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

The taurine (Tau) containing tripeptide derivative Z-Tau-Pro-Phe-NHiPr (I) 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 I adopts a type I beta-turn with the Pro and Phe residues located at the (i + 1) and (i + 2) corner positions, respectively. The him is stabilized by a 4 --> 1 H bond engaging one of the SO2 oxygen atoms and the isopropylamide NH. In CDCl3 solution the beta-turn folding is accompanied by a gamma-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 I with those of the already known sulfonamido-pseudopeptides, with particular reference to the models containing the Tau-Pro junction, is also reported. (C) 1997 John Wiley & Sons, Inc