1
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Li SH, Zhang X, Mei ZL, Liu Y, Ma JA, Zhang FG. Chemoenzymatic Synthesis of Fluorinated Mycocyclosin Enabled by the Engineered Cytochrome P450-Catalyzed Biaryl Coupling Reaction. J Am Chem Soc 2024; 146:19962-19973. [PMID: 38985576 DOI: 10.1021/jacs.4c03499] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/12/2024]
Abstract
Installing fluorine atoms onto natural products holds great promise for the generation of fluorinated molecules with improved or novel pharmacological properties. The enzymatic oxidative carbon-carbon coupling reaction represents a straightforward strategy for synthesizing biaryl architectures, but the exploration of this method for producing fluorine-substituted derivatives of natural products remains elusive. Here, in this study, we report the protein engineering of cytochrome P450 from Mycobacterium tuberculosis (MtCYP121) for the construction of a series of new-to-nature fluorine-substituted Mycocyclosin derivatives. This protocol takes advantage of a "hybrid" chemoenzymatic procedure consisting of tyrosine phenol lyase-catalyzed fluorotyrosine preparation from commercially available fluorophenols, intermolecular chemical condensation to give cyclodityrosines, and an engineered MtCYP121-catalyzed intramolecular biphenol coupling reaction to complete the strained macrocyclic structure. Computational mechanistic studies reveal that MtCYP121 employs Cpd I to abstract a hydrogen atom from the proximal phenolic hydroxyl group of the substrate to trigger the reaction. Then, conformational change makes the two phenolic hydroxyl groups close enough to undergo intramolecular hydrogen atom transfer with the assistance of a pocket water molecule. The final diradical coupling process completes the intramolecular C-C bond formation. The efficiency of the biaryl coupling reaction was found to be influenced by various fluorine substitutions, primarily due to the presence of distinct binding conformations.
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Affiliation(s)
- Shuo-Han Li
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China
| | - Xue Zhang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Ze-Long Mei
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China
| | - Yongjun Liu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Jun-An Ma
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China
| | - Fa-Guang Zhang
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China
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2
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Dias AHS, Cao Y, Skaf MS, de Visser SP. Machine learning-aided engineering of a cytochrome P450 for optimal bioconversion of lignin fragments. Phys Chem Chem Phys 2024; 26:17577-17587. [PMID: 38884162 DOI: 10.1039/d4cp01282h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/18/2024]
Abstract
Using machine learning, molecular dynamics simulations, and density functional theory calculations we gain insight into the selectivity patterns of substrate activation by the cytochromes P450. In nature, the reactions catalyzed by the P450s lead to the biodegradation of xenobiotics, but recent work has shown that fungi utilize P450s for the activation of lignin fragments, such as monomer and dimer units. These fragments often are the building blocks of valuable materials, including drug molecules and fragrances, hence a highly selective biocatalyst that can produce these compounds in good yield with high selectivity would be an important step in biotechnology. In this work a detailed computational study is reported on two reaction channels of two P450 isozymes, namely the O-deethylation of guaethol by CYP255A and the O-demethylation versus aromatic hydroxylation of p-anisic acid by CYP199A4. The studies show that the second-coordination sphere plays a major role in substrate binding and positioning, heme access, and in the selectivity patterns. Moreover, the local environment affects the kinetics of the reaction through lowering or raising barrier heights. Furthermore, we predict a site-selective mutation for highly specific reaction channels for CYP199A4.
