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Wang TC, Zhang Z, Rao G, Li J, Shirah J, Britt RD, Zhu Q, Yang Y. Threonine Aldolase-Catalyzed Enantioselective α-Alkylation of Amino Acids through Unconventional Photoinduced Radical Initiation. J Am Chem Soc 2024. [PMID: 38961805 DOI: 10.1021/jacs.4c05949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/05/2024]
Abstract
Visible light-driven pyridoxal radical biocatalysis has emerged as a promising strategy for the stereoselective synthesis of valuable noncanonical amino acids (ncAAs). Previously, the use of well-tailored photoredox catalysts represented the key to enable efficient pyridoxal phosphate (PLP) enzyme-catalyzed radical reactions. Here, we report a PLP-dependent threonine aldolase-catalyzed asymmetric α-C-H alkylation of abundant amino acids using Katritzky pyridinium salts as alkylating agents. The use of engineered threonine aldolases allowed for this redox-neutral radical alkylation to proceed efficiently, giving rise to challenging α-trisubstituted and -tetrasubstituted ncAA products in a protecting-group-free fashion with excellent enantiocontrol. Mechanistically, this enantioselective α-alkylation capitalizes on the unique reactivity of the persistent enzymatic quinonoid intermediate derived from the PLP cofactor and the amino acid substrate to allow for novel radical C-C coupling. Surprisingly, this photobiocatalytic process does not require the use of well-established photoredox catalysts and operates through an unconventional photoinduced radical generation involving a PLP-derived aldimine. The ability to develop photobiocatalytic reactions without relying on classic photocatalysts or photoenzymes opens up new avenues for advancing stereoselective intermolecular radical reactions that are not known in either organic chemistry or enzymology.
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Affiliation(s)
- Tian-Ci Wang
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106, United States
| | - Zheng Zhang
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106, United States
| | - Guodong Rao
- Department of Chemistry, University of California Davis, Davis, California 95616, United States
| | - Jiedong Li
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106, United States
| | - Josephine Shirah
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - R David Britt
- Department of Chemistry, University of California Davis, Davis, California 95616, United States
| | - Qilei Zhu
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Yang Yang
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106, United States
- Biomolecular Science and Engineering Program, University of California Santa Barbara, Santa Barbara, California 93106, United States
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2
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Fu H, Hyster TK. From Ground-State to Excited-State Activation Modes: Flavin-Dependent "Ene"-Reductases Catalyzed Non-natural Radical Reactions. Acc Chem Res 2024; 57:1446-1457. [PMID: 38603772 DOI: 10.1021/acs.accounts.4c00129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/13/2024]
Abstract
Enzymes are desired catalysts for chemical synthesis, because they can be engineered to provide unparalleled levels of efficiency and selectivity. Yet, despite the astonishing array of reactions catalyzed by natural enzymes, many reactivity patterns found in small molecule catalysts have no counterpart in the living world. With a detailed understanding of the mechanisms utilized by small molecule catalysts, we can identify existing enzymes with the potential to catalyze reactions that are currently unknown in nature. Over the past eight years, our group has demonstrated that flavin-dependent "ene"-reductases (EREDs) can catalyze various radical-mediated reactions with unparalleled levels of selectivity, solving long-standing challenges in asymmetric synthesis.This Account presents our development of EREDs as general catalysts for asymmetric radical reactions. While we have developed multiple mechanisms for generating radicals within protein active sites, this account will focus on examples where flavin mononucleotide hydroquinone (FMNhq) serves as an electron transfer radical initiator. While our initial mechanistic hypotheses were rooted in electron-transfer-based radical initiation mechanisms commonly used by synthetic organic chemists, we ultimately uncovered emergent mechanisms of radical initiation that are unique to the protein active site. We will begin by covering intramolecular reactions and discussing how the protein activates the substrate for reduction by altering the redox-potential of alkyl halides and templating the charge transfer complex between the substrate and