Synthesis, Characterization And Reactivity Of Acireductone Dioxygenase Model Complexes

One of the most challenging reactions in chemistry and biology is the selective oxidative cleavage of aliphatic carbon-carbon bonds. Acireductone dioxygenase (ARD) include Fe-ARD and Ni-ARD, they activate and use dioxygen regioselective carbon-carbon bond cleavage for same substrate, result in diffrient prdcuts. There is currently little known regarding the mechanistic details of such processes. In this work, efforts have focused on, understanding the role that Glu102, His98, metal ion effects, substrate electronic effects may play in directing the regiospecificity of carbon-carbon bond cleavage.We designed, synthesized and characterized a new model ligand{LH:[(1H-Imidazol-4-ylmethyl)-pyridin-2-ylmethyl-amino]-acetic acid)}, twelve new ARD model complexes [MIILS2] and [MIILS3R](MII:Ni, Fe) which including six model substrates1-p-R1-phenyl-2-R2-3-phenyl-propane-1,3-dione (S, S2:R1=H, R2=OH; S3R:R1=NO2, Br, H, Me, OMe, R2=H). Model ligands and complexes of our designed is very reasonable, because we consider both catalytic site and substrate binding-site of the natural enzyme.In order to studied complexes kinetics, the reaction between model complexes with O2was investigated by UV-vis monitoring. We also identified products of model complexes with O2by LC-MS, the ratio of products were determined from a calibration curve based on peak area in the LC-MS spectrum. The conclusions of our research as follows:①D The reaction rate of FeIILS3R complexes is much faster than NiIILS3R complexes.②The reaction rate is faster when model complexes include electron-donating functional groups.③Treatment Ni-ARD model complexes with O2leads to oxidative cleavage of the C1-C2and C2-C3bonds, leading to formation of carbon monoxide and benzoic acid, treatment Fe-ARD model complexes with O2leads to oxidative cleavage of the C1-C2bonds, leading to formation of benzoylformic acid and benzoic acid, the products structrue is simiar to products of nature ARD, so it is success to mimic the structrue and function of nature ARD.④When S3include electron-donating functional groups, superoxide radical attack to C3, result in oxidative cleavage C2-C3bond and get benzoic acid and oxo-p-R-acetic acid (R=H, Me, OMe). When S3include electron-withdrawing functional groups, superoxide radical attack to C1, result in oxidative cleavage C1-C2bond and get oxo-phenyl-acetic acid and 4-R-benzoic acid (R=NO2, Br). In consequence, the different functional groups of S3influence electron cloud of C1and C3, so treatment [MIILS3R] with O2leads to different products.