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Solid‐state conformations of α‐Aminoisobutyryl‐ L ‐prolyl sequences: Crystal structure of Boc‐Aib‐ L ‐Pro‐OBzl
Author(s) -
Kawai Masao,
Butsugan Yasuo,
Fukuyama Keiichi,
Taga Tooru
Publication year - 1987
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.360260110
Subject(s) - chemistry , orthorhombic crystal system , dipeptide , crystal structure , stereochemistry , residue (chemistry) , hydrogen bond , crystallography , pyrrolidine , molecule , peptide , organic chemistry , biochemistry
Abstract The protected dipeptide Boc‐Aib‐Pro‐OBzl, C 21 H 30 N 2 O 5 , crystallizes in the orthorhombic space group P2 1 2 1 2 1 , with a = 12.820, b = 10.529, c = 16.548Å, and Z = 4. The crystal structure has been solved by direct methods and refined to an R value of 0.074 for 1352 reflections. The Boc‐Aib‐Pro‐OBzl molecule has been shown to adopt an unfolded conformation in the solid state with ϕ Aib = 50.5°, Ψ Aib = 45.3°, ϕ Pro = −64.6°, and Ψ Pro = 148.1°. The result is in marked contrast with the reported crystal structure of Cbz‐Aib‐Pro‐NHMe, which adopts an intramolecularly hydrogen‐bonded β‐turn conformation. Comparison with 13 reported conformations of Aib‐Pro sequences in the crystalline state revealed that the Aib‐Pro sequence adopts an unfolded conformation if the residue that immediately follows the dipeptide sequence possesses no hydrogen available for hydrogen bonding, while a β‐turn conformation is preferred if the Pro residue is followed by an NH group. Correlation between pyrrolidine ring puckering of the Pro residue and main‐chain conformation in Aib‐Pro sequences is discussed.