[Au]/[Ag]-Catalyzed Activation of Glycosyl Alkynyl Carbonates and Their Application to the Syntheses of Various Glycoconjugates

Abstract

Glycoconjugates are very important classes of compounds in biology. They consist of carbohydrates of varying size and complexity, covalently linked to non-sugar moieties such as proteins, peptides, and lipids. Advances in glycobiology highlight the sophisticated functions served by naturally occurring glycoconjugates in different biological processes. Especially the sugar portions have been found to play an integral role in specific recognition events between cells and as factors controlling the generation of biological phenomena. But due to micro-heterogenous nature and lack of crystalline property makes these natural glycoconjugates inaccessible. Therefore, synthetic methods for the preparation of well-defined scaffolds are excellent tools to probe the natural glycoconjugate roles in different biological processes. Owing to the importance of this, many synthetic methods have been developed in the literature. Development of user-friendly and practical alternative approaches are always desirable and challenging.

In this regard, we have identified alkynyl glycosyl carbonates as glycosyl donors that are stable, solid compounds ideally suited for the fast and efficient synthesis of glycosides, oligosaccharides, nucleosides, phenolic, azido and amino acid glycoconjugates under mild [Au]/[Ag]catalytic conditions. With a simple operational protocol and low catalyst loading, this transformation was shown to be applicable to the synthesis of a biologically significant linear nonadacaarabinofuranoside and branched tridecasaccharide segment reminiscent of the mycobacterial cell surface. We have also explored the newly developed alkynyl carbonate donor chemistry for the synthesis of challenging 1,2-cis glycosidic bond containing N-linked core hexasaccharide from Chloroviruses.