CONFORMATIONAL STUDIES OF HETEROCHIRAL PEPTIDES WITH DIASTEREOISOMERIC RESIDUES - CRYSTAL AND MOLECULAR-STRUCTURES OF LINEAR DIPEPTIDES DERIVED FROM LEUCINE, ISOLEUCINE, AND ALLO-ISOLEUCINE(185 visite) Di Blasio B, Saviano M, Del Duca V, De Simone G, Rossi F, Pedone C, Benedetti E, Lorenzi GP
Parole chiave: Dipeptide, Isoleucine, Conference Paper, Conformational Transition, Crystal Structure, Diastereoisomer, Enantiomer, Peptide Analysis, Protein Conformation, X Ray Diffraction, Comparative Study, Crystallography, X-Ray, Models, Molecular, Stereoisomerism, Structure-Activity Relationship, Support, Non-U.S. Gov, Non-U. S. Gov,
Department of Chemistry, University of Napoli 'Federico II', Via Mezzocannone 4, 80134 Napoli, Italy
The x-ray diffraction analyses of three N- and C-terminally blocked L,D dipeptides, namely t-Boc-D-Leu-L-Leu-OMe (1), t-Boc-L-Ile-D-alle-OMe (2), and t-Boc-D-alle-L-Ile-OMe (3) containing enantiomeric or diastereomeric amino acid residues have been carried out. The structures were determined by direct methods and refined anisotropically to final R f actors of 0.077, 0.058, and 0.072 for (1), (2), and (3), respectively. Peptides 1-3 all assume a similar U-shaped structure with phi and psi torsion angles corresponding to one of the possible calculated minimum energy regions (regions E and G for L residues, and F*, D* and H* for D residues). The peptide backbones of 1-3 are almost super-imposable [provided that the appropriate inversion of the chiral centers of (2) is made]. Side-chain conformations of Leu residues in peptide (1) are g(-) (tg(-)) for the L-Leu residue and the mirrored g(+) (tg(+)) for the D-Leu residue; however, in peptides (2) and (3) the conformations of the isoconfigurational side chains of the Ile or allo-Ile residues are (g(-)t)t and (tg(+))t for the L-Ile and the D-allo-Ile moieties, respectively. In all cases, these conformations correspond to the more populated conformers of beta-branched residues statistically found in crystal structures of small peptides. The results seem to indicate that, at least in short peptides with enantiomeric or diastereo-isomeric residues, the change in chirality in the main-chain atoms perturbs the backbone conformation to a lesser extent and the side chain conformation to a greater extent. (C) 1995 John Wiley & Sons, Inc.
311 Records (302 escludendo Abstract e Conferenze). Impact factor totale: 1115.626 (1094.471 escludendo Abstract e Conferenze). Impact factor a 5 anni totale: 1173.473 (1139.463 escludendo Abstract e Conferenze).