Chemoenzymatic synthesis of α2–3-sialylated carbohydrate epitopes

Sialic acids are common terminal carbohydrates on cell surface. Together with internal carbohydrate structures, they play important roles in many physiological and pathological processes. In order to obtain α2–3-sialylated oligosaccharides, a highly efficient one-pot three-enzyme synthetic approach was applied. The P. multocida-α2–3-sialyltransferase (PmST1) involved in the synthesis was a multifunctional enzyme with extremely flexible donor and acceptor substrate specificities. Sialyltransferase acceptors, including type 1 structure (Galβ1–3GlcNAcβProN3), type 2 structures (Galβ1–4GlcNAcβProN3 and 6-sulfo-Galβ1–4GlcNAcβProN3), type 4 structure (Galβ1–3GalNAcβProN3), type 3 or core 1 structure (Galβ1–3GalNAcαProN3) and human milk oligoscaccharide or lipooligosaccharide lacto-N-tetraose (LNT) (Galβ1–3GlcNAcβ1–3Galβ1–4GlcβProN3), were chemically synthesized. They were then used in one-pot three-enzyme reactions with sialic acid precursor ManNAc or ManNGc, to synthesize a library of naturally occurring α2–3-linked sialosides with different internal sugar structures. The sialylated oligosaccharides obtained are valuable probes for their biological studies.