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Sandoval BA, Clayman PD, Oblinsky DG, Oh S, Nakano Y, Bird M, Scholes GD, Hyster TK. Photoenzymatic Reductions Enabled by Direct Excitation of Flavin-Dependent “Ene”-Reductases. J Am Chem Soc 2020; 143:1735-1739. [DOI: 10.1021/jacs.0c11494] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Kudisch B, Oblinsky DG, Black MJ, Zieleniewska A, Emmanuel MA, Rumbles G, Hyster TK, Scholes GD. Active-Site Environmental Factors Customize the Photophysics of Photoenzymatic Old Yellow Enzymes. J Phys Chem B 2020; 124:11236-11249. [PMID: 33231450 DOI: 10.1021/acs.jpcb.0c09523] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The development of non-natural photoenzymatic systems has reinvigorated the study of photoinduced electron transfer (ET) within protein active sites, providing new and unique platforms for understanding how biological environments affect photochemical processes. In this work, we use ultrafast spectroscopy to compare the photoinduced electron transfer in known photoenzymes. 12-Oxophytodienoate reductase 1 (OPR1) is compared to Old Yellow Enzyme 1 (OYE1) and morphinone reductase (MR). The latter enzymes are structurally homologous to OPR1. We find that slight differences in the amino acid composition of the active sites of these proteins determine their distinct electron-transfer dynamics. Our work suggests that the inside of a protein active site is a complex/heterogeneous dielectric network where genetically programmed heterogeneity near the site of biological ET can significantly affect the presence and lifetime of various intermediate states. Our work motivates additional tunability of Old Yellow Enzyme active-site reorganization energy and electron-transfer energetics that could be leveraged for photoenzymatic redox approaches.
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DeHovitz JS, Loh YY, Kautzky JA, Nagao K, Meichan AJ, Yamauchi M, MacMillan DWC, Hyster TK. Static to inducibly dynamic stereocontrol: The convergent use of racemic β-substituted ketones. Science 2020; 369:1113-1118. [PMID: 32855338 DOI: 10.1126/science.abc9909] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 07/07/2020] [Indexed: 12/16/2022]
Abstract
The synthesis of stereochemically complex molecules in the pharmaceutical and agrochemical industries requires precise control over each distinct stereocenter, a feat that can be challenging and time consuming using traditional asymmetric synthesis. Although stereoconvergent processes have the potential to streamline and simplify synthetic routes, they are currently limited by a narrow scope of inducibly dynamic stereocenters that can be readily epimerized. Here, we report the use of photoredox catalysis to enable the racemization of traditionally static, unreactive stereocenters through the intermediacy of prochiral radical species. This technology was applied in conjunction with biocatalysts such as ketoreductases and aminotransferases to realize stereoconvergent syntheses of stereodefined γ-substituted alcohols and amines from β-substituted ketones.
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Clayman PD, Hyster TK. Photoenzymatic Generation of Unstabilized Alkyl Radicals: An Asymmetric Reductive Cyclization. J Am Chem Soc 2020; 142:15673-15677. [PMID: 32857506 DOI: 10.1021/jacs.0c07918] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Flavin-dependent "ene"-reductases can generate stabilized alkyl radicals when irradiated with visible light; however, they are not known to form unstabilized radicals. Here, we report an enantioselective radical cyclization using alkyl iodides as precursors to unstabilized nucleophilic radicals. Evidence suggests this species is accessed by photoexcitation of a charge-transfer complex that forms between flavin and substrate within the protein active site. Stereoselective delivery of a hydrogen atom from the flavin semiquinone to the prochiral radical formed after cyclization provides high levels of enantioselectivity across a variety of substrates. Overall, this transformation demonstrates that photoenzymatic catalysis can address long-standing selectivity challenges in the radical literature.
