Ethynylpyridine polymers: Development of polymeric hosts for saccharide recognition

Saccharide recognition is one of the most attractive topics in host-guest and biomimicking chemistry. Herein we describe development of "mete-ethynylpyridine" poly-/oligomers as artificial hosts for saccharide recognition, which consist of 4-substituted pyridine rings linked 2,6-positions with acetylene bonds. When ethynylpyridine chains associate with a guest saccharide by multipoint hydrogen-bonds, a helical complex forms and its helicity is biassed by chirality of the guest saccharide. Substituents on the pyridine rings give additional characteristics such as solubility, amphiphilicity, basicity, and tautomeric ability. Amphiphilic polymer recognizes natural hexoses even in aqueous methanol. Basic and tautomeric ethynylpyridines switch their recognition ability by protonation and tautomerism, respectively. When a glycoside template is linked with ethynylpyridine oligomers covalently, the resulting helices are fixed by intramolecular association. Helical structure of azacrown-induced polymer is stabilized by collaboration with axial oligoammonium, accompanied with the improvement of glucoside recognition by pseudorotaxane formation between the crown and the oligoammonium.