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Nguyen NUN, Canseco DC, Xiao F, Nakada Y, Li S, Lam NT, Muralidhar S, Savla JJ, Hill JA, Wang Z, Ahmed MS, Hubbi M, Menendez-Montes I, Moon J, Ali SR, Villalobos E, Elhelaly WM, Thet S, Tan WLW, Anene-Nzelu CG, Foo R, Jagoree R, Cyert MS, Rothermel BA, Sadek HA. Abstract MP161: A Calcineurin-hoxb13 Axis Regulates Growth Mode of Mammalian Cardiomyocytes. Circ Res 2020. [DOI: 10.1161/res.127.suppl_1.mp161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A major factor in the progression to heart failure in humans is the inability of the adult heart to repair itself after injury. Our group recently demonstrated that the early postnatal mammalian heart is capable of regeneration following injury through proliferation of preexisting cardiomyocytes1,2. We recently also showed that Meis1, a TALE family homeodomain transcription factor, translocates to cardiomyocyte nuclei shortly after birth and mediates postnatal cell cycle arrest3. Here we report that Hoxb13 acts as a Meis1 cofactor in postnatal cardiomyocytes. Cardiomyocyte-specific deletion of Hoxb13 can both extend the postnatal window of cardiomyocyte proliferation and reactivate cardiomyocyte cell cycle in the adult heart. Moreover, adult Meis1/Hoxb13 double knockout hearts display widespread cardiomyocyte mitosis, sarcomere disassembly and an improvement in left ventricular systolic function following myocardial infarction both by echocardiography and MRI. ChIP-seq analysis demonstrates that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and cell cycle. Finally, we show that the calcium-activated protein phosphatase calcineurin dephosphorylates Hoxb13 at serine-204 (S204), resulting in its nuclear localization and cell cycle arrest. Collectively, these results demonstrate that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and proliferation and provide mechanistic insights into the link between hyperplastic and hypertrophic growth of cardiomyocytes.
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Affiliation(s)
| | | | - Feng Xiao
- UT Southwestern Med Cntr, Dallas, TX
| | - Yuji Nakada
- Univ of Alabama at Birmingham, Birmingham, AL
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- Cardiovascular Rsch Institute, Singapore
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Nguyen NUN, Canseco DC, Xiao F, Nakada Y, Li S, Lam NT, Muralidhar SA, Savla JJ, Hill JA, Le V, Zidan KA, El-Feky HW, Wang Z, Ahmed MS, Hubbi ME, Menendez-Montes I, Moon J, Ali SR, Le V, Villalobos E, Mohamed MS, Elhelaly WM, Thet S, Anene-Nzelu CG, Tan WLW, Foo RS, Meng X, Kanchwala M, Xing C, Roy J, Cyert MS, Rothermel BA, Sadek HA. A calcineurin-Hoxb13 axis regulates growth mode of mammalian cardiomyocytes. Nature 2020; 582:271-276. [PMID: 32499640 PMCID: PMC7670845 DOI: 10.1038/s41586-020-2228-6] [Citation(s) in RCA: 66] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2018] [Accepted: 02/24/2020] [Indexed: 11/08/2022]
Abstract
A major factor in the progression to heart failure in humans is the inability of the adult heart to repair itself after injury. We recently demonstrated that the early postnatal mammalian heart is capable of regeneration following injury through proliferation of preexisting cardiomyocytes1,2 and that Meis1, a three amino acid loop extension (TALE) family homeodomain transcription factor, translocates to cardiomyocyte nuclei shortly after birth and mediates postnatal cell cycle arrest3. Here we report that Hoxb13 acts as a cofactor of Meis1 in postnatal cardiomyocytes. Cardiomyocyte-specific deletion of Hoxb13 can extend the postnatal window of cardiomyocyte proliferation and reactivate the cardiomyocyte cell cycle in the adult heart. Moreover, adult Meis1-Hoxb13 double-knockout hearts display widespread cardiomyocyte mitosis, sarcomere disassembly and improved left ventricular systolic function following myocardial infarction, as demonstrated by echocardiography and magnetic resonance imaging. Chromatin immunoprecipitation with sequencing demonstrates that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and cell cycle. Finally, we show that the calcium-activated protein phosphatase calcineurin dephosphorylates Hoxb13 at serine-204, resulting in its nuclear localization and cell cycle arrest. These results demonstrate that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and proliferation and provide mechanistic insights into the link between hyperplastic and hypertrophic growth of cardiomyocytes.