flavin-cofactor. Protein engineering has been used to modify the fundamental photophysics of these reactions, highlighting the opportunity to tune these systems further by using directed evolution. This section highlights the range of coupling partners and radical termination mechanisms available to intramolecular reactions.The next section will focus on intermolecular reactions and the role of enzyme-templated ternary charge transfer complexes among the cofactor, alkyl halide, and coupling partner in gating electron transfer to ensure that it only occurs when both substrates are bound within the protein active site. We will highlight the synthetic applications available to this activation mode, including olefin hydroalkylation, carbohydroxylation, arene functionalization, and nitronate alkylation. This section also discusses how the protein can favor mechanistic steps that are elusive in solution for the asymmetric reductive coupling of alkyl halides and nitroalkanes. We are aware of several recent EREDs-catalyzed photoenzymatic transformations from other groups. We will discuss results from these papers in the context of understanding the nuances of radical initiation with various substrates.These biocatalytic asymmetric radical reactions often complement the state-of-the-art small-molecule-catalyzed reactions, making EREDs a valuable addition to a chemist's synthetic toolbox. Moreover, the underlying principles studied with these systems are potentially operative with other cofactor-dependent proteins, opening the door to different types of enzyme-catalyzed radical reactions. We anticipate that this Account will serve as a guide and inspire broad interest in repurposing existing enzymes to access new transformations.
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Affiliation(s)
- Haigen Fu
- NHC Key Laboratory of Biotechnology for Microbial Drugs, Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100050, China
| | - Todd K Hyster
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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3
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Ju S, Li D, Mai BK, Liu X, Vallota-Eastman A, Wu J, Valentine DL, Liu P, Yang Y. Stereodivergent photobiocatalytic radical cyclization through the repurposing and directed evolution of fatty acid photodecarboxylases. Nat Chem 2024:10.1038/s41557-024-01494-0. [PMID: 38632367 DOI: 10.1038/s41557-024-01494-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 02/28/2024] [Indexed: 04/19/2024]
Abstract
Despite their intriguing photophysical and photochemical activities, naturally occurring photoenzymes have not yet been repurposed for new-to-nature activities. Here we engineered fatty acid photodecarboxylases to catalyse unnatural photoredox radical C-C bond formation by leveraging the strongly oxidizing excited-state flavoquinone cofactor. Through genome mining, rational engineering and directed evolution, we developed a panel of radical photocyclases to facilitate decarboxylative radical cyclization with excellent chemo-, enantio- and diastereoselectivities. Our high-throughput experimental workflow allowed for the directed evolution of fatty acid photodecarboxylases. An orthogonal set of radical photocyclases was engineered to access all four possible stereoisomers of the stereochemical dyad, affording fully diastereo- and enantiodivergent biotransformations in asymmetric radical biocatalysis. Molecular dynamics simulations show that our evolved radical photocyclases allow near-attack conformations to be easily accessed, enabling chemoselective radical cyclization. The development of stereoselective radical photocyclases provides unnatural C-C-bond-forming activities in natural photoenzyme families, which can be used to tame the stereochemistry of free-radical-mediated reactions.
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Affiliation(s)
- Shuyun Ju
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, USA
| | - Dian Li
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, USA
| | - Binh Khanh Mai
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA
| | - Xin Liu
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, USA
| | - Alec Vallota-Eastman
- Interdepartmental Graduate Program for Marine Science, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Jianping Wu
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, USA
| | - David L Valentine
- Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA, USA
- Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Peng Liu
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA.
| | - Yang Yang
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, USA.
- Biomolecular Science and Engineering (BMSE) Program, University of California Santa Barbara, Santa Barbara, CA, USA.
