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Abstract
Oxidative cyclizations are important transformations that occur widely during natural product biosynthesis. The transformations from acyclic precursors to cyclized products can afford morphed scaffolds, structural rigidity, and biological activities. Some of the most dramatic structural alterations in natural product biosynthesis occur through oxidative cyclization. In this Review, we examine the different strategies used by nature to create new intra(inter)molecular bonds via redox chemistry. This Review will cover both oxidation- and reduction-enabled cyclization mechanisms, with an emphasis on the former. Radical cyclizations catalyzed by P450, nonheme iron, α-KG-dependent oxygenases, and radical SAM enzymes are discussed to illustrate the use of molecular oxygen and S-adenosylmethionine to forge new bonds at unactivated sites via one-electron manifolds. Nonradical cyclizations catalyzed by flavin-dependent monooxygenases and NAD(P)H-dependent reductases are covered to show the use of two-electron manifolds in initiating cyclization reactions. The oxidative installations of epoxides and halogens into acyclic scaffolds to drive subsequent cyclizations are separately discussed as examples of "disappearing" reactive handles. Last, oxidative rearrangement of rings systems, including contractions and expansions, will be covered.
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Affiliation(s)
- Man-Cheng Tang
- Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095, USA
| | - Yi Zou
- Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095, USA
| | - Kenji Watanabe
- Department of Pharmaceutical Sciences, University of Shizuoka, Shizuoka 422-8526, Japan
| | - Christopher T. Walsh
- Stanford University Chemistry, Engineering, and Medicine for Human Health (ChEM-H), Stanford University, 443 Via Ortega, Stanford, CA 94305
| | - Yi Tang
- Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095, USA
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2
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Abstract
In this viewpoint highlights are drawn from a deep analysis of the multifaceted problem of aflatoxin biosynthesis, one of the most highly rearranged polyketide natural products known. Fundamental chemical insights have emerged into how cytochrome P450-mediated skeletal rearrangements occur through probable cationic intermediates and oxidative dearomatizations, which are applicable more widely in natural product catabolism. So to where current experimental methods have failed in our hands, bioinformatic tools and fresh experimental strategies have been developed to identify linker regions in large, polydomain proteins and guide the dissection and reassembly of their component parts. It has been possible to deduce individual catalytic roles, how overall synthesis is coordinated and how these enzymes can be re-engineered in a rational manner to prepare non-natural products. These insights and innovations were often not planned or anticipated, but sprung from the inability to answer fundamental questions. Advances in science can take place by chance favoring the prepared mind, other times by refusing to give up and devising new solutions to address hard questions. Both ways forward played important roles in the investigation of aflatoxin biosynthesis. For these contributions I am pleased to share this special issue of NPR with John Vederas and Tom Simpson, who have been leaders in this field for the last third of a century.
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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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3
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Methods for the Synthesis and Modification of Linear Anthrafurandiones (Review). Chem Heterocycl Compd (N Y) 2014. [DOI: 10.1007/s10593-014-1459-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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4
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Abstract
Oxidative rearrangements are key reactions during the biosyntheses of many secondary metabolites in fungi.
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Affiliation(s)
- Russell Cox
- Institute for Organic Chemistry
- Leibniz University of Hannover
- 30167 Hannover, Germany
- School of Chemistry
- University of Bristol
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5
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Song ZL, Fan CA, Tu YQ. Semipinacol Rearrangement in Natural Product Synthesis. Chem Rev 2011; 111:7523-56. [PMID: 21851053 DOI: 10.1021/cr200055g] [Citation(s) in RCA: 385] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Zhen-Lei Song
- Key Laboratory of Drug-Targeting of Education Ministry and Department of Medicinal Chemistry, West China School of Pharmacy, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, P. R. China
- State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. China
| | - Chun-An Fan
- State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. China
| | - Yong-Qiang Tu
- State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. China
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6
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Expeditious Synthesis of Hippuristanol and Congeners with Potent Antiproliferative Activities. Chemistry 2009; 15:10356-9. [DOI: 10.1002/chem.200901732] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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7
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Ehrlich KC. Predicted roles of the uncharacterized clustered genes in aflatoxin biosynthesis. Toxins (Basel) 2009; 1:37-58. [PMID: 22069531 PMCID: PMC3202775 DOI: 10.3390/toxins1010037] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2009] [Revised: 09/22/2009] [Accepted: 09/24/2009] [Indexed: 11/21/2022] Open
Abstract
Biosynthesis of the toxic and carcinogenic aflatoxins (AFs) requires the activity of more than 27 enzymes. The roles in biosynthesis of newly described enzymes are discussed in this review. We suggest that HypC catalyzes the oxidation of norsolorinic acid anthrone; AvfA (AflI), the ring-closure step in formation of hydroxyversicolorone; HypB, the second oxidation step in conversion of O-methylsterigmatocystin to AF; and HypE and NorA (AflE), the final two steps in AFB(1) formation. HypD, an integral membrane protein, affects fungal development and lowers AF production while AflJ (AflS), has a partial methyltransferase domain that may be important in its function as a transcriptional co-activator.