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Cao J, Hyster TK. Pyridoxal-Catalyzed Racemization of α-Aminoketones Enables the Stereodivergent Synthesis of 1,2-Amino Alcohols Using Ketoreductases. ACS Catal 2020. [DOI: 10.1021/acscatal.0c01502] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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Nakano Y, Black MJ, Meichan AJ, Sandoval BA, Chung MM, Biegasiewicz KF, Zhu T, Hyster TK. Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using 'Ene'-Reductases with Photoredox Catalysts. Angew Chem Int Ed Engl 2020; 59:10484-10488. [PMID: 32181943 DOI: 10.1002/anie.202003125] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Indexed: 12/20/2022]
Abstract
Flavin-dependent 'ene'-reductases (EREDs) are highly selective catalysts for the asymmetric reduction of activated alkenes. This function is, however, limited to enones, enoates, and nitroalkenes using the native hydride transfer mechanism. Here we demonstrate that EREDs can reduce vinyl pyridines when irradiated with visible light in the presence of a photoredox catalyst. Experimental evidence suggests the reaction proceeds via a radical mechanism where the vinyl pyridine is reduced to the corresponding neutral benzylic radical in solution. DFT calculations reveal this radical to be "dynamically stable", suggesting it is sufficiently long-lived to diffuse into the enzyme active site for stereoselective hydrogen atom transfer. This reduction mechanism is distinct from the native one, highlighting the opportunity to expand the synthetic capabilities of existing enzyme platforms by exploiting new mechanistic models.
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Nakano Y, Black MJ, Meichan AJ, Sandoval BA, Chung MM, Biegasiewicz KF, Zhu T, Hyster TK. Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using ‘Ene’‐Reductases with Photoredox Catalysts. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202003125] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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Biegasiewicz KF, Cooper SJ, Gao X, Oblinsky DG, Kim JH, Garfinkle SE, Joyce LA, Sandoval BA, Scholes GD, Hyster TK. Photoexcitation of flavoenzymes enables a stereoselective radical cyclization. Science 2020; 364:1166-1169. [PMID: 31221855 DOI: 10.1126/science.aaw1143] [Citation(s) in RCA: 193] [Impact Index Per Article: 48.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Accepted: 05/29/2019] [Indexed: 12/21/2022]
Abstract
Photoexcitation is a common strategy for initiating radical reactions in chemical synthesis. We found that photoexcitation of flavin-dependent "ene"-reductases changes their catalytic function, enabling these enzymes to promote an asymmetric radical cyclization. This reactivity enables the construction of five-, six-, seven-, and eight-membered lactams with stereochemical preference conferred by the enzyme active site. After formation of a prochiral radical, the enzyme guides the delivery of a hydrogen atom from flavin-a challenging feat for small-molecule chemical reagents. The initial electron transfer occurs through direct excitation of an electron donor-acceptor complex that forms between the substrate and the reduced flavin cofactor within the enzyme active site. Photoexcitation of promiscuous flavoenzymes has thus furnished a previously unknown biocatalytic reaction.
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Hyster TK. Cluster Preface: Biocatalysis. Synlett 2020. [DOI: 10.1055/s-0039-1691581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Enzymes are valuable catalysts in chemical synthesis because they offer levels of efficiency and product selectivity that surpass what can be achieved using traditional catalytic strategies. This Cluster highlights advances in this important field, highlighting different ways in which biocatalysis can be used in organic chemistry.
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Sandoval BA, Hyster TK. Emerging strategies for expanding the toolbox of enzymes in biocatalysis. Curr Opin Chem Biol 2020; 55:45-51. [PMID: 31935627 DOI: 10.1016/j.cbpa.2019.12.006] [Citation(s) in RCA: 62] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 12/12/2019] [Accepted: 12/13/2019] [Indexed: 11/30/2022]
Abstract
Expanding the repertoire of reactions available to enzymes is an enduring challenge in biocatalysis. Owing to the synthetic versatility of transition metals, metalloenzymes have been favored targets for achieving new catalytic functions. Although less well explored, enzymes lacking metal centers can also be effective catalysts for non-natural reactions, providing access to reaction modalities that compliment those available to metals. By understanding how these activation modes can reveal new functions, strategies can be developed to access novel biocatalytic reactions. This review will cover discoveries in the last two years which access catalytic reactions that go beyond the native repertoire of metal-free biocatalysts.
