title: Crystal structures of two cyclic pseudopentapeptides containing psi[CH2S] and psi[CH2SO] backbone surrogates.
abstract: The solid state conformations of cyclo [Gly-Pro psi[CH2S] Gly-D-Phe-Pro] and cyclo [Gly-Pro psi[CH2-(S)-SO]Gly-D-Phe-Pro] have been characterized by X-ray diffraction analysis. Crystals of the sulfide trihydrate are orthorhombic, P2(1)2(1)2(1), with a = 10.156(3) A, b = 11.704(3) A, c = 21.913(4) A, and Z = 4. Crystals of the sulfoxide are monoclinic, P2(1) with a = 10.662(1) A, b = 8.552(3) A, c = 12.947(2) A, beta = 94.28(2), and Z = 2. Unlike their all-amide parent, which adopts an all-trans backbone conformation and a type II beta-turn encompassing Gly-Pro-Gly-D-Phe, both of these peptides contain a cis Gly1-Pro2 bond and form a novel turn structure, i.e., a type II' beta-turn consisting of Gly-D-Phe-Pro-Gly. The turn structure in each of these peptides is stabilized by an intramolecular H bond between the carbonyl oxygen of Gly1 and the amide proton of D-Phe4. In the cyclic sulfoxide, the sulfinyl group is not involved in H bonding despite its strong potential as a hydrogen-bond acceptor. The crystal structure made it possible to establish the absolute configuration of the sulfinyl group in this peptide. The two crystal structures also helped identify a type II' beta-turn in the DMSO-d6 solution conformers of these peptides.
authors.affiliation: Department of Chemistry, University of Louisville, Kentucky 40292.
authors.forename: S
authors.initials: S
authors.lastname: Ma
authors.forename: J F
authors.initials: JF
authors.lastname: Richardson
authors.forename: A F
authors.initials: AF
authors.lastname: Spatola
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D010456:Peptides, Cyclic; C082476:cyclo(glycyl-prolyl-psi(CH2SO)-glycyl-phenylalanyl-prolyl); C082475:cyclo(glycyl-prolyl-psi(CH2S)-glycyl-phenylalanyl-prolyl)