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Molecules 2013, 18(12), 14739-14746; doi:10.3390/molecules181214739
Article

Examination of the Potential for Adaptive Chirality of the Nitrogen Chiral Center in Aza-Aspartame

 and
*
Département de chimie, Université de Montréal, 2900 Boul. Edouard-Monpetit, Montréal, QC H3T 1J4, Canada
* Author to whom correspondence should be addressed.
Received: 3 October 2013 / Revised: 7 November 2013 / Accepted: 12 November 2013 / Published: 28 November 2013
(This article belongs to the Special Issue Dynamic Stereochemistry)
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Abstract

The potential for dynamic chirality of an azapeptide nitrogen was examined by substitution of nitrogen for the α-carbon of the aspartate residue in the sweetener S,S-aspartame. Considering that S,S- and R,S-aspartame possess sweet and bitter tastes, respectively, a bitter-sweet taste of aza-aspartame 9 could be indicative of a low isomerization barrier for nitrogen chirality inter-conversion. Aza-aspartame 9 was synthesized by a combination of hydrazine and peptide chemistry. Crystallization of 9 indicated a R,S-configuration in the solid state; however, the aza-residue chiral center was considerably flattened relative to its natural amino acid counterpart. On tasting, the authors considered aza-aspartame 9 to be slightly bitter or tasteless. The lack of bitter sweet taste of aza-aspartame 9 may be due to flattening from sp2 hybridization in the urea as well as a high barrier for sp3 nitrogen inter-conversion, both of which may interfere with recognition by taste receptors.
Keywords: azapeptide; peptide mimic; aspartame; dynamic chirality; hydrazine; taste; crystal structure; nitrogen chirality; semicarbazide azapeptide; peptide mimic; aspartame; dynamic chirality; hydrazine; taste; crystal structure; nitrogen chirality; semicarbazide
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Bouayad-Gervais, S.H.; Lubell, W.D. Examination of the Potential for Adaptive Chirality of the Nitrogen Chiral Center in Aza-Aspartame. Molecules 2013, 18, 14739-14746.

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