title: Conformational effects of chiral alpha,alpha-dialkyl amino acids. I. C-terminal tetrapeptides of emerimicin containing alpha-ethylalanine.
abstract: The syntheses and the crystal structures of the C-terminal tetrapeptide fragments of emerimicin IV and III, Boc-R-EtA-Hyp(Bzl)-Ala-Phol and Boc-R-EtA-Hyp(Bzl)-MeA-Phol, containing the chiral alpha,alpha-dialkyl amino acid, R-alpha-ethylalanine (R-EtA) are reported. The two peptides are isomorphous and assume a 3(10)-helical conformation in the crystal. A comparison of the crystal data on alpha,alpha-dialkyl amino acids indicates that alkyl substituents larger than a methyl group do not preclude peptides containing these amino acids from assuming the conformations associated with minima which have been well characterized for alpha-methylalanine.
authors.affiliation: Department of Pharmacology, Washington University School of Medicine, St. Louis, MO.
authors.forename: G R
authors.initials: GR
authors.lastname: Marshall
authors.forename: J D
authors.initials: JD
authors.lastname: Clark
authors.forename: J B
authors.initials: JB
authors.lastname: Dunbar
authors.forename: G D
authors.initials: GD
authors.lastname: Smith
authors.forename: J
authors.initials: J
authors.lastname: Zabrocki
authors.forename: A S
authors.initials: AS
authors.lastname: Redlinski
authors.forename: M T
authors.initials: MT
authors.lastname: Leplawy
mesh_terms: D000900:Anti-Bacterial Agents; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008958:Models, Molecular; D009842:Oligopeptides / Q000138:chemical synthesis; D054848:Peptaibols; D010446:Peptide Fragments; D010455:Peptides / Q000138:chemical synthesis; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014633:Valine
chemical_list: D000900:Anti-Bacterial Agents; D007202:Indicators and Reagents; D009842:Oligopeptides; D054848:Peptaibols; D010446:Peptide Fragments; D010455:Peptides; C032737:isovaline; D014633:Valine