Stabilization of gamma-turn conformations in peptides by disulfide bridging.

The ideal y-turn conformation in peptides is stabilized by the formation of two intramolecular hydrogen These are between the NH of residue i and the C=O of residue i + 2 (1 3, CJ and the C=O of residue i and the NH of residue i + 2 (3 1, C7).334 While this reverse-turn structural feature has been observed in proteins, '~~ unambiguous characterization of this conformation has yet to be realized in small peptides. Several examples of a single 3 + 1 (C,) hydrogen bond have been reported in crystal structures of cyclic peptides and inferred from spectroscopic studies in apolar solvents! We wish to describe the spectroscopic characterization of a y-turn conformation in a protected tripeptide, stabilized by formation of a disulfide crosslink.