Glycosylation Methods in the Total Synthesis of Complex Glycosylated Natural Products

Carbohydrates are the most abundant class of molecules in the biosphere. Glycosylated secondary metabolites play a major role in carbohydrate chemistry expanding the scope of potential drug motifs. Glycosylated natural products are made out of sugars covalently O-, C-, N- or S- linked to the aglycone counterpart. In the course of synthesizing potential glycosidic therapeutics, effective and straightforward regio and stereoselective glycosylation methods are in high demand. The susceptibility of aglycone in different reaction conditions, complexities of glycon units, and the stereoselectivity of the glycosidic bond make the glycosylation a unique task in each synthesis. However, these challenges have been solved by careful optimization of novel donor synthesis, the use of effective activators, and adapting better protecting groups. Recently developed novel glycosyl donors, and the boron mediated glycosylation of minimally protected sugars, open up versatile pathways in total synthesis. Lastly, Cu(I) catalyzed stereoselective glycosyl crosscoupling of anomeric radicals with visible light is a novel promising technique in glycosylation of complex natural products. In this presentation, such recent developments and novel methods in chemical O- and C- glycosylation, and glycosylation of semi-protected sugars will be discussed.

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