New dipeptides, structural analogues of known immunomodulating agents, were
prepared by stereospecific condensation between 2-substituted thiazolidine
-4-carborylate esters with N-substituted L-proline or L-thiaproline, The st
ructure of these compounds has been elucidated by combination of NMR method
s and X-ray analysis. In addition, NMR measurements on dipeptides indicated
the presence of S-cis and S-trans conformers around the amide bonds.