Stabilization of γ‐turn conformations in peptides by disulfide bridging

The ideal \γ-turn conformation in peptides is stabilized by the formation of two intramolecular hydrogen bonds. These are between the NH of residue i and the C = O of residue i + 2 (1 \→ 3, C₁₁) and the C = O of residue i and the NH of residue i + 2 (3 \→ 1, C₇). 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 (C₇) 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 \γ-turn conformation in a protected tripeptide, stabilized by formation of a disulfide crosslink.