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Affiliation(s)
- Ngoc Uyen Nhi Nguyen
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Diana C Canseco
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Feng Xiao
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yuji Nakada
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Shujuan Li
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Nicholas T Lam
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Shalini A Muralidhar
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jainy J Savla
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Joseph A Hill
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Molecular Biology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Victor Le
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Kareem A Zidan
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Hamed W El-Feky
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Zhaoning Wang
- Center for Regenerative Science and Medicine, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Mahmoud Salama Ahmed
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Maimon E Hubbi
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Ivan Menendez-Montes
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jesung Moon
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Shah R Ali
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Victoria Le
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Elisa Villalobos
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Magid S Mohamed
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Waleed M Elhelaly
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Suwannee Thet
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Chukwuemeka George Anene-Nzelu
- Cardiovascular Research Institute, National University of Singapore, Singapore, Singapore
- Genome Institute of Singapore, Singapore, Singapore
| | - Wilson Lek Wen Tan
- Cardiovascular Research Institute, National University of Singapore, Singapore, Singapore
- Genome Institute of Singapore, Singapore, Singapore
| | - Roger S Foo
- Cardiovascular Research Institute, National University of Singapore, Singapore, Singapore
- Genome Institute of Singapore, Singapore, Singapore
| | - Xun Meng
- The College of Life Sciences, Northwest University, Xi'an, China
| | - Mohammed Kanchwala
- Eugene McDermott Center for Human Growth and Development/Center for Human Genetics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Chao Xing
- Eugene McDermott Center for Human Growth and Development/Center for Human Genetics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jagoree Roy
- Department of Biology, Stanford University, Stanford, California, USA
| | - Martha S Cyert
- Department of Biology, Stanford University, Stanford, California, USA
| | - Beverly A Rothermel
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Hesham A Sadek
- Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Department of Molecular Biology, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Center for Regenerative Science and Medicine, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
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Nakada Y, Canseco DC, Thet S, Abdisalaam S, Asaithamby A, Santos CX, Shah AM, Zhang H, Faber JE, Kinter MT, Szweda LI, Xing C, Hu Z, Deberardinis RJ, Schiattarella G, Hill JA, Oz O, Lu Z, Zhang CC, Kimura W, Sadek HA. Hypoxia induces heart regeneration in adult mice. Nature 2016; 541:222-227. [DOI: 10.1038/nature20173] [Citation(s) in RCA: 439] [Impact Index Per Article: 54.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 10/21/2016] [Indexed: 01/08/2023]
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Canseco DC, Kimura W, Garg S, Mukherjee S, Bhattacharya S, Abdisalaam S, Das S, Asaithamby A, Mammen PPA, Sadek HA. Human ventricular unloading induces cardiomyocyte proliferation. J Am Coll Cardiol 2015; 65:892-900. [PMID: 25618530 DOI: 10.1016/j.jacc.2014.12.027] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Revised: 12/05/2014] [Accepted: 12/09/2014] [Indexed: 12/28/2022]
Abstract
