1
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Sinner EK, Li R, Marous DR, Townsend CA. ThnL, a B12-dependent radical S-adenosylmethionine enzyme, catalyzes thioether bond formation in carbapenem biosynthesis. Proc Natl Acad Sci U S A 2022; 119:e2206494119. [PMID: 35969793 PMCID: PMC9407657 DOI: 10.1073/pnas.2206494119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 07/19/2022] [Indexed: 11/18/2022] Open
Abstract
Complex carbapenems are important clinical antibiotics used to treat recalcitrant infections. Their biosynthetic gene clusters contain three essential B12-dependent radical S-adenosylmethionine (rSAM) enzymes. The majority of characterized enzymes in this subfamily catalyze methyl transfer, but only one is required to sequentially install all methionine-derived carbons in complex carbapenems. Therefore, it is probable that the other two rSAM enzymes have noncanonical functions. Through a series of fermentation and in vitro experiments, we show that ThnL uses radical SAM chemistry to catalyze thioether bond formation between C2 of a carbapenam precursor and pantetheine, uniting initial bicycle assembly common to all carbapenems with later tailoring events unique to complex carbapenems. ThnL also catalyzes reversible thiol/disulfide redox on pantetheine. Neither of these functions has been observed previously in a B12-dependent radical SAM enzyme. ThnL expands the known activity of this subclass of enzymes beyond carbon-carbon bond formation or rearrangement. It is also the only radical SAM enzyme currently known to catalyze carbon-sulfur bond formation with only an rSAM Fe-S cluster and no additional auxiliary clusters.
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Affiliation(s)
- Erica K. Sinner
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218
| | - Rongfeng Li
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218
| | - Daniel R. Marous
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218
| | - Craig A. Townsend
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218
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2
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Knox HL, Booker SJ. Structural characterization of cobalamin-dependent radical S-adenosylmethionine methylases. Methods Enzymol 2022; 669:3-27. [PMID: 35644177 DOI: 10.1016/bs.mie.2021.12.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Cobalamin-dependent radical S-adenosylmethionine (SAM) methylases catalyze key steps in the biosynthesis of numerous biomolecules, including protein cofactors, antibiotics, herbicides, and other natural products, but have remained a relatively understudied subclass of radical SAM enzymes due to their inherent insolubility upon overproduction in Escherichia coli. These enzymes contain two cofactors: a [4Fe-4S] cluster that is ligated by three cysteine residues, and a cobalamin cofactor typically bound by residues in the N-terminal portion of the enzyme. Recent advances in the expression and purification of these enzymes in their active states and with both cofactors present has allowed for more detailed biochemical studies as well as structure determination by X-ray crystallography. Herein, we use KsTsrM and TokK to highlight methods for the structural characterization of cobalamin-dependent radical SAM (RS) enzymes and describe recent advances in in the overproduction and purification of these enzymes.
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Affiliation(s)
- Hayley L Knox
- The Department of Chemistry, The Pennsylvania State University, University Park, PA, United States
| | - Squire J Booker
- The Department of Chemistry, The Pennsylvania State University, University Park, PA, United States; The Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, United States; The Howard Hughes Medical Institute, The Pennsylvania State University, University Park, PA, United States.
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3
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Sinner E, Marous DR, Townsend CA. Evolution of Methods for the Study of Cobalamin-Dependent Radical SAM Enzymes. ACS BIO & MED CHEM AU 2022; 2:4-10. [PMID: 35341020 PMCID: PMC8950095 DOI: 10.1021/acsbiomedchemau.1c00032] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
While bioinformatic evidence of cobalamin-dependent radical S-adenosylmethionine (SAM) enzymes has existed since the naming of the radical SAM superfamily in 2001, none were biochemically characterized until 2011. In the past decade, the field has flourished as methodological advances have facilitated study of the subfamily. Because of the ingenuity and perseverance of researchers in this field, we now have functional, mechanistic, and structural insight into how this class of enzymes harnesses the power of both the cobalamin and radical SAM cofactors to achieve catalysis. All of the early characterized enzymes in this subfamily were methylases, but the activity of these enzymes has recently been expanded beyond methylation. We anticipate that the characterized functions of these enzymes will become both better understood and increasingly diverse with continued study.
