title: Conformations of dehydrophenylalanine containing peptides. Nuclear Overhauser effect study of two acyclic tetrapeptides.
abstract: Two isomeric, acyclic tetrapeptides containing a Z-dehydrophenylalanine residue (delta Z-Phe) at position 2 or 3, Boc-Leu-Ala-delta Z-Phe-Leu-OMe (1) and Boc-Leu-delta Z-Phe-Ala-Leu-OMe (2), have been synthesized and their solution conformations investigated by 270 MHz 1H n.m.r. spectroscopy. In peptide 1 the Leu(4) NH group appears to be partially shielded from solvent, while in peptide 2 both Ala(3) and Leu(4) NH groups show limited solvent accessibility. Extensive difference nuclear Overhauser effect (n.O.e.) studies establish the occurrence of several diagnostic inter-residue n.O.e.s (Ci alpha H----Ni+1H and NiH----Ni+1H) between backbone protons. The simultaneous observation of "mutually exclusive" n.O.e.s suggests the presence of multiple solution conformations for both peptides. In peptide 1 the n.O.e. data are consistent with a dynamic equilibrium between an -Ala-delta Z-Phe- Type II beta-turn structure and a second species with delta Z-Phe adopting a partially extended conformation with psi values of +/- 100 degrees to +/- 150 degrees. In peptide 2 the results are compatible with an equilibrium between a highly folded consecutive beta-turn structure for the -Leu-delta Z-Phe-Ala- segment and an almost completely extended conformation.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore.
authors.forename: K
authors.initials: K
authors.lastname: Uma
authors.forename: V S
authors.initials: VS
authors.lastname: Chauhan
authors.forename: A
authors.initials: A
authors.lastname: Kumar
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D009842:Oligopeptides / Q000138:chemical synthesis; D010649:Phenylalanine / Q000031:analogs & derivatives*; D011487:Protein Conformation
chemical_list: D007202:Indicators and Reagents; D009842:Oligopeptides; D010649:Phenylalanine; C018632:phenyldehydroalanine