POLYMJ : Vol. 28 (1996) , No. 5 pp440-445

Chain-Length Effects on Helix-Forming Tendency in Sequential Peptides Containing Z-Dehydrophenylalanine Residues

Yoshihito Inai¹⁾, Kazuto Hasegawa¹⁾, Tadamichi Hirabayashi¹⁾ and Kenji Yokota¹⁾

1) Department of Materials Science and Engineering, Nagoya Institute of Technology

ABSTRACT: The present paper describes chain-length effects on helix-forming tendency in sequential peptides containing Z-dehydrophenylalanine (Δ^ZPhe) residues, i.e., (X-Δ^ZPhe)_n. For sequential peptides Boc-(L-Leu-Δ^ZPhe)_n-L-Leu-OMe (n=2–6) that take 3₁₀-helical conformation in CHCl₃, solvent dependence on their helical structures was investigated by CD spectroscopy. CD patterns corresponding to a right-handed helix were observed for peptides n=3–6 in CHCl₃, tetrahydrofuran, acetonitrile, methanol, and trimethyl phosphate. Such helical structures became less stable in dimethyl sulfoxide and trifluoroethanol. Conformational energy calculation was carried out for acetyl-(L-Ala-Δ^ZPhe)_n-NHCH₃ (n=1–12). Peptides above n=2 were predicted to form helical structures preferentially. In addition, rigidity of the helical structure containing Δ^ZPhe residues was found to be somewhat lower than that containing α-aminoisobutyric acid residue with strong helix-forming tendency. This can be ascribed to the conformational properties inherent in Δ^ZPhe residue that induces not only helical backbones, but β-turn backbones. Thus, Δ^ZPhe residue will be useful to design functional peptides having such backbones.

KEY WORDS Z-Dehydrophenylalanine/ Sequential Peptides/ Helix-Forming Tendency/ Chain-Length Effect/ Circular Dichroism Study/ Conformational Energy Calculation/ α-Aminoisobutyric Acid