SYNTHESIS OF METHYL 3-O-(α- AND β-D-GALACTOPYRANOSYL)-4-O-(β-D-GLUCOPYRANOSYLURONIC ACID)-α-L-RHAMNOPYRANOSIDE USING PHOTOLABILE METHYL 2,3-O-(2-NITROBENZYLIDENE)-α-L-RHAMNOPYRANOSIDE

Article abstract of DOI:10.1016/0008-6215(85)85183-1

The title branched-trisaccharide derivatives (9 and 13) have been synthesised from methyl 2,3-O-(2-nitrobenzylidene)-α-L-rhamnopyranoside (2) using the 2-nitrobenzylidene residue as a temporary blocking-group.Condensation of 2 with methyl (2,3,4-tri-O-acetyl-α-D-glucopyranosyl bromide)uronate afforded the blocked disaccharide 3 which, on sequential photolysis and oxidation, gave methyl 4-O-(methyl 2,3,4-tri-O-acetyl-β-D-glucopyranosyluronate)-2-O-(2-nitrobenzoyl)- (4) and -3-O-(2-nitrobenzoyl)-α-L-rhamnopyranoside (5) as a 4:1 mixture.Galactosylation of HO-3 of 4 gave two fully protected trisaccharides having βαα and ββα configuration which, on deacylation, saponification, and treatment with ion-exchange resins, gave the free acids 9 and 13.