NMR studies of some 1,2- and 1,3-linked disaccharides

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Abstract
1 H and 13C NMR spectroscopic studies have been performed on eight 1,2- and 1,3-linked disaccharides in which the glycosidic linkages have different stereochemical surroundings. The changes in glycosylation shift induced by an equatorial N-acetyl group at C-2′ or C-2 or an axial hydroxy group at C-2′vs. those from compounds with an equatorial hydroxy group were investigated. It was found that the difference in 1H NMR glycosylation shift between compounds with an equatorial hydroxy group and an axial was only minor. Compounds with an N-acetyl group had in some cases significantly changed 1H NMR glycosylation shifts. An upfield glycosylation shift of the C-2′ or C-2 signal was observed for the oligosaccharides containing 2-acetamido-2-deoxy-glucose and 2-acetamido-2-deoxy-galactose residues compared to oligosaccharides containing a glucose and a galactose residue, respectively. The minimum energy conformation was also calculated, using the HSEA-approach. It could, inter alia, be shown that signals from protons calculated to be near an NH-grouping were shifted upfield compared to analogous oligosaccharides containing only hydroxy groups.