Add time:08/18/2019         Source:sciencedirect.com

Methyl 2-azido-2-deoxy-β-d-galactopyranoside was subjected in sequence to isopropylidenation, benzylation, acid hydrolysis, and selective acetylation of HO-4, to give amorphous methyl 4-O-acetyl-2-azido-6-O-benzyl-2-deoxy-β-d-galactopyranoside. Condensation with 2,3,4-tri-O-benzyl-6-O-chloroacetyl-α-l-idopyranosyl chloride (easily prepared in three steps from known 1,6-di-O-acetyl-2,3,4-tri-O-benzyl-l-idopyranose) in 1,2-dichloroethane, in the presence of 2,4,6-trimethylpyridine, silver triflate, and molecular sieves, provided, after O-dechloroacetylation, 58% of amorphous methyl 4-O-acetyl-2-azido-6-O-benzyl-2-deoxy-3-O-(2,3,4-tri-O-benzyl-α-l-idopyranosyl)-β-d-galactopyranoside. Reduction with sodium borohydride, followed successively by N-acetylation, oxidation in the presence of chromium trioxide in acetone-sulfuric acid, O-sulfation of the sodium salt with the sulfur trioxide-trimethylamine complex, and catalytic hydrogenolysis, then gave the disodium salt of methyl 2-acetamido-2-deoxy-3-O-(α-l-idopyranosyluronic acid)-4-O-sulfo-β-d-galactopyranoside. The β-linked disaccharide was also isolated (30%) and converted, through the same sequence, into methyl 2-acetamido-2-deoxy-3-O-(β-l-idopyranosyluronic acid)-4-O-sulfo-β-d-galactopyranoside. The non-sulfated analogue of the title disaccharide was obtained on catalytic hydrogenolysis of methyl 2-acetamido-6-O-benzyl-2-deoxy-3-O-(α-l-idopyranosyluronic acid)-β-d-galactopyranoside. The following compounds were also synthesized: methyl 2-acetamido-2-deoxy-3-O-methyl-4-O-sulfo-β-d-galactopyranoside, methyl 2-acetamido-2-deoxy-3-O-methyl-6-O-sulfo-β-d-galactopyranoside, and methyl 2-acetamido-2-deoxy-3-O-methyl-4,6-di-O-sulfo-β-d-galactopyranoside. The conformation of the l-idopyranosiduronate residue of the synthetic disaccharides is discussed.

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