Abstract
We have studied artificial polymers consisted of pyridine rings linked at 2,6-positions with acetylene bonds. The artificial polymers can recognize various kinds of saccharides and form helical higher-order structures. In the present study, we newly developed such class of artificial polymers bearing azacrown side chains. The higher-order structure of the polymers was expected to be regulated by cation recognition at the azacrown moieties.
The synthesis of the new polymer is as follows. Citrazinic acid was converted to methyl 2,6-dibromoisonicotinate, and it was reduced and brominated to yield 2,6-dibromo-4-(bromomethyl)pyridine. Then, the bromine atom of the side chain was replaced with 1-aza-24-crown-8. The target polymer bearing azacrown side chains was obtained by repeating Sonogashira reaction on the monomer. Addition of a guest saccharide into a solution of the polymer induced a CD band around 340 nm, which indicates that host-guest association occurred between the polymer and the guest to form a chiral higher-order structure. Furthermore, when a polyammonium adduct was added to the mixture of the polymer and the saccharide, the induced CD band was remarkably enhanced, suggesting the presence of heterotropic positive allosterism.