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Sandoval BA, Kurtoic SI, Chung MM, Biegasiewicz KF, Hyster TK. Photoenzymatic Catalysis Enables Radical-Mediated Ketone Reduction in Ene-Reductases. Angew Chem Int Ed Engl 2019; 58:8714-8718. [PMID: 30951226 DOI: 10.1002/anie.201902005] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 03/22/2019] [Indexed: 11/12/2022]
Abstract
Flavin-dependent ene-reductases (EREDs) are known to stereoselectively reduce activated alkenes, but are inactive toward carbonyls. Demonstrated here is that in the presence of photoredox catalysts, these enzymes will reduce aromatic ketones. Mechanistic experiments suggest this reaction proceeds through ketyl radical formation, a reaction pathway that is distinct from the native hydride-transfer mechanism. Furthermore, this reactivity is accessible without modification of either the enzyme or cofactors, allowing both native and non-natural mechanisms to occur simultaneously. Based on control experiments, we hypothesize that binding to the enzyme active site attenuates the reduction potential of the substrate, enabling single-electron reduction. This reactivity highlights opportunities to access new catalytic manifolds by merging photoredox catalysis with biocatalysis.
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Sandoval BA, Kurtoic SI, Chung MM, Biegasiewicz KF, Hyster TK. Photoenzymatic Catalysis Enables Radical‐Mediated Ketone Reduction in Ene‐Reductases. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201902005] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Hyster TK, Dalton DM, Rovis T. Correction: Ligand design for Rh(iii)-catalyzed C-H activation: an unsymmetrical cyclopentadienyl group enables a regioselective synthesis of dihydroisoquinolones. Chem Sci 2018; 9:8024. [PMID: 30542552 PMCID: PMC6249631 DOI: 10.1039/c8sc90195c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Accepted: 09/24/2018] [Indexed: 12/03/2022] Open
Abstract
Correction for ‘Ligand design for Rh(iii)-catalyzed C–H activation: an unsymmetrical cyclopentadienyl group enables a regioselective synthesis of dihydroisoquinolones’ by Todd K. Hyster et al., Chem. Sci., 2015, 6, 254–258.
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Sandoval BA, Meichan AJ, Hyster TK. Enantioselective Hydrogen Atom Transfer: Discovery of Catalytic Promiscuity in Flavin-Dependent 'Ene'-Reductases. J Am Chem Soc 2017; 139:11313-11316. [PMID: 28780870 DOI: 10.1021/jacs.7b05468] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Flavin has long been known to function as a single electron reductant in biological settings, but this reactivity has rarely been observed with flavoproteins used in organic synthesis. Here we describe the discovery of an enantioselective radical dehalogenation pathway for α-bromoesters using flavin-dependent 'ene'-reductases. Mechanistic experiments support the role of flavin hydroquinone as a single electron reductant, flavin semiquinone as the hydrogen atom source, and the enzyme as the source of chirality.
