1
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Sakakibara Y, Itami K, Murakami K. Switchable Decarboxylation by Energy- or Electron-Transfer Photocatalysis. J Am Chem Soc 2024; 146:1554-1562. [PMID: 38103176 DOI: 10.1021/jacs.3c11588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2023]
Abstract
Kolbe dimerization and Hofer-Moest reactions are well-investigated carboxylic acid transformations, wherein new carbon-carbon and carbon-heteroatom bonds are constructed via electrochemical decarboxylation. These transformations can be switched by choosing an electrode that allows control of the reactive intermediate, such as carbon radical or carbocation. However, the requirement of a high current density diminishes the functional group compatibility with these electrochemical reactions. Here, we demonstrate the photocatalytic decarboxylative transformation of activated carboxylic acids in a switchable and functional group-compatible manner. We discovered that switching between Kolbe-type or Hofer-Moest-type reactions can be accomplished with suitable photocatalysts by controlling the reaction pathways: energy transfer (EnT) and single-electron transfer (SET). The EnT pathway promoted by an organo-photocatalyst yielded 1,2-diarylethane from arylacetic acids, whereas the ruthenium photoredox catalyst allows the construction of an ester scaffold with two arylmethyl moieties via the SET pathway. The resulting radical intermediates were coupled to olefins to realize multicomponent reactions. Consequently, four different products were selectively obtained from a simple carboxylic acid. This discovery offers new opportunities for selectively synthesizing multiple products via switchable reactions using identical substrates with minimal cost and effort.
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Affiliation(s)
- Yota Sakakibara
- Graduate School of Science, Nagoya University, Chikusa 464-8602, Nagoya, Japan
- Department of Chemistry, School of Science, Kwansei Gakuin University, Sanda 669-1330, Hyogo, Japan
- Japanese Science and Technology Agency (JST)-PRESTO, Chiyoda 102-0076, Tokyo, Japan
| | - Kenichiro Itami
- Graduate School of Science, Nagoya University, Chikusa 464-8602, Nagoya, Japan
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa 464-8602, Nagoya, Japan
| | - Kei Murakami
- Department of Chemistry, School of Science, Kwansei Gakuin University, Sanda 669-1330, Hyogo, Japan
- Japanese Science and Technology Agency (JST)-PRESTO, Chiyoda 102-0076, Tokyo, Japan
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2
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Spencer TA, Ditchfield R. Tryptophan Stabilization of a Biochemical Carbocation Evaluated by Analysis of π Complexes of 3-Ethylindole with the t-Butyl Cation. ACS OMEGA 2023; 8:26497-26507. [PMID: 37521644 PMCID: PMC10373456 DOI: 10.1021/acsomega.3c03259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 06/27/2023] [Indexed: 08/01/2023]
Abstract
Understanding how the highly unstable carbocation intermediates in terpenoid biosynthesis are stabilized and protected during their transient existence in enzyme active sites is an intriguing challenge which has to be addressed computationally. Our efforts have focused on evaluating the stabilization afforded via carbocation-π complexation between a biochemical carbocation and an aromatic amino acid residue. This has involved making measurements on an X-ray structure of an enzyme active site that shows a π donor proximate to a putative carbocation site and using these to build models which are analyzed computationally to provide an estimated stabilization energy (SE). Previously, we reported estimated SEs for several such carbocation-π complexes involving phenylalanine. Herein, we report the first such estimate involving tryptophan as the π donor. Because there was almost no published information about indole as a π-complexation donor, we first located computationally equilibrium π and σ complexes of 3-ethylindole with the t-butyl cation as relevant background information. Then, measurements on the X-ray structure of the enzyme CotB2 complexed with geranylgeranyl thiodiphosphate (GGSPP), specifically on the geometric relationship of the putative carbocation at C15 of GGSPP to W186, were used to build a model that afforded a computed SE of -15.3 kcal/mol.
