Folded structures in protonated reduced dipeptides.

ABSTRACT

Reduced dipeptides with the general formula RCO-Xaa-rXbb-N+HR'R" (rXbb, reduced analogue of residue Xbb NH-C alpha HR1-CrH2) are shown to adopt a folded conformation in solution and in the solid state. The protonated reduced amide bond is an active proton donor capable of interacting with a peptide carbonyl to give a strong hydrogen bond topologically equivalent to the i+2 or i+3-->i interaction. The resulting conformation is similar to the y- or beta-turn structure found in peptides and proteins.