Co-oligomers involving (1H)-4-pyridone and 4-alkoxypyridine rings were studied, and it was found that their supramolecular transformation was caused by saccharide recognition-In the co-oligomers, pyridone and pyridine rings are alternately linked at their 2,6-position with an acetylene bond. The pyridine rings behave as a hydrogen bonding acceptor, and the pyridone rings and tautomerized 4-pyridinol work as a donor. Pyridine-pyridone-pyridine 3-mer was found to self-dimerize on the basis of vapor pressure osmometry in CHCl3, and the association constant was obtained as 2.3 x 10(3) M-1 by H-1 NMR titration. Longer 5-, 7-, 9-, and 11-mer oligomers showed considerable broadening and anisotropy in the H-1 NMR spectra due to self-association. These longer oligomers recognized octyl beta-D-glucopyranoside and changed their form into a chiral helical complex, showing characteristic circular dichroism.
Remarkably Strong, Uncharged Hydrogen-Bonding Interactions of Polypyridine-Macrocyclic Receptors for Deoxyribofuranosides
Novel macrocyclic saccharide receptors that possess a pyridine-pyridone-pyridine arrangement as a hydrogen-bonding motif are presented. The artificial receptors exhibited a remarkably strong binding affinity for deoxyribofuranoside derivatives in CDCl3 (K-a = 19 000 M-1 -Delta G(298) = 24.4 kJ/mol), one of the highest values of artificial receptors having only uncharged hydrogen-bonding sites for monosaccharide derivatives. Selective extraction of deoxyribose by the receptors was also observed; the extractabilities,;or affinities to the receptors of various pentoses and hexoses, decreased in the following order: deoxyribose > lyxose congruent to ribose > arabinose congruent to fructose congruent to xylose > glucose > mannose > galactose.