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3
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Chen W, Yi X, Liu Z, Tang X, Zheng A. Carbocation chemistry confined in zeolites: spectroscopic and theoretical characterizations. Chem Soc Rev 2022; 51:4337-4385. [PMID: 35536126 DOI: 10.1039/d1cs00966d] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Acid-catalyzed reactions inside zeolites are one type of broadly applied industrial reactions, where carbocations are the most common intermediates of these reaction processes, including methanol to olefins, alkene/aromatic alkylation, and hydrocarbon cracking/isomerization. The fundamental research on these acid-catalyzed reactions is focused on the stability, evolution, and lifetime of carbocations under the zeolite confinement effect, which greatly affects the efficiency, selectivity and deactivation of zeolite catalysts. Therefore, a profound understanding of the carbocations confined in zeolites is not only beneficial to explain the reaction mechanism but also drive the design of new zeolite catalysts with ideal acidity and cages/channels. In this review, we provide both an in-depth understanding of the stabilization of carbocations by the pore confinement effect and summary of the advanced characterization methods to capture carbocations in zeolites, including UV-vis spectroscopy, solid-state NMR, fluorescence microscopy, IR spectroscopy and Raman spectroscopy. Also, we clarify the relationship between the activity and stability of carbocations in zeolite-catalyzed reactions, and further highlight the role of carbocations in various hydrocarbon conversion reactions inside zeolites with diverse frameworks and varying acidic properties.
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Affiliation(s)
- Wei Chen
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
| | - Xianfeng Yi
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
| | - Zhiqiang Liu
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
| | - Xiaomin Tang
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
| | - Anmin Zheng
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, P. R. China. .,University of Chinese Academy of Sciences, Beijing 100049, P. R. China
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4
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Zev S, Gupta PK, Pahima E, Major DT. A Benchmark Study of Quantum Mechanics and Quantum Mechanics-Molecular Mechanics Methods for Carbocation Chemistry. J Chem Theory Comput 2021; 18:167-178. [PMID: 34905380 DOI: 10.1021/acs.jctc.1c00746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Carbocations play key roles in classical organic reactions and have also been implicated in several enzyme families. A hallmark of carbocation chemistry is multitudes of competing reaction pathways, and to be able to distinguish between pathways with quantum chemical calculations, it is necessary to approach chemical accuracy for relative energies between carbocations. Here, we present an extensive study of the performance of selected density functional theory (DFT) methods in describing the thermochemistry and kinetics of carbocations and their corresponding neutral alkenes both in the gas-phase and within a hybrid quantum mechanics-molecular mechanics (QM/MM) framework. The density functionals are benchmarked against accurate ab initio methods such as CBS-QB3 and DLPNO-CCSD(T). Based on the findings in the gas-phase calculations of carbocations and alkenes, the best functionals are chosen and tested further for non-covalent interactions in model systems using QM and QM/MM methods. We compute the interaction energies between a model carbocation/alkane and model π, dipole, and hydrophobic systems using DFT and QM(DFT)/MM and compare with DLPNO-CCSD(T). These latter model systems are representative of side chains of amino acids such as phenylalanine/tyrosine, tryptophan, asparagine/glutamine, serine/threonine, methionine, and other hydrophobic groups. The Lennard-Jones parameters of the QM atoms in QM(DFT)/MM calculations are modified to obtain an optimal fit with the QM energies. Finally, a selected carbocation reaction is studied in the gas phase and in implicit chloroform solvent using QM and in explicit chloroform solvent using QM/MM and umbrella sampling simulations. This study highlights the highest accuracy possible with selected density functionals and QM/MM methods but also some limitations in using QM/MM methods for carbocation systems.
