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Chatterjee R, Jindal G. Role of mutations in a chemoenzymatic enantiodivergent C(sp 3)-H insertion: exploring the mechanism and origin of stereoselectivity. Chem Sci 2023; 14:8810-8822. [PMID: 37621422 PMCID: PMC10445471 DOI: 10.1039/d3sc02788k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 07/23/2023] [Indexed: 08/26/2023] Open
Abstract
New-to-nature enzymes have emerged as powerful catalysts in recent years for streamlining various stereoselective organic transformations. While synthetic strategies employing engineered enzymes have witnessed proliferating success, there is limited clarity on the mechanistic front and more so when considering molecular-level insights into the role of selected mutations, dramatically escalating catalytic competency and selectivity. We have investigated the mechanism and correlation between mutations and exquisite stereoselectivity of a lactone carbene insertion into the C(sp3)-H bond of substituted aniline, catalyzed by two mutants of a cytochrome P450 variant, "P411" (engineered through directed evolution) in which the axial cysteine has been mutated to serine, utilizing various computational tools. The pivotal role of S264 and L/R328 mutations in the active site has been delineated computationally using two cluster models, thus rationalizing the enantiodivergence. This report provides much-needed insights into the origin of enantiodivergence, furnishing a mechanistic framework for understanding the anchoring effects of H-bond donor residues with the lactone ring. This study is expected to have important implications in the rational design of stereodivergent enzymes and toward successful in silico enzyme designing.
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Affiliation(s)
- Ritwika Chatterjee
- Department of Organic Chemistry, Chemical Sciences Division, Indian Institute of Science Bangalore 560012 India
| | - Garima Jindal
- Department of Organic Chemistry, Chemical Sciences Division, Indian Institute of Science Bangalore 560012 India
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Epping RF, Vesseur D, Zhou M, de Bruin B. Carbene Radicals in Transition-Metal-Catalyzed Reactions. ACS Catal 2023; 13:5428-5448. [PMID: 37123600 PMCID: PMC10127290 DOI: 10.1021/acscatal.3c00591] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 03/21/2023] [Indexed: 04/08/2023]
Abstract
Discovered as organometallic curiosities in the 1970s, carbene radicals have become a staple in modern-day homogeneous catalysis. Carbene radicals exhibit nucleophilic radical-type reactivity orthogonal to classical electrophilic diamagnetic Fischer carbenes. Their successful catalytic application has led to the synthesis of a myriad of carbo- and heterocycles, ranging from simple cyclopropanes to more challenging eight-membered rings. The field has matured to employ densely functionalized chiral porphyrin-based platforms that exhibit high enantio-, regio-, and stereoselectivity. Thus far the focus has largely been on cobalt-based systems, but interest has been growing for the past few years to expand the application of carbene radicals to other transition metals. This Perspective covers the advances made since 2011 and gives an overview on the coordination chemistry, reactivity, and catalytic application of carbene radical species using transition metal complexes and catalysts.
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Affiliation(s)
- Roel F.J. Epping
- Homogeneous, Supramolecular and Bio-Inspired Catalysis Group, van ‘t Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - David Vesseur
- Homogeneous, Supramolecular and Bio-Inspired Catalysis Group, van ‘t Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Minghui Zhou
- Homogeneous, Supramolecular and Bio-Inspired Catalysis Group, van ‘t Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Bas de Bruin
- Homogeneous, Supramolecular and Bio-Inspired Catalysis Group, van ‘t Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
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Hakey BM, Leary DC, Martinez JC, Darmon JM, Akhmedov NG, Petersen JL, Milsmann C. Carbene Transfer from a Pyridine Dipyrrolide Iron–Carbene Complex: Reversible Migration of a Diphenylcarbene Ligand into an Iron–Nitrogen Bond. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00260] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Brett M. Hakey
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Dylan C. Leary
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Jordan C. Martinez
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Jonathan M. Darmon
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Novruz G. Akhmedov
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Jeffrey L. Petersen
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Carsten Milsmann
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
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Stroscio GD, Zhou C, Truhlar DG, Gagliardi L. Multiconfiguration Pair-Density Functional Theory Calculations of Iron(II) Porphyrin: Effects of Hybrid Pair-Density Functionals and Expanded RAS and DMRG Active Spaces on Spin-State Orderings. J Phys Chem A 2022; 126:3957-3963. [PMID: 35674705 DOI: 10.1021/acs.jpca.2c02347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Iron(II) porphyrins play critical roles in enzymes and synthetic catalysts. Computationally determining the spin-state ordering for even the unsubstituted iron(II) porphyrin (FeP) is challenging due to its large size. Multiconfiguration pair-density functional theory (MC-PDFT), a method capable of accurately capturing correlation with lower cost than comparably accurate methods, was previously used to predict a triplet ground state for FeP across a wide range of active spaces up to (34e, 35o). The purpose of this present MC-PDFT study is to determine the effects of including nonlocal exchange in the energy calculation and of using a larger active space size [DMRG(40e, 42o) and RAS(40, 2, 2; 16, 6, 20)] on the calculated FeP spin-state ordering. The recently developed hybrid MC-PDFT method, which uses a weighted average of the MC-PDFT energy and the energy expectation value of the reference wave function, is applied with a weight of the reference wave function energy of λ. We find that increasing λ stabilizes the quintet relative to the triplets. The hybrid tPBE0 functional (tPBE with λ set to 0.25) consistently predicts a triplet ground state with the quintet lying above by 0.10-0.16 eV, depending on the reference wave function. These values are particularly interesting in light of tPBE0's very strong performance for a diverse set of other systems.