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Affiliation(s)
- Kenneth C Ehrlich
- Southern Regional Research Center, ARS, USDA/1100 Robert E. Lee Blvd, New Orleans, LA 70124, USA.
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8
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Shchekotikhin AE, Luzikov YN, Buyanov VN, Preobrazhenskaya MN. Heterocyclic analogs of 5,12-naphthacenequinone 8.* Synthesis of furano-anthraquinones. Chem Heterocycl Compd (N Y) 2009. [DOI: 10.1007/s10593-009-0244-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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9
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Pontius A, Krick A, Kehraus S, Brun R, König GM. Antiprotozoal activities of heterocyclic-substituted xanthones from the marine-derived fungus Chaetomium sp. JOURNAL OF NATURAL PRODUCTS 2008; 71:1579-1584. [PMID: 18683985 DOI: 10.1021/np800294q] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Investigations of the marine-derived fungus Chaetomium sp. led to the isolation of the new natural products chaetoxanthones A, B, and C (1-3). Compounds 1 and 2 are substituted with a dioxane/tetrahydropyran moiety rarely found in natural products. Compound 3 was identified as a chlorinated xanthone substituted with a tetrahydropyran ring. The configurational analysis of these compounds employed CD spectroscopy, modified Mosher's method, and selective NOE gradient measurements. Compound 2 showed selective activity against Plasmodium falciparum with an IC50 value of 0.5 microg/mL without being cytotoxic toward cultured eukaryotic cells. Compound 3 displayed a moderate activity against Trypanosoma cruzi with an IC50 value of 1.5 microg/mL.
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Affiliation(s)
- Alexander Pontius
- Institute for Pharmaceutical Biology, University of Bonn, Nussallee 6, 53115 Bonn, Germany
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10
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Bérard D, Giroux MA, Racicot L, Sabot C, Canesi S. Intriguing formal [2+3] cycloaddition promoted by a hypervalent iodine reagent. Tetrahedron 2008. [DOI: 10.1016/j.tet.2008.05.114] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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11
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Shchekotikhin AE, Shevtsova EK, Traven’ VF. Synthesis and fluorescence of anthra[2,3-b]furan-5,10-dione derivatives. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY 2007. [DOI: 10.1134/s1070428007110164] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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12
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Henry KM, Townsend CA. Synthesis and fate of o-carboxybenzophenones in the biosynthesis of aflatoxin. J Am Chem Soc 2005; 127:3300-9. [PMID: 15755146 DOI: 10.1021/ja045520z] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
o-Carboxybenzophenones have long been postulated to be intermediates in the oxidative rearrangement of anthraquinone natural products to xanthones in vivo. Many of these Baeyer-Villiger-like cleavages are believed to be carried out by cytochrome P450 enzymes. In the biosynthesis of the fungal carcinogen, aflatoxin, six cytochromes P450 are encoded by the biosynthetic gene cluster. One of these, AflN, is known to be involved in the conversion of the anthraquinone versicolorin A (3) to the xanthone demethylsterigmatocystin (5) en route to the mycotoxin. An aryl deoxygenation, however, also takes place in this overall transformation and is proposed to be due to the requirement that an NADPH-dependent oxidoreductase, AflM, be active for this process to take place. What is known about other fungal anthraquinone --> xanthone conversions is reviewed, notably, the role of the o-carboxybenzophenone sulochrin (25) in geodin (26) biosynthesis. On the basis of mutagenesis experiments in the aflatoxin pathway and these biochemical precedents, total syntheses of a tetrahydroxy-o-carboxybenzophenone bearing a fused tetrahydrobisfuran and its 15-deoxy homologue are described. The key steps of the syntheses entail rearrangement of a 1,2-disubstituted alkene bearing an electron-rich benzene ring under Kikuchi conditions to give the 2-aryl aldehyde 43 followed by silyltriflate closure to a differentially protected dihydrobenzofuran 44. Regiospecific bromination, conversion to the substituted benzoic acid, and condensation with an o-bromobenzyl alcohol gave esters 47 and 50. The latter could be rearranged with strong base, oxidized, and deprotected to the desired o-carboxybenzophenones. These potential biosynthetic intermediates were examined in whole-cell and ground-cell experiments for their ability to support aflatoxin formation in the blocked mutant DIS-1, defective in its ability to synthesize the first intermediate in the pathway, norsolorinic acid. Against expectation, neither of these compounds was converted into aflatoxin under conditions where the anthraquinones versicolorin A and B readily afforded aflatoxins B1 and B2. This outcome is evaluated further in a companion paper appearing later in this journal.
