Rotational isomerism about the Ca-CO bond in proline derivatives. 1H and 13C NMR studies of benzyloxycarbonyl-Pro-N-methylamide and pivaloyl-Pro-N-methylamide

Nagaraj, R and Venkatachalapathi, YV and Balaram, P (1980) Rotational isomerism about the Ca-CO bond in proline derivatives. 1H and 13C NMR studies of benzyloxycarbonyl-Pro-N-methylamide and pivaloyl-Pro-N-methylamide. In: Journal of Peptide Research, 16 (4). 291 -298.

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Abstract

The 270 MHz 1H n.m.r. spectrum of benzyloxycarbonyl-Pro-N-methylamide in CDCl3 is exchange broadened at 293° K. Spectral lines due to two species are frozen out at 253° K and a dynamically averaged spectrum is obtained at 323° K. A selective broadening of the Cβ and Cγ resonances in the 13C n.m.r. spectrum is observed at 253° K, with a splitting of the Cβ and Cγ resonances into a pair of lines of unequal intensity. A similar broadening of Cβ and Cγ peaks is also detected in pivaloyl-Pro-N-methylamide where cis-trans interconversion about the imide bond is precluded by the bulky t-butyl group. The rate process is thus attributed to rotation about the Cα-CO bond (ψ) and a barrier (ΔG#) of 14kcal mol-1 is estimated. 13C n.m.r. data for pivaloyl-Pro-N-methylamide in a number of solvents is presented and the differences in the Cβ and Cγ chemical shifts are interpreted in terms of rotational isomerism about the Cα-CO bond.

Item Type:	Journal Article
Publication:	Journal of Peptide Research
Publisher:	John Wiley and Sons
Additional Information:	Copyright of this article belongs to John Wiley and Sons.
Keywords:	activation barriers;nuclear magnetic resonance;peptide conformation;proline;rotational isomerism.
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	22 Feb 2010 09:09
Last Modified:	19 Sep 2010 05:55
URI:	http://eprints.iisc.ac.in/id/eprint/25643

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