title: Crystal and molecular structure of Boc-D-Ala-delta Phe-Gly-delta Phe- D-Ala-OMe: a 3 10-helical dehydropeptide.
abstract: The crystal and molecular structure of the pentapeptide Boc-D-Ala-delta Phe-Gly-delta Phe-D-Ala-OMe, containing two dehydrophenylalanine residues, was determined by x-ray diffraction. The molecule crystallizes in the orthorombic P2(1)2(1)2(1) space group, with a = 10.439(3), b = 15.319(3) and c = 21.099(4) A. In the solid state, the conformation of the pentapeptide is characterized by the presence of two type III' beta-turns. Thus the peptide assumes a left-handed 3(10-helical conformation, the left sense being due to the D configuration of the alanine residues. The two unsaturated residues are located in the (i + 1) position of the first beta-turn and in the (i + 2) position of the second beta-turn, respectively. In the crystal, the helical molecules are linked head to tail by hydrogen bonds. Lateral hydrogen bonds are also formed between molecules related by a twofold screw symmetry. This gives rise to a typical mode of packing characterized by infinite helical "chains,' similar to the packing found in other oligopeptides that adopt a 3(10)-helical structure.
authors.affiliation: Dipartimento di Chimica, Università di Napoli.
authors.forename: M R
authors.initials: MR
authors.lastname: Ciajolo
authors.forename: A
authors.initials: A
authors.lastname: Tuzi
authors.forename: C R
authors.initials: CR
authors.lastname: Pratesi
authors.forename: A
authors.initials: A
authors.lastname: Fissi
authors.forename: O
authors.initials: O
authors.lastname: Pieroni
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009842:Oligopeptides / Q000138:chemical synthesis*
chemical_list: D009842:Oligopeptides; C068717:tert-butyloxycarbonyl-alanyl-dehydrophenylalanyl-glycyl-dehydrophenylalanyl-alanyl-methoxy