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Affiliation(s)
- Erica
K. Sinner
- Department
of Chemistry, Johns Hopkins University, 3400 N Charles St., Baltimore, Maryland 21218, United States
| | - Daniel R. Marous
- Department
of Chemistry, Wittenberg University, 200 W Ward St., Springfield, Ohio 45504, United States
| | - Craig A. Townsend
- Department
of Chemistry, Johns Hopkins University, 3400 N Charles St., Baltimore, Maryland 21218, United States
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4
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Watkins-Dulaney EJ, Dunham NP, Straathof S, Turi S, Arnold FH, Buller AR. Asymmetric Alkylation of Ketones Catalyzed by Engineered TrpB. Angew Chem Int Ed Engl 2021; 60:21412-21417. [PMID: 34269506 DOI: 10.1002/anie.202106938] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Indexed: 11/12/2022]
Abstract
The β-subunit of tryptophan synthase (TrpB) catalyzes a PLP-mediated β-substitution reaction between indole and serine to form L-Trp. A succession of TrpB protein engineering campaigns to expand the enzyme's nucleophile substrate range has enabled the biocatalytic production of diverse non-canonical amino acids (ncAAs). Here, we show that ketone-derived enolates can serve as nucleophiles in the TrpB reaction to achieve the asymmetric alkylation of ketones, an outstanding challenge in synthetic chemistry. We engineered TrpB by directed evolution to catalyze the asymmetric alkylation of propiophenone and 2-fluoroacetophenone with a high degree of selectivity. In reactions with propiophenone, preference for the opposite product diastereomer emerges over the course of evolution, demonstrating that full control over the stereochemistry at the new chiral center can be achieved. The addition of this new reaction to the TrpB platform is a crucial first step toward the development of efficient methods to synthesize non-canonical prolines and other chirally dense nitrogen heterocycles.
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Affiliation(s)
- Ella J Watkins-Dulaney
- Division of Biology and Biological Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA, 91125, USA
| | - Noah P Dunham
- Division of Chemistry and Chemical Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA, 91125, USA
| | - Sabine Straathof
- Division of Chemistry and Chemical Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA, 91125, USA
| | - Soma Turi
- Division of Chemistry and Chemical Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA, 91125, USA
| | - Frances H Arnold
- Division of Biology and Biological Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA, 91125, USA.,Division of Chemistry and Chemical Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA, 91125, USA
| | - Andrew R Buller
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI, 53706, USA
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5
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Watkins‐Dulaney EJ, Dunham NP, Straathof S, Turi S, Arnold FH, Buller AR. Asymmetric Alkylation of Ketones Catalyzed by Engineered TrpB. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202106938] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Ella J. Watkins‐Dulaney
- Division of Biology and Biological Engineering California Institute of Technology, MC 210-41 1200 E. California Boulevard Pasadena CA 91125 USA
| | - Noah P. Dunham
- Division of Chemistry and Chemical Engineering California Institute of Technology, MC 210-41 1200 E. California Boulevard Pasadena CA 91125 USA
| | - Sabine Straathof
- Division of Chemistry and Chemical Engineering California Institute of Technology, MC 210-41 1200 E. California Boulevard Pasadena CA 91125 USA
| | - Soma Turi
- Division of Chemistry and Chemical Engineering California Institute of Technology, MC 210-41 1200 E. California Boulevard Pasadena CA 91125 USA
| | - Frances H. Arnold
- Division of Biology and Biological Engineering California Institute of Technology, MC 210-41 1200 E. California Boulevard Pasadena CA 91125 USA
- Division of Chemistry and Chemical Engineering California Institute of Technology, MC 210-41 1200 E. California Boulevard Pasadena CA 91125 USA
| | - Andrew R. Buller
- Department of Chemistry University of Wisconsin—Madison 1101 University Avenue Madison WI 53706 USA
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6
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Gracia‐Vitoria J, Osante I, Cativiela C. The Crucial Role of
S
‐oxidation State on the Selectivity and Reaction Rate of the 1,3‐Dipolar Cycloaddition of Azomethine Ylides and Homochiral Thiazolines. European J Org Chem 2021. [DOI: 10.1002/ejoc.202100237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Jaime Gracia‐Vitoria
- Departamento de Química Orgánica Instituto de Síntesis Química y Catálisis Homogénea ISQCH CSIC-Universidad de Zaragoza Calle de Pedro Cerbuna, 12 50009 Zaragoza Spain
| | - Iñaki Osante
- Departamento de Química Orgánica Instituto de Síntesis Química y Catálisis Homogénea ISQCH CSIC-Universidad de Zaragoza Calle de Pedro Cerbuna, 12 50009 Zaragoza Spain
| | - Carlos Cativiela
- Departamento de Química Orgánica Instituto de Síntesis Química y Catálisis Homogénea ISQCH CSIC-Universidad de Zaragoza Calle de Pedro Cerbuna, 12 50009 Zaragoza Spain
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7
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Wei Q, Zeng HC, Zou Y. Divergent Biosynthesis of Fungal Dioxafenestrane Sesquiterpenes by the Cooperation of Distinctive Baeyer–Villiger Monooxygenases and α-Ketoglutarate-Dependent Dioxygenases. ACS Catal 2021. [DOI: 10.1021/acscatal.0c05319] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Qian Wei
- College of Pharmaceutical Sciences, Medical Research Institute, Southwest University, Chongqing 400715, People’s Republic of China
| | - Hai-Chun Zeng
- College of Chemical and Engineering, Chongqing University of Science & Technology, Chongqing 401331, People’s Republic of China
| | - Yi Zou
- College of Pharmaceutical Sciences, Medical Research Institute, Southwest University, Chongqing 400715, People’s Republic of China
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8
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Lin YC, Ribaucourt A, Moazami Y, Pierce JG. Concise Synthesis and Antimicrobial Evaluation of the Guanidinium Alkaloid Batzelladine D: Development of a Stereodivergent Strategy. J Am Chem Soc 2020; 142:9850-9857. [PMID: 32396001 PMCID: PMC7685371 DOI: 10.1021/jacs.0c04091] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Herein, we describe a stereodivergent route to (±)-batzelladine D (2), (+)-batzelladine D (2), (-)-batzelladine D (2), and a series of stereochemical analogues and explore their antimicrobial activity for the first time. The concise synthetic approach enables access to the natural products in a sequence of 8-12 steps from readily available building blocks. Highlights of the synthetic strategy include gram-scale preparation of a late stage intermediate, pinpoint stereocontrol around the tricyclic skeleton, and a modular strategy that enables analogue generation. A key bicyclic β-lactam intermediate not only serves as the key controlling element for pyrrolidine stereochemistry but also serves as a preactivated coupling partner to install the ester side chain. The stereocontrolled synthesis allowed for the investigation of the antimicrobial activity of batzelladine D, demonstrating promising activity that is more potent for non-natural stereoisomers.
