Synthesis of Oligosaccharides Containing the S -Gal p (α1 → 3)Gal p Unit, Glycomimetic of the Epitope Recognized by Lytic Antibodies.

Two important activities take place in the surface of Trypanosoma cruzi , the agent of Chagas disease: the trans -sialidase (TcTS) catalyzes the transfer of sialic acid from the host glycoconjugates to the mucin-like glycoproteins from the parasite and the presence of lytic antibodies recognize the epitope α-Gal p (1 → 3)-β-Gal p (1 → 4)-α-GlcNAc p. This antigenic structure is known to be present in the parasite mucins; however, in order to be substrates of trans -sialidase, some of the galactose residues should be in the β-Gal p configuration. To study the interaction between both activities, it is important to count the synthetic structures as well as the structural-related glycomimetics. With this purpose, we addressed the synthesis of a trisaccharide and two isomeric tetrasaccharides containing the 1- S -α-Gal p (1 → 3)-β-Gal p motif, the thio analog of the epitope recognized by lytic antibodies. Starting with a common lactose precursor, the sulfur function was incorporated by double inversion of the configuration of the galactose residue that was further glycosylated using different activated donors. Both tetrasaccharides were good acceptors of sialic acid in the reaction catalyzed by TcTS, as determined by high-performance anion exchange chromatography.