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Affiliation(s)
- Gautam D Stroscio
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Pritzker School of Molecular Engineering, James Franck Institute, University of Chicago, Chicago, Illinois 60637-5418, United States.,Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Chen Zhou
- Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, United States
| | - Donald G Truhlar
- Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, United States
| | - Laura Gagliardi
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Pritzker School of Molecular Engineering, James Franck Institute, University of Chicago, Chicago, Illinois 60637-5418, United States.,Argonne National Laboratory, Lemont, Illinois 60439, United States
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5
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Balhara R, Jindal G. Does an Enol Pathway Preclude High Stereoselectivity in Iron-Catalyzed Indole C-H Functionalization via Carbene Insertion? J Org Chem 2022; 87:7919-7933. [PMID: 35652604 DOI: 10.1021/acs.joc.2c00573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
C-H functionalization of indoles via Fe carbenoids presents an attractive strategy to obtain biologically important structural motifs. However, obtaining good stereoselectivity with Fe has been a significant challenge. It is unclear whether the low selectivity is due to a radical pathway or an ionic mechanism involving metal-free species. We therefore present a density functional theory (DFT) study of indole alkylation with diazoacetates catalyzed by Fe(ClO4)TMEDA/spirobisoxazoline and myoglobin. We explore three mechanistic pathways: nucleophilic, radical, and oxocarbenium routes. The nucleophilic pathway is the most feasible with the formation of an enol species that tautomerizes to furnish the alkylated indole. While this mechanism is routinely proposed, the stereochemical model has been conspicuously absent until now. We show that the conventionally invoked enol pathway is not responsible for the low enantiomeric excess. The enol intermediate can stay coordinated to the catalyst via different binding sites placing the enol in proximity to the chiral environment and affecting the stereoselective proton transfer. Both the binding strength and the chiral environment are crucial for obtaining high selectivity. Our study provides the much needed insights for the modest-low selectivities of Fe systems and could help in expediting the discovery of an efficient catalytic system. These mechanistic underpinnings could also be applicable to other metal (Rh, Pd, Cu, etc.)-catalyzed X-H insertion reactions.
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Affiliation(s)
- Reena Balhara
- Department of Organic Chemistry, Indian Institute of Science, Bangalore, Karnataka 560012, India
| | - Garima Jindal
- Department of Organic Chemistry, Indian Institute of Science, Bangalore, Karnataka 560012, India
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Vitillo JG, Cramer CJ, Gagliardi L. Multireference Methods are Realistic and Useful Tools for Modeling Catalysis. Isr J Chem 2022. [DOI: 10.1002/ijch.202100136] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Jenny G. Vitillo
- Department of Science and High Technology and INSTM Università degli Studi dell'Insubria Via Valleggio 9 I-22100 Como Italy
| | - Christopher J. Cramer
- Underwriters Laboratories Inc. 333 Pfingsten Road Northbrook Illinois 60602 United States
| | - Laura Gagliardi
- Department of Chemistry Pritzker School of Molecular Engineering James Franck Institute University of Chicago Chicago Illinois 60637 United States
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7
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Chen X, Cao C, Yang YF, She YB. Computational Insights into Different Regioselectivities in Ir-Porphyrin-Catalyzed C–H Insertion Reaction of Quinoid Carbene. Org Chem Front 2022. [DOI: 10.1039/d1qo01727f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The mechanisms and regioselectivities of Ir-porphyrin-catalyzed C–H insertion reaction of quinoid carbene (QC) were investigated with density functional theory (DFT) calculations. The competing catalytic cycles were identified as the hydrogen-atom...
