Synthesis of (1 → 4)-β-d-xylo-oligosaccharides of dp 4–10 by a blockwise approach

Dibutyltin oxide-mediated regioselective chloroacetylation of methyl 1-thio-β-xylobioside, followed by treatment of the product with 4-methylbenzoyl chloride-pyridine, gave methyl 4-O-chloroacetyl-2,3-di-O-(4-methylbenzoyl)-β-d-xylopyranosyl-(1 → 4)-2,3-di-O-(4-methylbenzoyl)-1-thio-β-d-xylopyranoside (18) in 70% yield. Coupling of 18 with benzyl alcohol afforded the disaccharide benzyl β-glycoside, which was O-dechloroacetylated to provide methyl 2,3-di-O-(4-methylbenzoyl)-β-d-xylopyranosyl-(1 → 4)-2,3-di-O-(4-methylbenzoyl)-1-thio-β-d-xylopyranoside (20). A homologous series of (1 → 4)-β-d-xylo-oligosaccharides from the tetra- to the deca-saccharide have been synthesized in a blockwise manner by using 20 as the glycosyl acceptor, 18, methyl 1-thio-β-xylobioside pentaacetate, and methyl 1-thio-β-xylotrioside heptaacetate as the glycosyl donors, and a combination of N-iodosuccinimide-silver triflate as the promoter.