Selective sialylation of 2,3-di- O-(β- d-galactopyranosyl)- d-galactose catalyzed by Trypanosoma cruzi trans-sialidase

Abstract

Trypanosoma cruzi, the agent of Chagas’ disease, expresses on its surface a trans-sialidase (TcTS) that transfers sialic acid from host glycoconjugates to terminal β-galactopyranosyl units of parasite mucins. This process is involved in infection and pathogenesis. The trisaccharide 2,3-di- O-(β- d-galactopyranosyl)- d-galactose 1 is an external unit in the larger oligosaccharides of the mucins and a site for sialylation. The trisaccharide was previously synthesized in our laboratory. The last step of the synthesis was the hydrogenolysis of the crystalline benzyl trisaccharide. Herein we prove that the trisaccharide 1, its alditol 3 and the benzyl glycoside 2 are good acceptors of sialic acid and effective inhibitors of the sialylation of N-acetyllactosamine catalyzed by TcTS. Furthermore, selective sialylation of the 1→3 linked galactopyranose in glycoside 2 was determined by one and two-dimensional NMR analysis. In contrast, the flexible 2,3-di- O-(β- d-galactopyranosyl)- d-galactitol 3 is sialylated in either one of the two possible sites.