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Affiliation(s)
- Kevin M Henry
- Department of Chemistry, The Johns Hopkins University, Charles and 34th Streets, Baltimore, Maryland 21218, USA
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13
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Kaiser F, Schwink L, Velder J, Schmalz HG. Studies towards the total synthesis of mumbaistatin: synthesis of highly substituted benzophenone and anthraquinone building blocks. Tetrahedron 2003. [DOI: 10.1016/s0040-4020(03)00427-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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14
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Yabe K, Chihaya N, Hamamatsu S, Sakuno E, Hamasaki T, Nakajima H, Bennett JW. Enzymatic conversion of averufin to hydroxyversicolorone and elucidation of a novel metabolic grid involved in aflatoxin biosynthesis. Appl Environ Microbiol 2003; 69:66-73. [PMID: 12513978 PMCID: PMC152417 DOI: 10.1128/aem.69.1.66-73.2003] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The pathway from averufin (AVR) to versiconal hemiacetal acetate (VHA) in aflatoxin biosynthesis was investigated by using cell-free enzyme systems prepared from Aspergillus parasiticus. When (1'S,5'S)-AVR was incubated with a cell extract of this fungus in the presence of NADPH, versicolorin A and versicolorin B (VB), as well as other aflatoxin pathway intermediates, were formed. When the same substrate was incubated with the microsome fraction and NADPH, hydroxyversicolorone (HVN) and VHA were formed. However, (1'R,5'R)-AVR did not serve as the substrate. In cell-free experiments performed with the cytosol fraction and NADPH, VHA, versicolorone (VONE), and versiconol acetate (VOAc) were transiently produced from HVN in the early phase, and then VB and versiconol (VOH) accumulated later. Addition of dichlorvos (dimethyl 2,2-dichlorovinylphosphate) to the same reaction mixture caused transient formation of VHA and VONE, followed by accumulation of VOAc, but neither VB nor VOH was formed. When VONE was incubated with the cytosol fraction in the presence of NADPH, VOAc and VOH were newly formed, whereas the conversion of VOAc to VOH was inhibited by dichlorvos. The purified VHA reductase, which was previously reported to catalyze the reaction from VHA to VOAc, also catalyzed conversion of HVN to VONE. Separate feeding experiments performed with A. parasiticus NIAH-26 along with HVN, VONE, and versicolorol (VOROL) demonstrated that each of these substances could serve as a precursor of aflatoxins. Remarkably, we found that VONE and VOROL had ring-opened structures. Their molecular masses were 386 and 388 Da, respectively, which were 18 Da greater than the molecular masses previously reported. These data demonstrated that two kinds of reactions are involved in the pathway from AVR to VHA in aflatoxin biosynthesis: (i) a reaction from (1'S,5'S)-AVR to HVN, catalyzed by the microsomal enzyme, and (ii) a new metabolic grid, catalyzed by a new cytosol monooxygenase enzyme and the previously reported VHA reductase enzyme, composed of HVN, VONE, VOAc, and VHA. A novel hydrogenation-dehydrogenation reaction between VONE and VOROL was also discovered.
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Affiliation(s)
- Kimiko Yabe
- National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan.
