Synthesis of β- d-glucose oligosaccharides from Phytophthora parasitica

Abstract

The glucohexaose, β- d-Glc p-(1→3)-[β- d-Glc p-(1→3)-β- d-Glc p-(1→3)-β- d-Glc p-(1→6)]-β- d-Glc p-(1→3)- d-Glc p, 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.