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Hakey BM, Leary DC, Xiong J, Harris CF, Darmon JM, Petersen JL, Berry JF, Guo Y, Milsmann C. High Magnetic Anisotropy of a Square-Planar Iron-Carbene Complex. Inorg Chem 2021; 60:18575-18588. [PMID: 34431660 PMCID: PMC9106389 DOI: 10.1021/acs.inorgchem.1c01860] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Among Earth-abundant catalyst systems, iron-carbene intermediates that perform C-C bond forming reactions such as cyclopropanation of olefins and C-H functionalization via carbene insertion are rare. Detailed descriptions of the possible electronic structures for iron-carbene bonds are imperative to obtain better mechanistic insights and enable rational catalyst design. Here, we report the first square-planar iron-carbene complex (MesPDPPh)Fe(CPh2), where [MesPDPPh]2- is the doubly deprotonated form of [2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine]. The compound was prepared via reaction of the disubstituted diazoalkane N2CPh2 with (MesPDPPh)Fe(thf) and represents a rare example of a structurally characterized, paramagnetic iron-carbene complex. Temperature-dependent magnetic susceptibility measurements and applied-field Mössbauer spectroscopic studies revealed an orbitally near-degenerate S = 1 ground state with large unquenched orbital angular momentum resulting in high magnetic anisotropy. Spin-Hamiltonian analysis indicated that this S = 1 spin system has uniaxial magnetic properties arising from a ground MS = ±1 non-Kramers doublet that is well-separated from the MS = 0 sublevel due to very large axial zero-field splitting (D = -195 cm-1, E/D = 0.02 estimated from magnetic susceptibility data). This remarkable electronic structure gives rise to a very large, positive magnetic hyperfine field of more than +60 T for the 57Fe nucleus along the easy magnetization axis observed by Mössbauer spectroscopy. Computational analysis with complete active space self-consistent field (CASSCF) calculations provides a detailed electronic structure analysis and confirms that (MesPDPPh)Fe(CPh2) exhibits a multiconfigurational ground state. The majority contribution originates from a configuration best described as a singlet carbene coordinated to an intermediate-spin FeII center with a (dxy)2{(dxz),(dz2)}3(dyz)1(dx2-y2)0 configuration featuring near-degenerate dxz and dz2 orbitals.
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Affiliation(s)
- Brett M Hakey
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Dylan C Leary
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Jin Xiong
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Caleb F Harris
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Jonathan M Darmon
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Jeffrey L Petersen
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - John F Berry
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Yisong Guo
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Carsten Milsmann
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
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9
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Balhara R, Chatterjee R, Jindal G. A computational approach to understand the role of metals and axial ligands in artificial heme enzyme catalyzed C-H insertion. Phys Chem Chem Phys 2021; 23:9500-9511. [PMID: 33885085 DOI: 10.1039/d1cp00412c] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Engineered heme enzymes such as myoglobin and cytochrome P450s metalloproteins are gaining widespread importance due to their efficiency in catalyzing non-natural reactions. In a recent strategy, the naturally occurring Fe metal in the heme unit was replaced with non-native metals such as Ir, Rh, Co, Cu, etc., and axial ligands to generate artificial metalloenzymes. Determining the best metal-ligand for a chemical transformation is not a trivial task. Here we demonstrate how computational approaches can be used in deciding the best metal-ligand combination which would be highly beneficial in designing new enzymes as well as small molecule catalysts. We have used Density Functional Theory (DFT) to shed light on the enhanced reactivity of an Ir system with varying axial ligands. We look at the insertion of a carbene group generated from diazo precursors via N2 extrusion into a C-H bond. For both Ir(Me) and Fe systems, the first step, i.e., N2 extrusion is the rate determining step. Strikingly, neither the better ligand overlap with 5d orbitals on Ir nor the electrophilicity on the carbene centre play a significant role. A comparison of Fe and Ir systems reveals that a lower distortion in the Ir(Me)-porphyrin on moving from the reactant to the transition state renders it catalytically more active. We notice that for both metal porphyrins, the free energy barriers are affected by axial ligand substitution. Further, for Fe porphyrin, the axial ligand also changes the preferred spin state. We show that for the carbene insertion into the C-H bond, Fe porphyrin systems undergo a stepwise HAT (hydrogen atom transfer) instead of a concerted hydride transfer process. Importantly, we find that the substitution of the axial Me ligand on Ir to imidazole or chloride, or without an axial substitution changes the rate determining step of the reaction. Therefore, an optimum ligand that can balance the barriers for both steps of the catalytic cycle is essential. We subsequently used the QM cluster approach to delineate the protein environment's role and mutations in improving the catalytic activity of the Ir(Me) system.
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Affiliation(s)
- Reena Balhara
- Department of Organic Chemistry, Indian Institute of Science, Bangalore 560012, India.
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