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15
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Kaiser F, Schwink L, Velder J, Schmalz HG. Studies toward the total synthesis of mumbaistatin, a highly potent glucose-6-phosphate translocase inhibitor. Synthesis of a mumbaistatin analogue. J Org Chem 2002; 67:9248-56. [PMID: 12492326 DOI: 10.1021/jo026232t] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A strategy for the total synthesis of the highly potent glucose-6-phosphate translocase inhibitor mumbaistatin (1) and structural analogues was elaborated. Such compounds represent a lead structure in the development of potential new drugs for the treatment of diabetes. To evaluate the general strategy, the close mumbaistatin analogue 10 was synthesized in a convergent manner. The anthraquinone building block 20 was efficiently prepared via aryne/phthalide annulation. After conversion of 20 into the corresponding 9,10-dimethoxyanthracene-1-carbaldehyde derivative (13), coupling with a lithiated arene (12) and subsequent multiple oxidation under Jones conditions yielded the mumbaistatin analogue 10. The preparation of the functionalized arene intermediates was achieved exploiting highly regioselective bromination and ortho-lithiation reactions.
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Affiliation(s)
- Florian Kaiser
- Institut für Organische Chemie, Universität zu Köln, Greinstrasse 4, D-50939 Köln, Germany
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16
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Graybill TL, Casillas EG, Pal K, Townsend CA. Silyl Triflate-Mediated Ring-Closure and Rearrangement in the Synthesis of Potential Bisfuran-Containing Intermediates of Aflatoxin Biosynthesis. J Am Chem Soc 1999. [DOI: 10.1021/ja990591x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Todd L. Graybill
- Contribution from the Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218
| | - Eduard G. Casillas
- Contribution from the Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218
| | - Kollol Pal
- Contribution from the Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218
| | - Craig A. Townsend
- Contribution from the Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218
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17
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Minto RE, Townsend CA. Enzymology and Molecular Biology of Aflatoxin Biosynthesis. Chem Rev 1997; 97:2537-2556. [PMID: 11851470 DOI: 10.1021/cr960032y] [Citation(s) in RCA: 169] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Robert E. Minto
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218
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18
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Silva JC, Minto RE, Barry CE, Holland KA, Townsend CA. Isolation and characterization of the versicolorin B synthase gene from Aspergillus parasiticus. Expansion of the aflatoxin b1 biosynthetic gene cluster. J Biol Chem 1996; 271:13600-8. [PMID: 8662689 DOI: 10.1074/jbc.271.23.13600] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Versicolorin B synthase catalyzes the side chain cyclization of racemic versiconal hemiacetal to the bisfuran ring system of(-)-versicolorin B, an essential transformation in the aflatoxin biosynthetic pathway of Aspergillus parasiticus. The dihydrobisfuran is key to the mutagenic nature of aflatoxin B1. The protein, which shows 58% similarity and 38% identity with glucose oxidase from Aspergillus niger, possesses an amino-terminal sequence homologous to the ADP-binding region of other flavoenzymes. However, this enzyme does not require flavin or nicotinamide cofactors for its cyclase activity. The 643-amino acid native enzyme contains three potential sites for N-linked glycosylation, Asn-Xaa-Thr or Asn-Xaa-Ser. The cDNA and genomic clones of versicolorin B synthase were isolated by screening the respective libraries with random-primed DNA probes generated from an exact copy of an internal vbs sequence. This probe was created through polymerase chain reaction by using nondegenerate polymerase chain reaction primers derived from the amino acid sequences of peptide fragments of the enzyme. The 1985-base genomic vbs DNA sequence is interrupted by one intron of 53 nucleotides. Southern blotting, nucleotide sequencing, and detailed restriction mapping of the vbs-containing genomic clones revealed the presence of omtA, a methyltransferase active in the biosynthesis, 3.3 kilobases upstream of vbs and oriented in the opposite direction from vbs. The presence of omtA in close proximity to vbs supports the theory that the genes encoding the aflatoxin biosynthetic enzymes in A. parasiticus are clustered.
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Affiliation(s)
- J C Silva
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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19
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Demonstration of Baeyer-Villiger oxidation and the course of cyclization in bisfuran ring formation during aflatoxin B1 biosynthesis. Bioorg Med Chem Lett 1993. [DOI: 10.1016/s0960-894x(01)81247-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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