LINEAR OLIGOPEPTIDE .279. STRUCTURES OF PEPTIDES FROM ALPHA-AMINO-ACIDS METHYLATED AT THE ALPHA-CARBON

The structural preferences of peptides (and depsipeptides) from the ac hiral MeAib and Hib residues, and the chiral Iva, (alphaMe)Val, (alpha Me)Leu, and (alphaMe)Phe residues, as determined by conformational ene rgy computations, x-ray diffraction analyses, and H-1-nmr and spectros copic studies, are reviewed and compared with literature data on Aib-c ontaining peptides. The results obtained indicate that helical structu res are preferentially adopted by peptides rich in these alpha-amino a cids methylated at the alpha-carbon. Intriguing experimental findings on the impact of the chirality of Iva, (alphaMe) Val, and (alphaMe) Ph e residues on helix screw sense are illustrated.