Chiroptical and lectin recognition properties of glycoconjugated poly(phenylacetylene)s featuring variable saccharide functionalities

We report the chiroptical properties and lectin affinities of poly(phenylacetylene)s featuring saccharide functionalities including D-glucopyranoside and D-galactopyranoside. The glycoconjugated poly(phenylacetylene)s were synthesized by rhodium mediated polymerization from phenylacetylene monomers containing a series of saccharide groups; 4-ethynylphenyl 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranoside (PA-(alpha-Glc-OAc), beta-D-glucopyranoside (PA-beta-Glc-OAc), alpha-D-galactopyranoside (PA-alpha-Gal-OAc), and beta-D-galactopyranoside (PA-beta-Gal-OAc). On the basis of CD and UV-vis experiments, these polymers were found to have biased helical conformations in a variety of solvents, such as CHCl3, THF, and HFIP. The deprotection of the acetyl groups using CH3ONa provided the linear saccharide arrays with diverse saccharide functionalities; poly-PA-alpha-Glc, poly-PA-beta-Glc, poly-PA-alpha-Gal, and poly-PA-beta-Gal. CD experiments revealed that poly-PA-alpha-Glc and poly-PA-,beta-Glc have identical helical structures, and poly-PA-alpha-Gal and poly-PA-beta-Gal feature mirror-imaged helical structures. The binding affinities to lectins were demonstrated by a fluorometric assay using the fluorescein isothiocyanate labeled lectins, such as Concanavalin A (FITC-Con A) and peanut agglutinin (FITC-PNA). As expected, increasingly enhanced affinities for Con A and PNA were observed for the helical saccharide arrays in comparison to the monomeric models. Accordingly, the enhanced affinities are essentially correlated with the multivalency and conformational organization of the saccharide functionalities in the arrays.