Synthesis of 3- and 2′-fucosyl-lactose and 3,2′-difucosyl-lactose from partially benzylated lactose derivatives

Abstract

O-β- d-Galactopyranosyl-(1→4)- O-[α- l-fucopyranosyl-(1→3)]- d-glucose has been synthesised by reaction of benzyl 2,6-di- O-benzyl-4- O-(2,3,4,6-tetra- O-benzyl-β- d-galactopyranosyl)-β- d-glucopyranoside with 2,3,4-tri- O-benzyl-α- l-fucopyranosyl bromide in the presence of mercuric bromide, followed by hydrogenolysis. Benzylation of benzyl 3′,4′- O-isopropylidene-β-lactoside, via tributylstannylation, in the presence of tetrabutylammonium bromide or N-methylimidazole, gave benzyl 2,6-di- O-benzyl-4- O-(6- O-benzyl-3,4- O-isopropylidene-β- d-galactopyranosyl)-β- d-glucopyranoside ( 6). α-Fucosylation of 6 in the presence of tetraethylammonium bromide provided either benzyl 2,6-di- O-benzyl-4- O-[6- O-benzyl-3,4- O-isopropylidene-2- O-(2,3,4-tri- O-benzyl-α- l-fucopyransoyl)-β- d- galactopyranosyl]-β- d-glucopyranoside ( 13, 73%) or a mixture of 13 (42%) and benzyl 2,6-di- O-benzyl-4- O-[6- O-benzyl-3,4,- O-isopropylidene-2- O-(2,3,4-tri- O-benzyl-α- l-fucopyranosyl)-β- d- galactopyranosyl-3- O-(2,3,4-tri- O-benzyl-α- l-fucopyranosyl)-β- d-glucopyranoside ( 16, 34%). α-Fucosylation of 13 in the presence of mercuric bromide and 2,6-di- tert-butyl-4-methylpyridine gave 16 (73%). Hydrogenolysis and acid hydrolysis of 13 and 16 afforded O-α- l-fucopyranosyl-(1→2)- O-β- d-galactopyranosyl-(1→4)- d-glucose and O-α- l-fucopyranosyl-(1→2)- O-β- d-galactopyranosyl-(1→4)- O-[α- l-fucopyranosyl-(1→3)]- d-glucose, respectively.