Synthetic Glycans and Glycomimetics: A Promising Alternative to Natural Polysaccharides.

A large quantity of polysaccharide-derived conjugate vaccines have been developed to combat various pathogenic infections. Another prominent polysaccharide, heparin, is listed as an essential drug by the World Health Organization (WHO) to treat thrombus. One of their common problems is that they all derive from natural polysaccharides. Specifically, capsular polysaccharides are mainly obtained from bacterial fermentation and unfractionated heparin is extracted from animal tissues such as porcine mucosa. The quality of natural polysaccharides is inconsistent and traces of contamination would cause a disaster. By contrast, the use of chemical or chemoenzymatic methods could provide structurally homogeneous and quality-controlled glycans. To date, large numbers of polysaccharide fragments and their analogues have been synthesized and evaluated. Some of them even showed comparable activities to their corresponding natural polysaccharides. Here, the latest advances in these synthetic glycan analogues ranging from carbohydrate-based vaccines, heparin-related therapeutics and glycomimetics of polysaccharides are summarized.