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Abstract
Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.
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Affiliation(s)
- Dirk Leifert
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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Momeni T, Zadsirjan V, Hadi Meshkatalsadat M, Pourmohammadi‐Mahunaki M. Applications of Cobalt‐Catalyzed Reactions in the Total Synthesis of Natural Products. ChemistrySelect 2022. [DOI: 10.1002/slct.202202816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Tayebeh Momeni
- Department of Chemistry Qom University of Technology Qom Iran 3718146645
- Department of Chemistry School of Science Alzahra University Vanak Tehran Iran
| | - Vahideh Zadsirjan
- Department of Chemistry Malek Ashtar University of Technology Tehran Iran
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Zev S, Ringel M, Driller R, Loll B, Brück T, Major DT. Understanding the competing pathways leading to hydropyrene and isoelisabethatriene. Beilstein J Org Chem 2022; 18:972-978. [PMID: 35965858 PMCID: PMC9359192 DOI: 10.3762/bjoc.18.97] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 07/18/2022] [Indexed: 11/23/2022] Open
Abstract
Terpene synthases are responsible for the biosynthesis of terpenes, the largest family of natural products. Hydropyrene synthase generates hydropyrene and hydropyrenol as its main products along with two byproducts, isoelisabethatrienes A and B. Fascinatingly, a single active site mutation (M75L) diverts the product distribution towards isoelisabethatrienes A and B. In the current work, we study the competing pathways leading to these products using quantum chemical calculations in the gas phase. We show that there is a great thermodynamic preference for hydropyrene and hydropyrenol formation, and hence most likely in the synthesis of the isoelisabethatriene products kinetic control is at play.
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Affiliation(s)
- Shani Zev
- Department of Chemistry and Institute for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Marion Ringel
- Werner Siemens Chair of Synthetic Biotechnology, Department of Chemistry, Technical University of Munich, Lichtenbergstraße 4, 85748 Garching, Germany
| | - Ronja Driller
- Institute for Chemistry and Biochemistry, Structural Biochemistry Laboratory, Freie Universität Berlin, Takustr. 6, 14195 Berlin, Germany,
- Department of Molecular Biology and Genetics, Aarhus University, Danish Research Institute of Translational Neuroscience – DANDRITE, Universitetsbyen 81, 8000 Aarhus C, Denmark
| | - Bernhard Loll
- Institute for Chemistry and Biochemistry, Structural Biochemistry Laboratory, Freie Universität Berlin, Takustr. 6, 14195 Berlin, Germany,
| | - Thomas Brück
- Werner Siemens Chair of Synthetic Biotechnology, Department of Chemistry, Technical University of Munich, Lichtenbergstraße 4, 85748 Garching, Germany
| | - Dan T Major
- Department of Chemistry and Institute for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
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Xiao S, Ai L, Liu Q, Yang B, Huang J, Xue W, Chen Y. Total Synthesis of Natural Terpenoids Enabled by Cobalt Catalysis. Front Chem 2022; 10:941184. [PMID: 35783212 PMCID: PMC9241582 DOI: 10.3389/fchem.2022.941184] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 05/17/2022] [Indexed: 12/01/2022] Open
Abstract
Transition metal catalysis plays an essential role in the total synthesis of natural products. Cobalt-mediated asymmetric catalysis has successfully been used as a primary or a secondary step in the total synthesis of natural products, especially terpenoids. Terpenoids represent one of the most prominent families among various categories of natural products, attracting immense attention due to their promising physiological activities. This review summarizes the recent advances toward the total synthesis of terpenoids by cobalt-mediated asymmetric catalysis, which may shed some light on their future synthetic efforts toward natural pesticides such as celanguline, azadirachtin, etc.
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Affiliation(s)
| | | | | | | | | | - Wei Xue
- *Correspondence: Yang Chen, ; Wei Xue,
| | - Yang Chen
- *Correspondence: Yang Chen, ; Wei Xue,
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Varela K, Al Mahmud H, Arman HD, Martinez LR, Wakeman CA, Yoshimoto FK. Autoxidation of a C2-Olefinated Dihydroartemisinic Acid Analogue to Form an Aromatic Ring: Application to Serrulatene Biosynthesis. JOURNAL OF NATURAL PRODUCTS 2022; 85:951-962. [PMID: 35357832 PMCID: PMC9035337 DOI: 10.1021/acs.jnatprod.1c01101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Dihydroartemisinic acid (DHAA) is a plant natural product that undergoes a spontaneous endoperoxide-forming cascade reaction to yield artemisinin in the presence of air. The endoperoxide functional group gives artemisinin its biological activity that kills Plasmodium falciparum, the parasite that causes malaria. To enhance our understanding of the mechanism of this cascade reaction, 2,3-didehydrodihydroartemisinic acid (2,3-didehydro-DHAA), a DHAA derivative with a double bond at the C2-position, was synthesized. When 2,3-didehydro-DHAA was exposed to air over time, instead of forming an endoperoxide, this compound predominantly underwent aromatization. This olefinated DHAA analogue reveals the requirement of a monoalkene functional group to initiate the endoperoxide-forming cascade reaction to yield artemisinin from DHAA. In addition, this aromatization process was exploited to illustrate the autoxidation process of a different plant natural product, dihydroserrulatene, to form the aromatic ring in serrulatene. This spontaneous aromatization process has applications in other natural products such as leubethanol and erogorgiaene. Due to their similarity in structure to antimicrobial natural products, the synthesized compounds in this study were tested for biological activity. A group of the tested compounds had minimum inhibitory concentration (MIC) values ranging from 12.5 to 25 μg/mL against the bacterial pathogen Staphylococcus aureus and the fungal pathogen Cryptococcus neoformans.
