Can a single pyridinedicarboxylic acid be ample enough to nucleate supramolecular double helices in enantiomeric pseudopeptides?

Abstract

Two enantiomeric pseudopeptides I & II, comprising a single pyridinedicarboxylic acid and a flexible dipeptidyl fragment H-Xaa-mABA-OMe (Xaa: L-Ala, pseudopeptide I; D-Ala, pseudopeptide II, mABA: meta aminobenzoic acid), have been synthesized using Boc chemistry. X-ray crystallographic analysis reveals that in the solid state, both the enantiomers form a dimeric unit stabilized by intermolecular hydrogen bonding interactions. Interestingly, these dimeric subunits self-assemble to form a supramolecular double helical architecture using various noncovalent interactions. To date, significant examples are documented in the literature where DNA analogues/derivatives or several rigid templates have been employed as synthons for double helical self assembly. However, to the best of our knowledge, this novel example represents one of the very few reports of a supramolecular double helix design resulting from the self assembly of a flexible dimeric peptidyl unit, solely nucleated by the conformational features, of the peptides. Concentration and temperature dependant NMR experiments were performed for pseudopeptide I (one of the enantiomers) to decipher the existence of the dimeric unit in solution. Pseudopeptide II (one of the enantiomers) was subjected to iodine and gas absorption studies, which demonstrates its candidature in the design of nanoporous materials.