Preparation of spacer-containing di-, tri-, and tetrasaccharide fragments of the circulating anodic antigen of Schistosoma mansoni for diagnostic purposes

The chemical synthesis of β-d-GlcpA-(1⃗3)-β-d-GalpNAc-(1⃗O)CH2CH=CH2, β-d-GalpNAc-(1⃗6)-[β-d-GlcpA-(1⃗3)]-β-d-GalpNAc-(1⃗O)CH2CH=CH2, and β-d-GlcpA-(1⃗3)-β-d-GalpNAc-(1⃗6)-[β-d-GlcpA-(1⃗3)]-β-d-GalpNAc-(1⃗O)CH2CH=CH2 is described. These oligosaccharides represent fragments of the circulating anodic antigen, secreted by the parasite Schistosoma mansoni in the circulatory system of the host. The applied synthesis strategy includes the preparation of a non-oxidised backbone oligosaccharide, with a levulinoyl group at O-6 of the β-d-glucose residue. After the selective removal of the levulinoyl group, the obtained hydroxyl functions were converted into carboxyl groups, using pyridinium dichromate and acetic anhydride in dichloromethane, to afford the desired glucuronic-acid-containing oligosaccharides. Subsequently, the allyl glycosides have been elongated with cysteamine to give the corresponding amine-spacer-containing oligosaccharides.