Effect of phenyl ring position in the Cα-methylated α-amino acid side chain on peptide preferred conformation

The preferred conformations of Cα-methyl phenylglycine, Cα-methyl phenylalanine, and Cα-methyl homophenylalanine residues, as determined in model peptides (including homopeptides) by Fourier transform ir absorption, 1H-nmr, CD, and x-ray diffraction techniques, are compared with the aim of investigating the effect of phenyl ring position in the Cα-methylated amino acid side chain. This study shows that (a) β-turn and 310-helical structures are preferentially adopted by peptides rich in these Cα-methylated, aromatic α-amino acids and (b) turn and helix handedness is critically biased by the position of side-chain branching.