Synthesis of β-d-glucose oligosaccharides from Phytophthora parasitica Original Research Article

The glucohexaose, β-d-Glcp-(1→3)-[β-d-Glcp-(1→3)-β-d-Glcp-(1→3)-β-d-Glcp-(1→6)]-β-d-Glcp-(1→3)-d-Glcp, was synthesized as its allyl glycoside via 3+3 strategy. The trisaccharide donor, 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→3)-2,4,6-tri-O-acetyl-β-d-glucopyranosyl-(1→3)-2,4,6-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (11), was obtained by 3-selective coupling of isopropyl 4,6-O-benzylidene-1-thio-β-d-glucopyranoside (2) with 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→3)-2-O-acetyl-4,6-O-benzylidene-α-d-glucopyranosyl trichloroacetimidate (6), followed by hydrolysis, acetylation, dethiolation, and trichloroacetimidation. Meanwhile, the trisaccharide acceptor, allyl 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→3)-2-O-acetyl-β-d-glucopyranosyl-(1→3)-4,6-di-O-acetyl-2-O-benzoyl-α-d-glucopyranoside (14), was prepared by coupling of allyl 4,6-di-O-acetyl-2-O-benzoyl-α-d-glucopyranoside (12) with 6, followed by debenzylidenation. Condensation of 14 with 11, followed by deacylation, gave the target hexaoside. A β-(1→3)-linked tetrasaccharide 29 was also synthesized with methyl 2-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranosyl-(1→3)-2,4,6-tri-O-acetyl-β-d-glucopyranoside (25) as the acceptor and acylated β-(1→3)-linked disaccharide 21 as the donor.