Peptides containing the sulfonamide junction: Synthesis,structure, and conformation of Z-Tau-Pro-Phe-NHiPr

The taurine (Tau) containing tripeptide derivative Z-Tau-Pro-Phe-NHiPr (1) has been synthesized as suitable sulfonamido-pseudopeptide model to investigate formation and conformational properties of folded secondary structures stabilized by intramolecular H bonds directly involving the sulfonamide junction. In the crystal the pseudopeptide 1 adopts a type I β-turn with the Pro and Phe residues located at the (i + 1) and (i + 2) corner positions, respectively. The turn is stabilized by a 4 → 1 H bond engaging one of the SO₂ oxygen atoms and the isopropylamide NH. In CDCl₃ solution the β-turn folding is accompanied by a γ-turn centered at the Pro and involving a 3 → 1 H bond between the SO₂ and the Phe NH. A comparison of the structural and conformational properties found in 1 with those of the already known sulfonamido-pseudopeptides, with particular reference to the models containing the Tau-Pro junction, is also reported. © 1997 John Wiley & Sons, Inc. Biopoly 41: 555–567, 1997.