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Wiley, European Journal of Organic Chemistry, 17(2013), p. 3494-3503, 2013

DOI: 10.1002/ejoc.201300066

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The Role of the Chiralcis-1,3-Disubstituted 2,2-Dimethylcyclobutane Motif in the Conformational Bias of Several Types of γ-Peptides

This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

Three series of new γ-peptides have been synthesized by starting from conveniently protected cis-3-amino-2,2-dimethylcyclobutane-1-carboxylic acid derivatives. The first series is constructed with only one enantiomer of this γ-amino acid, whereas in the second one both enantiomeric cyclobutane residues are joined in alternating fashion. The high degrees of rigidity in these γ-peptides induce the adoption of extended but sterically constrained conformations in both cases. The third series is the product of alternation of a cyclobutane residue with linear γ-aminobutyric acid (GABA). Conformational bias in these three systems accounts for the cyclobutane being a major disrupting factor to the formation of strong intramolecular hydrogen bonds, leading to extended conformations. In contrast, investigation of cyclobutane/GABA hybrid γ-peptides of a fourth series, in which the carbocyclic moiety is not a part of the polyamide skeleton but acts as a chiral polyfunctional platform, reveals that these peptides are able to produce intramolecular hydrogen bonds leading to well defined folded conformations.