Structures of peptides from alpha-amino acids methylated at the alpha-carbon

The structural preferences of peptides (and depsipeptides) from the achiral MeAib and Hib residues, and the chiral Iva, (alphaMe)Val, (alphaMe)Leu, and (alphaMe)Phe residues, as determined by conformational energy computations, x-ray diffraction analyses, and H-1-nmr and spectroscopic studies, are reviewed and compared with literature data on Aib-containing peptides. The results obtained indicate that helical structures are preferentially adopted by peptides rich in these alpha-amino acids methylated at the alpha-carbon. Intriguing experimental findings on the impact of the chirality of Iva, (alphaMe) Val, and (alphaMe) Phe residues on helix screw sense are illustrated.