H N.M.R. studies of protected alpha-aminoisobutyric acid containing peptides. Chemical shift nonequivalence of benzyloxycarbonyl methylene protons

Iqbal, M and Nagaraj, R and Balaram, Padmanabhan (1981) H N.M.R. studies of protected alpha-aminoisobutyric acid containing peptides. Chemical shift nonequivalence of benzyloxycarbonyl methylene protons. In: International Journal of Peptide and Protein Research International Journal of Peptide and Protein Research, 18 (2). pp. 208-213.

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Abstract

The benzylic methylene protons in a large number of benzyloxycarbonyl alpha-aminoisobutyric acid (Z-Aib) containing peptides, show chemical shift nonequivalence. The magnitude of the geminal nonequivalence is correlated with the involvement of the urethane carbonyl group, in an intramolecular hydrogen bond. Studies of the model compounds Z-Aib-Aib-Ala-NHMe, and Z-Aib-Aib-Aib-Pro-OMe clearly establish the presence of intramolecular hydrogen bonds, involving the urethane CO group. In both compounds marked anisochrony of the benzylic methylene protons is demonstrated. In Z-Aib-Aib-Pro-OMe, where a 4 leads to 1 hydrogen bonded beta-turn is not possible, the benzylic-CH2-protons appear as a singlet in CDCl3 and have a very small chemical shift difference in (CD3)2SO. The observation of such nonequivalence is of value in establishing whether the amino terminal Aib-Pro beta-turn is retained in large peptide-fragments of alamethicin.

Item Type:	Journal Article
Publication:	International Journal of Peptide and Protein Research International Journal of Peptide and Protein Research
Publisher:	Wiley interscience
Additional Information:	Copyright of this article belongs to Wiley interscience.
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	19 Feb 2010 09:32
Last Modified:	19 Sep 2010 05:55
URI:	http://eprints.iisc.ac.in/id/eprint/25656

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