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Stereochemistry of α-aminoisobutyric acid peptides in solution: Helical conformations of protected decapeptides with repeating Aib-L-Ala and Aib-L-Val sequences

✍ Scribed by E. K. S. Vijaya kumar; P. Balaram

Publisher
Wiley (John Wiley & Sons)
Year
1983
Tongue
English
Weight
396 KB
Volume
22
Category
Article
ISSN
0006-3525

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✦ Synopsis

The decapeptides Boc-(Aib-L-Ala)s-OMe and Boc-(Aib-L-Val)s-OMe have been studied by 270-MHz lH-nmr in CDCl3 and (CD&SO solutions. Intramolecular hydrogen-bonded NH groups have been delineated using the temperature and solvent dependence of the NH chemical shifts and differential broadening of the NH resonances, induced by addition of a nitroxide radical. Both peptides have eight solvent-shielded NH groups, suggesting that dlo-helical conformations are maintained in the two solvents. In alternating Aib-X sequences, the Aib residues appear to play a dominant role in determining the preferred conformations, overriding the intrinsic stereochemical preferences of the X residues.

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As models of the helical N-terminal part of alamethicin the undecapeptides Boc-L-Ala-[Aib-Ala]2-Glu(0Bzl)-Ala-[Aib-Ala],-OMe (1) and Boc-~-Ala-[Aib-Ala]~-Gly-Ala-[Aib-Ala]~-OMe (2) were synthesized. 1 was examined by X-ray crystallography using direct methods for solution of the phase problem. The u