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4
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Liu Y, Bender SG, Sorigue D, Diaz DJ, Ellington AD, Mann G, Allmendinger S, Hyster TK. Asymmetric Synthesis of α-Chloroamides via Photoenzymatic Hydroalkylation of Olefins. J Am Chem Soc 2024; 146:7191-7197. [PMID: 38442365 DOI: 10.1021/jacs.4c00927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
Photoenzymatic intermolecular hydroalkylations of olefins are highly enantioselective for chiral centers formed during radical termination but poorly selective for centers set in the C-C bond-forming event. Here, we report the evolution of a flavin-dependent "ene"-reductase to catalyze the coupling of α,α-dichloroamides with alkenes to afford α-chloroamides in good yield with excellent chemo- and stereoselectivity. These products can serve as linchpins in the synthesis of pharmaceutically valuable motifs. Mechanistic studies indicate that radical formation occurs by exciting a charge-transfer complex templated by the protein. Precise control over the orientation of molecules within the charge-transfer complex potentially accounts for the observed stereoselectivity. The work expands the types of motifs that can be prepared using photoenzymatic catalysis.
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Affiliation(s)
- Yi Liu
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Sophie G Bender
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Damien Sorigue
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
- Aix-Marseille University, CEA, CNRS, Institute of Biosciences and Biotechnologies, BIAM Cadarache, 13108 Saint-Paul-lez-Durance, France
| | - Daniel J Diaz
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
- Institute for Foundations of Machine Learning, University of Texas at Austin, Austin, Texas 78712, United States
| | - Andrew D Ellington
- Department of Molecular Bioscience, University of Texas at Austin, Austin, Texas 78712, United States
| | - Greg Mann
- Novartis Pharm. AG, Basel 4002, Switzerland
| | | | - Todd K Hyster
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
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5
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Zhao H, Zong Y, Sun Y, An G, Wang J. An Organocatalytic System for Z-Alkene Synthesis via a Hydrogen-Bonding-Assisted Photoinduced Electron Donor-Acceptor Complex. Org Lett 2024; 26:1739-1744. [PMID: 38367258 DOI: 10.1021/acs.orglett.4c00433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2024]
Abstract
A general catalytic donor for the combination of a photoinduced electron donor-acceptor (EDA) complex and energy transfer was developed. This mild and metal-free protocol allows facile access to various Z-alkenes. Mechanism studies revealed that the organophotocatalyst, 4-CzIPN, formed a distinct three-component EDA complex with redox-active esters and (C6H5O)2P(O)OH to trigger the photoredox catalysis. The E → Z isomerization was achieved via electron exchange energy transfer from 4-CzIPN.
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Affiliation(s)
- Hui Zhao
- School of Chemistry and Materials Science, Heilongjiang University, Harbin, Heilongjiang 150080, P. R.China
| | - Yingxiao Zong
- Key Laboratory of Hexi Corridor Resources Utilization of Gansu, College of Chemistry and Chemical Engineering, Hexi University, Zhangye, Gansu 734000, P. R. China
| | - Yue Sun
- School of Chemistry and Materials Science, Heilongjiang University, Harbin, Heilongjiang 150080, P. R.China
| | - Guanghui An
- School of Chemistry and Materials Science, Heilongjiang University, Harbin, Heilongjiang 150080, P. R.China
| | - Junke Wang
- Key Laboratory of Hexi Corridor Resources Utilization of Gansu, College of Chemistry and Chemical Engineering, Hexi University, Zhangye, Gansu 734000, P. R. China
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6
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Petchey MR, Ye Y, Spelling V, Finnigan JD, Gittings S, Johansson MJ, Hayes MA, Hyster TK. Regiodivergent Radical Termination for Intermolecular Biocatalytic C-C Bond Formation. J Am Chem Soc 2024; 146:5005-5010. [PMID: 38329236 PMCID: PMC10885151 DOI: 10.1021/jacs.4c00482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 01/24/2024] [Accepted: 01/24/2024] [Indexed: 02/09/2024]
Abstract
Radical hydrofunctionalizations of electronically unbiased dienes are challenging to render regioselective, because the products are nearly identical in energy. Here, we report two engineered FMN-dependent "ene"-reductases (EREDs) that catalyze regiodivergent hydroalkylations of cyclic and linear dienes. While previous studies focused exclusively on the stereoselectivity of alkene hydroalkylation, this work highlights that EREDs can control the regioselectivity of hydrogen atom transfer, providing a method for selectively preparing constitutional isomers that would be challenging to prepare using traditional synthetic methods. Engineering the ERED from Gluconabacter sp. (GluER) furnished a variant that favors the γ,δ-unsaturated ketone, while an engineered variant from a commercial ERED panel favors the δ,ε-unsaturated ketone. The effect of beneficial mutations has been investigated using substrate docking studies and the mechanism probed by isotope labeling experiments. A variety of α-bromo ketones can be coupled with cyclic and linear dienes. These interesting building blocks can also be further modified to generate difficult-to-access heterocyclic compounds.
