Site-selective reactions for the synthesis of glycoconjugates in polysaccharide vaccine development

Carbohydrates are often found linked to lipids or proteins, to form glycoconjugates such as glycolipids, glycoproteins and proteoglycans. These glycoconjugates play important biological roles, involving cell-cell recognition, inflammation, immune response, tumor metastasis and in viral/bacterial/parasitic infections. However, it is difficult to obtain these naturally occurring glycoconjugates as they are often heterogeneous compositions, which causes batch-to-batch variability of structure and activity often leading an incomplete understanding of their mechanism of action. Thus, the efficient preparation of synthetic glycoconjugates, possessing well-defined compositions and reproducible biological properties is highly desirable. In the present review, we summarize the advances in site-selective approaches for glycoconjugate synthesis and, in particular, the preparation of polysaccharide vaccines.