Conformational analysis of peptide surrogates

Abstract

We have investigated the conformational effects of modifying the amide link of peptides. We studied a reverse amide bond Ψ[NHCO], a reduced amide bond Ψ[CH 2 NH] and a retro‐reduced bond Ψ[NHCH 2 ] as surrogates for the amide link [CONH] in native peptides. A complete search of the conformational space available to residues with these modified links was carried out. The local minima and the rotational barriers were described and compared to the minima of the native residue. The results are compatible with the available observed structural data. These modified links have been incorporated in secondary structure units such as β turns, α helices, and parallel and anti‐parallel β sheets. It was found that a reduced amide link can lead to stabilised β turns, while the retro modification can be incorporated in stable β sheets. A significant reduction in the stability of α helices is caused by the retro links, while a reduced amide link results in only a small destabilisation.