Racemization at proline residues during peptide bond formation : A study of diastereomeric mixtures of synthetic alamethicin fragments by 270 MHz 1H NMR

Nagaraj, R and Balaram, P (1981) Racemization at proline residues during peptide bond formation : A study of diastereomeric mixtures of synthetic alamethicin fragments by 270 MHz 1H NMR. In: Tetrahedron, 37 (10). pp. 2001-2005.

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Abstract

The stepwise synthesis of amino terminal pentapeptide of alamethicin, Z-Aib-Pro-Aib-Ala-Aib-OMe, by the dicyclohexylcarbodiimide mediated couplings leads to extensive racemization at the Ala and Pro residues. Racemization is largely suppressed by the use of additives like N-hydroxysuccinimide and 1-hydroxybenzotriazole. The presence of diastereomeric peptides may be detected by the observation of additional methyl ester and benzylic methylene signals in the 270 MHz 1H NMR spectra. Unambiguous spectral assignment of the signals to the diastereomers has been carried out by the synthesis and NMR studies of the D-Ala tetra and pentapeptides. The racemization at Pro is of particular relevance in view of the reported lack of inversion at C-terminal Pro on carboxyl activation.

Item Type:	Journal Article
Publication:	Tetrahedron
Publisher:	Elsevier Science
Additional Information:	Copyright of this article belongs to Elsevier Science.
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	21 Feb 2010 12:46
Last Modified:	19 Sep 2010 05:55
URI:	http://eprints.iisc.ac.in/id/eprint/25646

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