Synthesis, Characterization And Reactivity Study Of Lipoxygenase Model Compounds

Five iron(II,III)-containing coordination compounds with benzimidazolyl-rich ligand have been synthesized and characterized by ultraviolet-visible spectra(UV-Vis), infrared spectra(IR), molar conductivity, cyclic voltammetry(CV) and X-ray diffraction analysis.The grometric structure of these complexs show a distorted octahedron. It's interesting that the complexes [Fe(2H⁺-DTPB)(^-OC₂H₅)](ClO₄)₄·3H₂O and [Fe(2H⁺-DTPB)(^-OC₂H₅)](NO₃)₄·3H₂O have a same coordinated structure, the center atom is bounded by three benzimidazolyl nitrogens and two amino nitrogens of DTPB, the sixth position is occupied by ethyloxy group. The two uncoordinated benzimidazolyl groups are expanding in the space, and the trialkylamino nitrogens are protonated. In addition, the mearement of lipoxygenase-mimic activity suggest that complex Fe(NTB)(sal)Cl₂·H₂O is a inhibitor toward the oxidation of linoleic acid(LA).The lipoxygenase-mimicking activity of some compounds have been determined by the classic method of thiobabituric acid (TBA) and the pseudo-first-order rate constants of LA oxidation have been acquired. The results show that most model complexes can catalyze LA oxidation in the conditions of pH=7.0-8.5 and T=60℃, complexes Fe(CTB)(NO₃)₂·0.5H₂O·0.5C₂H₅OH and Fe(NTB)(sal)Cl₂·H₂O show inhibitor in this conditions, however complex Fe(EDTB)Cl.ClO₄·2H₂O lack any oxidation activities. The pseudo-frist- order rate constants of the model compounds are 10^-2-10^-3min^-1.Electrospray ionization mass spectrometry (ESI-MS) assays incidated that oxidative products of LA areα-hydroxyethanal, nonenal, nonanal acid and their TBA-adducts. The ESR spin trapping spectrum suggest that the pathway of LA oxidation may be a radical mechanism. Moreover, OO·^- also selectively attack on CH₂ group of carbon-11 situation, the most prominent examples are complexes [Fe(DTPB)(OC₂H₅)](ClO₄)₄·3H₂O and [Fe(DTPB) (OC₂H₅)](NO₃)₄·3H₂O, the pathway of LA cleavage may be McLafferty rearrangement and theα-cleavage of oxygenation of 1,4-pentadiene which would reduce the step of radical mechanism of LA oxidation.