Synthesis of a hexasaccharide, the repeating unit of O-deacetylated GXM of C. neoformans serotype A.
beta-D-GlcpA-(1-->2)-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-alpha-D-Manp-(1-->3)[-beta-D-Xylp-(1-->2)]-alpha-D-Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar A, was synthesized as its allyl glycoside. Thus, 3-O-selective acetylation of allyl 4,6-O-benzylidene-alpha-D-mannopyranoside afforded 2, and subsequent glycosylation of 2 with 2,3,4-tri-O-benzoyl-D-xylopyranosyl trichloroacetimidate furnished the beta-(1-->2)-linked disaccharide 4. Debenzylidenation followed by benzoylation gave allyl 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-3-O-acetyl-4,6-di-O-benzoyl-alpha-D-mannopyranoside (5), and selective 3-O-deacetylation gave the disaccharide acceptor 6. Coupling of 6 with 2-O-acetyl-3,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate yielded the trisaccharide 8, and subsequent deallylation and trichloroacetimidation gave 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-[2-O-acetyl-3,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->3)]-4,6-di-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate (9). Condensation of the trisaccharide donor 9 with the disaccharide acceptor 6 gave the pentasaccharide 10 whose 2-O-deacetylation gave the acceptor 11. Glycosylation of 11 with methyl 2,3,4-tri-O-acetyl-alpha-D-glucopyranosyluronate trichloroacetimidate and subsequent deprotection gave the target hexasaccharide.
Zhang
Jianjun
J
Research Center for Eco-Environmental Sciences, Academia Sinica, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, PR China.
Kong
Fanzuo
F
D000107:Acetylation; D000498:Allyl Compounds / Q000138:chemical synthesis; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D003455:Cryptococcus neoformans / Q000737:chemistry*; D005965:Glucuronates / Q000737:chemistry; D006031:Glycosylation; D008358:Mannose / Q000737:chemistry; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000138:chemical synthesis*; D011134:Polysaccharides / Q000737:chemistry*; D012703:Serotyping / Q000379:methods; D014994:Xylose / Q000737:chemistry
D000498:Allyl Compounds; D005965:Glucuronates; D009844:Oligosaccharides; D011134:Polysaccharides; C027478:glucuronoxylomannan; D014994:Xylose; D008358:Mannose