Synthesis, Characterization And Reactivity Of Model Ligands And Complexes For The Active Site Of Quercetin 2, 3-dioxygenase

Dioxygen activation and biomimetic oxidation of carbohydrate using dioxygen is one of the most active areas,and have received considerable attention in the recent years.This work focus on this active area,aiming at getting insights into the catalytic role of Glu73,metal ion effects,electronic effect of the ligands and the co-ligands effect on the structure and reactivity of Quercetin 2,3-dioxygenase,the following exploratory work has been accomplished:Three new bis(2-pyridylalkyl)amine model ligands carrying a non-substituted(a phenyl group) or a meta-Br(electron-withdrawing group) substituted ortho-benzoic acid derivative as the ligand sidearm(L5,L6 and L7H) have been designed and synthesized,which have been characterized by IR,UV-vis,ESI/MS,~1HNMR and melting point measurement.L7H has never been reported before.Seven novel binary complexes and five ternary model complexes M(Ⅱ)(M:Fe,Co and Cu) have been designed,synthesized,and characterized as the structural and functional models for the active site of Quercetin 2,3-dioxygenase.The designs of model ligands and complexes are very unique which focus on both catalytic site and the substrate binding site of the enzyme.The structures of complex 6 and 7 were determined by X-ray diffraction,and both complexes exhibit a similar distorted square pyramidal geometry.The reactivity of the model complexes towards flavonol and dioxygen have been investigated by UV-vis monitoring.Although the structures of the model complexes are similar,the reactivities are different significantly.The caboxylate effects,electronic effect and rigidity of the ligands,co-ligands effects,metal ion effects on the reactivity of the model complexes have been investigated.The conclusions of our study are as follows:With the same metal ion,the reactivity of complexes with substituted caboxlate group are much higher than the non-substituted one:L1H＞L5.With the same metal ion,the reactivity of complexes with substituted electron-withdrawing group Br are much higher than the non-substituted one:L7H＞L1H.With the same metal ion and ligand,the reactivity of complexes with coligand OAc~- are much higher than Cl~-:OAc＞CI.With the same ligand,the reactivity of different metal ion model complexes are quite different and in the order:Fe＞Co＞Cu.