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Affiliation(s)
- Artur Hermano Sampaio Dias
- Manchester Institute of Biotechnology and Department of Chemical Engineering, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
- Institute of Chemistry and Centre for Computing in Engineering & Sciences, University of Campinas, Campinas, SP 13083-861, Brazil
| | - Yuanxin Cao
- Manchester Institute of Biotechnology and Department of Chemical Engineering, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
| | - Munir S Skaf
- Institute of Chemistry and Centre for Computing in Engineering & Sciences, University of Campinas, Campinas, SP 13083-861, Brazil
| | - Sam P de Visser
- Manchester Institute of Biotechnology and Department of Chemical Engineering, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
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3
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Tripathi A, Dubey KD. The mechanistic insights into different aspects of promiscuity in metalloenzymes. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2024; 141:23-66. [PMID: 38960476 DOI: 10.1016/bs.apcsb.2023.12.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/05/2024]
Abstract
Enzymes are nature's ultimate machinery to catalyze complex reactions. Though enzymes are evolved to catalyze specific reactions, they also show significant promiscuity in reactions and substrate selection. Metalloenzymes contain a metal ion or metal cofactor in their active site, which is crucial in their catalytic activity. Depending on the metal and its coordination environment, the metal ion or cofactor may function as a Lewis acid or base and a redox center and thus can catalyze a plethora of natural reactions. In fact, the versatility in the oxidation state of the metal ions provides metalloenzymes with a high level of catalytic adaptability and promiscuity. In this chapter, we discuss different aspects of promiscuity in metalloenzymes by using several recent experimental and theoretical works as case studies. We start our discussion by introducing the concept of promiscuity and then we delve into the mechanistic insight into promiscuity at the molecular level.
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Affiliation(s)
- Ankita Tripathi
- Department of Chemistry, School of Natural Science, Shiv Nadar Institution of Eminence, Greater Noida, Uttar Pradesh, India
| | - Kshatresh Dutta Dubey
- Department of Chemistry, School of Natural Science, Shiv Nadar Institution of Eminence, Greater Noida, Uttar Pradesh, India.
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Zhou TP, Feng J, Wang Y, Li S, Wang B. Substrate Conformational Switch Enables the Stereoselective Dimerization in P450 NascB: Insights from Molecular Dynamics Simulations and Quantum Mechanical/Molecular Mechanical Calculations. JACS AU 2024; 4:1591-1604. [PMID: 38665654 PMCID: PMC11040706 DOI: 10.1021/jacsau.4c00075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 03/20/2024] [Accepted: 03/21/2024] [Indexed: 04/28/2024]
Abstract
P450 NascB catalyzes the coupling of cyclo-(l-tryptophan-l-proline) (1) to generate (-)-naseseazine C (2) through intramolecular C-N bond formation and intermolecular C-C coupling. A thorough understanding of its catalytic mechanism is crucial for the engineering or design of P450-catalyzed C-N dimerization reactions. By employing MD simulations, QM/MM calculations, and enhanced sampling, we assessed various mechanisms from recent works. Our study demonstrates that the most favorable pathway entails the transfer of a hydrogen atom from N7-H to Cpd I. Subsequently, there is a conformational change in the substrate radical, shifting it from the Re-face to the Si-face of N7 in Substrate 1. The Si-face conformation of Substrate 1 is stabilized by the protein environment and the π-π stacking interaction between the indole ring and heme porphyrin. The subsequent intermolecular C3-C6' bond formation between Substrate 1 radical and Substrate 2 occurs via a radical attack mechanism. The conformational switch of the Substrate 1 radical not only lowers the barrier of the intermolecular C3-C6' bond formation but also yields the correct stereoselectivity observed in experiments. In addition, we evaluated the reactivity of the ferric-superoxide species, showing it is not reactive enough to initiate the hydrogen atom abstraction from the indole NH group of the substrate. Our simulation provides a comprehensive mechanistic insight into how the P450 enzyme precisely controls both the intramolecular C-N cyclization and intermolecular C-C coupling. The current findings align with the available experimental data, emphasizing the pivotal role of substrate dynamics in governing P450 catalysis.
