N-Substituted Aza-Glycine Promotes C8 CO···HN Hydrogen Bonding: A Novel Motif to Design Constrained Peptidomimetic.

Abstract

Peptidomimetic modifications enhance their rigidity, cell permeability, and proteolytic stability of peptides, presenting significant promise for drug development. One such modification involves the isosteric replacement of the peptide backbone CαH with a nitrogen (N) atom, resulting in azapeptides. In azapeptides, there are two backbone N atoms within a single residue, with the possibility of substituting either one or both simultaneously. Previous studies have effectively mimicked the side chain substitution patterns in peptides by focusing on substituents on the nitrogen at the Cα position of azapeptides. In this study, explored the unconventional substitution at the N-terminus nitrogen by using N-substituted aza-glycine (azGly). We investigated peptide-azapeptide dimers featuring N-acetyl-proline at the N-terminus of an N-methyl azGly residue. These hybrid peptides produced turn structures stabilized by an unusual C8 CO∙∙∙HN hydrogen bond, stabilizing the proline amide in its trans conformation. Computational studies confirmed the stabilizing effect of this C8 hydrogen bond, which was further validated by NMR and CD spectroscopic studies. Overall, we provide a novel strategy for introducing non-natural C8 hydrogen bond into peptide backbone via the incorporation of N-substituted azGly, which could be leveraged to design of more rigid and stable peptidomimetics, with potential applications in drug development.