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Estimation of the 2.0(5) helix type i -> i hydrogen bond energy at Aib*-Oxa motif: an isodesmic approach

Thirupathi, Ravula and Prabhakaran, Erode N (2014) Estimation of the 2.0(5) helix type i -> i hydrogen bond energy at Aib*-Oxa motif: an isodesmic approach. In: TETRAHEDRON LETTERS, 55 (23). pp. 3418-3421.

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Official URL: http://dx.doi.org/10.1016/j.tetlet.2014.04.064

Abstract

Bending at the valence angle N-C-alpha-C' (tau) is a known control feature for attenuating the stability of the rare intramolecular hydrogen bonded pseudo five-membered ring C-5 structures, the so called 2.0(5) helices, at Aib. The competitive 3(10)-helical structures still predominate over the C5 structures at Aib for most values of tau. However at Aib*, a mimic of Aib where the carbonyl 0 of Aib is replaced with an imidate N (in 5,6-dihydro-4H-1,3-oxazine = Oxa), in the peptidomimic Piv-Pro-Aib*-Oxa (1), the C(5)i structure is persistent in both crystals and in solution. Here we show that the i -> i hydrogen bond energy is a more determinant control for the relative stability of the C5 structure and estimate its value to be 18.5 +/- 0.7 kJ/mol at Aib* in 1, through the computational isodesmic reaction approach, using two independent sets of theoretical isodesmic reactions. (C) 2014 Elsevier Ltd. All rights reserved.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to the PERGAMON-ELSEVIER SCIENCE LTD,ENGLAND.
Keywords: 2.0(5) Helix; Hydrogen bond; Isodesmic reaction; Oxazine; alpha-Aminoisobutyric acid
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Depositing User: Id for Latest eprints
Date Deposited: 22 Jul 2014 11:36
Last Modified: 22 Jul 2014 11:36
URI: http://eprints.iisc.ac.in/id/eprint/49415

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