Synthesis of the spacer-containing beta-D-GalpNAc-(1-->4)-beta-D- GlcpNAc-(1-->3)-alpha-D-Galp moiety, representing the non-fucosylated backbone trisaccharide of the glycocalyx glycan of the parasite Schistosoma mansoni.

The chemical synthesis of beta-D-GalpNAc-(1-->4)-beta-D-GlcpNAc- (1-->3)-alpha-D-Galp-(1-->O)-(CH2)5NH2 is described. This structure represents the nonfucosylated backbone trisaccharide of the glycocalyx glycan of the cercarial stage of the parasite Schistosoma mansoni. Synthesis of the trisaccharide was achieved via a stepwise coupling approach. 5-Azidopentyl 4-O-acetyl-2,6-di-O-benzyl-alpha-D-galactopyranoside was condensed with ethyl 6-O-benzyl-2-deoxy-3,4-di-O-dimethylisopropylsilyl- 2-phthalimido-1-thio-beta-D-glucopyranoside, using N-iodosuccinimide and silver trifluoromethanesulfonate as a catalyst system, followed by the removal of the silyl ether groups to afford a disaccharide acceptor. Coupling of ethyl 4,6-di-O-acetyl-3-O- allyloxycarbonyl-2-deoxy-2-phthalimido-1-thio-beta-D-galactopyrano side to the disaccharide acceptor, using methylsulfenyl bromide and silver trifluoromethanesulfonate as a catalyst system, gave a protected trisaccharide. Deprotection of this compound yielded the target structure.