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Affiliation(s)
- Shani Zev
- Department of Chemistry and Institute for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Prashant Kumar Gupta
- Department of Chemistry and Institute for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Efrat Pahima
- Department of Chemistry and Institute for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Dan Thomas Major
- Department of Chemistry and Institute for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
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5
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Grand C, Cogen JM, Wills ST. Stability of phenolic antioxidants in the presence of sulfonic acid: Model compound studies for moisture-crosslinked polyethylene. Polym Degrad Stab 2021. [DOI: 10.1016/j.polymdegradstab.2021.109746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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6
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Yang Z, Yang Y, Zhang X, Du W, Zhang J, Qian G, Duan X, Zhou X. High‐yield production of
p
‐diethynylbenzene through consecutive bromination/dehydrobromination in a microreactor system. AIChE J 2021. [DOI: 10.1002/aic.17498] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Zhirong Yang
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
| | - Yue Yang
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
| | - Xuefeng Zhang
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
| | - Wei Du
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
| | - Jing Zhang
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
| | - Gang Qian
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
| | - Xuezhi Duan
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
| | - Xinggui Zhou
- State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai China
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7
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Spencer TA, Ditchfield R. A simpler method affords evaluation of π stabilization by phenylalanine of several biochemical carbocations. Org Biomol Chem 2020; 18:7597-7607. [PMID: 32955057 DOI: 10.1039/d0ob01565b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/25/2024]
Abstract
Carbocations are important intermediates in the biosynthesis of terpenes and steroids, and it is challenging to try to understand how these relatively unstable species survive even transiently during biochemical reactions. Carbocation-π interaction with aromatic amino acid residues is an important factor in helping to stabilize these positively charged species. However, the short lifetimes of these active site carbocations makes experimental evaluation of the stabilization afforded by such interaction impossible. Computational studies, however, have provided some insight into this phenomenon. Herein we report a simple, computationally efficient method to estimate such stabilization energies afforded by phenylalanine to biochemical carbocation intermediates. A model is constructed in which the biochemical carbocation is replaced by an appropriate carbocation mimic (t-butyl or dimethylallyl). This substitute carbocation is then aligned with an ethylbenzene serving as a surrogate for each proximate phenylalanine in a geometry that replicates as closely as possible the orientation of that phenylalanine using measurements made on an X-ray structure of an enzyme active site in which a carbocation surrogate is bound. Density functional theory computations on such models were then used to yield estimates of stabilization energies. Application of this method to the tertiary carbocation formed in the reaction catalyzed by geranyl diphosphate C-methyl transferase gave a stabilization energy (-12.3 kcal mol-1) that was essentially identical to that obtained previously by analysis of a much more computationally demanding model of the active site. As a check on the accuracy of the simpler method, it was applied with similar success to the farnesyl cation formed in the reaction catalyzed by aristolochene synthase that is stabilized by cation-π interaction with two phenylalanines. Application of this method is also described to estimate carbocation-π stabilization, by the same two phenylalanines, of the final carbocation intermediate leading to aristolochene through analysis of the X-ray structure of an inhibitor of that carbocation bound in the active site of aristolochene synthase. Finally, the stabilization, by either of two phenylalanines, of six carbocation intermediates in the oxidosqualene cyclase-catalyzed formation of lanosterol is estimated by comparable analysis of an X-ray structure of that reaction product bound in the enzyme active site.
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Affiliation(s)
- Thomas A Spencer
- Department of Chemistry, 6128 Burke Laboratory, Dartmouth College, Hanover, NH 03755, USA.
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8
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Kazim M, Siegler MA, Lectka T. A Protonated Quinone Methide Stabilized by a Combination of Partial Aromatization and π-Interaction: Spectroscopic and Crystallographic Analysis. J Org Chem 2019; 84:8284-8288. [PMID: 31117575 DOI: 10.1021/acs.joc.9b00923] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have expanded the repertoire of cation-π interactions to include a carbocation-π system resulting from the protonation of a π-stacked para-quinone methide (p-QM). This unusual carbocation is stabilized by a combination of partial aromatization of the QM moiety and through-space interaction with the π-system of the adjacent aromatic ring. Single crystal X-ray analysis of the protonated form reveals a structure consisting of a hydrogen-bound complex involving two molecules of the precursor and one proton.
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Affiliation(s)
- Muhammad Kazim
- Department of Chemistry , Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - Maxime A Siegler
- Department of Chemistry , Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - Thomas Lectka
- Department of Chemistry , Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
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9
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Franconetti A, Jiménez-Barbero J, Cabrera-Escribano F. The Stabilization of Glycosyl Cations Through Cooperative Noncovalent Interactions: A Theoretical Perspective. Chemphyschem 2018; 19:659-665. [DOI: 10.1002/cphc.201700988] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 10/25/2017] [Indexed: 01/18/2023]
Affiliation(s)
- Antonio Franconetti
- Department of Organic Chemistry; Faculty of Chemistry; University of Seville; C/ Profesor García González 1 41012 Sevilla Spain
| | - Jesús Jiménez-Barbero
- Molecular Recognition and Host-Pathogen Interactions; CIC bioGUNE; Bizkaia Technology Park, Building 801 A 48170 Derio Spain
- Basque Foundation for Science; Maria Diaz de Haro 13 48009 Bilbao Spain
- Department of Organic Chemistry II; Faculty of Science and Technology; University of the BasqueCountry; 48940 Leioa Bizkaia Spain
| | - Francisca Cabrera-Escribano
- Department of Organic Chemistry; Faculty of Chemistry; University of Seville; C/ Profesor García González 1 41012 Sevilla Spain
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10
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Kirpichenko SV, Albanov AI, Shainyan BA. Mechanism of Protodephenylation of 1,3-Silaheterocyclohexanes. Effect of Heteroatom. RUSS J GEN CHEM+ 2018. [DOI: 10.1134/s1070363218010152] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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11
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Hare SR, Pemberton RP, Tantillo DJ. Navigating Past a Fork in the Road: Carbocation-π Interactions Can Manipulate Dynamic Behavior of Reactions Facing Post-Transition-State Bifurcations. J Am Chem Soc 2017; 139:7485-7493. [PMID: 28504880 DOI: 10.1021/jacs.7b01042] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Dynamics calculations are described for carbocation rearrangements involving product-forming pathways with post-transition-state bifurcations. We show that noncovalent interactions with associated benzene rings (a simple model of aromatic amino acid side chains) can switch inherent dynamical tendencies for competing modes of disrotation, establishing that meaningful changes in dynamically controlled product selectivity can be achieved with few weak noncovalent interactions.