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Affiliation(s)
- You-Chen Lin
- Department of Chemistry, College of Sciences, NC State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
- Comparative Medicine Institute, NC State University, Raleigh, North Carolina 27695, United States
| | - Aubert Ribaucourt
- Department of Chemistry, College of Sciences, NC State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Yasamin Moazami
- Department of Chemistry, College of Sciences, NC State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Joshua G Pierce
- Department of Chemistry, College of Sciences, NC State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
- Comparative Medicine Institute, NC State University, Raleigh, North Carolina 27695, United States
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9
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Hamed RB, Gomez-Castellanos JR, Henry L, Warhaut S, Claridge TDW, Schofield CJ. Biocatalytic production of bicyclic β-lactams with three contiguous chiral centres using engineered crotonases. Commun Chem 2019; 2. [PMID: 31157308 PMCID: PMC6542682 DOI: 10.1038/s42004-018-0106-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
There is a need to develop asymmetric routes to functionalised β-lactams, which remain the most important group of antibacterials. Here we describe biocatalytic and protein engineering studies concerning carbapenem biosynthesis enzymes, aiming to enable stereoselective production of functionalised carbapenams with three contiguous chiral centres. Structurally-guided substitutions of wildtype carboxymethylproline synthases enable tuning of their C-N and C-C bond forming capacity to produce 5-carboxymethylproline derivatives substituted at C-4 and C-6, from amino acid aldehyde and malonyl-CoA derivatives. Use of tandem enzyme incubations comprising an engineered carboxymethylproline synthase and an alkylmalonyl-CoA forming enzyme (i.e. malonyl-CoA synthetase or crotonyl-CoA carboxylase reductase) can improve stereocontrol and expand the product range. Some of the prepared 4,6-disubstituted-5-carboxymethylproline derivatives are converted to bicyclic β-lactams by carbapenam synthetase catalysis. The results illustrate the utility of tandem enzyme systems involving engineered crotonases for asymmetric bicyclic β-lactam synthesis. Beta-lactams are important antiobiotics but synthesising functionalised derivatives in high enantiomeric purity can be challenging. Here malonyl-CoA derivatives are applied in an enantioselective multi-enzyme cascade, yielding beta-lactams bearing three contiguous chiral centres in high diastereomeric purity.
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Affiliation(s)
- Refaat B Hamed
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | - J Ruben Gomez-Castellanos
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | - Luc Henry
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | - Sven Warhaut
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | - Timothy D W Claridge
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | - Christopher J Schofield
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
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10
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Synthesis of cis- and trans-(±)-3-mercaptoproline and pipecolic acid derivatives via thio-Michael addition. Tetrahedron Lett 2018. [DOI: 10.1016/j.tetlet.2018.03.057] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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11
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Tichy EM, Hardwick SW, Luisi BF, Salmond GPC. 1.8 Å resolution crystal structure of the carbapenem intrinsic resistance protein CarF. Acta Crystallogr D Struct Biol 2017; 73:549-556. [PMID: 28695855 PMCID: PMC7610886 DOI: 10.1107/s2059798317002236] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2016] [Accepted: 02/09/2017] [Indexed: 11/10/2022] Open
Abstract
The natural production of the β-lactam antibiotic carbapenem in bacteria involves a group of enzymes that form a synthetic pathway as well as proteins that protect the cell from self-intoxification by the products. Here, the crystal structure of CarF, one of the two proteins that confer resistance to synthesis of the antibiotic in the host organism, is reported. The CarF fold places it within a widely occurring structural family, indicating an ancient structural origin from which the resistance function has been derived.