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Affiliation(s)
- Kaitlyn Varela
- Department of Chemistry, The University of Texas at San Antonio (UTSA), San Antonio, Texas 78249, United States
| | - Hafij Al Mahmud
- Biological Sciences, Texas Tech University, Lubbock, Texas 79409, United States
| | - Hadi D Arman
- Department of Chemistry, The University of Texas at San Antonio (UTSA), San Antonio, Texas 78249, United States
| | - Luis R Martinez
- Department of Oral Biology, University of Florida College of Dentistry, Center for Immunology and Transplantation, Center for Translational Research in Neurodegenerative Disease, and The Emerging Pathogens Institute, Gainesville, Florida 32610, United States
| | - Catherine A Wakeman
- Biological Sciences, Texas Tech University, Lubbock, Texas 79409, United States
| | - Francis K Yoshimoto
- Department of Chemistry, The University of Texas at San Antonio (UTSA), San Antonio, Texas 78249, United States
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coll toledano J. Pseudopterosins and Seco-Pseudopterosins: Compilation and Revision of Conflicting NMR Data, Names, Numbering Systems and Structural Elucidation. Nat Prod Commun 2022. [DOI: 10.1177/1934578x221079415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The present review is focussed on the structural elucidation of the bicyclic and tricyclic diterpenoid title compounds isolated from Pseudopterogorgia species, displaying a direct structural relationship with the biosynthetic precursor GGPP (regular isoprenoid skeletons). A compilation of 1H and 13C NMR spectroscopic data is presented grouped by similar spin systems. Apparent inconsistencies or potential missassignments are discussed, pointing out convenient revisions of data assignment to improve structure correlations. Some hemisynthetic intermediates in the structural elucidation process are included, as well as data of representative synthetic compounds.
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Schumacher CE, Rausch M, Greven T, Neudörfl JM, Schneider T, Schmalz HG. Total Synthesis and Antibiotic Properties of Amino‐Functionalized Aromatic Terpenoids Related to Erogorgiaene and the Pseudopterosins. European J Org Chem 2022. [DOI: 10.1002/ejoc.202200058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
| | - Marvin Rausch
- University of Bonn: Rheinische Friedrich-Wilhelms-Universitat Bonn Pharmaceutical Microbiology GERMANY
| | - Tobias Greven
- University of Cologne: Universitat zu Koln Chemistry GERMANY
| | | | - Tanja Schneider
- University of Bonn: Rheinische Friedrich-Wilhelms-Universitat Bonn Pharmaceutical Biology GERMANY
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Movahhed S, Westphal J, Kempa A, Schumacher CE, Sperlich J, Neudörfl J, Teusch N, Hochgürtel M, Schmalz H. Total Synthesis of (+)-Erogorgiaene and the Pseudopterosin A-F Aglycone via Enantioselective Cobalt-Catalyzed Hydrovinylation. Chemistry 2021; 27:11574-11579. [PMID: 34096655 PMCID: PMC8456859 DOI: 10.1002/chem.202101863] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Indexed: 12/04/2022]
Abstract
Due to their pronounced bioactivity and limited availability from natural resources, metabolites of the soft coral Pseudopterogorgia elisabethae, such as erogorgiaene and the pseudopterosines, represent important target molecules for chemical synthesis. We have now developed a particularly short and efficient route towards these marine diterpenes exploiting an operationally convenient enantioselective cobalt-catalyzed hydrovinylation as the chirogenic step. Other noteworthy C-C bond forming transformations include diastereoselective Lewis acid-mediated cyclizations, a Suzuki coupling and a carbonyl ene reaction. Starting from 4-methyl-styrene the anti-tubercular agent (+)-erogorgiaene (>98 % ee) was prepared in only 7 steps with 46 % overall yield. In addition, the synthesis of the pseudopterosin A aglycone was achieved in 12 steps with 30 % overall yield and, surprisingly, was found to exhibit a similar anti-inflammatory activity (inhibition of LPS-induced NF-κB activation) as a natural mixture of pseudopterosins A-D or iso-pseudopterosin A, prepared by β-D-xylosylation of the synthetic aglycone.
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Affiliation(s)
| | | | - Alexander Kempa
- TH Köln, Faculty of Applied Natural SciencesKaiser-Wilhelm-Allee, G. E3951373LeverkusenGermany
| | | | - Julia Sperlich
- TH Köln, Faculty of Applied Natural SciencesKaiser-Wilhelm-Allee, G. E3951373LeverkusenGermany
| | | | - Nicole Teusch
- TH Köln, Faculty of Applied Natural SciencesKaiser-Wilhelm-Allee, G. E3951373LeverkusenGermany
| | - Matthias Hochgürtel
- TH Köln, Faculty of Applied Natural SciencesKaiser-Wilhelm-Allee, G. E3951373LeverkusenGermany
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