title: Conformational investigation of alpha, beta-dehydropeptides. Part III. Molecular and crystal structure of acetyl-L-prolyl-alpha, beta-dehydrovaline methylamide.
abstract: The crystal structure of Ac-Pro-delta Val-NHCH3 was examined to determine the influence of the alpha,beta-dehydrovaline residue on the nature of peptide conformation. The peptide crystallizes from methanol-diethyl ether solution at 4 degrees in needle-shaped form in orthorhombic space group P2(1)2(1)2(1) with a = 11.384(2) A, b = 13.277(2) A, c = 9.942(1) A, V = 1502.7(4) A3, Z = 4, Dm = 1.17 g.cm-3 and Dc = 1.18 g.cm-3. The structure was solved by direct methods using SHELXS-86 and refined to an R value of 0.057 for 1922 observed reflections. The peptide is found to adopt a beta-bend between the type I and the type III conformation with phi 1 = -68.3(4) degrees, psi 1 = -20.1(4) degrees, phi 2 = -73.5(4) degrees and psi 2 = -14.1(4) degrees. An intramolecular hydrogen bond between the carbonyl oxygen of ith residue and the NH of (i + 3)th residue stabilizes the beta-bend. An additional intermolecular N...O hydrogen bond joins molecules into infinite chains. In the literature described crystal structures of peptides having a single alpha,beta-dehydroamino acid residue in the (i + 2) position and forming a beta-bend reveal a type II conformation.
authors.affiliation: Department of Organic Chemistry, Pedagogical University of Opole, Poland.
authors.forename: E
authors.initials: E
authors.lastname: Ciszak
authors.forename: G
authors.initials: G
authors.lastname: Pietrzyński
authors.forename: B
authors.initials: B
authors.lastname: Rzeszotarska
mesh_terms: D000595:Amino Acid Sequence; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003460:Crystallization; D004151:Dipeptides / Q000737:chemistry*; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D004151:Dipeptides; C076889:acetylprolyl-alpha,beta-dehydrovaline methylamide