Saccharide recognition-induced transformation of pyridine-pyridone alternate oligomers from self-dimer to helical complex

(Chemical Equation Presented) 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 × 10³ M^-1 by ¹H NMR titration. Longer 5-, 7-, 9-, and 11-mer oligomers showed considerable broadening and anisotropy in the ¹H NMR spectra due to self-association. These longer oligomers recognized octyl β-D- glucopyranoside and changed their form into a chiral helical complex, showing characteristic circular dichroism.