New Mechanistic Insights in the Cytochrome P-450 Model Reactions: Direct Identification of the Reactive Intermediates
- PDF / 319,286 Bytes
- 5 Pages / 595.276 x 790.866 pts Page_size
- 64 Downloads / 217 Views
New Mechanistic Insights in the Cytochrome P-450 Model Reactions: Direct Identification of the Reactive Intermediates Arunava Agarwala Æ Debkumar Bandyopadhyay
Received: 29 December 2007 / Accepted: 11 April 2008 / Published online: 30 April 2008 Ó Springer Science+Business Media, LLC 2008
Abstract In CH3CN–H20 medium the porphyrin _ Fe(IV)=O and porphyrin-C6F5IO adduct, and tBuO/tBuO O_ radicals have been spectroscopically identified. The involvement of multiple reactive intermediates in C6F5IO oxidizing system has also been demonstrated. Keywords Catalysis Hydroxylation Epoxidation Hydroperoxide
1 Introduction The iron (III) porphyrin compounds have been extensively used in modeling reactions catalyzed by cytochrome P450 [1]. Among many reactions catalyzed by this monooxygenase family of enzymes, the epoxidation and hydroxylation of hydrocarbons have been very thoroughly studied [1–4]. There has been considerable success in epoxidation but selective hydroxylation of unactivated C–H bonds still remained very elusive specially where hydroperoxides and hydrogen peroxide were the terminal oxidants [5–10]. The mechanistic studies were then more emphasized and it has now been realized that depending upon the terminal oxidants more than one potential reactive intermediates such as 1–4 (Scheme 1) are concomitantly evolved in these oxidizing systems [11– 14]. It was long been known that in case of iodosylarenes, the oxoiron(IV) porphyrin cation radical (2) was the only reactive intermediate responsible in the direct oxygen transfer step to a substrate [2–10]. However the Collman group has claimed for the first time that the catalyst-iodosylarene adduct (1) along A. Agarwala D. Bandyopadhyay (&) Department of Chemistry, Indian Institute of Technology, Delhi, New Delhi 110016, India e-mail: [email protected]
123
with 2 to be the major reactive intermediates in this oxidizing system [15]. Secondly in the reactions of iron(III) porphyrins with t-BuOOH, the evolution of alkoxy radicals have been proposed over several decades [16–19]. Incidentally neither of this catalyst-iodosylarene adduct (1) nor the alkoxy radical intermediates have ever been directly generated and identified in solution. It is not important today to know how they are formed, but it is certainly important to stabilize them in solution because this would assist more efficient oxygenation of substrates by such terminal oxidants. Herein we report for the first time: the evolution, stabilization and definitive spectroscopic identification of these two reactive intermediates in solution. Secondly we also report that in case of iodosylarene the oxo-iron(IV) porphyrin (3) is also definitively formed in the reactions of the iron(III) porphyrin with an iodosylarene both in stoichiometric and in catalytic reagent concentrations. In order to demonstrate these results we have used F20TPPFe(III)Cl (F20TPP = meso-tetrakis (pentafluorophenyl) porphinato dianion) as the catalyst, C6F5IO and t-BuOOH as the terminal oxidants and CH3CN–H2O (9.09%) as the so
Data Loading...
