title: Crystal structure of a dipeptide Boc-Aib-Phe-OMe.
abstract: In order to understand the effect of the restrictions posed by the Aib residue on peptide conformation we studied the crystal structure of a dipeptide tBoc-Aib-Phe-OMe. Crystals of this compound are triclinic, space group P1 with a = 9.600(1) A, b = 10.262(1) A, c = 10.799(1) A, alpha = 98.43 degrees (1), beta = 99.18 degrees (1), gamma = 98.87 degrees (1), V = 1021.69(18) A3 and Z = 2. The structure was solved by direct methods and refined to an R-factor of 4.98%. The backbone conformational angles for the Aib residue in molecule A are in the left-handed helical region, while in molecule B they are in the right-handed helical region. The Phe residue in molecule A is in the right-handed helical conformation, while in molecule B it is in the beta-region. The peptide units are trans and show significant deviation from planarity [(omega 1 = 166.67(5) degrees and omega 2 = -177.9(5)].
authors.affiliation: Biophysics Department, Roswell Park Cancer Institute, Buffalo, New York, USA.
authors.forename: R
authors.initials: R
authors.lastname: Balakrishnan
authors.forename: R
authors.initials: R
authors.lastname: Parthasarathy
authors.forename: N
authors.initials: N
authors.lastname: Ramasubbu
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray / Q000379:methods; D004151:Dipeptides / Q000737:chemistry*; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D004151:Dipeptides; D009842:Oligopeptides; C107408:tert-butyloxycarbonyl-aminobutyryl-phenylalanine methyl ester