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Affiliation(s)
- Stephanie R Hare
- Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States
| | - Ryan P Pemberton
- Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States
| | - Dean J Tantillo
- Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States
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12
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Patra T, Parveen F, Upadhyayula S. Mechanistic insights into solvent induced alkylation of p-cresol with tert-butyl alcohol using Brönsted acidic ionic liquids. MOLECULAR CATALYSIS 2017. [DOI: 10.1016/j.mcat.2016.12.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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13
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Thoughts about the electrophilic aromatic substitution mechanism: the Friedel-crafts alkylation and acylation of benzene with acetyl and t-butyl cations in the gas phase. Struct Chem 2017. [DOI: 10.1007/s11224-017-0915-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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14
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Ditchfield R, Spencer TA. Carbocation–π interaction: evaluation of the stabilization by phenylalanine of a biochemical carbocation intermediate. Org Biomol Chem 2016; 14:9543-9548. [DOI: 10.1039/c6ob01761d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Computational analyses, using primarily density functional theory, have been used to determine the stabilization associated with the carbocation–π interaction of a biochemical carbocation intermediate binding to a phenylalanine residue in an enzyme active site.
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Affiliation(s)
- Robert Ditchfield
- Department of Chemistry
- 6128 Burke Laboratory
- Dartmouth College
- Hanover
- USA
| | - Thomas A. Spencer
- Department of Chemistry
- 6128 Burke Laboratory
- Dartmouth College
- Hanover
- USA
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15
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Hong YJ, Tantillo DJ. Tension between Internal and External Modes of Stabilization in Carbocations Relevant to Terpene Biosynthesis: Modulating Minima Depth via C–H···π Interactions. Org Lett 2015; 17:5388-91. [DOI: 10.1021/acs.orglett.5b02740] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Young J. Hong
- Department
of Chemistry, Univeristy of California—Davis, Davis, California 95616, United States
| | - Dean J. Tantillo
- Department
of Chemistry, Univeristy of California—Davis, Davis, California 95616, United States
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16
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Kinzel D, Zilberg S, González L. Origin of the Regioselectivity in the Gas-Phase Aniline+CH 3+Electrophilic Aromatic Substitution. Chemphyschem 2015; 16:2366-74. [DOI: 10.1002/cphc.201500256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Indexed: 11/09/2022]
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17
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Hamlin TA, Hamann CS, Tantillo DJ. Delocalization of Charge and Electron Density in the Humulyl Cation—Implications for Terpene Biosynthesis. J Org Chem 2015; 80:4046-53. [DOI: 10.1021/acs.joc.5b00381] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Trevor A. Hamlin
- Department
of Chemistry and Biochemistry, Albright College, 13th and Bern
Streets, Reading, Pennsylvania 19604, United States
| | - Christian S. Hamann
- Department
of Chemistry and Biochemistry, Albright College, 13th and Bern
Streets, Reading, Pennsylvania 19604, United States
| | - Dean J. Tantillo
- Department
of Chemistry, University of California—Davis, 1 Shields Avenue, Davis, California 95616, United States
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18
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Kinzel D, Zilberg S, González L. Gas-phase electrophilic aromatic substitution mechanism with strong electrophiles explained by ab initio non-adiabatic dynamics. Phys Chem Chem Phys 2014; 16:18686-9. [PMID: 25080210 DOI: 10.1039/c4cp01456a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Ab initio non-adiabatic dynamics is used to monitor the attack of CH3(+) to benzene. The results show that in the gas phase the reaction is ultrafast and is governed by a single electron transfer producing a radical pair.
