The −BF–NH– Link as a Peptide-Bond Surrogate B

A new peptidomimetic is proposed, resulting from substitution of the CO carbonyl group by a B–F bond at the amide linkage. The effects of such chemical alteration are theoretically investigated through comparative calculations on dimethyl-fluoro-aminoborane H₃C–BF–NH–CH₃ and N-methylacetamide H₃C–CO–NH–CH₃, the simplest model of a peptide linkage. While little difference is found regarding size, electronic structure, and plaque rigidity, substantial distinctions are, however, observed between the polarities and association energies of the two compounds, with a B–F···H–N hydrogen bond estimated to be about one-third as strong as the natural CO···H–N one. The conformational maps of the corresponding dipeptide models exhibit similarities and distinctions, which partly account for helical oligomer properties. Although capable of a high level of organization, the chains made of fluoro-aminoborane units show overall less structuration and more plasticity than their peptidic counterparts. Contrasts with fluorine-containing peptidomimetic 2-fluoro-2-butene are further underlined.