Synthesis of the carbohydrate moiety from the parasite Echinococcus multilocularis and their antigenicity against human sera

Stereocontrolled syntheses of biotin-labeled oligosaccharide portions with a Galβ1-3GalNAc core of the Em2 glycoprotein antigen obtained from the parasite Echinococcus multilocularis have been accomplished. Trisaccharide Galβ1-3(GlcNAcβ1-6)GalNAcα1-R (G), tetrasaccharide Galβ1-3(Galβ1-4GlcNAcβ1-6)GalNAcα1-R (J) and pentasaccharide Galβ1-3(Galα1-4Galβ1-4GlcNAcβ1-6) GalNAcα1-R (K) (R = biotinylated probe) were synthesized by block synthesis by the use of 5-(methoxycarbonyl)pentyl 2,3,4,6-tetra-O-acetyl-β- d-galactopyranosyl-(1→3)-2-azido-4-O-benzyl-2-deoxy-α-d- galactopyranoside as a common glycosyl acceptor. Moreover, linear trisaccharide Galα1-4Galβ1-3GalNAcα1-R (H) and branched tetrasaccharide Galα1-4Galβ1-3(GlcNAcβ1-6)GalNAcα1-R (I) were synthesized by stepwise condensation. We examined the antigenicity of these five oligosaccharides by an enzyme linked immunosorbent assay (ELISA). Our results demonstrate that biotinylated oligosaccharides H, I and K show good serodiagnostic potential to detect infections caused by the parasite E. multilocularis. Among them the linear sequence Galα1-4Galβ1- 3GalNAcα1-R in oligosaccharide (H) appears to show the highest sensitivity (95%). Moreover, our study clarified the dominant carbohydrate epitope of Em2 antigen.