Kinetics of oxygen exchange at the anomeric carbon atom of D-glucose and D-erythrose using the oxygen-18 isotope effect in carbon-13 nuclear magnetic resonance spectroscopy

Abstract

The 18O isotope induced shift in 13C nuclear magnetic resonance (NMR) spectroscopy affords a new and convenient method for the study of oxygen exchange at the anomeric carbon atom of simple sugars. The efficacy of the technique was confirmed by a study of the oxygen exchange reaction of D-[1-13C] glucose. At pH 7.0 and 61 degrees C, the incorporation of 18O from solvent H2(18)O onto the C-1 carbon atom of the diastereomeric alpha- and beta-pyranose sugars was followed by 13C NMR spectroscopy in a continuous assay mode. The pseudo-first-order rate constant for exchange of both the alpha and the beta anomers was 9.5 X 10(-5) s-1, which is in agreement with a rate constant obtained in a previous study by a chemical conversion-mass spectrometry technique. The new technique was applied to a study of the oxygen exchange at the anomeric carbon atom of D-[1-13C]erythrose, a furanose sugar for which no experimental data were available. In unbuffered, aqueous solutions the incorporation of the 18O label from the medium (H2(18)O) onto the C-1 carbon atom of the alpha- and beta-D-[1-13C]erythrose and the D-[1-13C]erythrose hydrate forms was followed by 13C NMR at 10, 23, and 36 degrees C. From analysis of the data for the alpha and beta diastereomers, the pseudo-first-order rate constants for exchange were 1.4 X 10(-4) s-1 at 10 degrees C, 4.8 X 10(-4) s-1 at 23 degrees C, and 8 X 10(-4) s-1 at 36 degrees C, and the apparent energy of activation for the exchange reaction was 12.1 kcal/mol. Particularly in conjunction with the use of specifically 13C-enriched sugars, the new technique for studying oxygen exchange reactions of carbohydrates has many distinct advantages over earlier approaches, including the ability to follow simultaneously the exchange reactions of all of the sugar species for which a 13C NMR signal can be detected, the continuity of the assay, the avoidance of possible artifacts due to incomplete or selective derivatization reactions, and the simplicity of the data analysis.

Microwave Spectroscopy of Biomolecular Building Blocks

“…29) may be present in linear or cyclic furanose forms. Aqueous solution NMR studies [228,229] have shown that furanose forms (25% and 65% of α and β furanose forms, respectively) are in equilibrium with an appreciable amount of acyclic forms. The five-membered ring structures contain an asymmetric carbon C 1 which leads to the appearance of two stereochemical α and β anomeric species, according to the position of the anomeric OH group (see Fig.…”

Gas-Phase IR Spectroscopy and Structure of Biological Molecules

“…29) may be present in linear or cyclic furanose forms. Aqueous solution NMR studies [228,229] have shown that furanose forms 378 J.L. Alonso and J.C. L opez (25% and 65% of α and β furanose forms, respectively) are in equilibrium with an appreciable amount of acyclic forms.…”

“…with the solvent, provide an in-depth understanding of protein structure. In a last part, it is shown how conformationselective spectroscopy is able to document the diversity of the PES landscape of 228 E. Gloaguen and M. Mons these species, thus revealing their flexibility. It is also shown how coupling IR and UV information enables spectroscopists to target conformer-selective photophysics in peptides.…”

Stable Isotopically-Enriched D-Glucose: Strategies to Introduce Carbon, Hydrogen and Oxygen Isotopes at Various Sites

“…Consequently, aldoses whose aqueous solutions contain an appreciable amount of hydrate form at equilibrium (e.g., aldotetroses 37 ) undergo 0-1 exchange more readily than aldoses whose aqueous solutions contain minor amounts (e.g., aldohexoses). The rate and extent of exchange at 0-1 can be monitored by 1 3 C NMR spectroscopy by observing of the oxygen isotope effect on the chemical shift of C-l. 38 …”