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Affiliation(s)
- Daniel Kinzel
- Institute of Theoretical Chemistry, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria.
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19
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Hong YJ, Tantillo DJ. Branching Out from the Bisabolyl Cation. Unifying Mechanistic Pathways to Barbatene, Bazzanene, Chamigrene, Chamipinene, Cumacrene, Cuprenene, Dunniene, Isobazzanene, Iso-γ-bisabolene, Isochamigrene, Laurene, Microbiotene, Sesquithujene, Sesquisabinene, Thujopsene, Trichodiene, and Widdradiene Sesquiterpenes. J Am Chem Soc 2014; 136:2450-63. [DOI: 10.1021/ja4106489] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Young J. Hong
- Department
of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
| | - Dean J. Tantillo
- Department
of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
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20
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Pemberton RP, Hong YJ, Tantillo DJ. Inherent dynamical preferences in carbocation rearrangements leading to terpene natural products. PURE APPL CHEM 2013. [DOI: 10.1351/pac-con-12-11-22] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
An introduction to the application of quantum chemical dynamics calculations to mechanistic problems in the field of terpene biosynthesis is provided. A bare bones introduction to the fundamentals of chemical dynamics is followed by a brief account of previous applications to terpene-forming carbocation reactions, a discussion of questions in this field that dynamics calculations may help answer, and a description of current problems to which dynamics calculations are being applied.
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21
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Kushida T, Yamaguchi S. Boracyclophanes: Modulation of the σ/π Character in Boron-Benzene Interactions. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201303830] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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22
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Kushida T, Yamaguchi S. Boracyclophanes: Modulation of the σ/π Character in Boron-Benzene Interactions. Angew Chem Int Ed Engl 2013; 52:8054-8. [DOI: 10.1002/anie.201303830] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2013] [Indexed: 11/10/2022]
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23
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Hong YJ, Tantillo DJ. C–H⋯π interactions as modulators of carbocation structure – implications for terpene biosynthesis. Chem Sci 2013. [DOI: 10.1039/c3sc50571e] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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24
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Sidorkin VF, Doronina EP, Belogolova EF. Cage Complexes of Carbenium and Silylium Cations with an Aromatic Base. Is the η6Coordination Type Realizable? Organometallics 2012. [DOI: 10.1021/om3008053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Valery F. Sidorkin
- A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky, 1, Irkutsk 664033, Russian Federation
| | - Evgeniya P. Doronina
- A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky, 1, Irkutsk 664033, Russian Federation
| | - Elena F. Belogolova
- A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky, 1, Irkutsk 664033, Russian Federation
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25
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Abstract
A theoretical investigation of the isopropylbenzenium ion system has been carried out with structures determined with B3LYP. Energies are calculated with the high accuracy composite methods, G3 (G3B3) and CBS (CBS-QB3). The main goal has been to resolve the following issue: Are there any stable ion π-electron complexes of the type C(6)H(6)/C(3)H(7)(+) or C(6)H(7)(+)/C(3)H(6) in this system? Two minimum points on the potential energy surface (PES) corresponding to benzenium ion/propene complexes were found. Due to free internal rotation, they represent only one species. The barrier for forming an isopropylbenzenium ion from the complex is low, so the lifetime will be short. Computation of the IR spectrum of the complex shows that there is a very intense absorption line due to C-H stretching, in an otherwise empty region, that may be used to identify the complex, if present. No stable C(6)H(6)/C(3)H(7)(+) complex was found, but a quasi-stable species structurally corresponding to the earlier described stable C(6)H(6)/C(4)H(9)(+) complex was observed. A simplistic explanation why the benzene/isopropyl cation, in contrast to benzene/tert-butyl cation, does not form a stable ion/π-electron complex is given.
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Affiliation(s)
- Stein Kolboe
- inGAP Center for Research Based Innovation, Department of Chemistry, University of Oslo, Blindern, Oslo, Norway.
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26
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Hong YJ, Tantillo DJ. Theoretical calculations on carbocations involved in the biosynthesis of bergamotenes and related terpenes—the same and not the same. Chem Commun (Camb) 2012; 48:1571-3. [DOI: 10.1039/c1cc14414f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Abstract
A complete pathway (structures and energies of intermediates and transition state structures connecting them) from geranylgeranyl diphosphate to taxadiene, obtained using quantum chemical calculations, is described. This pathway is fully consistent with previous labeling experiments, despite differing in several subtle ways (in terms of conformations of certain carbocation intermediates and in the concertedness and synchronicity of certain bond-forming events) from previous mechanistic proposals. Also, on the basis of the theoretical results, it is proposed that the 2-fluoro-geranylgeranyl diphosphate substrate analogue in the recently reported X-ray crystal structure of taxadiene synthase is bound in a nonproductive orientation.
