Synthesis of the spacer-containing β-D-GalpNAc-(1→4)-β-D-GlcpNAc-(1→3)-α-D-Galp moiety, representing the non-fucosylated backbone trisaccharide of the glycocalyx glycan of the parasite Schistosoma mansoni

Abstract

The chemical synthesis of beta-d-GalpNAc-(1->4)-beta-d-GlcpNAc-(1->3)-beta-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-dimethyli- sopropylsilyl-2-phthalimido-1-thio-beta-d-glucopyranoside, using N-iodosuccinimide and silver tri- ¯uoromethanesulfonate 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-galactopyranoside to the disaccharide acceptor, using methylsulfenyl bro- mide and silver tri¯uoromethanesulfonate as a catalyst system, gave a protected trisaccharide. Deprotection of this compound yielded the target structure.