Synthesis of 6-O-(5-acetamido-3,5-dideoxy-α-D-glycero-D-galacto-2-nonulopyranosylonic acid)-D-galactose [6-O-(N-acetyl-α-D-neuraminyl)-D-galactose]

Abstract

Condensation of methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,5-trideoxy-beta-D-glycero-D-galacto-2-nonulopyranosonate with benzyl 2,3,4-tri-O-benzyl-beta-D-galactopyranoside, using silver salicylate as promoter, gave benzyl 2,3,4-tri-O-benzyl-6-O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-alpha-D-glycero-D-galacto-2-nonulopyranosylonate)-beta-D-galactopyranoside (11) as the main product in 65% yield. Furthermore, the following by-products were formed: methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-O-salicyloyl-D- glycero-D-galacto-2-nonulopyranosonate, methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enopyranosonate, and an impure compound that gave, after O-deacetylation and catalytic hydrogenolysis, 6-O-(methyl 5-acetamido-3,5-dideoxy-beta-D-glycero-D-galacto-2-n nonulopyranosylonate)-D-galactose. O-Deacetylation of 11 gave benzyl 2,3,4-tri-O-benzyl-6-O-(methyl 5-acetamido-3,5-dideoxy-alpha-D-glycero-D-galacto-2-nonulopyranosylonate)-beta-D- galactopyranoside, which was converted into 6-O-(methyl 5-acetamido-3,5-dideoxy-alpha-D-glycero-D-galacto-2-nonulopyranosylonate)-D-galactose (13) by catalytic hydrogenolysis. Saponification of 13 gave the title compound as its potassium salt.