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Affiliation(s)
- Young J Hong
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
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28
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Ditchfield R, Spencer TA. Carbocation-π interaction: the 1,1-dimethylallyl cation and benzene. Tetrahedron Lett 2011. [DOI: 10.1016/j.tetlet.2011.05.036] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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29
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Affiliation(s)
- Stein Kolboe
- inGAP Center for Research Based Innovation, Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway
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30
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Hong YJ, Tantillo DJ. How Many Secondary Carbocations Are Involved in the Biosynthesis of Avermitilol? Org Lett 2011; 13:1294-7. [DOI: 10.1021/ol103079v] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Young J. Hong
- Department of Chemistry, University of California−Davis, One Shields Avenue, Davis, California 95616, United States
| | - Dean J. Tantillo
- Department of Chemistry, University of California−Davis, One Shields Avenue, Davis, California 95616, United States
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31
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Bernardino R, Costa Cabral B. Complexation of Calix[4]arene With Alkali Metal Cations: Conformational Binding Selectivity and Cation-π Driven Inclusion. Supramol Chem 2010. [DOI: 10.1080/10610270290006574] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Affiliation(s)
- R.J. Bernardino
- a Centro de Física da Matéria Condensada , Universidade de Lisboa , Av. Professor Gama Pinto 2, Lisboa , 1649-003 , Portugal
- b Departamento de Engenharia Química Industrial , Instituto Politécnico de Tomar , Tomar , Portugal
| | - B.J. Costa Cabral
- a Centro de Física da Matéria Condensada , Universidade de Lisboa , Av. Professor Gama Pinto 2, Lisboa , 1649-003 , Portugal
- c Departamento de Química e Bioquímica, Faculdade de Ciências , Universidade de Lisboa , Edifício C8, Lisboa , 1749-016 , Portugal
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32
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Spencer TA, Popovici-Müller J, van Beusichem B, MacMillan CV, Lavey CF, Sin JM, Ditchfield R. Bridged aromatic alkenes for the study of carbocation–π interaction. Tetrahedron 2010. [DOI: 10.1016/j.tet.2010.04.029] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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33
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Xu XF, Zilberg S, Haas Y. Electrophilic Aromatic Substitution: The Role of Electronically Excited States. J Phys Chem A 2010; 114:4924-33. [DOI: 10.1021/jp911250g] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- X. F. Xu
- Institute of Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - S. Zilberg
- Institute of Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Y. Haas
- Institute of Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem, Israel
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34
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Hong YJ, Tantillo DJ. Quantum chemical dissection of the classic terpinyl/pinyl/bornyl/camphyl cation conundrum—the role of pyrophosphate in manipulating pathways to monoterpenes. Org Biomol Chem 2010; 8:4589-600. [DOI: 10.1039/c0ob00167h] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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35
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Adams NG, Mathews LD, Osborne, Jr D. Laboratory chemistry relevant to understanding and modeling the ionosphere of Titan. Faraday Discuss 2010; 147:323-35; discussion 379-403. [DOI: 10.1039/c003233f] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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36
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A comparative study of modern and robust computational methods applied to π-complexes of moderate size: The case of the ethene/benzenium ion complex. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2008.12.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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37
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Kolboe S, Svelle S, Arstad B. Theoretical Study of Ethylbenzenium Ions: The Mechanism for Splitting Off Ethene, and the Formation of a π Complex of Ethene and the Benzenium Ion. J Phys Chem A 2008; 113:917-23. [DOI: 10.1021/jp8070234] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Stein Kolboe
- Innovative Natural Gas Processes and Products (inGAP) Center of Research Based Innovation, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway, and SINTEF Materials and Chemistry, Department of Hydrocarbon Process Chemistry, P.O. Box 124, Blindern, N-0314 Oslo, Norway
| | - Stian Svelle
- Innovative Natural Gas Processes and Products (inGAP) Center of Research Based Innovation, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway, and SINTEF Materials and Chemistry, Department of Hydrocarbon Process Chemistry, P.O. Box 124, Blindern, N-0314 Oslo, Norway
| | - Bjørnar Arstad
- Innovative Natural Gas Processes and Products (inGAP) Center of Research Based Innovation, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway, and SINTEF Materials and Chemistry, Department of Hydrocarbon Process Chemistry, P.O. Box 124, Blindern, N-0314 Oslo, Norway
