Peptides from chiral Cαα-disubstituted glycines. On the helical screw sense of isovaline peptides

Article abstract of DOI:10.1002/recl.19951140706

The preferred conformation of three N^α-acetylated Aib/Iva host/guest pentapeptide esters and their N^α-benzyloxycarbonylated synthetic precursors, prepared by solution methods and fully characterized, were examined in chloroform solution using FT-IR absorption and 1H-NMR and in the crystal state by X-ray diffraction.All these peptides are folded in a 3₁₀-helix structure, irrespective of the experimental conditions used in the conformational analysis.In the crystal state the screw sense preference of the helical structure that is formed seems to be governed by the position of the single Iva residue in the peptide main chain, the ethyl side-chain disposition, and the nature of the N^α-blocking group.