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Affiliation(s)
- Evelyn M. Tichy
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB2 1QW, England
| | - Steven W. Hardwick
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB2 1QW, England
| | - Ben F. Luisi
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB2 1QW, England
| | - George P. C. Salmond
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB2 1QW, England
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12
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δ-(l-α-aminoadipyl)-l-cysteinyl-d-valine synthetase (ACVS): discovery and perspectives. ACTA ACUST UNITED AC 2017; 44:517-524. [DOI: 10.1007/s10295-016-1850-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 10/06/2016] [Indexed: 11/30/2022]
Abstract
Abstract
The δ-(l-α-aminoadipyl)-l-cysteinyl-d-valine (ACV) tripeptide is the first dedicated intermediate in the biosynthetic pathway leading to the penicillin and cephalosporin classes of β-lactam natural products in bacteria and fungi. It is synthesized nonribosomally by the ACV synthetase (ACVS) enzyme, which has been purified and partially characterized from many sources. Due to its large size and instability, many details regarding the reaction mechanism of ACVS are still not fully understood. In this review we discuss the chronology and associated methodology that led to the discovery of ACVS, some of the main findings regarding its activities, and some recent/current studies being conducted on the enzyme. In addition, we conclude with perspectives on what can be done to increase our understating of this very important protein in the future.
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13
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Dunbar KL, Scharf DH, Litomska A, Hertweck C. Enzymatic Carbon-Sulfur Bond Formation in Natural Product Biosynthesis. Chem Rev 2017; 117:5521-5577. [PMID: 28418240 DOI: 10.1021/acs.chemrev.6b00697] [Citation(s) in RCA: 354] [Impact Index Per Article: 50.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Sulfur plays a critical role for the development and maintenance of life on earth, which is reflected by the wealth of primary metabolites, macromolecules, and cofactors bearing this element. Whereas a large body of knowledge has existed for sulfur trafficking in primary metabolism, the secondary metabolism involving sulfur has long been neglected. Yet, diverse sulfur functionalities have a major impact on the biological activities of natural products. Recent research at the genetic, biochemical, and chemical levels has unearthed a broad range of enzymes, sulfur shuttles, and chemical mechanisms for generating carbon-sulfur bonds. This Review will give the first systematic overview on enzymes catalyzing the formation of organosulfur natural products.
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Affiliation(s)
- Kyle L Dunbar
- Department of Biomolecular Chemistry, Leibniz Institute for Natural Product Research and Infection Biology (HKI) , Beutenbergstrasse 11a, 07745 Jena, Germany
| | - Daniel H Scharf
- Life Sciences Institute, University of Michigan , 210 Washtenaw Avenue, Ann Arbor, Michigan 48109-2216, United States
| | - Agnieszka Litomska
- Department of Biomolecular Chemistry, Leibniz Institute for Natural Product Research and Infection Biology (HKI) , Beutenbergstrasse 11a, 07745 Jena, Germany
| | - Christian Hertweck
- Department of Biomolecular Chemistry, Leibniz Institute for Natural Product Research and Infection Biology (HKI) , Beutenbergstrasse 11a, 07745 Jena, Germany.,Friedrich Schiller University , 07743 Jena, Germany
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14
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15
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Hamed RB, Henry L, Claridge TDW, Schofield CJ. Stereoselective Production of Dimethyl-Substituted Carbapenams via Engineered Carbapenem Biosynthesis Enzymes. ACS Catal 2017. [DOI: 10.1021/acscatal.6b02509] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Refaat B. Hamed
- Department
of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
- Department
of Pharmacognosy, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt
| | - Luc Henry
- Department
of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Timothy D. W. Claridge
- Department
of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Christopher J. Schofield
- Department
of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
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16
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Townsend CA. Convergent biosynthetic pathways to β-lactam antibiotics. Curr Opin Chem Biol 2016; 35:97-108. [PMID: 27693891 DOI: 10.1016/j.cbpa.2016.09.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 09/14/2016] [Accepted: 09/15/2016] [Indexed: 02/05/2023]
Abstract
Five naturally-occurring families of β-lactams have inspired a class of drugs that constitute >60% of the antimicrobials used in human medicine. Their biosynthetic pathways reveal highly individualized synthetic strategies that yet converge on a common azetidinone ring assembled in structural contexts that confer selective binding and inhibition of d,d-transpeptidases that play essential roles in bacterial cell wall (peptidoglycan) biosynthesis. These enzymes belong to a single 'clan' of evolutionarily distinct serine hydrolases whose active site geometry and mechanism of action is specifically matched by these antibiotics for inactivation that is kinetically competitive with their native function. Unusual enzyme-mediated reactions and catalytic multitasking in these pathways are discussed with particular attention to the diverse ways the β-lactam itself is generated, and more broadly how the intrinsic reactivity of this core structural element is modulated in natural systems through the introduction of ring strain and electronic effects.