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38
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Fondren LD, Adams NG, Stavish L. Gas Phase Reactions of CH3+ with a Series of Homo- and Heterocyclic Molecules. J Phys Chem A 2008; 113:592-8. [DOI: 10.1021/jp8091336] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- L. Dalila Fondren
- Department of Chemistry, University of Georgia, Athens, Georgia 30602
| | - Nigel G. Adams
- Department of Chemistry, University of Georgia, Athens, Georgia 30602
| | - Leah Stavish
- Department of Chemistry, University of Georgia, Athens, Georgia 30602
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39
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Lodewyk MW, Gutta P, Tantillo DJ. Computational Studies on Biosynthetic Carbocation Rearrangements Leading to Sativene, Cyclosativene, α-Ylangene, and β-Ylangene. J Org Chem 2008; 73:6570-9. [DOI: 10.1021/jo800868r] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Michael W. Lodewyk
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616
| | - Pradeep Gutta
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616
| | - Dean J. Tantillo
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616
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40
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Kolboe S, Svelle S. Does an Ethene/Benzenium Ion Complex Exist? A Discrepancy between B3LYP and MP2 Predictions. J Phys Chem A 2008; 112:6399-400. [DOI: 10.1021/jp8027879] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Stein Kolboe
- Innovative Natural Gas Processes and Products (inGAP) Center of Research Based Innovation, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway
| | - Stian Svelle
- Innovative Natural Gas Processes and Products (inGAP) Center of Research Based Innovation, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway
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41
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Amiri A, Monajjemi M, Ketabi S. Quantum simulation on donor and acceptor II calix[4]arene substrate and alkali metal ions: the driven inclusion. PHYSICS AND CHEMISTRY OF LIQUIDS 2007. [DOI: 10.1080/00319100500424191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
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42
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Carbocation–π interaction with Car–Parrinello molecular dynamics: Ab initio molecular dynamics investigation of complex of methyl cation with benzene. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2006.12.076] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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43
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Amiri A, Monajjemi M, Zare K, Ketabi S. Complexation behaviour ofp-t-butyl-calix[4]arene propoxy derivatives toward alkali metal cations in chloroform. PHYSICS AND CHEMISTRY OF LIQUIDS 2006. [DOI: 10.1080/00319100500502400] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
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44
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Fujii T, Arulmozhiraja S, Nakamura M, Shiokawa Y. Detection of Cu(hfac)(tmvs) by Li+ ion attachment mass spectrometry. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.05.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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45
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Ab initio Study of the Complexes of Trimethyl Ether of Monodeoxycalix[4]arene with Potassium Ion: Cation-π Interactions. B KOREAN CHEM SOC 2006. [DOI: 10.5012/bkcs.2006.27.4.508] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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46
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Ma Q, Chakraborty D, Faglioni F, Muller RP, Goddard WA, Harris T, Campbell C, Tang Y. Alkylation of Phenol: A Mechanistic View. J Phys Chem A 2006; 110:2246-52. [PMID: 16466262 DOI: 10.1021/jp0560213] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The current work utilizes the ab initio density functional theory (DFT) to develop a molecular level of the mechanistic understanding on the phenol alkylation in the presence of a cation-exchange resin catalyst, Amberlyst-15. The catalyst is modeled with the benzene sulfonic acid, and the effect of this acid on olefins such as isopropene (i-Pr) and tributene (t-Bu) in a phenol solution mimics the experimental condition. A neutral-pathway mechanism is established to account for early-stage high concentration of the phenolic ether observed in experiments. The mechanism involves an exothermic reaction between olefin and the benzene sulfonic acid to form ester followed by three reaction pathways leading to direct O-alkylation, o-C-alkylation, and p-C-alkylation. Our calculations conclude that O-alkylation to form the phenolic ether is the most energetically favorable in the neutral condition. An ionic rearrangement mechanism describes intramolecular migrations of the alkyl group from the phenolic ether to form C-alkylphenols, while the positively charged protonation significantly lowers transition barriers for these migrations. The ionic rearrangement mechanism accounts for high yields of o-C-alkylphenol and p-C-alkylphenol. Competition between the H atom and the alkyl R group at the substitutive site of the protonated ortho configuration is found to be the determining factor to the ortho/para ratio of C-alkylation products.