BACKGROUND The adult mammalian heart is incapable of meaningful regeneration after substantial cardiomyocyte loss, primarily due to the inability of adult cardiomyocytes to divide. Our group recently showed that mitochondria-mediated oxidative DNA damage is an important regulator of postnatal cardiomyocyte cell cycle arrest. However, it is not known whether mechanical load also plays a role in this process. We reasoned that the postnatal physiological increase in mechanical load contributes to the increase in mitochondrial content, with subsequent activation of DNA damage response (DDR) and permanent cell cycle arrest of cardiomyocytes. OBJECTIVES The purpose of this study was to test the effect of mechanical unloading on mitochondrial mass, DDR, and cardiomyocyte proliferation. METHODS We examined the effect of human ventricular unloading after implantation of left ventricular assist devices (LVADs) on mitochondrial content, DDR, and cardiomyocyte proliferation in 10 matched left ventricular samples collected at the time of LVAD implantation (pre-LVAD) and at the time of explantation (post-LVAD). RESULTS We found that post-LVAD hearts showed up to a 60% decrease in mitochondrial content and up to a 45% decrease in cardiomyocyte size compared with pre-LVAD hearts. Moreover, we quantified cardiomyocyte nuclear foci of phosphorylated ataxia telangiectasia mutated protein, an upstream regulator of the DDR pathway, and we found a significant decrease in the number of nuclear phosphorylated ataxia telangiectasia mutated foci in the post-LVAD hearts. Finally, we examined cardiomyocyte mitosis and cytokinesis and found a statistically significant increase in both phosphorylated histone H3-positive, and Aurora B-positive cardiomyocytes in the post-LVAD hearts. Importantly, these results were driven by statistical significance in hearts exposed to longer durations of mechanical unloading. CONCLUSIONS Prolonged mechanical unloading induces adult human cardiomyocyte proliferation, possibly through prevention of mitochondria-mediated activation of DDR.
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Affiliation(s)
- Diana C Canseco
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Wataru Kimura
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Sonia Garg
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Shibani Mukherjee
- Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Souparno Bhattacharya
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Salim Abdisalaam
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Sandeep Das
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Aroumougame Asaithamby
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Pradeep P A Mammen
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.
| | - Hesham A Sadek
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.
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Abstract
SIGNIFICANCE Utilizing oxygen (O2) through mitochondrial oxidative phosphorylation enables organisms to generate adenosine triphosphate (ATP) with a higher efficiency than glycolysis, but it results in increased reactive oxygen species production from mitochondria, which can result in stem cell dysfunction and senescence. RECENT ADVANCES In the postnatal organism, the hematopoietic system represents a classic example of the role of stem cells in cellular turnover and regeneration. However, in other organs such as the heart, both the degree and source of cellular turnover have been heavily contested. CRITICAL ISSUES Although recent evidence suggests that the major source of the limited cardiomyocyte turnover in the adult heart is cardiomyocyte proliferation, the identity and potential role of undifferentiated cardiac progenitor cells remain controversial. Several types of cardiac progenitor cells have been identified, and several studies have identified an important role of redox and metabolic regulation in survival and differentiation of cardiac progenitor cells. Perhaps a simple way to approach these controversies is to focus on the multipotentiality characteristics of a certain progenitor population, and not necessarily its ability to give rise to all cell types within the heart. In addition, it is important to note that cycling cells in the heart may express markers of differentiation or may be truly undifferentiated, and for the purpose of this review, we will refer to these cycling cells as progenitors. FUTURE DIRECTIONS We propose that hypoxia, redox signaling, and metabolic phenotypes are major regulators of cardiac renewal, and may prove to be important therapeutic targets for heart regeneration.