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Affiliation(s)
- Craig A Townsend
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA.
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17
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Ding W, Li Q, Jia Y, Ji X, Qianzhu H, Zhang Q. Emerging Diversity of the Cobalamin-Dependent Methyltransferases Involving Radical-Based Mechanisms. Chembiochem 2016; 17:1191-7. [PMID: 27028019 DOI: 10.1002/cbic.201600107] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Indexed: 11/10/2022]
Abstract
Cobalamins comprise a group of cobalt-containing organometallic cofactors that play important roles in cellular metabolism. Although many cobalamin-dependent methyltransferases (e.g., methionine synthase MetH) have been extensively studied, a new group of methyltransferases that are cobalamin-dependent and utilize radical chemistry in catalysis is just beginning to be appreciated. In this Concept article, we summarize recent advances in the understanding of the radical-based and cobalamin-dependent methyltransferases and discuss the functional and mechanistic diversity of this emerging class of enzymes.
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Affiliation(s)
- Wei Ding
- Key Laboratory of Cell Activities and Stress Adaptations, (Ministry of Education), School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.,Department of Chemistry, Fudan University, Shanghai, 200433, China
| | - Qien Li
- Key Laboratory of Cell Activities and Stress Adaptations, (Ministry of Education), School of Life Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Youli Jia
- Key Laboratory of Cell Activities and Stress Adaptations, (Ministry of Education), School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.,Department of Chemistry, Fudan University, Shanghai, 200433, China
| | - Xinjian Ji
- Department of Chemistry, Fudan University, Shanghai, 200433, China
| | - Haocheng Qianzhu
- Department of Chemistry, Fudan University, Shanghai, 200433, China
| | - Qi Zhang
- Department of Chemistry, Fudan University, Shanghai, 200433, China.
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18
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Hamed RB, Gomez-Castellanos JR, Sean Froese D, Krysztofinska E, Yue WW, Schofield CJ. Use of Methylmalonyl-CoA Epimerase in Enhancing Crotonase Stereoselectivity. Chembiochem 2016; 17:471-3. [DOI: 10.1002/cbic.201500644] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Indexed: 11/11/2022]
Affiliation(s)
- Refaat B. Hamed
- Department of Chemistry; University of Oxford; Chemistry Research Laboratory; Mansfield Road Oxford OX1 3TA UK
- Department of Pharmacognosy, Faculty of Pharmacy; Assiut University; Assiut 71526 Egypt
| | - J. Ruben Gomez-Castellanos
- Department of Chemistry; University of Oxford; Chemistry Research Laboratory; Mansfield Road Oxford OX1 3TA UK
| | - D. Sean Froese
- Structural Genomics Consortium; University of Oxford; Old Road Campus Roosevelt Drive Headington OX3 7DQ UK
| | - Ewelina Krysztofinska
- Structural Genomics Consortium; University of Oxford; Old Road Campus Roosevelt Drive Headington OX3 7DQ UK
| | - Wyatt W. Yue
- Structural Genomics Consortium; University of Oxford; Old Road Campus Roosevelt Drive Headington OX3 7DQ UK
| | - Christopher J. Schofield
- Department of Chemistry; University of Oxford; Chemistry Research Laboratory; Mansfield Road Oxford OX1 3TA UK
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19
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Decuyper L, Piens N, Mincke J, Bomon J, De Schrijver B, Mollet K, De Winter K, Desmet T, D'hooghe M. A nitrilase-mediated entry to 4-carboxymethyl-β-lactams from chemically prepared 4-(cyanomethyl)azetidin-2-ones. RSC Adv 2016. [DOI: 10.1039/c6ra08213k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
4-(Cyanomethyl)azetidin-2-ones were efficiently prepared from 1,2:5,6-di-O-isopropylidene-d-mannitol, followed by a nitrilase-catalyzed hydrolysis to 4-carboxymethyl β-lactams without affecting the sensitive four-membered ring system.