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Emmanuel MA, Greenberg NR, Oblinsky DG, Hyster TK. Accessing non-natural reactivity by irradiating nicotinamide-dependent enzymes with light. Nature 2017; 540:414-417. [PMID: 27974767 DOI: 10.1038/nature20569] [Citation(s) in RCA: 207] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 10/14/2016] [Indexed: 12/25/2022]
Abstract
Enzymes are ideal for use in asymmetric catalysis by the chemical industry, because their chemical compositions can be tailored to a specific substrate and selectivity pattern while providing efficiencies and selectivities that surpass those of classical synthetic methods. However, enzymes are limited to reactions that are found in nature and, as such, facilitate fewer types of transformation than do other forms of catalysis. Thus, a longstanding challenge in the field of biologically mediated catalysis has been to develop enzymes with new catalytic functions. Here we describe a method for achieving catalytic promiscuity that uses the photoexcited state of nicotinamide co-factors (molecules that assist enzyme-mediated catalysis). Under irradiation with visible light, the nicotinamide-dependent enzyme known as ketoreductase can be transformed from a carbonyl reductase into an initiator of radical species and a chiral source of hydrogen atoms. We demonstrate this new reactivity through a highly enantioselective radical dehalogenation of lactones-a challenging transformation for small-molecule catalysts. Mechanistic experiments support the theory that a radical species acts as an intermediate in this reaction, with NADH and NADPH (the reduced forms of nicotinamide adenine nucleotide and nicotinamide adenine dinucleotide phosphate, respectively) serving as both a photoreductant and the source of hydrogen atoms. To our knowledge, this method represents the first example of photo-induced enzyme promiscuity, and highlights the potential for accessing new reactivity from existing enzymes simply by using the excited states of common biological co-factors. This represents a departure from existing light-driven biocatalytic techniques, which are typically explored in the context of co-factor regeneration.
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Hyster TK, Dalton DM, Rovis T. Correction: Ligand design for Rh(iii)-catalyzed C-H activation: an unsymmetrical cyclopentadienyl group enables a regioselective synthesis of dihydroisoquinolones. Chem Sci 2017; 8:1666. [PMID: 30123475 PMCID: PMC6063143 DOI: 10.1039/c6sc90080a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 12/06/2016] [Indexed: 11/21/2022] Open
Abstract
Correction for ‘Ligand design for Rh(iii)-catalyzed C–H activation: an unsymmetrical cyclopentadienyl group enables a regioselective synthesis of dihydroisoquinolones’ by Todd K. Hyster et al., Chem. Sci., 2015, 6, 254–258.
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Hyster TK, Ward TR. Genetische Optimierung von Metalloenzymen: Weiterentwicklung von Enzymen für nichtnatürliche Reaktionen. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201508816] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Hyster TK, Ward TR. Genetic Optimization of Metalloenzymes: Enhancing Enzymes for Non-Natural Reactions. Angew Chem Int Ed Engl 2016; 55:7344-57. [PMID: 26971363 DOI: 10.1002/anie.201508816] [Citation(s) in RCA: 119] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2015] [Indexed: 12/30/2022]
Abstract
Artificial metalloenzymes have received increasing attention over the last decade as a possible solution to unaddressed challenges in synthetic organic chemistry. Whereas traditional transition-metal catalysts typically only take advantage of the first coordination sphere to control reactivity and selectivity, artificial metalloenzymes can modulate both the first and second coordination spheres. This difference can manifest itself in reactivity profiles that can be truly unique to artificial metalloenzymes. This Review summarizes attempts to modulate the second coordination sphere of artificial metalloenzymes by using genetic modifications of the protein sequence. In doing so, successful attempts and creative solutions to address the challenges encountered are highlighted.
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Prier CK, Hyster TK, Farwell CC, Huang A, Arnold FH. Asymmetric Enzymatic Synthesis of Allylic Amines: A Sigmatropic Rearrangement Strategy. Angew Chem Int Ed Engl 2016; 55:4711-5. [PMID: 26970325 DOI: 10.1002/anie.201601056] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Indexed: 11/12/2022]
Abstract
Sigmatropic rearrangements, while rare in biology, offer opportunities for the efficient and selective synthesis of complex chemical motifs. A "P411" serine-ligated variant of cytochrome P450(BM3) has been engineered to initiate a sulfimidation/[2,3]-sigmatropic rearrangement sequence in whole E. coli cells, a non-natural function for any enzyme, providing access to enantioenriched, protected allylic amines. Five mutations in the enzyme substantially enhance its activity toward this new function, demonstrating the evolvability of the catalyst toward challenging nitrene transfer reactions. The evolved catalyst additionally performs the highly enantioselective imidation of non-allylic sulfides.
