Recent Developments of Highly Selective Sialylation

Sialic acids usually occur as glycosides of functional glycoconjugates such as glycoprooteins and glycolips, that are involved in a wide range of biological phenomena, for example, recognition and adhesion of cellcell, recognition by bacteria and viruses, and tumorigenesis and metastasis. So the synthesis of sialosides is an important field in the design of novel medicines and vaccines. In the last decades, significant efforts for improving stereoselectivity of sialylation have been made. This review summarizes the latest progress in sialylation that can be characterized into several categories: the application of novel leaving group at C-2; combination of leaving group at C-2 with modification of the amino protective groups at the C-5 position; participation of neighboring group at C-1; the influence of O-substituents at C-4 or C-7 on sialylation; some special structure to generate β-sialylation; and using novel promoters and their applications in the synthesis of sialosides.