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Affiliation(s)
- Lena Decuyper
- SynBioC Research Group
- Department of Sustainable Organic Chemistry and Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
| | - Nicola Piens
- SynBioC Research Group
- Department of Sustainable Organic Chemistry and Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
| | - Jens Mincke
- SynBioC Research Group
- Department of Sustainable Organic Chemistry and Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
| | - Jeroen Bomon
- SynBioC Research Group
- Department of Sustainable Organic Chemistry and Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
| | - Bert De Schrijver
- SynBioC Research Group
- Department of Sustainable Organic Chemistry and Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
| | - Karen Mollet
- SynBioC Research Group
- Department of Sustainable Organic Chemistry and Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
| | - Karel De Winter
- Department of Biochemical and Microbial Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
- Belgium
| | - Tom Desmet
- Department of Biochemical and Microbial Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
- Belgium
| | - Matthias D'hooghe
- SynBioC Research Group
- Department of Sustainable Organic Chemistry and Technology
- Faculty of Bioscience Engineering
- Ghent University
- B-9000 Ghent
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20
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Ma G, Zhu W, Su H, Cheng N, Liu Y. Uncoupled Epimerization and Desaturation by Carbapenem Synthase: Mechanistic Insights from QM/MM Studies. ACS Catal 2015. [DOI: 10.1021/acscatal.5b01275] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Guangcai Ma
- Key Laboratory
of Colloid
and Interface Chemistry, Ministry of Education, School of Chemistry
and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Wenyou Zhu
- Key Laboratory
of Colloid
and Interface Chemistry, Ministry of Education, School of Chemistry
and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Hao Su
- Key Laboratory
of Colloid
and Interface Chemistry, Ministry of Education, School of Chemistry
and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Na Cheng
- Key Laboratory
of Colloid
and Interface Chemistry, Ministry of Education, School of Chemistry
and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Yongjun Liu
- Key Laboratory
of Colloid
and Interface Chemistry, Ministry of Education, School of Chemistry
and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
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21
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Consecutive radical S-adenosylmethionine methylations form the ethyl side chain in thienamycin biosynthesis. Proc Natl Acad Sci U S A 2015; 112:10354-8. [PMID: 26240322 DOI: 10.1073/pnas.1508615112] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Despite their broad anti-infective utility, the biosynthesis of the paradigm carbapenem antibiotic, thienamycin, remains largely unknown. Apart from the first two steps shared with a simple carbapenem, the pathway sharply diverges to the more structurally complex members of this class of β-lactam antibiotics, such as thienamycin. Existing evidence points to three putative cobalamin-dependent radical S-adenosylmethionine (RS) enzymes, ThnK, ThnL, and ThnP, as potentially being responsible for assembly of the ethyl side chain at C6, bridgehead epimerization at C5, installation of the C2-thioether side chain, and C2/3 desaturation. The C2 substituent has been demonstrated to be derived by stepwise truncation of CoA, but the timing of these events with respect to C2-S bond formation is not known. We show that ThnK of the three apparent cobalamin-dependent RS enzymes performs sequential methylations to build out the C6-ethyl side chain in a stereocontrolled manner. This enzymatic reaction was found to produce expected RS methylase coproducts S-adenosylhomocysteine and 5'-deoxyadenosine, and to require cobalamin. For double methylation to occur, the carbapenam substrate must bear a CoA-derived C2-thioether side chain, implying the activity of a previous sulfur insertion by an as-yet unidentified enzyme. These insights allow refinement of the central steps in complex carbapenem biosynthesis.
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22
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Tichy EM, Luisi BF, Salmond GPC. Crystal structure of the carbapenem intrinsic resistance protein CarG. J Mol Biol 2014; 426:1958-70. [PMID: 24583229 PMCID: PMC4361734 DOI: 10.1016/j.jmb.2014.02.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 02/15/2014] [Accepted: 02/20/2014] [Indexed: 10/25/2022]
Abstract
In the Gram-negative enterobacterium Erwinia (Pectobacterium) and Serratia sp. ATCC 39006, intrinsic resistance to the carbapenem antibiotic 1-carbapen-2-em-3-carboxylic acid is mediated by the CarF and CarG proteins, by an unknown mechanism. Here, we report a high-resolution crystal structure for the Serratia sp. ATCC 39006 carbapenem resistance protein CarG. This structure of CarG is the first in the carbapenem intrinsic resistance (CIR) family of resistance proteins from carbapenem-producing bacteria. The crystal structure shows the protein to form a homodimer, in agreement with results from analytical gel filtration. The structure of CarG does not show homology with any known antibiotic resistance proteins nor does it belong to any well-characterised protein structural family. However, it is a close structural homologue of the bacterial inhibitor of invertebrate lysozyme, PliI-Ah, with some interesting structural variations, including the absence of the catalytic site responsible for lysozyme inhibition. Both proteins show a unique β-sandwich fold with short terminal α-helices. The core of the protein is formed by stacked anti-parallel sheets that are individually very similar in the two proteins but differ in their packing interface, causing the splaying of the two sheets in CarG. Furthermore, a conserved cation binding site identified in CarG is absent from the homologue.
