title: Structural studies of model peptides containing beta-, gamma- and delta-amino acids.
abstract: The crystal structures of five model peptides Piv-Pro-Gly-NHMe (1), Piv-Pro-betaGly-NHMe (2), Piv-Pro-betaGly-OMe (3), Piv-Pro-deltaAva-OMe (4) and Boc-Pro-gammaAbu-OH (5) are described (Piv: pivaloyl; NHMe: N-methylamide; betaGly: beta-glycine; OMe: O-methyl ester; deltaAva: delta-aminovaleric acid; gammaAbu: gamma-aminobutyric acid). A comparison of the structures of peptides 1 and 2 illustrates the dramatic consequences upon backbone homologation in short sequences. 1 adopts a type II beta-turn conformation in the solid state, while in 2, the molecule adopts an open conformation with the beta-residue being fully extended. Piv-Pro-betaGly-OMe (3), which differs from 2 by replacement of the C-terminal NH group by an O-atom, adopts an almost identical molecular conformation and packing arrangement in the solid state. In peptide 4, the observed conformation resembles that determined for 2 and 3, with the deltaAva residue being fully extended. In peptide 5, the molecule undergoes a chain reversal, revealing a beta-turn mimetic structure stabilized by a C-H...O hydrogen bond.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore, 560 012, India.
authors.forename: Anindita
authors.initials: A
authors.lastname: Sengupta
authors.forename: Subrayashastry
authors.initials: S
authors.lastname: Aravinda
authors.forename: Narayanaswamy
authors.initials: N
authors.lastname: Shamala
authors.forename: K Muruga Poopathi
authors.initials: KM
authors.lastname: Raja
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D003460:Crystallization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D000596:Amino Acids; D010455:Peptides