods used for the synthesis of peptides, was investigated. Initial experiments with O-benzoyl-DL-lactic acid and DL-valine benzyl ester unexpectedly gave N-benzoyl-DL-valine benzyl ester. However, coupling between O-benzyloxycarbonyl-DL-lactic acid and either DL-valine, or DL-valine benzyl ester, occurred in good yield. A simpler method, which was reported to give a 39% yield of L-lactyl-L-valine, gave only 10% of product but was modified to give L-lactyl-L-valine-1-14C in 90% yield.