A series of (LacNAc)n oligomers with n=1-4 (at first with [13C] in natural abundance then enriched in [13C]-Gal and/or [13C]-GlcNAc at specific sites in the sequence) have been prepared by enzymatic synthesis using the appropriate glycosyltransferases and sugar nucleotide substrates. Specifically, oligo-N-acetyllactosamine synthesis was performed using human milk ?(1,4)-galactosyltransferase and a system of coupled reactions that produce UDP-Gal (the sugar nucleotide substrate for this enzyme) needed to elongate lactose/lactosamine. To date, hexamers of the lactosamine series and octamers of the lacto-neotetraose series have been synthesized and their structures confirmed by NMR spectroscopy. Specific labeling of targeted residues is required in order to differentiate between identical residues and to locate where on the polylactosamine chain interactions are occurring. This work was begun by synthesizing a tetra-N-acetyllactosamine containing a terminal [1-13C]-galactosyl residue. The next synthetic step is to extend the length and place a labeled galactosyl residue at specific points within the chain. We can then confirm whether the galectin always prefers the terminal residues when presented with a longer repeating oligolactosamine. A paper has been submitted to Glycobiology describing this work.
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