Synthesis and conformational preferences of cyclic unnatural di- and tripeptides containing an L-valine unit: Part 2

Stereoselective syntheses of non-proteinogenic di- 14a,b, 15a,b and 16a,b and tripeptides 14c, 15c and 16c containing all L-valine unit and a cyclic unnatural alpha-amino acid have been accomplished starting from the L-valine derived chiral synthon 1. The conformational preferences of these unnatural peptides were investigated by H-1 NMR and IR spectroscopies and by molecular modelling calculations. X-ray analysis of pseudopeptides 15a and 15b is also reported