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Affiliation(s)
- Wataru Kimura
- 1 Division of Cardiology, Department of Internal Medicine, UT Southwestern Medical Center , Dallas, Texas
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Cummings DF, Canseco DC, Sheth P, Johnson JE, Schetz JA. Synthesis and structure-affinity relationships of novel small molecule natural product derivatives capable of discriminating between serotonin 5-HT1A, 5-HT2A, 5-HT2C receptor subtypes. Bioorg Med Chem 2010; 18:4783-92. [PMID: 20570529 PMCID: PMC2946983 DOI: 10.1016/j.bmc.2010.05.017] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2010] [Revised: 05/03/2010] [Accepted: 05/04/2010] [Indexed: 10/19/2022]
Abstract
Efforts to develop ligands that distinguish between clinically relevant 5-HT2A and 5-HT2C serotonin receptor subtypes have been challenging, because their sequences have high homology. Previous studies reported that a novel aplysinopsin belonging to a chemical class of natural products isolated from a marine sponge was selective for the 5-HT2C over the 5-HT2A receptor subtype. Our goal was to explore the 5-HT2A/2C receptor structure-affinity relationships of derivatives based on the aplysinopsin natural product pharmacophore. Twenty aplysinopsin derivatives were synthesized, purified and tested for their affinities for cloned human serotonin 5-HT1A, 5-HT2A, and 5-HT2C receptor subtypes. Four compounds in this series had >30-fold selectivity for 5-HT2A or 5-HT2C receptors. The compound (E)-5-((5,6-dichloro-1H-indol-3-yl)methylene)-2-imino-1,3-dimethylimidazolidin-4-one (UNT-TWU-22, 16) had approximately 2100-fold selectivity for the serotonin 5-HT2C receptor subtype: an affinity for 5-HT2C equal to 46 nM and no detectable affinity for the 5-HT1A or 5-HT2A receptor subtypes. The two most important factors controlling 5-HT2A or 5-HT2C receptor subtype selectivity were the combined R1,R3-alkylation of the imidazolidinone ring and the type and number of halogens on the indole ring of the aplysinopsin pharmacophore.
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MESH Headings
- Animals
- Binding, Competitive
- Humans
- Imidazolidines/chemical synthesis
- Imidazolidines/chemistry
- Imidazolidines/pharmacology
- Indoles/chemical synthesis
- Indoles/chemistry
- Indoles/pharmacology
- Porifera/chemistry
- Receptor, Serotonin, 5-HT1A/chemistry
- Receptor, Serotonin, 5-HT1A/metabolism
- Receptor, Serotonin, 5-HT2A/chemistry
- Receptor, Serotonin, 5-HT2A/metabolism
- Receptor, Serotonin, 5-HT2C/chemistry
- Receptor, Serotonin, 5-HT2C/metabolism
- Structure-Activity Relationship
- Tryptophan/analogs & derivatives
- Tryptophan/chemical synthesis
- Tryptophan/chemistry
- Tryptophan/pharmacology
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Affiliation(s)
- David F. Cummings
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107
| | - Diana C. Canseco
- Department of Biology, Texas Woman’s University, Denton, TX 76204
| | - Pratikkumar Sheth
- Department of Environmental and Occupational Health, School of Public Health, University of North Texas Health Science Center, Fort Worth, TX 76107
| | - James E. Johnson
- Department of Chemistry and Physics, P. O. Box 425859-5859, Texas Woman’s University, Denton, TX 76204-5859
| | - John A. Schetz
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107
- Department of Psychiatry, Texas College of Osteopathic Medicine, 3500 Camp Bowie Blvd., Fort Worth, TX 76107
- Department of Health Policy and Management, School of Public Health, University of North Texas Health Science Center, Fort Worth, TX 76107
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Johnson JE, Carvallo C, Dolliver DD, Sanchez N, Garza V, Canseco DC, Eggleton GL, Fronczek FR. Bisamidoximes: Synthesis and Complexation with Iron(III). Aust J Chem 2007. [DOI: 10.1071/ch07157] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Bisamidoximes have been synthesized by the reaction of 4-methylbenzohydroximoyl chloride with 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, and 3,3′-diamino-N-methyl-dipropylamine. A monoamidoxime and a trisamidoxime were also prepared in the present work by the reaction of 4-methylbenzohydroximoyl chloride with N,N-dimethylethylenediamine and tris(2-aminoethyl)amine. Single crystal X-ray structures of three of the bisamidoximes have shown that the two amidoxime moieties have the Z configuration in all three compounds. Job’s method of continuous variations showed that three of the bisamidoximes prepared in this work form 1:1 complexes with iron(iii) and therefore are acting as tetradentate ligands.
