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Chirality-Driven Folding of Short β-Lactam Pseudopeptides


Aizpurua, Jesus M; Palomo, Claudio; Balentová, Eva; Jimenez, Azucena; Andreieff, Elena; Sagartzazu-Aizpurua, Maialen; Miranda, José Ignacio; Linden, Anthony (2013). Chirality-Driven Folding of Short β-Lactam Pseudopeptides. Journal of Organic Chemistry, 78(2):224-237.

Abstract

Novel enantiopure pseudopeptide models containing a central -(β-lactam)-(Aa)- scaffold characterized by the combined presence of an α-alkyl-α-amino-β-lactam (i+1) residue and a α-substituted (i + 2) amino acid have been readily synthesized from α-alkyl serines. The conformational analysis of such β-lactam pseudopeptides conducted in CDCl3 and DMSO-d6 solutions using 1D- and 2D-NMR techniques revealed an equilibrium between β-II turn and γ-turn conformers, which was ultimately modulated by the relative configuration of the -(β-lactam)-(Aa)- residues. Long-range chiral effects on the α-lactam pseudopeptide conformers were also found when two (i) and (i + 3) chiral residues were attached to the termini of a central -(β-lactam)-(Aib)- segment. In such mimetics, heterochiral (i) and (i + 3) residues reinforced a β-II turn conformer, whereas homochiral corner residues stabilized an overlapped β-II/ β-I double turn motif. No β-hairpin nucleation was observed in any instance. In good agreement with the conformers found in solution, β-turned and open structures were also characterized by X-ray crystallography. Relative stabilities of the different conformers were estimated computationally at a B3LYP/6-31++G** calculation level, and finally, a conformation equilibrium model based on steric inter-residual interactions around the -(β-lactam)-(i + 2)- segment was proposed to account for the observed chiral effects.

Abstract

Novel enantiopure pseudopeptide models containing a central -(β-lactam)-(Aa)- scaffold characterized by the combined presence of an α-alkyl-α-amino-β-lactam (i+1) residue and a α-substituted (i + 2) amino acid have been readily synthesized from α-alkyl serines. The conformational analysis of such β-lactam pseudopeptides conducted in CDCl3 and DMSO-d6 solutions using 1D- and 2D-NMR techniques revealed an equilibrium between β-II turn and γ-turn conformers, which was ultimately modulated by the relative configuration of the -(β-lactam)-(Aa)- residues. Long-range chiral effects on the α-lactam pseudopeptide conformers were also found when two (i) and (i + 3) chiral residues were attached to the termini of a central -(β-lactam)-(Aib)- segment. In such mimetics, heterochiral (i) and (i + 3) residues reinforced a β-II turn conformer, whereas homochiral corner residues stabilized an overlapped β-II/ β-I double turn motif. No β-hairpin nucleation was observed in any instance. In good agreement with the conformers found in solution, β-turned and open structures were also characterized by X-ray crystallography. Relative stabilities of the different conformers were estimated computationally at a B3LYP/6-31++G** calculation level, and finally, a conformation equilibrium model based on steric inter-residual interactions around the -(β-lactam)-(i + 2)- segment was proposed to account for the observed chiral effects.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2013
Deposited On:21 Oct 2013 08:56
Last Modified:05 Apr 2016 17:03
Publisher:American Chemical Society
ISSN:0022-3263
Funders:Ministerio de Ciencia y Competitividad (MEC, Spain) (Project No. CTQ2010-21625-C02-01), Gobierno Vasco (ETORTEK-nanoIKER IE-11/304), Universidad del País Vasco UPV/EHU (UFI QOSYC 11/22), SGIker UPV/EHU for NMR facilities, Gobierno Vasco to M.S.-A, UPV/EHU to E.A.
Additional Information:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Organic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/jo302368y
Publisher DOI:https://doi.org/10.1021/jo302368y

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