Total synthesis of Le(A)-LacNAc pentasaccharide as a ligand for Clostridium difficile toxin A.

The toxins TcdA and TcdB produced by the human pathogen Clostridium difficile gain entrance to host epithelial cells by recognizing cell-surface carbohydrate ligands. Inhibiting the attachment of these toxins to host cells has been proposed to be a viable therapy to treat C. difficile infections. Glycan array screening previously revealed that the Le(A)-LacNAc pentasaccharide binds strongly to TcdA. Here we report the efficient syntheses of the pentasaccharide and a structurally related tetrasaccharide motif. These compounds will be used to better define the carbohydrate-binding specificity of toxins from C. difficile, which will hopefully lead to the development of improved therapeutics.