51
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Greer EM, Cosgriff CV, Lavinda O. A Curtin-Hammett pentamethylene chain symmetrization process in the Bergman cyclization of an 11-membered ring enediyne. J PHYS ORG CHEM 2013. [DOI: 10.1002/poc.3018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Edyta M. Greer
- Department of Natural Sciences; Baruch College; 17 Lexington Ave. New York NY 10010 USA
| | | | - Olga Lavinda
- Department of Natural Sciences; Baruch College; 17 Lexington Ave. New York NY 10010 USA
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52
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Corrosion Behavior and Adsorption Thermodynamics of Some Schiff Bases on Mild Steel Corrosion in Industrial Water Medium. INTERNATIONAL JOURNAL OF CORROSION 2013. [DOI: 10.1155/2013/543204] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The inhibition performance and adsorption behavior of (E)-2-(3-nitrobenzylidene) hydrazine carbothioamide (SB1) and (E)-2-(4-(dimethylamino) benzylidene) hydrazine carbothioamide (SB2) on mild steel corrosion in industrial water medium have been investigated by gravimetric, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results revealed that inhibition efficiency depends on both the concentration of the inhibitors and temperature of the system. Increasing temperature reduces the inhibition efficiency of both inhibitors. Polarization studies indicated that these compounds behave as mixed type of inhibitors. The adsorption of both inhibitors was spontaneous and followed Langmuir adsorption isotherm. Thermodynamic parameters are calculated and discussed. The relation between inhibition efficiency and molecular structures of SB1and SB2was discussed by considering quantum chemical parameters. The surface adsorbed film was characterized by scanning electron microscopy (SEM).
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53
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Theoretical approach to the corrosion inhibition efficiency of some quinoxaline derivatives of steel in acid media using the DFT method. RESEARCH ON CHEMICAL INTERMEDIATES 2012. [DOI: 10.1007/s11164-012-0671-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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54
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Gilmore K, Manoharan M, Wu JIC, Schleyer PVR, Alabugin IV. Aromatic Transition States in Nonpericyclic Reactions: Anionic 5-Endo Cyclizations Are Aborted Sigmatropic Shifts. J Am Chem Soc 2012; 134:10584-94. [DOI: 10.1021/ja303341b] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Kerry Gilmore
- Department of Chemistry and
Biochemistry, Florida State University,
Tallahassee, Florida 32306-4390, United States
| | - Mariappan Manoharan
- School of Science, Engineering
and Mathematics, Bethune-Cookman University, Daytona Beach, Florida 32114, United States
| | - Judy I-Chia Wu
- Center for Computational Chemistry,
Department of Chemistry, University of Georgia, Athens, Georgia 30602-2525, United States
| | - Paul v. R. Schleyer
- Center for Computational Chemistry,
Department of Chemistry, University of Georgia, Athens, Georgia 30602-2525, United States
| | - Igor V. Alabugin
- Department of Chemistry and
Biochemistry, Florida State University,
Tallahassee, Florida 32306-4390, United States
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55
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Dong H, Chen BZ, Huang MB, Lindh R. The bergman cyclizations of the enediyne and its N-substituted analogs using multiconfigurational second-order perturbation theory. J Comput Chem 2011; 33:537-49. [DOI: 10.1002/jcc.22889] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Revised: 09/15/2011] [Accepted: 10/18/2011] [Indexed: 11/06/2022]
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56
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LI XIANGZHU, PALDUS JOSEF. REDUCED MULTIREFERENCE COUPLED-CLUSTER METHOD AND ITS APPLICATION TO THE PYRIDYNE DIRADICALS. JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2011. [DOI: 10.1142/s0219633608004131] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The reduced multireference (RMR) coupled-cluster (CC) method with singles and doubles (RMR CCSD) that employs a modest-size MR CISD wave function as an external source for the most important (primary) triples and quadruples in order to account for the nondynamic correlation effects in the presence of quasidegeneracy, and which is further perturbatively corrected for the remaining (secondary) triples, RMR CCSD(T), is employed to compute the molecular geometry and the energy of the lowest-lying singlet and triplet states, as well as the corresponding singlet–triplet splitting, for all possible isomers of the m, n-pyridyne diradicals. A comparison is made with earlier results that were obtained by other authors, and the role of the multireference effects for both the geometry and the spin multiplicity of the lowest state, as described by the RMR-type methods, is demonstrated on the example of 2,6- and 3,5-pyridynes.