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Affiliation(s)
- Tai-Ping Zhou
- State
Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian
Provincial Key Laboratory of Theoretical and Computational Chemistry,
College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Jianqiang Feng
- State
Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian
Provincial Key Laboratory of Theoretical and Computational Chemistry,
College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Yongchao Wang
- State
Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian
Provincial Key Laboratory of Theoretical and Computational Chemistry,
College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Shengying Li
- State
Key Laboratory of Microbial Technology, Shandong University, Qingdao 266237, China
| | - Binju Wang
- State
Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian
Provincial Key Laboratory of Theoretical and Computational Chemistry,
College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
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Li X, Liu Y. Multiscale Study on the Intramolecular C-S Bond Formation Catalyzed by P450 Monooxygenase CxnD Involved in the Biosynthesis of Chuangxinmycin: The Critical Roles of Noncrystal Water Molecule and Conformational Change. Inorg Chem 2024; 63:4086-4098. [PMID: 38376137 DOI: 10.1021/acs.inorgchem.3c03748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2024]
Abstract
Cytochrome P450 monooxygenase CxnD catalyzes intramolecular C-S bond formation in the biosynthesis of chuangxinmycin, which is representative of the synthesis of sulfur-containing natural heterocyclic compounds. The intramolecular cyclization usually requires the activation of two reaction sites and a large conformational change; thus, illuminating its detailed reaction mechanism remains challengeable. Here, the reaction pathway of CxnD-catalyzed C-S bond formation was clarified by a series of calculations, including Gaussian accelerated molecular dynamics simulations and quantum mechanical-molecular mechanical calculations. Our results revealed that the C-S formation follows a diradical coupling mechanism. CxnD first employs Cpd I to abstract the hydrogen atom from the imino group of the indole ring, and then, the resulted Cpd II further extracts another hydrogen atom from the thiol group of the side chain to afford a diradical intermediate, in which a noncrystal water molecule entering into the active site after the formation of Cpd I was proved to play an indispensable role. Moreover, the diradical intermediate cannot directly perform the coupling reaction. It should first undergo a series of conformational changes leading to the proximity of two reaction sites. It is the flexibility of the active site of the enzyme and the side chain of the substrate that makes the diradical coupling to be successful.
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Affiliation(s)
- Xinyi Li
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Yongjun Liu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
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6
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Costa GJ, Egbemhenghe A, Liang R. Computational Characterization of the Reactivity of Compound I in Unspecific Peroxygenases. J Phys Chem B 2023; 127:10987-10999. [PMID: 38096487 DOI: 10.1021/acs.jpcb.3c06311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2023]
Abstract
Unspecific peroxygenases (UPOs) are emerging as promising biocatalysts for selective oxyfunctionalization of unactivated C-H bonds. However, their potential in large-scale synthesis is currently constrained by suboptimal chemical selectivity. Improving the selectivity of UPOs requires a deep understanding of the molecular basis of their catalysis. Recent molecular simulations have sought to unravel UPO's selectivity and inform their design principles. However, most of these studies focused on substrate-binding poses. Few researchers have investigated how the reactivity of CpdI, the principal oxidizing intermediate in the catalytic cycle, influences selectivity in a realistic protein environment. Moreover, the influence of protein electrostatics on the reaction kinetics of CpdI has also been largely overlooked. To bridge this gap, we used multiscale simulations to interpret the regio- and enantioselective hydroxylation of the n-heptane substrate catalyzed by Agrocybe aegerita UPO (AaeUPO). We comprehensively characterized the energetics and kinetics of the hydrogen atom-transfer (HAT) step, initiated by CpdI, and the subsequent oxygen rebound step forming the product. Notably, our approach involved both free energy and potential energy evaluations in a quantum mechanics/molecular mechanics (QM/MM) setting, mitigating the dependence of results on the choice of initial conditions. These calculations illuminate the thermodynamics and kinetics of the HAT and oxygen rebound steps. Our findings highlight that both the conformational selection and the distinct chemical reactivity of different substrate hydrogen atoms together dictate the regio- and enantio-selectivity. Building on our previous study of CpdI's formation in AaeUPO, our results indicate that the HAT step is the rate-limiting step in the overall catalytic cycle. The subsequent oxygen rebound step is swift and retains the selectivity determined by the HAT step. We also pinpointed several polar and charged amino acid residues whose electrostatic potentials considerably influence the reaction barrier of the HAT step. Notably, the Glu196 residue is pivotal for both the CpdI's formation and participation in the HAT step. Our research offers in-depth insights into the catalytic cycle of AaeUPO, which will be instrumental in the rational design of UPOs with enhanced properties.
