SYNTHESIS OF THE SPACER-CONTAINING -GALPNAC-(1-]4)-BETA-D-GLCPNAC-(1-]3)-ALPHA-D-GALP MOIETY, REPRESENTING THE NONFUCOSYLATED BACKBONE TRISACCHARIDE OF THE GLYCOCALYX GLYCAN OF THE PARASITE SCHISTOSOMA-MANSONI

The chemical synthesis of D-GlcpNAc-(1-->3)-alpha-D-Galp-(1-->O)-(CH2) (5)NH2 is described. This structure represents the nonfucosylated back bone trisaccharide of the glycocalyx glycan of the cercarial stage of the parasite Schistosoma mansoni. Synthesis of the trisaccharide was a chieved via a stepwise coupling approach. 5-Azidopentyl O-acetyl-2,6-d i-O-benzyl-alpha-D-galactopyranoside was condensed with ethyl silyl-2- phthalimido-1-thio-beta-D-glucopyranoside, using N-iodosuccinimide and silver trifluoromethanesulfonate as a catalyst system, followed by th e removal of the silyl ether groups to afford a disaccharide acceptor. Coupling of ethyl eoxy-2-phthalimido-1-thio-beta-D-galactopyranoside to the disaccharide acceptor, using methylsulfenyl bromide and silver trifluoromethanesulfonate as a catalyst system, gave a protected trisa ccharide. Deprotection of this compound yielded the target structure. (C) 1998 Elsevier Science Ltd. All rights reserved.