Correlated C−C and C−O Bond Conformations in Saccharide Hydroxymethyl Groups: Parametrization and Application of Redundant 1H−1H, 13C−1H, and 13C−13C NMR J-Couplings
Autor: | Thomas Klepach, Ian Carmichael, Christophe Thibaudeau, Brian Hertz, Anthony S. Serianni, Roland Stenutz, Shikai Zhao, Qingquan Wu |
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Rok vydání: | 2004 |
Předmět: |
Fermi contact interaction
Stereochemistry Molecular Sequence Data Biochemistry Catalysis chemistry.chemical_compound Colloid and Surface Chemistry Polysaccharides Carbohydrate Conformation Hydroxymethyl Nuclear Magnetic Resonance Biomolecular Basis set Pyrans Coupling Carbon Isotopes Carbon-13 Galactose General Chemistry Carbon-13 NMR NMR spectra database Crystallography Glucose Carbohydrate Sequence Models Chemical chemistry Isotope Labeling Density functional theory Protons |
Zdroj: | Journal of the American Chemical Society. 126:15668-15685 |
ISSN: | 1520-5126 0002-7863 |
Popis: | Methyl alpha- and beta-pyranosides of d-glucose and d-galactose 1-4 were prepared containing single sites of (13)C-enrichment at C4, C5, and C6 (12 compounds), and (1)H and (13)C[(1)H] NMR spectra were obtained to determine a complete set of J-couplings ((1)J, (2)J, and (3)J) involving the labeled carbon and nearby protons and carbons within the exocyclic hydroxymethyl group (CH(2)OH) of each compound. In parallel theoretical studies, the dependencies of (1)J, (2)J, and (3)J involving (1)H and (13)C on the C5-C6 (omega) and C6-O6 (theta;) torsion angles in aldohexopyranoside model compounds were computed using density functional theory (DFT) and a special basis set designed to reliably recover the Fermi contact contribution to the coupling. Complete hypersurfaces for (1)J(C5,C6), (2)J(C5,H6)(R), (2)J(C5,H6)(S), (2)J(C6,H5), (2)J(C4,C6), (3)J(C4,H6)(R), (3)J(C4,H6)(S), and (3)J(C6,H4), as well as (2)J(H6)(R)(,H6)(S), (3)J(H5,H6)(R), and (3)J(H5,H6)(S), were obtained and used to parametrize new equations correlating these couplings to omega and/or theta;. DFT-computed couplings were also tested for accuracy by measuring J-couplings in (13)C-labeled 4,6-O-ethylidene derivatives of d-glucose and d-galactose in which values of omega and theta; were constrained. Using a new computer program, Chymesa, designed to utilize multiple J-couplings sensitive to exocyclic CH(2)OH conformation, the ensemble of experimental couplings observed in 1-4 were analyzed to yield preferred rotamer populations about omega and theta;. Importantly, due to the sensitivity of some couplings, most notably (2)J(H6)(R)(,H6)(S), (2)J(C5,H6)(R), and (2)J(C5,H6)(S), to both omega and theta;, unique information on correlated conformation about both torsion angles was obtained. The latter treatment represents a means of evaluating correlated conformation in 1,6-linked oligosaccharides, since psi and theta; are redundant in these linkages. In the latter regard, multiple, redundant scalar couplings originating from both sides of the glycosidic linkage can be used collectively to evaluate conformational correlations between psi/theta; and C5-C6 bond rotamers. |
Databáze: | OpenAIRE |
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