Design of peptides with alpha,beta-dehydro-residues: Syntheses and Crystal structures of (i) N-tertiarybutyloxycarbonyl-L-Ala-triangle Phe-L-Ala-OCH3 and (ii) N-tertiarybutyloxycarbonyl-L-Leu-triangle Phe-L-Leu-OCH3

摘要

In order to contribute to design rules with alpha,beta-dehydro amino acid residues, two peptides (i) Boc-Ala-Delta Phe-Ala-OCH3 and (ii) Boc-Leu-Delta Phe-Leu-OCH3 were synthesized and their crystal structures were determined. Peptide (i) with Ala residues on both sides of Delta Phe adopted a type II beta-turn conformation with dihedral angles of two corner residues, phi(1) = -62.6(4)degrees, psi(1) = 138.9(5)degrees, delta(2) = 76.3(4)degrees and psi(2) = 13.1(3)degrees, while the peptide (ii) with Leu residues formed an unfolded conformation with dihedral angles, phi(1) = -81.9(5), psi(1) = -28.3(4)degrees, phi(2) = 56.7(5)degrees and psi(2) = 42.6(4)degrees. The structure of peptide (i) was stabilized by an intramolecular 4 -> 1 hydrogen bond between Ala(3) NH and BOC carbonyl oxygen atom, whereas that of peptide (ii) was stabilized by van der Waals forces involving the side chains of two Leu residues.