Post-polymerization functionalization approach for highly water-soluble well-defined regioregular head-to-tail glycopolythiophenes

Two bromide-bearing regioregular head-to-tail polythiophenes (polymers 1 and 3) were prepared by using Grignard metathesis method to polymerize 2,5-dibromo-3-bromohexylthiophene (2) and 2,5-dibromo3-(11-bromo-3,6,9-trioxa-1- undecoxy)thiophene (7), respectively. Well-defined regioregular head-to-tail glycopolythiophenes were prepared through post-polymerization functionalization approach by treating the bromidebearing polythiophenes with 1-thiolethyl- α-D-mannose tetraacetate (3a) or 1-thiol-β-D-glucose tetraacetrate (3b) in THF solution with a basic condition, respectively, and followed by sequential deacetylation under Zemplén conditions in methanol and methylene chloride containing sodium methoxide at room temperature. Glycopolythiophenes (polymers C and D) with hydrophilic tetra(ethylene glycol) as tethered spacers between the polymer backbone and carbohydrate residues are highly water-soluble while glycopolythiophenes (polymers A and B) with hydrophobic hexyl tethered spacers are completely insoluble in water. All polythiophenes display low fluorescence with fluorescent quantum yield ranging from 0.4% to 3%. However, water-soluble polymers C and D in 0.1 M phosphate buffer (pH 7.2) show a little higher fluorescent intensity than their precursor polymer 3 in chloroform solution. α-Mannose-bearing glycopolythiophene (polymer C) exhibits specific binding to Concanavalin A through multivalent interactions with a binding constant of 2.15 x 105. © 2007 American Chemical Society