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Affiliation(s)
- Mark R. Petchey
- Compound
Synthesis and Management, Discovery Sciences,
BioPharma R&D, AstraZeneca,
Pepparedsleden 1, 431 83 Mölndal, Sweden
| | - Yuxuan Ye
- Department
of Chemistry and Chemical Biology, Cornell
University, Ithaca 14850, New York, United States
| | - Victor Spelling
- Early
Chemical Development, Pharmaceutical Sciences, BioPharma R&D, AstraZeneca,
Pepparedsleden 1, 431 83 Mölndal, Sweden
| | - James D. Finnigan
- Prozomix
Ltd., Building 4, West
End Industrial Estate, Haltwhistle NE49 9HA, U.K.
| | - Samantha Gittings
- Prozomix
Ltd., Building 4, West
End Industrial Estate, Haltwhistle NE49 9HA, U.K.
| | - Magnus J. Johansson
- Medicinal
Chemistry, Research and Early Development, Cardiovascular, Renal and
Metabolism (CVRM), BioPharma R&D, AstraZeneca, Pepparedsleden 1, 431 83 Mölndal, Sweden
| | - Martin A. Hayes
- Compound
Synthesis and Management, Discovery Sciences,
BioPharma R&D, AstraZeneca,
Pepparedsleden 1, 431 83 Mölndal, Sweden
| | - Todd K. Hyster
- Department
of Chemistry and Chemical Biology, Cornell
University, Ithaca 14850, New York, United States
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7
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Singh PP, Sinha S, Nainwal P, Singh PK, Srivastava V. Novel applications of photobiocatalysts in chemical transformations. RSC Adv 2024; 14:2590-2601. [PMID: 38226143 PMCID: PMC10788709 DOI: 10.1039/d3ra07371h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Accepted: 12/28/2023] [Indexed: 01/17/2024] Open
Abstract
Photocatalysis has proven to be an effective approach for the production of reactive intermediates under moderate reaction conditions. The possibility for the green synthesis of high-value compounds using the synergy of photocatalysis and biocatalysis, benefiting from the selectivity of enzymes and the reactivity of photocatalysts, has drawn growing interest. Mechanistic investigations, substrate analyses, and photobiocatalytic chemical transformations will all be incorporated in this review. We seek to shed light on upcoming synthetic opportunities in the field by precisely describing mechanistically unique techniques in photobiocatalytic chemistry.
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Affiliation(s)
- Praveen P Singh
- Department of Chemistry, United College of Engineering & Research Prayagraj U. P.-211010 India
| | - Surabhi Sinha
- Department of Chemistry, United College of Engineering & Research Prayagraj U. P.-211010 India
| | - Pankaj Nainwal
- School of Pharmacy, Graphic Era Hill University Dehradun Uttarakhand India
| | - Pravin K Singh
- Department of Chemistry, CMP Degree College, University of Allahabad Prayagraj U. P.-211002 India
| | - Vishal Srivastava
- Department of Chemistry, CMP Degree College, University of Allahabad Prayagraj U. P.-211002 India
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8
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Buller R, Lutz S, Kazlauskas RJ, Snajdrova R, Moore JC, Bornscheuer UT. From nature to industry: Harnessing enzymes for biocatalysis. Science 2023; 382:eadh8615. [PMID: 37995253 DOI: 10.1126/science.adh8615] [Citation(s) in RCA: 26] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 10/17/2023] [Indexed: 11/25/2023]
Abstract
Biocatalysis harnesses enzymes to make valuable products. This green technology is used in countless applications from bench scale to industrial production and allows practitioners to access complex organic molecules, often with fewer synthetic steps and reduced waste. The last decade has seen an explosion in the development of experimental and computational tools to tailor enzymatic properties, equipping enzyme engineers with the ability to create biocatalysts that perform reactions not present in nature. By using (chemo)-enzymatic synthesis routes or orchestrating intricate enzyme cascades, scientists can synthesize elaborate targets ranging from DNA and complex pharmaceuticals to starch made in vitro from CO2-derived methanol. In addition, new chemistries have emerged through the combination of biocatalysis with transition metal catalysis, photocatalysis, and electrocatalysis. This review highlights recent key developments, identifies current limitations, and provides a future prospect for this rapidly developing technology.
