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

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.