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Conformation of Boc-L-Ala-Aib-L-Ala-OMe in the Crystal and in Solution

✍ Scribed by Bosch, Roland ;Jung, Günther ;Voges, Klaus-Peter ;Winter, Werner

Publisher: John Wiley and Sons
Year: 1984
Tongue: English
Weight: 560 KB
Volume: 1984
Category: Article
ISSN: 0947-3440
DOI: 10.1002/jlac.198419840609

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✦ Synopsis

Abstract

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.

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