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Affiliation(s)
- R Buller
- Competence Center for Biocatalysis, Institute of Chemistry and Biotechnology, Zurich University of Applied Sciences, 8820 Wädenswil, Switzerland
| | - S Lutz
- Codexis Incorporated, Redwood City, CA 94063, USA
| | - R J Kazlauskas
- Department of Biochemistry, Molecular Biology and Biophysics, Biotechnology Institute, University of Minnesota, Saint Paul, MN 55108, USA
| | - R Snajdrova
- Novartis Institutes for BioMedical Research, Global Discovery Chemistry, 4056 Basel, Switzerland
| | - J C Moore
- MRL, Merck & Co., Rahway, NJ 07065, USA
| | - U T Bornscheuer
- Institute of Biochemistry, Dept. of Biotechnology and Enzyme Catalysis, Greifswald University, Greifswald, Germany
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9
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Chen H, Fu W, Yang Y. P450-catalyzed atom transfer radical cyclization. Methods Enzymol 2023; 693:31-49. [PMID: 37977735 DOI: 10.1016/bs.mie.2023.09.007] [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
Cytochromes P450 have been extensively studied for both fundamental enzymology and biotechnological applications. Over the past decade, by taking inspiration from synthetic organic chemistry, new classes of P450-catalyzed reactions that were not previously encountered in the biological world have been developed to address challenging problems in organic chemistry and asymmetric catalysis. In particular, by repurposing and evolving P450 enzymes, stereoselective biocatalytic atom transfer radical cyclization (ATRC) was developed as a new means to impose stereocontrol over transient free radical intermediates. In this chapter, we describe the detailed experimental protocol for the directed evolution of P450 atom transfer radical cyclases. We also delineate protocols for analytical and preparative scale biocatalytic atom transfer radical cyclization processes. These methods will find application in the development of new P450-catalyzed radical reactions, as well as other synthetically useful processes.
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Affiliation(s)
- Heyu Chen
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, United States
| | - Wenzhen Fu
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, United States
| | - Yang Yang
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, United States; Biomolecular Science and Engineering (BMSE) Program, University of California, Santa Barbara, CA, United States.
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10
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Abstract
The ability to site-selectively modify equivalent functional groups in a molecule has the potential to streamline syntheses and increase product yields by lowering step counts. Enzymes catalyze site-selective transformations throughout primary and secondary metabolism, but leveraging this capability for non-native substrates and reactions requires a detailed understanding of the potential and limitations of enzyme catalysis and how these bounds can be extended by protein engineering. In this review, we discuss representative examples of site-selective enzyme catalysis involving functional group manipulation and C-H bond functionalization. We include illustrative examples of native catalysis, but our focus is on cases involving non-native substrates and reactions often using engineered enzymes. We then discuss the use of these enzymes for chemoenzymatic transformations and target-oriented synthesis and conclude with a survey of tools and techniques that could expand the scope of non-native site-selective enzyme catalysis.
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Affiliation(s)
- Dibyendu Mondal
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Harrison M Snodgrass
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Christian A Gomez
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Jared C Lewis
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
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