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Affiliation(s)
- Gustavo J Costa
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States
| | - Abel Egbemhenghe
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States
| | - Ruibin Liang
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States
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7
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Sahil M, Singh T, Ghosh S, Mondal J. 3site Multisubstrate-Bound State of Cytochrome P450cam. J Am Chem Soc 2023; 145:23488-23502. [PMID: 37867463 DOI: 10.1021/jacs.3c06144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2023]
Abstract
We identified a multisubstrate-bound state, hereby referred as a 3site state, in cytochrome P450cam via integrating molecular dynamics simulation with nuclear magnetic resonance (NMR) pseudocontact shift measurements. The 3site state is a result of simultaneous binding of three camphor molecules in three locations around P450cam: (a) in a well-established "catalytic" site near heme, (b) in a kink-separated "waiting" site along channel-1, and (c) in a previously reported "allosteric" site at E, F, G, and H helical junctions. These three spatially distinct binding modes in the 3site state mutually communicate with each other via homotropic allostery and act cooperatively to render P450cam functional. The 3site state shows a significantly superior fit with NMR pseudo contact shift (PCS) data with a Q-score of 0.045 than previously known bound states and consists of D251 free of salt-bridges with K178 and R186, rendering the enzyme functionally primed. To date, none of the reported cocomplex of P450cam with its redox partner putidaredoxin (pdx) has been able to match solution NMR data and controversial pdx-induced opening of P450cam's channel-1 remains a matter of recurrent discourse. In this regard, inclusion of pdx to the 3site state is able to perfectly fit the NMR PCS measurement with a Q-score of 0.08 and disfavors the pdx-induced opening of channel-1, reconciling previously unexplained remarkably fast hydroxylation kinetics with a koff of 10.2 s-1. Together, our findings hint that previous experimental observations may have inadvertently captured the 3site state as an in vitro solution state, instead of the catalytic state alone, and provided a distinct departure from the conventional understanding of cytochrome P450.
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Affiliation(s)
- Mohammad Sahil
- Tata Institute of Fundamental Research, Hyderabad 500046, India
| | - Tejender Singh
- Tata Institute of Fundamental Research, Hyderabad 500046, India
| | - Soumya Ghosh
- Tata Institute of Fundamental Research, Hyderabad 500046, India
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8
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Stout CN, Renata H. Self-sufficient P450-reductase chimeras for biocatalysis. Methods Enzymol 2023; 693:51-71. [PMID: 37977738 DOI: 10.1016/bs.mie.2023.09.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
In recent years, cytochromes P450 have emerged as powerful, versatile biocatalysts for the site-selective functionalization of small molecules. Catalyzing an impressive range of chemical transformations, these enzymes have been widely used to effect C-H oxidation, biaryl coupling, and carbon-heteroatom bond formation, among many other reactions. However, the majority of P450s are multi-protein systems that employ secondary redox partners in key steps of the catalytic cycle, which limits their broader applicability. In response, the discovery of self-sufficient P450s, such as P450BM3 and P450RhF, has provided a template for the construction of artificial, self-sufficient P450-reductase fusions. In this chapter, we describe a procedure for the design, assembly, and application of two engineered, self-sufficient P450s of Streptomyces origin via fusion with an exogenous reductase domain. In particular, we generated artificial chimeras of P450s PtmO5 and TleB by linking them covalently with the reductase domain of P450RhF. Upon verification of their activities, both enzymes were employed in preparative-scale biocatalytic reactions. This approach can feasibly be applied to any P450 of interest, thereby laying the groundwork for the production of self-sufficient P450s for diverse chemical applications.
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Affiliation(s)
- Carter N Stout
- Skaggs Doctoral Program in the Chemical and Biological Sciences, Scripps Research, La Jolla, CA, United States
| | - Hans Renata
- Department of Chemistry, BioScience Research Collaborative, Rice University, Houston, TX, United States.
