Résumé
Condensation of crystalline methyl 2-azido-4,6-
O-benzylidene-2-deoxy-β-
d-galactopyranoside with methyl (2,3,4-tri-
O-acetyl-α-
l-idopyranosyl bromide)-uronate in dichloromethane, in the presence of silver triflate and molecular sieve, provided 54% of methyl 2-azido-4,6-
O-benzylidene-2-deoxy-3-
O-(methyl 2,3,4,-tri-
O-acetyl-α-
l-idopyranosyluronate)-β-
d- galactopyranoside. The use of methyl (2,3,4-tri-
O-acetyl-α-
l-idopyranosyl trichloroacetimidate)uronate as glycosyl donor, in the presence of trimethylsilyl triflate, improved the yield to 68%. Regio-selective opening of the benzylidene group with sodium cyanoborohydride followed successively by
O-sulfation with the sulfur trioxide-trimethylamine complex, saponification, catalytic hydrogenolysis and selective
N-acetylation gave the di-sodium salt of methyl 2-acetamido-2-deoxy-3-
O-(α-
l-idopyranosyluronic acid)-4-
O-sulfo-β-
d-galactopyranoside. Condensation of methyl 2-azido-4,6-
O-benzylidene-2-deoxy-β-
d-galactopyranoside with methyl (2,3,4-tri-
O-acetyl-α-
d-glucopyranosyl bromide)uronate in dichloromethane, in the presence of silver triflate and molecular sieve, gave methyl 2-azido-4,6-
O-benzylidene-2-deoxy-3-
O-(methyl 2,3,4-tri-
O-acetyl-β-
d-glucopyranosyluronate)-β-
d-galactopyranoside in 85% yield. The sequence already described then gave the disodium salt of methyl 2-acetamido-2-deoxy-3-
O-(β-
d-glucopyranosyluronic acid)-4-
O-sulfo-β-
d-galactopyranoside.