Regioselective Aliphatic Carbon鈥揅arbon Bond Cleavage by a Model System of Relevance to Iron-Containing Acireductone Dioxygenase

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• 作者：Caleb J. Allpress ; Katarzyna Grubel ; Ewa Szajna-Fuller ; Atta M. Arif ; Lisa M. Berreau
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：January 16, 2013
• 年：2013
• 卷：135
• 期：2
• 页码：659-668
• 全文大小：441K
• 年卷期：v.135,no.2(January 16, 2013)
• ISSN：1520-5126

文摘

Mononuclear Fe(II) complexes ([(6-Ph₂TPA)Fe(PhC(O)C(R)C(O)Ph)]X (3-X: R = OH, X = ClO₄ or OTf; 4: R = H, X = ClO₄)) supported by the 6-Ph₂TPA chelate ligand (6-Ph₂TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-(2-pyridylmethyl)amine) and containing a 尾-diketonate ligand bound via a six-membered chelate ring have been synthesized. The complexes have all been characterized by ¹H NMR, UV鈥搗is, and infrared spectroscopy and variably by elemental analysis, mass spectrometry, and X-ray crystallography. Treatment of dry CH₃CN solutions of 3-OTf with O₂ leads to oxidative cleavage of the C(1)鈥揅(2) and C(2)鈥揅(3) bonds of the acireductone via a dioxygenase reaction, leading to formation of carbon monoxide and 2 equiv of benzoic acid as well as two other products not derived from dioxygenase reactivity: 2-oxo-2-phenylethylbenzoate and benzil. Treatment of CH₃CN/H₂O solutions of 3-X with O₂ leads to the formation of an additional product, benzoylformic acid, indicative of the operation of a new reaction pathway in which only the C(1)鈥揅(2) bond is cleaved. Mechanistic studies show that the change in regioselectivity is due to the hydration of a vicinal triketone intermediate in the presence of both an iron center and water. This is the first structural and functional model of relevance to iron-containing acireductone dioxygenase (Fe-ARD鈥?, an enzyme in the methionine salvage pathway that catalyzes the regiospecific oxidation of 1,2-dihydroxy-3-oxo-(S)-methylthiopentene to form 2-oxo-4-methylthiobutyrate. Importantly, this model system is found to control the regioselectivity of aliphatic carbon鈥揷arbon bond cleavage by changes involving an intermediate in the reaction pathway, rather than by the binding mode of the substrate, as had been proposed in studies of acireductone enzymes.