Study of CH/π Interactions in the Molecular Recognition between Acetyl Galactopyranoside and 6-substituted 2-Methoxypyridines and 2(1H)-Pyridones

Abstract

A series of 6-substituted 2-methoxypyridine and 2(1H)-pyridones was designed and synthesized for its evaluation in the molecular recognition of acetyl 2,3,4,6-tetra-O-methyl-b-D-galactopyranoside substrate. ¹H-NMR titration (affinity constant K_a determination) and chemical shift perturbation experiments were performed to evaluate the capacity of these receptors to form CH/π interactions with the substrate. The addition of 2-methoxypyridines to the substrate effected up-field shift for the H³, H⁴ and H⁵ proton signals and down-field shift for the H² proton signal of galactopyranoside substrate. The determined affinity constant K_a values for the association between 2(1H)-pyridones and galactopyranoside showed that molecular recognition was weak. These results have demonstrated the existence of weak CH/π interactions and have reflected their weak intermolecular nature. Finally DFT calculations were performed to illustrate the geometry of the molecular recognition between 2(1H)-pyridones and galactopyranoside.