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Efficient synthesis of linear trisaccharide from QS- 21

Adjuvants are key components of vaccines that improve and/or modulate the immune response to the applied antigen. The natural compound QS-21, a saponin isolated from the bark of Quillaja saponaria Molina tree, is one of the strongest known immunoadjuvants. However, QS-21 has a few major drawbacks which inhibit its wider use, e.g. chemical instability, accessibility and difficult purification ; which led to the development of QS- 21 derivatives and simpler variants. The linear trisaccharide Xyl(β1-4)Rha(α1-2)Fuc was found to be a crucial structural domain for the immunostimulatory activity of the QS-21 derivatives.1 Thus, its efficient synthesis is very important in the further development of QS-21 derivatives and analogs. Currently reported syntheses of the trisaccharide have shortcomings in extremely moisture-sensitive glycosylations, relatively high number of steps and low total yields.2 In this work, a simple, efficient and robust method of glycosylation using glycosyl fluorides as donors and silyl ethers as acceptors was used for the synthesis of trisaccharide Xyl(β1- 4)Rha(α1-2)Fuc. That led to the simplification of the synthetic pathway and reduction of the total number of steps, making the trisaccharide more easily accessible.

Quillaja saponaria, immunoadjuvants, oligosaccharide synthesis

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