Conformational properties of sulfonamido peptides

A systematic analysis of the conformation of the sulfonamide bond at various levels of ab initio MO theory shows distinct differences in comparison to the amide/peptide bond. Most important are (i) the different values of the torsion angle v (/CaSNCa), which are about 2100 and 608 in the two basic conformers of the sulfonamide bond, but about 180 and 08 for the peptide bond, (ii) the rotation barriers around the SN bond, which are distinctly lower than for the peptide bond, thus making sulfonamido peptides more flexible, and (iii) the pyramidal nature of the sulfonamide nitrogen in the conformers in comparison to a practically planar arrangement of the peptide bond. Despite these differences, sulfonamido peptides are able to form a great number of characteristic elements of secondary structure, which can be derived from the conformer pool of the monomer constituents. Some of them correspond to typical elements of secondary structures in native peptides and proteins. Although these conformers agree in type with their native counterparts and show similar shapes, the values of the torsion angles w and c in the a-aminosulfonic acid monomers differ due to the special conformational properties of the sulfonamide bond