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Molecular and crystal structures of Aib‐containing oligopeptides Boc‐Leu 4 ‐Aib‐Leu 4 ‐OBzl and Boc‐(Leu 4 ‐Aib) 2 ‐OBzl
Author(s) -
Okuyama K.,
Saga Y.,
Nakayama M.,
Narita M.
Publication year - 1991
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360310807
Subject(s) - chemistry , molecule , hydrogen bond , intramolecular force , solvent , peptide , monoclinic crystal system , stereochemistry , crystal structure , residue (chemistry) , intermolecular force , crystallography , polymer chemistry , organic chemistry , biochemistry
Sample peptides Boc‐Leu 4 ‐Aib‐Leu 4 ‐OBzl and Boc‐(Leu 4 ‐Aib) 2 ‐OBzl, were crystallized by the solvent‐evaporation method. Both crystals are monoclinic, with space group of P2 1 and Z = 2. The cell parameters are a = 16.580(7), b = 21.105(7), c = 11.583(4) Å, and β = 104.90(3)° (Boc‐Leu 4 ‐Aib‐Leu 4 ‐OBzl), and a = 15.247(9), b = 19.04(l), c = 16.311(9) Å, and β = 117.10(1)° [Boc‐(Leu 4 ‐Aib) 2 ‐OBzl]. Crystal structures were solved by the direct method and refined to R values of 0.096 (the former peptide) and 0.112 (the latter). Peptide backbones fold into a right‐handed α‐helix, except for the C‐terminal Aib residue in Boc‐(Leu 4 ‐Aib) 2 ‐OBzl. Both peptide molecules are stabilized by six (the former) or seven (the latter) intramolecular (5 → 1) hydrogen bonds, and arranged in the head‐to‐tail fashion, which makes an infinite column. In this column, one (the former) or two (the latter) intermolecular hydrogen bonds link the neighboring molecules. In the case of Boc‐Leu 4 ‐Aib‐Leu 4 ‐OBzl, the solvent molecule N, N‐dimethylformamide was found in the difference Fourier map. There was a hydrogen bond between peptide and solvent molecule. Along the lateral direction, only hydrophobic contacts were observed between adjacent peptide molecules.