The polypeptide 3(10)-helix as a template for molecular recognition studies. Structural characterization of a side-chain functionalized octapeptide.

A N alpha-blocked, Aib-rich octapeptide methylamide containing two N omega-benzoylated L-Lys residues at positions 3 and 6 was synthesized by solution methods and fully characterized. A solution and crystal-state conformational analysis, performed by using FT-IR, 1H NMR, CD, and X-ray diffraction techniques, showed that the peptide is folded into a regular, right-handed 3(10)-helix stabilized by seven consecutive N-H...O=C intramolecular H-bonds of the beta-turn III type. The two benzamidobutyl L-Lys side chains, located on the same side of the helix after one complete turn, generate a cleft the minimal width of which was found to be 3.47 A.