Chemo-enzymatic synthesis of imidazolium-tagged sialyllactosamine probes

Two novel α-linked sialyltrisaccharide imidazolium-type probes (ITags) based on the structures of biologically relevant 6'-sialyllactosamine and 3'-sialyllactosamine were efficiently and stereoselectively prepared using a chemo-enzymatic approach. The apparent kinetic parameters for the enzyme catalyzed transformations with α-2,3-sialyltransferase (α-2,3-ST) and α-2,6-sialyltransferase (α-2,6-ST) were measured by LC-MS using the ionic probes. This strategy demonstrates the suitability of the ITags to probe glycosyltransferase activity and their versatility in the preparation of sialylated epitopes for glycobiology research.