SYNTHESIS OF THE 2''-HYDROXY, 4''-DEOXY AND 4''-EPI ANALOGS OF BETA-D-GALNAC-(1-]3)-ALPHA-D-GAL-(1-]4)-BETA-D-GAL, THE TERMINAL TRISACCHARIDE OF GLOBOTETRAOSE

Radical deoxygenation of methyl 3,6-di-O-benzoyl-2-deoxy-4-0-imidazol-1-yl-thiocarbonyloxy-2-phthalimido-beta-D-glucopyranoside 5 gave methyl 3,6-di-O-benzoyl-2,4-dideoxy-2-phthalimido-beta-D-glucopyranoside 6, which was converted into the corresponding methyl thioglycoside donor 9. Methylsulfenyl trifluoromethane-sulfonate-promoted glycosylation of 2-(trimethylsilyl)ethyl 2,3,6-tri-O-benzyl-4-O-(2,4,6-tri-O-benzyl-alpha-D-galactopyranosyl)-beta-D-galactopyranoside 10, followed by removal of protecting groups gave the 4''-deoxy analogue 12 of the terminal trisaccharide of globotetraose. Silver trifluoromethanesulfonate-promoted glycosylation of the same disaccharide alcohol 10 with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-alpha/beta-D-glucopyranosyl bromide 13 and 2.3,4,6-tetra-0-acetyl-alpha-D-galactopyranosyl bromide 16, followed by deblocking, gave the 2''-hydroxy and 4''-epi analogues 15 and 18. respectively.