DIFFERENTIATION OF THE BRANCH-SPECIFIC EN ZYMATIC GALACTOSYLATION BY NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

A spacer-modified biantennary trisaccharide glycoside (2) carrying two GlcNAc end groups was galactosylated by UDP-Gal and beta-(1-->4)-D-ga lactosyltransferase to yield compounds 3a, 3b and 4. The non-separable monogalactosylated compounds 3a and 3b were investigated by NMR spect roscopy (COSY, COLOC, RELAY) to determine a potential branch-specific transgalactosylation found for native acceptor-oligosaccharides (1). S ince the ''3-branch'' is galactosylated at the same rate as the ''6-br anch'' the presence not only of the center-mannosyl unit but also of t he flanking mannosyl residues replaced by spacers in compound 2 are ne cessary for site specificity.