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Tong G, Griffin S, Sader A, Crowell AB, Beavers K, Watson J, Buchan Z, Chen S, Shenvi RA. C5 methylation confers accessibility, stability and selectivity to picrotoxinin. Nat Commun 2023; 14:8308. [PMID: 38097583 PMCID: PMC10721898 DOI: 10.1038/s41467-023-44030-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Accepted: 11/28/2023] [Indexed: 12/17/2023] Open
Abstract
Minor changes to complex structures can exert major influences on synthesis strategy and functional properties. Here we explore two parallel series of picrotoxinin (PXN, 1) analogs and identify leads with selectivity between mammalian and insect ion channels. These are the first SAR studies of PXN despite its >100-year history and are made possible by advances in total synthesis. We observe a remarkable stabilizing effect of a C5 methyl, which completely blocks C15 alcoholysis via destabilization of an intermediate twist-boat conformer; suppression of this secondary hydrolysis pathway increases half-life in plasma. C5 methylation also decreases potency against vertebrate ion channels (γ-Aminobutyric acid type A (GABAA) receptors) but maintains or increases antagonism of homologous invertebrate GABA-gated chloride channels (resistance to dieldrin (RDL) receptors). Optimal 5MePXN analogs appear to change the PXN binding pose within GABAARs by disruption of a hydrogen bond network. These discoveries were made possible by the lower synthetic burden of 5MePXN (2) and were illuminated by the parallel analog series, which allowed characterization of the role of the synthetically simplifying C5 methyl in channel selectivity. These are the first SAR studies to identify changes to PXN that increase the GABAA-RDL selectivity index.
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Affiliation(s)
- Guanghu Tong
- Department of Chemistry, Scripps Research, 10550 North Torrey Pines Road, La Jolla, California, 92037, USA
| | - Samantha Griffin
- Corteva Agriscience, 9330 Zionsville Road, Indianapolis, Indiana, 46268, USA
| | - Avery Sader
- Corteva Agriscience, 9330 Zionsville Road, Indianapolis, Indiana, 46268, USA
| | - Anna B Crowell
- Department of Chemistry and Biochemistry, Oberlin College, 119 Woodland Street, Oberlin, Ohio, 44074, USA
| | - Ken Beavers
- Corteva Agriscience, 9330 Zionsville Road, Indianapolis, Indiana, 46268, USA
| | - Jerry Watson
- Corteva Agriscience, 9330 Zionsville Road, Indianapolis, Indiana, 46268, USA
| | - Zachary Buchan
- Corteva Agriscience, 9330 Zionsville Road, Indianapolis, Indiana, 46268, USA
| | - Shuming Chen
- Department of Chemistry and Biochemistry, Oberlin College, 119 Woodland Street, Oberlin, Ohio, 44074, USA.
| | - Ryan A Shenvi
- Department of Chemistry, Scripps Research, 10550 North Torrey Pines Road, La Jolla, California, 92037, USA.
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Chen SS, Koppaka A, Periana RA, Ess DH. Theory and Experiment Demonstrate that Sb(V)-Promoted Methane C-H Activation and Functionalization Outcompete Superacid Protonolysis in Sulfuric Acid. J Am Chem Soc 2021; 143:18242-18250. [PMID: 34665603 DOI: 10.1021/jacs.1c08170] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Sb(V) in strong Brønsted acid solvents is traditionally assumed to react with light alkanes through superacid protonolysis, which results in carbocation intermediates, H2, and carbon oligomerization. In contrast to this general assumption, our density functional theory (DFT) calculations revealed an accessible barrier for C-H activation between methane and Sb(V) in sulfuric acid that could potentially outcompete superacid protonolysis. This prompted us to experimentally examine this reaction in sulfuric acid with oleum, which has never been reported because of presumed superacid reactivity. Reaction of methane at 180 °C for 3 h resulted in very high yields of methyl bisulfate without significant overoxidation. Our DFT calculations show that a C-H activation and Sb-Me bond functionalization mechanism to give methyl bisulfate outcompetes methane protonolysis and many other possible reaction mechanisms, such as electron transfer, proton-coupled electron transfer, and hydride abstraction. Our DFT calculations also explain experimental hydrogen-deuterium exchange studies and the absence of methane carbo-functionalization/oligomerization products. Overall, this work demonstrates that in very strong Brønsted acid solvent, Sb(V) can induce innersphere reaction mechanisms akin to transition metals and outcompete superacid reactivity.
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Affiliation(s)
- Shu-Sen Chen
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
| | - Anjaneyulu Koppaka
- The Scripps Energy and Materials Center, Department of Chemistry, The Scripps Research Institute, Jupiter, Florida 33458, United States
| | - Roy A Periana
- The Scripps Energy and Materials Center, Department of Chemistry, The Scripps Research Institute, Jupiter, Florida 33458, United States
| | - Daniel H Ess
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
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Klare HFT, Oestreich M. The Power of the Proton: From Superacidic Media to Superelectrophile Catalysis. J Am Chem Soc 2021; 143:15490-15507. [PMID: 34520196 DOI: 10.1021/jacs.1c07614] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Superacidic media became famous in connection with carbocations. Yet not all reactive intermediates can be generated, characterized, and eventually isolated from these Brønsted acid/Lewis acid cocktails. The counteranion, that is the conjugate base, in these systems is often too nucleophilic and/or engages in redox chemistry with the newly formed cation. The Brønsted acidity, especially superacidity, is in fact often not even crucial unless protonation of extremely weak bases needs to be achieved. Instead, it is the chemical robustness of the aforementioned counteranion that determines the success of the protolysis. The advent of molecular Brønsted superacids derived from weakly coordinating, redox-inactive counteranions that do withstand the enormous reactivity of superelectrophiles such as silicon cations completely changed the whole field. This Perspective summarizes general aspects of medium and molecular Brønsted acidity and shows how applications of molecular Brønsted superacids have advanced from stoichiometric reactions to catalytic processes involving protons and in situ generated superelectrophiles.
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Affiliation(s)
- Hendrik F T Klare
- Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623 Berlin, Germany
| | - Martin Oestreich
- Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623 Berlin, Germany
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Huang T, Xu Z, Yan P, Liu X, Fan H, Zhang ZC. Direct Partial Oxidation of Methane Catalyzed by an In Situ Generated Active Au(III) Complex at Low Temperature in Ionic Liquids. Organometallics 2021. [DOI: 10.1021/acs.organomet.0c00714] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tingyu Huang
- State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Key Laboratory of Energy Biotechnology, Dalian Institute of Chemical Physics, Chinese Academy of Science, 457 Zhongshan Road, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 10049, China
| | - Zhanwei Xu
- State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Key Laboratory of Energy Biotechnology, Dalian Institute of Chemical Physics, Chinese Academy of Science, 457 Zhongshan Road, Dalian 116023, China
| | - Peifang Yan
- State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Key Laboratory of Energy Biotechnology, Dalian Institute of Chemical Physics, Chinese Academy of Science, 457 Zhongshan Road, Dalian 116023, China
| | - Xiumei Liu
- State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Key Laboratory of Energy Biotechnology, Dalian Institute of Chemical Physics, Chinese Academy of Science, 457 Zhongshan Road, Dalian 116023, China
| | - Hongjun Fan
- State Key Laboratory of Molecular Reaction Dynamics, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Science, 457 Zhongshan Road, Dalian 116023, China
| | - Z. Conrad Zhang
- State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Key Laboratory of Energy Biotechnology, Dalian Institute of Chemical Physics, Chinese Academy of Science, 457 Zhongshan Road, Dalian 116023, China
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