title: Crystal and molecular structure of the doubly unsaturated dehydropeptide Ac-delta Phe-Ala-delta Phe-NH-Me.
abstract: The dehydropeptide Ac-delta Phe-L-Ala-delta Phe-NH-Me, containing two dehydro-phenylalanine (delta Phe) residues, crystallizes from methanol/water in space group P2(1)2(1)2(1), with a = 12.508 (2), b = 12.746 (1) and c = 15.465 (9). In the crystalline state, the peptide chain assumes a right-handed 3(10)-helical conformation stabilized by two intramolecular hydrogen bonds, between the N-terminal acetyl group and the NH of delta Phe3, and between the CO of delta Phe1 and the NH of the C-terminal methylamide group, respectively. The two consecutive 10-membered rings formed by the hydrogen bonds have torsion angles quite close to the standard values for type III beta-bends. delta Phe1 is located in the (i + 1) position of the first beta-bend, while delta Phe2 is located in the (i + 2) position of the other beta-bend. In the crystal, the molecules are linked head to tail by intermolecular hydrogen bonds to form long helical chains. The axes of the helices are parallel to the c axis, but neighboring helices run in antiparallel directions. This crystal packing is similar to the packing motifs frequently observed in Aib-containing peptides.
authors.affiliation: Dipartimento di Chimica, Università di Napoli, Italy.
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; D007482:Iothalamate Meglumine; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D009842:Oligopeptides; C077026:acetyl dehydrophenylalanyl-alanyl-N-methyldehydrophenylalaninamide; C001694:meglumine ioxithalamate; D007482:Iothalamate Meglumine