Synthesis of stigmasteryl (β1→4)-oligoglucosides

ABSTRACT

Stigmasteryl (β1→4)-oligoglucosides were prepared with cellobiose, cellotriose, and cellotetraose as glycan chains. For the preparation of the peracetylated oligoglucosyl donors anomeric acetate was deprotected and the respective hemiacetals were converted into trichloroacetimidates. Glycosylation with stigmasterol yielded both α- and β-anomers because during the treatment with Lewis acid the 2-OAc is cleaved to some extent; thus, with the emerging hydroxyl group neighboring group participation does not take place. Due to their different number of hydroxyl groups (0 vs. 1) separation of the two products proved to be facile. Saponification led to the desired stigmasteryl glucosides.

KEYWORDS:

• Glycosylation
• neighboring group participation
• peracetylated glycans
• saponins
• stigmasterol