title: 13C-Labeled Idohexopyranosyl Rings: Effects of Methyl Glycosidation and C6 Oxidation on Ring Conformational Equilibria.
abstract: An ensemble of JHH, JCH, and JCCvalues was measured in aqueous solutions of methyl α- and β-d-idohexopyranosides containing selective13C-enrichment at various carbons. By comparing these J-couplings to those reported previously in the α- and β-d-idohexopyranoses, methyl glycosidation was found to affect ring conformational equilibria, with the percentages of4C1forms based on3JHHanalysis as follows: α-d-idopyranose, ∼18%; methyl α-d-idopyranoside, ∼42%; methyl β-d-idopyranoside, ∼74%; β-d-idopyranose, 82%. JCHand JCCvalues were analyzed with assistance from theoretical values obtained from density functional theory (DFT) calculations. Linearized plots of the percentages of4C1against limiting JCHand JCCvalues in the chair forms were used to (a) determine the compatibility of the experimental JCHand JCCvalues with4C1/1C4ratios determined from JHHanalysis and (b) determine the sensitivity of specific JCHand JCCvalues to ring conformation. Ring conformational equilibria for methyl idohexopyranosides differ significantly from those predicted from recent molecular dynamics (MD) simulations, indicating that equilibria determined by MD for ring configurations with energetically flat pseudorotational itineraries may not be quantitative. J-couplings in methyl α-l-[6-13C]idopyranosiduronic acid and methyl α-d-[6-13C]glucopyranosiduronic acid were measured as a function of solution pH. The ring conformational equilibrium is pH-dependent in the iduronic acid.
authors.affiliation: Department of Chemistry and Physics, Fayetteville State University , Fayetteville, North Carolina 28301, United States.
authors.forename: Bidisha
authors.initials: B
authors.lastname: Bose-Basu
authors.forename: Wenhui
authors.initials: W
authors.lastname: Zhang
authors.forename: Jamie L W
authors.initials: JL
authors.lastname: Kennedy
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Hadad
authors.forename: Ian
authors.initials: I
authors.lastname: Carmichael
authors.forename: Anthony S
authors.identifier: 0000-0001-6114-1446
authors.initials: AS
authors.lastname: Serianni
mesh_terms: D002236:Carbohydrate Conformation; D002247:Carbon Isotopes; D006031:Glycosylation; D006601:Hexoses / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007067:Iduronic Acid / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D010084:Oxidation-Reduction
chemical_list: D002247:Carbon Isotopes; D006601:Hexoses; C010997:idose; D007067:Iduronic Acid; C000615229:Carbon-13