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Johnson JE, Lu L, Dai H, Canseco DC, Small KM, Dolliver DD, Fronczek FR. Synthesis and Characterization of α,β-Unsaturated Hydroximoyl Chlorides and Hydroximates. Aust J Chem 2006. [DOI: 10.1071/ch06188] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
New α,β-unsaturated hydroximoyl chlorides (PhC(Cl)=CHC(Cl)=NOCH3) and hydroximates (PhC(OCH3)=CHC(OCH3)=NOCH3) were prepared. The ZZ-isomer of PhC(Cl)=CHC(Cl)=NOCH3 was prepared in four steps from ethyl benzoylacetate. Ultraviolet irradiation of the ZZ-isomer gives a mixture of all four possible isomers. Sodium methoxide was reacted with these isomers to determine the configuration about the carbon–carbon double bond for each. The Z-isomers reacted with sodium methoxide to give the corresponding alkyne by elimination whereas the E-isomers gave the substitution product. The configuration about the carbon–nitrogen double bond was determined from the 1H NMR chemical shift of the NOCH3 group.
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Johnson JE, Dolliver DD, Yu L, Canseco DC, McAllister MA, Rowe JE. Mechanism of methoxide ion substitution in the z and e isomers of o-methylbenzohydroximoyl halides. J Org Chem 2004; 69:2741-9. [PMID: 15074922 DOI: 10.1021/jo030299e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Kinetics and stereochemical studies have been carried out on the reactions of the Z and E isomers of O-methylbenzohydroximoyl halides [1Z and 1E, ArC(X)=NOCH(3)] with sodium methoxide in 9:1 DMSO-methanol. The reactions of methoxide ion with hydroximoyl fluorides (X = F) are stereospecific. The reaction with 1Z (X = F) gives only the Z substitution product (1Z, X =OCH(3)). The reaction of methoxide ion with 1E (X = F) is less selective, giving ca. 85% E substitution product. The Hammett rho-values for the Z and E isomers (X = F) are +2.94 and +3.30, respectively. The element effects for 1Z (Ar = C(6)H(5)) are 2.21 (X = Br):1.00 (X = Cl):79.7 (X = F). The 1E element effects are (Ar = C(6)H(5)) 1.00 (X = Cl):18.3 (X = F) and (Ar = 4-CH(3)OC(6)H(4)) 1.97 (X = Br):1.00 (X = Cl):12.1 (X = F). The entropies of activation for these reactions are negative (for example, DeltaS() = -15 eu for 1Z and DeltaS() = -14 eu for 1E, Ar = 4-CH(3)OC(6)H(4), X = F). These experimental observations are consistent with a mechanism proceeding through a tetrahedral intermediate. Ab initio calculations were carried out to help explain the stereospecificity of these reactions. These calculations indicate that the tetrahedral intermediate from the Z isomer undergoes rapid elimination to the Z substitution product before stereomutation can take place. These calculations also show that the lowest barrier for rotation around the carbon-nitrogen single bond in the tetrahedral intermediate derived from 1E leads to an intermediate that eliminates fluoride ion to give E product.
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Affiliation(s)
- James E Johnson
- Department of Chemistry and Physics, Texas Woman's University, Denton, Texas 76204-5859, USA.
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Abstract
A series of methyl (Z)-O-methylbenzothiohydroximates were prepared either by reaction of the corresponding (Z)-N-methoxybenzenecarboximidoyl bromides with potassium fluoride in dimethyl sulfoxide, or by reaction of N-methoxybenzamides with Lawesson’s reagent followed by alkylation. Irradiation of the Z isomers led to a photostationary equilibrium containing mixtures of approx. 40% E and 60% Z, from which the E isomers were isolated.
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