Sialidase substrate specificity studies using chemoenzymatically synthesized sialosides containing C5-modified sialic acids

para-Nitrophenol-tagged sialyl galactosides containing sialic acid derivatives in which the C5 hydroxyl group of sialic acids was systematically substituted with a hydrogen, a fluorine, a methoxyl or an azido group were successfully synthesized using an efficient chemoenzymatic approach. These compounds were used as valuable probes in high-throughput screening assays to study the importance of the C5 hydroxyl group of sialic acid in the recognition and the cleavage of sialoside substrates by bacterial sialidases.