Enhancement of plant and bacterial lectin binding affinities by three-dimensional organized cluster glycosides constructed on helical poly(phenylacetylene) backbones.
A series of poly(phenylacetylene)s bearing diverse saccharide pendants--N-acetyl-D-glucosamine, D-lactose, and N-acetyl-D-neuraminic acid--were synthesized by rhodium-mediated polymerizations of the corresponding acetyl-protected glycosylated phenylacetylenes followed by deprotection. The circular dichroism spectra of these glycosylated poly(phenylacetylene)s each displayed split-type Cotton effects in the long absorption region of the conjugated polymer backbone (260-500 nm), thus indicating predominantly one-handed helical conformations in their backbones. The binding affinities of these glycosylated poly(phenylacetylene)s, and those of previously reported phenylacetylenes bearing D-galactose, towards plant and bacterial lectins were investigated by hemagglutination inhibition assay and isothermal titration calorimetry (ITC). The stoichiometries of binding vary strongly, depending on the lectin binding sites and the accessibilities of the carbohydrate residues in the helices. The measured affinities also vary, with the maximum value observed for the interaction between poly-PA-α-Gal and lectin I from Pseudomonas aeruginosa, with a K(d) value of 4 μM per monosaccharide representing a 200-fold increase relative to the corresponding monomer.