A practical synthesis of alpha-D-Manp-(1->3)-alpha-D-Manp-(1->2)-[alpha-D-Glcp-(1->3)]-alpha-D-Manp-(1->2)-alpha-D-Manp-(1->2)-alpha-D-Manp,an O-specific heterohexasaccharide fragment of Citrobacter braakii O7a,3b,1c

摘要

An O-specific heterohexasaccharide fragment of Citrobacter braakii O7a,3b,1c,alpha-D-Manp-(1->3)-alpha-D-Manp-(1->2)-[alpha-D-Glcp-(1->3]-alpha-D-Manp-(1->2)-alpha-D-Manp-(1->2)-alpha-D-Manp was synthesized as its mthyl glycoside.Acetylation of allyl 4,6-O-benzylidene-alpha-D-mannopyranoside,followed by debenzylidenization and benzoylation gave allyl 2,3-di-O-acetyl-4,6-di-O-benzoyl-alpha-D-mannopyranoside (3),and subsequent deacetylation of 3 with CH_3COCl-MeOH gave the monosaccharide acceptor 4.Condensation fo isopropyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-glucopyranoside (6)with 4 selectively sfforded the alpha-(1->3)-linked disaccharide 7.Condensation of 7 with the (1-3)-linked disaccharide donor 9,followed by deallylationand trichloroacetimidation,afforded the tetrasaccharide donor 12.Coupling of 12 with disaccharide acceptor 13,followed by debenzylation and deacylation,furnished the target heteroheasaccharide 16.