Stereoselective synthesis of unnatural tetrapeptides 20a and 20b, 21a and 21b and 30 and 31, containing two l-valine units and two unnatural α-amino acids (ornithine and modified aspartic acid), has been accomplished starting from the l-valine derived chiral synthon 1. Structural investigations of these non-proteinogenic peptides have been carried out on the acetamido derivatives using 1H NMR, IR spectroscopic techniques and a conformational ...