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Prier CK, Hyster TK, Farwell CC, Huang A, Arnold FH. Asymmetric Enzymatic Synthesis of Allylic Amines: A Sigmatropic Rearrangement Strategy. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201601056] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Farwell C, Zhang RK, McIntosh JA, Hyster TK, Arnold FH. Enantioselective Enzyme-Catalyzed Aziridination Enabled by Active-Site Evolution of a Cytochrome P450. ACS CENTRAL SCIENCE 2015; 1:89-93. [PMID: 26405689 PMCID: PMC4571169 DOI: 10.1021/acscentsci.5b00056] [Citation(s) in RCA: 126] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Indexed: 05/21/2023]
Abstract
One of the greatest challenges in protein design is creating new enzymes, something evolution does all the time, starting from existing ones. Borrowing from nature's evolutionary strategy, we have engineered a bacterial cytochrome P450 to catalyze highly enantioselective intermolecular aziridination, a synthetically useful reaction that has no natural biological counterpart. The new enzyme is fully genetically encoded, functions in vitro or in whole cells, and can be optimized rapidly to exhibit high enantioselectivity (up to 99% ee) and productivity (up to 1,000 catalytic turnovers) for intermolecular aziridination, demonstrated here with tosyl azide and substituted styrenes. This new aziridination activity highlights the remarkable ability of a natural enzyme to adapt and take on new functions. Once discovered in an evolvable enzyme, this non-natural activity was improved and its selectivity tuned through an evolutionary process of accumulating beneficial mutations.
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Hyster TK, Rovis T. Correction: Pyridine synthesis from oximes and alkynes via rhodium(iii) catalysis: Cp* and Cpt provide complementary selectivity. Chem Commun (Camb) 2015; 51:5778. [DOI: 10.1039/c5cc90120k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Correction for ‘Pyridine synthesis from oximes and alkynes via rhodium(iii) catalysis: Cp* and Cpt provide complementary selectivity’ by Todd K. Hyster et al., Chem. Commun., 2011, 47, 11846–11848.
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Hyster TK, Dalton DM, Rovis T. Ligand Design for Rh(III)-Catalyzed C-H Activation: An Unsymmetrical Cyclopentadienyl Enables a Regioselective Synthesis of Dihydroisoquinolones. Chem Sci 2015; 6:254-258. [PMID: 25489470 PMCID: PMC4256080 DOI: 10.1039/c4sc02590c] [Citation(s) in RCA: 113] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Accepted: 09/22/2014] [Indexed: 12/21/2022] Open
Abstract
We report the regioselective synthesis of dihydroisoquinolones from aliphatic alkenes and O-pivaloyl benzhydroxamic acids mediated by a Rh(III) precatalyst bearing sterically bulky substituents. While the prototypical Cp* ligand provides product with low selectivity, sterically bulky Cpt affords product with excellent regioselectivity for a range of benzhydroxamic acids and alkenes. Crystallographic evidence offers insight as to the source of the increased regioselectivity.
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Hyster TK, Farwell CC, Buller AR, McIntosh JA, Arnold FH. Enzyme-controlled nitrogen-atom transfer enables regiodivergent C-H amination. J Am Chem Soc 2014; 136:15505-8. [PMID: 25325618 PMCID: PMC4227740 DOI: 10.1021/ja509308v] [Citation(s) in RCA: 124] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2014] [Indexed: 12/18/2022]
Abstract
We recently demonstrated that variants of cytochrome P450BM3 (CYP102A1) catalyze the insertion of nitrogen species into benzylic C-H bonds to form new C-N bonds. An outstanding challenge in the field of C-H amination is catalyst-controlled regioselectivity. Here, we report two engineered variants of P450BM3 that provide divergent regioselectivity for C-H amination-one favoring amination of benzylic C-H bonds and the other favoring homo-benzylic C-H bonds. The two variants provide nearly identical kinetic isotope effect values (2.8-3.0), suggesting that C-H abstraction is rate-limiting. The 2.66-Å crystal structure of the most active enzyme suggests that the engineered active site can preorganize the substrate for reactivity. We hypothesize that the enzyme controls regioselectivity through localization of a single C-H bond close to the iron nitrenoid.
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