Natural-abundance 17O NMR of monosaccharides

Abstract

Natural-abundance “high-resolution” ¹⁷O NMR spectra of d-glucose, d-mannose, d-galactose, and some methoxy derivatives of d-glucose were recorded in aqueous solution. The sensitivity and spectral resolution was improved by optimizing the accumulation and manipulation of data. The water solvent peak was suppressed through use of ¹⁷O-depleted water or displaced by addition of paramagnetic shift reagents. With Dy³⁺ the ¹⁷O NMR spectrum of d-glucose remained unaltered; however, the water peak was shifted outside the carbohydrate spectral region. The ¹⁷O NMR resonances were assigned from earlier data for some specifically ¹⁷O-enriched monosaccharide derivatives. The anomeric hydroxyl resonances could also be located because of their exchange with the ¹⁷O-depleted water. Although the chemical shifts of the monosacharides generally parallel the sequence of chemical shifts for simple primary and secondary alcohols and substituted ethers, several exceptions were found and discussed in terms of steric and electrostatic repulsive forces between oxygens.