title: Structure of benzyloxycarbonyl-L-alanyl-alpha-aminoisobutyl-alpha-aminoisobutylic acid.
abstract: The x-ray diffraction study of the C-terminally unprotected tripeptide benzyloxy-carbonyl-L-alanyl-alpha-aminoisobutyl-alpha- aminoisobutylic acid (Z-L-Ala-Aib-Aib-OH) has shown that the molecule adopts a consecutive type III beta-turn, which characterizes a right-handed 3(10) helix. A very weak 4----1 intramolecular hydrogen bond with the long N...O distance of 3.32 A, and a unique "oxy analogue" of the 4----1 hydrogen bond wih the O...O distance of 2.77 A, were observed. The stability of the observed conformation with the asymmetric Aib residues was theoretically evaluated by a conformation-energy calculation. The stereochemical characteristics of Aib and Ala residues were made clear by a comparison of the conformations of the short peptides containing both Aib and Ala residues.
authors.affiliation: Faculty of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Taga
authors.forename: M
authors.initials: M
authors.lastname: Itoh
authors.forename: K
authors.initials: K
authors.lastname: Machida
authors.forename: T
authors.initials: T
authors.lastname: Fujita
authors.forename: T
authors.initials: T
authors.lastname: Ichihara
mesh_terms: D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009842:Oligopeptides; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D009842:Oligopeptides