title: Three conformers in a crystal of N-Ac-L-Leu-L-Tyr-OMe.
abstract: C18H26N2O5, three independent molecules with different conformations, Mr = 350.4, orthorhombic, P2(1)2(1)2(1), a = 16.077 (10), b = 28.935 (18), c = 12.597 (6) A, V = 5860.0 A3, Z = 12, Dx = 1.191 g cm-3, lambda(Cu K alpha) = 1.54178 A, F(000) = 2256, room temperature, final R = 4.9% for 4596 data with [F omicron] greater than 3 sigma and 5.4% for all 4977 measured data. The three independent molecules have different conformations for the backbones and the side-chains, although each molecule is relatively flat and has an approximate H shape. The backbone in one of the conformations has phi, psi angles near those for a beta-turn. There is extensive intermolecular hydrogen bonding, but there are no intramolecular hydrogen bonds. The 75-atom structure was solved with the aid of the Connection Machine computer, a parallel processor for which the symbolic addition procedure was programmed.
authors.affiliation: Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC 20375.
authors.forename: I L
authors.initials: IL
authors.lastname: Karle
authors.forename: J L
authors.initials: JL
authors.lastname: Flippen-Anderson
mesh_terms: D000595:Amino Acid Sequence; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D003460:Crystallization; D003461:Crystallography; D004151:Dipeptides / Q000138:chemical synthesis; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation
chemical_list: D004151:Dipeptides; C062175:N-acetylleucyl-tyrosine methyl ester; D002918:Chymotrypsin