[Synthesis of spaced trisaccharides with blood group A and B specificity, their fragments, and structural analogs]

Abstract

Trisaccharides GalNAc alpha 1----3(Fuc alpha 1----2)Gal and Gal alpha 1----3(Fuc alpha 1----2)Gal, which are the determinant fragments of the human blood group specific antigens A and B, respectively, were synthesized as R-glycosides (R = beta-OCH2CH2CH2NHCOCF3). 4,6-BdGal-R was acetylated selectively at 3-OH, the 3-O-acetate was alpha-fucosylated and then deacetylated to give a protected H-disaccharide bearing a free 3-OH. The disaccharide was alpha-glycosylated with 2-azido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-galactopyranosyl chloride (GCl) or 2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl bromide (GBr) to give protected spacered trisaccharides A and B, respectively. Disaccharides GalNAc alpha 1----3Gal-R and Gal alpha 1----3Gal-R were synthesized in two ways. 1. Hydrogenolysis followed by benzylidenation of Bzl3-2-O-Ac-Gal-R gave 4,6-Bd-2-O-Ac-Gal-R, which was alpha-glycosylated with GCl and GBr. 2. The required disaccharides were isolated from the mixture of di- and trisaccharides which was obtained by selective glycosylation of 4,6-Bd-Gal-R with GCl and GBr. Synthesis of GalNAc alpha 1----3(GalNAc alpha 1----2)Gal and Gal alpha 1----3(Gal alpha 1----2)Gal, non-natural analogues of A and B trisaccharides, is also described. Deprotected R-glycosides were converted to OCH2CH2CH2NH2 (R1) derivatives, N-biotinyl derivatives were synthesized from GalNAc alpha 1----3(Fuc alpha 1----2)Gal-R1 and Gal alpha 1----3(Fuc alpha 1----2)Gal-R1 glycosides. The oligosaccharides, their macromolecular forms, and affinity sorbents obtained from them were used in the epitope specificity studies of the monoclonal antibodies and blood group typing.