A Convergent Synthesis of 6--Branched β-Glucan Oligosaccharides.

β-Glucans are important carbohydrate antigens on the surface of fungal cells useful for antifungal vaccine development. This paper has described a highly convergent and efficient strategy for the synthesis of structurally defined branched β-glucan oligosaccharides that can be used for detailed studies of β-glucans and for the design of β-glucan-based vaccines. The strategy was highlighted by assembling the title compounds via preactivation-based glycosylation with thioglycosides as glycosyl donors. It was used to successfully prepare β-glucan oligosaccharides that had a β-1,3-linked nonaglucan backbone with β-1,6-glucotetraose, β-1,3-glucodiose and β-1,3-glucotetraose branches at the 6--position of the nonaglucan central sugar unit. The structure and size of the glycosyl donors and acceptors used in the syntheses did not significantly affect the glycosylation efficiency, suggesting that the strategy can be generally useful for the synthesis of more complex structures.