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Affiliation(s)
- E M Tichy
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB21QW, UK
| | - B F Luisi
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB21QW, UK
| | - G P C Salmond
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB21QW, UK
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23
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Li R, Lloyd EP, Moshos KA, Townsend CA. Identification and characterization of the carbapenem MM 4550 and its gene cluster in Streptomyces argenteolus ATCC 11009. Chembiochem 2014; 15:320-31. [PMID: 24420617 PMCID: PMC3972073 DOI: 10.1002/cbic.201300319] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Revised: 10/25/2013] [Indexed: 11/11/2022]
Abstract
Nearly 50 naturally occurring carbapenem β-lactam antibiotics, most produced by Streptomyces, have been identified. The structural diversity of these compounds is limited to variance of the C-2 and C-6 side chains as well as the stereochemistry at C-5/C-6. These structural motifs are of interest both for their antibiotic effects and their biosynthesis. Although the thienamycin gene cluster is the only active gene cluster publically available in this group, more comparative information is needed to understand the genetic basis of these structural differences. We report here the identification of MM 4550, a member of the olivanic acids, as the major carbapenem produced by Streptomyces argenteolus ATCC 11009. Its gene cluster was also identified by degenerate PCR and targeted gene inactivation. Sequence analysis revealed that the genes encoding the biosynthesis of the bicyclic core and the C-6 and C-2 side chains are well conserved in the MM 4550 and thienamycin gene clusters. Three new genes, cmmSu, cmm17 and cmmPah were found in the new cluster, and their putative functions in the sulfonation and epimerization of MM 4550 are proposed. Gene inactivation showed that, in addition to cmmI, two new genes, cmm22 and -23, encode a two-component response system thought to regulate the production of MM 4550. Overexpression of cmmI, cmm22 and cmm23 promoted MM 4550 production in an engineered strain. Finally, the involvement and putative roles of all genes in the MM 4550 cluster are proposed based on the results of bioinformatics analysis, gene inactivation, and analysis of disruption mutants. Overall, the differences between the thienamycin and MM 4550 gene clusters are reflected in characteristic structural elements and provide new insights into the biosynthesis of the complex carbapenems.
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Affiliation(s)
- Rongfeng Li
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218 (USA)
| | - Evan P. Lloyd
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218 (USA)
| | | | - Craig. A Townsend
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218 (USA)
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24
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Phelan RM, Townsend CA. Mechanistic insights into the bifunctional non-heme iron oxygenase carbapenem synthase by active site saturation mutagenesis. J Am Chem Soc 2013; 135:7496-502. [PMID: 23611403 PMCID: PMC3683866 DOI: 10.1021/ja311078s] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The carbapenem class of β-lactam antibiotics is known for its remarkable potency, antibacterial spectrum, and resistance to β-lactamase-mediated inactivation. While the biosynthesis of structurally "complex" carbapenems, such as thienamycin, share initial biochemical steps with carbapenem-3-carboxylate ("simple" carbapenem), the requisite inversion at C5 and formation of the characteristic α,β-unsaturated carboxylate are different in origin between the two groups. Here, we consider carbapenem synthase, a mechanistically distinct bifunctional non-heme iron α-ketoglutarate-dependent enzyme responsible for the terminal reactions, C5 epimerization and desaturation, in simple carbapenem production. Interestingly, this enzyme accepts two stereoisomeric substrates and transforms each to a common active antibiotic. Owing both to enzyme and product instability, resorting to saturation mutagenesis of active site and selected second-sphere residues gave clearly differing profiles of CarC tolerance to structural modification. Guided by a crystal structure and the mutational data, in silico docking was used to suggest the positioning of each disastereomeric substrate in the active site. The two orientations relative to the reactive iron-oxo center are manifest in the two distinct reactions, C5-epimerization and C2/3-desaturation. These observations favor a two-step reaction scheme involving two complete oxidative cycles as opposed to a single catalytic cycle in which an active site tyrosine, Tyr67, after hydrogen donation to achieve bicyclic ring inversion, is further hypothesized to serve as a radical carrier.
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Affiliation(s)
- Ryan M. Phelan
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218
| | - Craig A. Townsend
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218
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25
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Origins of the β-lactam rings in natural products. J Antibiot (Tokyo) 2013; 66:401-10. [DOI: 10.1038/ja.2013.24] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 02/26/2013] [Accepted: 03/05/2013] [Indexed: 11/08/2022]
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26
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Hamed RB, Henry L, Gomez-Castellanos JR, Asghar A, Brem J, Claridge TDW, Schofield CJ. Stereoselective preparation of lipidated carboxymethyl-proline/pipecolic acid derivatives via coupling of engineered crotonases with an alkylmalonyl-CoA synthetase. Org Biomol Chem 2013; 11:8191-6. [DOI: 10.1039/c3ob41525b] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Hamed RB, Gomez-Castellanos JR, Henry L, Ducho C, McDonough MA, Schofield CJ. The enzymes of β-lactam biosynthesis. Nat Prod Rep 2013; 30:21-107. [DOI: 10.1039/c2np20065a] [Citation(s) in RCA: 146] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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28
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Current world literature. Curr Opin Infect Dis 2012; 25:718-28. [PMID: 23147811 DOI: 10.1097/qco.0b013e32835af239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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29
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Insights into fluorometabolite biosynthesis in Streptomyces cattleya DSM46488 through genome sequence and knockout mutants. Bioorg Chem 2012; 44:1-7. [PMID: 22858315 DOI: 10.1016/j.bioorg.2012.06.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Accepted: 06/20/2012] [Indexed: 11/20/2022]
Abstract
Streptomyces cattleya DSM 46488 is unusual in its ability to biosynthesise fluorine containing natural products, where it can produce fluoroacetate and 4-fluorothreonine. The individual enzymes involved in fluorometabolite biosynthesis have already been demonstrated in in vitro investigations. Candidate genes for the individual biosynthetic steps were located from recent genome sequences. In vivo inactivation of individual genes including those encoding the S-adenosyl-l-methionine:fluoride adenosyltransferase (fluorinase, SCATT_41540), 5'-fluoro-5'-deoxyadenosine phosphorylase (SCATT_41550), fluoroacetyl-CoA thioesterase (SCATT_41470), 5-fluoro-5-deoxyribose-1-phosphate isomerase (SCATT_20080) and a 4-fluorothreonine acetaldehyde transaldolase (SCATT_p11780) confirm that they are essential for fluorometabolite production. Notably gene disruption of the transaldolase (SCATT_p11780) resulted in a mutant which could produce fluoroacetate but was blocked in its ability to biosynthesise 4-fluorothreonine, revealing a branchpoint role for the PLP-transaldolase.
