Synthesis of the laminara-oligosaccharide methyl β-glycosides of dp 3-8

Article abstract of DOI:10.1016/0008-6215(93)80061-I

Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-α-D-glucopyranoside has been prepared in a good yield by anomerization of the corresponding β-thioglucoside with tin(IV) chloride and transformed, in three steps, into ethyl 2-O-benzoyl-4,6-O-benzylidene-1-thio-α-D-glucopyranoside (18). Chloroacetylation of 18, followed by treatment of the product with chlorine gave crystalline 2-O-benzoyl-4,6-O-benzylidene-3-O-chloroacetyl-β-D-glucopyranosyl chloride (20). This was coupled with methanol in the presence of silver carbonate-silver perchlorate and the product was O-dechloroacetylated to afford methyl 2-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranoside (22). Silver triflate-promoted glucosylation of 18 with 20 gave a β-(1 → 3)-linked disaccharide derivative, reaction of which with chlorine yielded crystalline O-(2-O-benzoyl-4,6-O-benzylidene-3-O-chloroacetyl-β-D-glucopyranosyl) -(1 → 3)-2-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranosyl chloride (24). Likewise, condensation of 22 with 20 gave a β-(1 → 3)linked disaccharide glycoside, which was partially deprotected to give methyl O-(2-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranosyl)-(1 → 3)-2-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranoside (26). The methyl β-glycosides of a homologous series of (1 → 3)-linked β-D-gluco-oligosaccharides from the tri- to the octa-saccharide have been synthesized in a blockwise manner by using 22 and 26 as the glycosyl acceptors, 24 as the disaccharide donor, and silver triflate as the promoter. Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-α-D-glucopyrano- side has been prepared in a good yield by anomerization of the corresponding B-thioglucoside with tin(IV) chloride and transformed, in three steps.