The photochemistry of carbohydrate derivatives. Part 6. Synthesis of 3-(methoxycarbonyl) propyl pyranosides of 2,3-di-O-(β-D-galactopyranosyl)-α-D-galactose and 3-O-(α-D-galactopyranosyl)-2-O-(β-D-galactopyranosyl)-α-D-galactose using photolabile O-(2-nitrobenzylidene) acetals as temporary blocking groups

Abstract

The branched trisaccharide glycosides (7) and (8) named in the title have been prepared from 3-(methoxycarbonyl) propyl 3,4-O-(2-nitrobenzylidene)-6-O-pivaloyl-α-D-galactopyranoside (2). Galactosylation of compound (2) afforded the fully protected β-galactosyl-α-galactoside derivative (3) which upon sequential photolysis and oxidation was regioselectively converted into the partially blocked 4-O-(2-nitrobenzoyl) disaccharide (4). Further galactosylation of compound (4) gave a mixture of equal amounts of the di-(β-galactosyl)-α-galactoside derivative (5) and the β-galactosyl-α-galactosyl-α-galactoside derivative (6) which were separated, and these yielded the title compounds upon subsequent deacylation.