A novel peptide conformation: the gamma-bend ribbon

Unlike the extensively investigated relationship between the peptide -bend ribbon and its prototypical 3(10)-helix conformation, the corresponding relationship between the narrower -bend ribbon and its regular -helix counterpart still remains to be studied, as the latter 3D-structures have not yet been experimentally authenticated. In this paper, we describe the results of the first characterization, both in the crystal state and in solution, of the -bend ribbon conformation using X-ray diffraction and FT-IR absorption, electronic CD and 2D-NMR spectroscopies applied to an appropriate set of synthetic, homo-chiral, sequential dipeptide oligomers based on (S)-Ala and the known -bend inducer, C-tetrasubstituted, N-alkylated -amino acid residue (S)-C-methyl-azetidine-carboxylic acid.