Structure determination of galacto-oligosaccharides by pyridylamination and NMR spectroscopy

Galacto-oligosaccharides formed from lactose by the action of some β-galactosidases were subjected to gel chromatography on Bio-Gel P-2, and the resulting oligosaccharide fractions were converted into pyridylamino (PA) derivatives. Each PA-oligosaccharide fraction, which consisted of several isomers in a given size-class, was then subjected to HPLC on an ODS column. Twenty-one individual galacto-oligosaccharide components were isolated in this way. The structures of most of these compounds, namely six disaccharides, five trisaccharides, two tetrasaccharides, and a pentasaccharide, were determined by 13C-NMR spectroscopy. The results obtained will be useful for the study of the activity of various galacto-oligosaccharides on the growth of Bifidobacterium species.