The photochemistry of carbohydrate derivatives. Part 7. The synthesis of methyl 3,4-di-O-(β-D-glucopyranosyl)-α-L-rhamnopyranoside from photolabile methyl 2,3-O-(2-nitrobenzylidene)-α-L-rhamnopyranoside

Abstract

Methyl endo/exo-2,3-O-(2-nitrobenzylidene)-α-L-rhamnopyranoside (1) was glucosylated to give the fully protected β-(1 → 4)-linked disaccharide derivative (5) as an endo/exo mixture which, upon photolysis and oxidation gave, after chromatography, the partially protected disaccharide (15) with an unprotected 3-hydroxy group. Further glucosylation at this position gave the fully blocked trisaccharide (17) which was de-esterified to give methyl 3,4-di-O-(β-D-glucopyranosyl)-α-L-rhamnopyranoside (18).