Intramolecularly hydrogen-bonded peptide conformations.

Over the past few years the possible occurrence of intramolecularly hydrogen-bonded structures in linear and cyclic peptides has attracted increasing attention. In this review emphasis is given to solid-state studies, particularly by X-ray diffraction and infrared absorption techniques. Conformational energy calculations are also considered. The discussion is focused both on model peptides and biological activity polypeptide molecules. The tetrapeptide system (Formula: see text), examined allows one to discuss the extended C5 structure and the various folded conformations, namely the C7 (gamma-turn), C8, C10 (beta-turn), C11, and C13 conformations. The four latter forms may include cis peptide configurations. The oxy-analogs to the C7, C10, and C13 conformations and structures containing bifurcated hydrogen bonds are also discussed. The last sections describe intramolecularly hydrogen-bonded peptide structures involving: (1) a side-chain group, (2) the N-protecting group (in synthetic model compounds), and (3) a beta-amino acid.