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30
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Buller AR, Labonte JW, Freeman MF, Wright NT, Schildbach JF, Townsend CA. Autoproteolytic activation of ThnT results in structural reorganization necessary for substrate binding and catalysis. J Mol Biol 2012; 422:508-18. [PMID: 22706025 PMCID: PMC3428426 DOI: 10.1016/j.jmb.2012.06.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Revised: 06/02/2012] [Accepted: 06/08/2012] [Indexed: 11/01/2022]
Abstract
cis-Autoproteolysis is a post-translational modification necessary for the function of ThnT, an enzyme involved in the biosynthesis of the β-lactam antibiotic thienamycin. This modification generates an N-terminal threonine nucleophile that is used to hydrolyze the pantetheinyl moiety of its natural substrate. We determined the crystal structure of autoactivated ThnT to 1.8Å through X-ray crystallography. Comparison to a mutationally inactivated precursor structure revealed several large conformational rearrangements near the active site. To probe the relevance of these transitions, we designed a pantetheine-like chloromethyl ketone inactivator and co-crystallized it with ThnT. Although this class of inhibitor has been in use for several decades, the mode of inactivation had not been determined for an enzyme that uses an N-terminal nucleophile. The co-crystal structure revealed the chloromethyl ketone bound to the N-terminal nucleophile of ThnT through an ether linkage, and analysis suggests inactivation through a direct displacement mechanism. More importantly, this inactivated complex shows that three regions of ThnT that are critical to the formation of the substrate binding pocket undergo rearrangement upon autoproteolysis. Comparison of ThnT with other autoproteolytic enzymes of disparate evolutionary lineage revealed a high degree of similarity within the proenzyme active site, reflecting shared chemical constraints. However, after autoproteolysis, many enzymes, like ThnT, are observed to rearrange in order to accommodate their specific substrate. We propose that this is a general phenomenon, whereby autoprocessing systems with shared chemistry may possess similar structural features that dissipate upon rearrangement into a mature state.
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Affiliation(s)
- Andrew R. Buller
- Department of Biophysics, The Johns Hopkins University, Baltimore, MD 21218, USA
| | - Jason W. Labonte
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA
| | - Michael F. Freeman
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA
| | - Nathan T. Wright
- Department of Biology, The Johns Hopkins University, Baltimore, MD 21218, USA
| | - Joel F. Schildbach
- Department of Biology, The Johns Hopkins University, Baltimore, MD 21218, USA
| | - Craig A. Townsend
- Department of Biophysics, The Johns Hopkins University, Baltimore, MD 21218, USA
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA
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31
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Labonte JW, Kudo F, Freeman MF, Raber ML, Townsend CA. Engineering the synthetic potential of β-lactam synthetase and the importance of catalytic loop dynamics. MEDCHEMCOMM 2012; 3:960-966. [PMID: 23616913 DOI: 10.1039/c2md00305h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The 2-azetidinone ring of the Class A and D β-lactamase inhibitor clavulanic acid (1) is synthesized by the ATP-utilizing enzyme β-lactam synthetase (βLS). A hydroxyethyl group attached to C-6 of 1 in the (S) configuration markedly enhances the efficacy of this compound against Class C β-lactamases. Guided by a series of X-ray structures of βLS, we have engineered this enzyme to act upon a methylated substrate analogue to give selectively the (3S)-methyl β-lactam core, which, upon closure of the second ring of the bicyclic system of 1, would lead to the (6S)-methylated clavulanic acid derivative.
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Affiliation(s)
- Jason W Labonte
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD, USA. ; Tel: 410 516 7444
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