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Affiliation(s)
- Qisheng Ma
- California Institute of Technology, Pasadena, California 91125, USA
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47
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Ruan C, Yang Z, Hallowita N, Rodgers MT. Cation−π Interactions with a Model for the Side Chain of Tryptophan: Structures and Absolute Binding Energies of Alkali Metal Cation−Indole Complexes†. J Phys Chem A 2005; 109:11539-50. [PMID: 16354046 DOI: 10.1021/jp053830d] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Threshold collision-induced dissociation techniques are employed to determine bond dissociation energies (BDEs) of mono- and bis-complexes of alkali metal cations, Li+, Na+, K+, Rb+, and Cs+, with indole, C8H7N. The primary and lowest energy dissociation pathway in all cases is endothermic loss of an intact indole ligand. Sequential loss of a second indole ligand is observed at elevated energies for the bis-complexes. Density functional theory calculations at the B3LYP/6-31G level of theory are used to determine the structures, vibrational frequencies, and rotational constants of these complexes. Theoretical BDEs are determined from single point energy calculations at the MP2(full)/6-311+G(2d,2p) level using the B3LYP/6-31G* geometries. The agreement between theory and experiment is very good for all complexes except Li+ (C8H7N), where theory underestimates the strength of the binding. The trends in the BDEs of these alkali metal cation-indole complexes are compared with the analogous benzene and naphthalene complexes to examine the influence of the extended pi network and heteroatom on the strength of the cation-pi interaction. The Na+ and K+ binding affinities of benzene, phenol, and indole are also compared to those of the aromatic amino acids, phenylalanine, tyrosine, and tryptophan to elucidate the factors that contribute to the binding in complexes to the aromatic amino acids. The nature of the binding and trends in the BDEs of cation-pi complexes between alkali metal cations and benzene, phenol, and indole are examined to help understand nature's preference for engaging tryptophan over phenylalanine and tyrosine in cation-pi interactions in biological systems.
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Affiliation(s)
- Chunhai Ruan
- Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA
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48
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Ignat'ev IS, Kochina TA. Proton Migration in Benzene Complexes of Methyl and Silyl Cations. RUSS J GEN CHEM+ 2005. [DOI: 10.1007/s11176-005-0400-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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49
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Chiavarino B, Crestoni ME, Fornarini S, Lemaire J, Aleese LM, Maitre P. Infrared Spectroscopy of Protonated Phenylsilane in the Gas Phase. Chemphyschem 2005; 6:437-40. [PMID: 15799466 DOI: 10.1002/cphc.200400511] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Barbara Chiavarino
- Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università di Roma "La Sapienza", Piazzale A. Moro 5, 00185 Roma, Italy
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50
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Thoma R, Schulz-Gasch T, D'Arcy B, Benz J, Aebi J, Dehmlow H, Hennig M, Stihle M, Ruf A. Insight into steroid scaffold formation from the structure of human oxidosqualene cyclase. Nature 2004; 432:118-22. [PMID: 15525992 DOI: 10.1038/nature02993] [Citation(s) in RCA: 260] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2004] [Accepted: 09/02/2004] [Indexed: 11/09/2022]
Abstract
In higher organisms the formation of the steroid scaffold is catalysed exclusively by the membrane-bound oxidosqualene cyclase (OSC; lanosterol synthase). In a highly selective cyclization reaction OSC forms lanosterol with seven chiral centres starting from the linear substrate 2,3-oxidosqualene. Valuable data on the mechanism of the complex cyclization cascade have been collected during the past 50 years using suicide inhibitors, mutagenesis studies and homology modelling. Nevertheless it is still not fully understood how the enzyme catalyses the reaction. Because of the decisive role of OSC in cholesterol biosynthesis it represents a target for the discovery of novel anticholesteraemic drugs that could complement the widely used statins. Here we present two crystal structures of the human membrane protein OSC: the target protein with an inhibitor that showed cholesterol lowering in vivo opens the way for the structure-based design of new OSC inhibitors. The complex with the reaction product lanosterol gives a clear picture of the way in which the enzyme achieves product specificity in this highly exothermic cyclization reaction.
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Affiliation(s)
- Ralf Thoma
- F. Hoffmann-La Roche AG, Pharma Research Discovery Chemistry, 4070 Basel, Switzerland
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