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.
Subject(s)
Anti-Bacterial Agents , Oligopeptides , Valine , Indicators and Reagents , Magnetic Resonance Spectroscopy , Mass Spectrometry , Models, Molecular , Oligopeptides/chemical synthesis , Peptaibols , Peptide Fragments , Peptides/chemical synthesis , Protein Conformation , Structure-Activity RelationshipABSTRACT
The crystal structure of the synthetic tetrapeptide, Boc-Hyp-Aib-Aib-Phol, an analogue of the C-terminal tetrapeptide in the antibiotic antiamoebin I, was determined as part of a study of the conformation of peptaibophol antibiotics. The crystals are orthorhombic, space group P212121, with cell parameters a = 16.576 (1) A, b = 17.657 (1) A, c = 10.435 (1) A, V = 3053.9 (2) A3, Z = 4, Dc = 1.163 g.cm-3. The three amino acids from a single turn of a 3 10-helix, stabilized by two intramolecular hydrogen bonds. The Aib residues adopt the usual conformation in the region between the 3 10- and alpha-helices. The terminal hydroxy methyl group of the phenylalaninol residue is disordered. The position of the benzyl side chain of the amino alcohol relative to the backbone corresponds to a conformation also observed in phenylalanine residues.
