title: Conformational properties of oxazole-amino acids: effect of the intramolecular N-H···N hydrogen bond.
abstract: Oxazole ring occurs in numerous natural peptides, but conformational properties of the amino acid residue containing the oxazole ring in place of the C-terminal amide bond are poorly recognized. A series of model compounds constituted by the oxazole-amino acids occurring in nature, that is, oxazole-alanine (L-Ala-Ozl), oxazole-dehydroalanine (ΔAla-Ozl), and oxazole-dehydrobutyrine ((Z)-ΔAbu-Ozl), was investigated using theoretical calculations supported by FTIR and NMR spectra and single-crystal X-ray diffraction. It was found that the main feature of the studied oxazole-amino acids is the stable conformation β2 with the torsion angles φ and ψ of -150°, -10° for L-Ala-Ozl, -180°, 0° for ΔAla-Ozl, and -120°, 0° for (Z)-ΔAbu-Ozl, respectively. The conformation β2 is stabilized by the intramolecular N-H···N hydrogen bond and predominates in the low polar environment. In the case of the oxazole-dehydroamino acids, the π-electron conjugation that is spread on the oxazole ring and C(α)═C(β) double bond is an additional stabilizing interaction. The tendency to adopt the conformation β2 clearly decreases with increasing the polarity of environment, but still the oxazole-dehydroamino acids are considered to be more rigid and resistant to conformational changes.
authors: Faculty of Chemistry, University of Opole , Oleska 48, 45-052 Opole, Poland.
authors: Dawid
authors: D
authors: Siodłak
authors: Monika
authors: M
authors: Staś
authors: Małgorzata A
authors: MA
authors: Broda
authors: Maciej
authors: M
authors: Bujak
authors: Tadeusz
authors: T
authors: Lis
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives / Q000737:chemistry; D000596:Amino Acids / Q000737:chemistry*; D000613:Aminobutyrates / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008962:Models, Theoretical; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D010080:Oxazoles / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D000613:Aminobutyrates; D010080:Oxazoles; D012997:Solvents; C088694:dehydrobutyrine; D006859:Hydrogen; C015102:dehydroalanine; D009584:Nitrogen; D000409:Alanine