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9
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Diao W, Farrell JD, Wang B, Ye F, Wang Z. Preorganized Internal Electric Field Promotes a Double-Displacement Mechanism for the Adenine Excision Reaction by Adenine DNA Glycosylase. J Phys Chem B 2023; 127:8551-8564. [PMID: 37782825 DOI: 10.1021/acs.jpcb.3c04928] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Adenine DNA glycosylase (MutY) is a monofunctional glycosylase, removing adenines (A) misinserted opposite 8-oxo-7,8-dihydroguanine (OG), a common product of oxidative damage to DNA. Through multiscale calculations, we decipher a detailed adenine excision mechanism of MutY that is consistent with all available experimental data, involving an initial protonation step and two nucleophilic displacement steps. During the first displacement step, N-glycosidic bond cleavage is accompanied by the attack of the carboxylate group of residue Asp144 at the anomeric carbon (C1'), forming a covalent glycosyl-enzyme intermediate to stabilize the fleeting oxocarbenium ion. After departure of the excised base, water nucleophiles can be recruited to displace Asp144, completing the catalytic cycle with retention of stereochemistry at the C1' position. The two displacement reactions are found to mostly involve the movement of the oxocarbenium ion, occurring with large charge reorganization and thus sensitive to the internal electric field (IEF) exerted by the polar protein environment. Intriguingly, we find that the negatively charged carboxylate group is a good nucleophile for the oxocarbenium ion, yet an unactivated water molecule is not, and that the electric field catalysis strategy is used by the enzyme to enable its unique double-displacement reaction mechanism. A strong IEF, pointing toward 5' direction of the substrate sugar ring, greatly facilitates the second displacement reaction at the expense of elevating the barrier of the first one, thereby allowing both reactions to occur. These findings not only increase our understanding of the strategies used by DNA glycosylases to repair DNA lesions, but also have important implications for how internal/external electric field can be applied to modulate chemical reactions.
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Affiliation(s)
- Wenwen Diao
- Center for Advanced Materials Research, Beijing Normal University, Zhuhai 519087, China
- Wenzhou Institute, University of Chinese Academy of Sciences, Wenzhou, Zhejiang 325000, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - James D Farrell
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Binju Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Fangfu Ye
- Wenzhou Institute, University of Chinese Academy of Sciences, Wenzhou, Zhejiang 325000, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Oujiang Laboratory (Zhejiang Lab for Regenerative Medicine, Vision and Brain Health), Wenzhou, Zhejiang 325000, China
| | - Zhanfeng Wang
- Center for Advanced Materials Research, Beijing Normal University, Zhuhai 519087, China
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Zhang X, Liu Y. Direct Electrophilic Attack of Compound I on the Indole Ring in the Peroxygenase Mechanism of Dehaloperoxidase DHP B in Degrading Haloindole: Electron Transfer Promotes the Reaction. Inorg Chem 2023; 62:13230-13240. [PMID: 37561650 DOI: 10.1021/acs.inorgchem.3c01425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
The H2O2-dependent degradation of haloindole catalyzed by the dehaloperoxidase (DHP) from Amphitrite ornate has been reported to employ the peroxygenase mechanism, and the two oxidized products 5-halo-2-oxindole and 5-halo-3-oxindole have a similar amount. According to a previous experimental study, compound I (Cpd I) was suggested to be responsible for triggering the reaction, and the reaction may undergo three possible intermediates; however, the reaction details are still unclear. To clarify the reaction mechanism of DHP, the computational model was constructed on the basis of the high-resolution crystal structure, and a series of the quantum mechanical/molecular mechanical calculations were performed. Based on our calculation results, it is confirmed that the reaction starts from the direct electrophilic attack of Cpd I on the indole ring of the substrate, and the resulted intermediate contains both a carbocation and an oxygen anion, whereas the common hydrogen abstraction by Cpd I was calculated to correspond to a relatively higher barrier. In addition, a net electron transfer from the substrate to the iron center is observed during the attack of Cpd I on the indole ring; therefore, the carbocation/oxygen anion intermediate can easily undergo an intramolecular hydride transfer to form the product 5-halo-2-oxindole or isomerize to the epoxide intermediate which finally generates another product 5-halo-3-oxindole. It is the zwitterionic characteristic of the intermediate that makes the intermolecular hydride transfer quite easy, and it is the high electron affinity of the iron center that promotes the single-electron oxidation of the reaction intermediate. Our calculations well explain the formation of two oxidized products 5-halo-2-oxindole and 5-halo-3-oxindole.
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Affiliation(s)
- Xianghui Zhang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Yongjun Liu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
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