Chemoenzymatic synthesis of [3,9-13C]-labeled NeuAc and KDN

The chemoenzymatic synthesis of 13C-labeled sialic acid (NeuAc) and 3-deoxy-d-glycero-d-galacto-2-nonulosonic acid (KDN) as useful molecular probes for studying the conformation of sialyl or KDN oligosaccharides attached to proteins was performed by using [6-13C]-ManNAc, [6-13C]-Man and [3-13C]-pyruvic acid sodium salt. In the synthesis of the compounds, 5,6-anhydro intermediates were found to easily provide not only 6-13C-labeled but also 5-, and 6-modified NeuAc and KDN analogs. Furthermore, it was demonstrated that identical results are obtained by NMR for both [3,9-13C]-NeuAc and 1:1 mixtures of [3-13C]- and [9-13C]-NeuAc.