The photochemistry of carbohydrate derivatives. Part 5. Synthesis of methyl 2,3-di-O-(β-D-glucopyranosyl)-α-L-fucopyranoside and methyl 2,3-di-O-(β-D-galactopyranosyl)-α-L-fucopyranoside using photolabile O-(2-nitrobenzylidene) acetals as temporary blocking groups

Abstract

The branched trisaccharide derivatives (6) and (12) named in the title have been synthesised from methyl 3,4-O-(2-nitrobenzylidene)-α-L-fucopyranoside (1) using the 2-nitrobenzylidene residue as a temporary blocking group.

Glucosylation and galactosylation of compound (1) afforded the blocked disaccharides (2) and (7), respectively, and upon sequential photolysis and oxidation these were regioselectively transformed into the partially blocked 4-O-(2-nitrobenzoyl) disaccharides (4) and (9), the 3-O-(2-nitrobenzoyl) positional isomers being formed in <5 and 3% yield, respectively.

Further glycosylations of compounds (4) and (9) gave the fully protected trisaccharide derivatives (5) and (11), respectively, which were converted into the title compounds (6) and (12) upon deacylation.