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Conformation of Boc‐ L ‐Ala‐Aib‐ L ‐Ala‐OMe in the Crystal and in Solution
Author(s) -
Bosch Roland,
Jung Günther,
Voges KlausPeter,
Winter Werner
Publication year - 1984
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.198419840609
Subject(s) - chemistry , geminal , hydrogen bond , crystallography , tripeptide , intermolecular force , solvent , crystal (programming language) , stereochemistry , crystal structure , peptide , molecule , organic chemistry , biochemistry , computer science , programming language
Boc‐ L ‐Ala‐Aib‐ L ‐OMe ( 1 ) crystallizes in the space group P 2 1 with a = 11.732(1), b = 6.013(1), c = 14.195(2) Å, β = 91.76(1)→, and Z = 2( R value for 3089 reflexions: 0.047). The peptide adopts a new type of β‐turn with a very wide 4→1 hydrogen bond distance of 3.621 Å. As for Ac‐ L ‐Ala‐Aib‐ L ‐Ala‐Me this distortion can be attributed to strong intermolecular hydrogen bonds forming a two‐dimensional network in the bc plane. Temperature and solvent dependent 1 H and 13 C NMR reveal a hydrogen bond from Boc–CO to NH– 3 Ala in solution, E/Z isomerism of the Boc urethane bond, and a large magnetic nonequivalence of the two geminal Aib methyl groups. The unusual conformation of 1 is reflected also in its CD spectrum, which differs from most of comparable Aib containing tripeptides.