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Affiliation(s)
- XIANGZHU LI
- Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1, Canada
| | - JOSEF PALDUS
- Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1, Canada
- Department of Chemistry and (GWC)2 – Waterloo Campus, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1, Canada
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57
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Vinogradova OV, Balova IA, Popik VV. Synthesis and Reactivity of Cinnoline-Fused Cyclic Enediyne. J Org Chem 2011; 76:6937-41. [DOI: 10.1021/jo201148h] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Olga V. Vinogradova
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Irina A. Balova
- Department of Chemistry, St. Petersburg State University, 198504 St. Petersburg, Russian Federation
| | - Vladimir V. Popik
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
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58
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Laroche C, Li J, Kerwin SM. Cytotoxic 1,2-dialkynylimidazole-based aza-enediynes: aza-Bergman rearrangement rates do not predict cytotoxicity. J Med Chem 2011; 54:5059-69. [PMID: 21667990 DOI: 10.1021/jm200289j] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A new class of potential antitumor agents inspired by the enediyne antitumor antibiotics has been synthesized: the 1,2-dialkynylimidazoles. The aza-Bergman rearrangement of these 1,2-dialkynylimidazoles has been investigated theoretically at the B3LYP/6-31G(d,p) level and experimentally by measuring the kinetics of rearrangement in 1,4-cyclohexadiene. There is a good correlation between the theoretical and experimental results; subtle substituent effects on the initial aza-Bergman cyclization barrier predicted by theory are confirmed by experiment. Yet, despite the ability of these 1,2-dialkynylimidazoles to undergo Bergman rearrangement to diradical/carbene intermediates under relatively mild conditions, there is no correlation between the rate of Bergman cyclization and cytotoxicity to A459 cells. In addition, cytotoxic 1,2-dialkynylimidazoles do not cause nicking of supercoiled plasmid DNA or cleavage of bovine serum albumin. An alternative mechanism for cytotoxicity involving the unexpected selective thiol addition to the N-ethynyl group of certain 1,2-dialkynylimidazoles is proposed.
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Affiliation(s)
- Christophe Laroche
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Texas 78712, USA
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59
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Quantitative structure activity relationships of some pyridine derivatives as corrosion inhibitors of steel in acidic medium. J Mol Model 2011; 18:1173-88. [PMID: 21695505 DOI: 10.1007/s00894-011-1148-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Accepted: 06/03/2011] [Indexed: 10/18/2022]
Abstract
Quantum chemical calculations using the density functional theory (B3LYP/6-31G DFT) and semi-empirical AM1 methods were performed on ten pyridine derivatives used as corrosion inhibitors for mild steel in acidic medium to determine the relationship between molecular structure and their inhibition efficiencies. Quantum chemical parameters such as total negative charge (TNC) on the molecule, energy of highest occupied molecular orbital (E (HOMO)), energy of lowest unoccupied molecular orbital (E (LUMO)) and dipole moment (μ) as well as linear solvation energy terms, molecular volume (Vi) and dipolar-polarization (π) were correlated to corrosion inhibition efficiency of ten pyridine derivatives. A possible correlation between corrosion inhibition efficiencies and structural properties was searched to reduce the number of compounds to be selected for testing from a library of compounds. It was found that theoretical data support the experimental results. The results were used to predict the corrosion inhibition of 24 related pyridine derivatives.
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60
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Alabugin IV, Gilmore KM, Peterson PW. Hyperconjugation. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2011. [DOI: 10.1002/wcms.6] [Citation(s) in RCA: 214] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Igor V. Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, USA
| | - Kerry M. Gilmore
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, USA
| | - Paul W. Peterson
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, USA
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61
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DeKorver KA, Li H, Lohse AG, Hayashi R, Lu Z, Zhang Y, Hsung RP. Ynamides: a modern functional group for the new millennium. Chem Rev 2010; 110:5064-106. [PMID: 20429503 DOI: 10.1021/cr100003s] [Citation(s) in RCA: 722] [Impact Index Per Article: 51.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Kyle A DeKorver
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53705, USA
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62
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Greer EM, Lavinda O. Theoretical Study of the Bergman Cyclization of 2,3-Diethynyl-1-nitrotropylium Ion: Formation of a Nitroxide Radical Amenable to EPR Detection for Biological Applications. J Org Chem 2010; 75:8650-3. [DOI: 10.1021/jo101451d] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Edyta M. Greer
- Department of Natural Sciences, Baruch College, 17 Lexington Avenue, New York, New York 10010, United States
| | - Olga Lavinda
- Department of Natural Sciences, Baruch College, 17 Lexington Avenue, New York, New York 10010, United States
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63
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Abstract
For over 40 years, natural products have served us well in combating cancer. The main sources of these successful compounds are microbes and plants from the terrestrial and marine environments. The microbes serve as a major source of natural products with anti‐tumour activity. A number of these products were first discovered as antibiotics. Another major contribution comes from plant alkaloids, taxoids and podophyllotoxins. A vast array of biological metabolites can be obtained from the marine world, which can be used for effective cancer treatment. The search for novel drugs is still a priority goal for cancer therapy, due to the rapid development of resistance to chemotherapeutic drugs. In addition, the high toxicity usually associated with some cancer chemotherapy drugs and their undesirable side‐effects increase the demand for novel anti‐tumour drugs active against untreatable tumours, with fewer side‐effects and/or with greater therapeutic efficiency. This review points out those technologies needed to produce the anti‐tumour compounds of the future.
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Affiliation(s)
- Arnold L Demain
- Charles A Dana Research Institute for Scientists Emeriti, Drew University, Madison, NJ 07940, USA.
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64
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Poloukhtine A, Rassadin V, Kuzmin A, Popik VV. Nucleophilic Cycloaromatization of Ynamide-Terminated Enediynes. J Org Chem 2010; 75:5953-62. [DOI: 10.1021/jo101238x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Valentin Rassadin
- Department of Chemistry, University of Georgia, Athens, Georgia 30602
| | - Alexander Kuzmin
- Department of Chemistry, University of Georgia, Athens, Georgia 30602
| | - Vladimir V. Popik
- Department of Chemistry, University of Georgia, Athens, Georgia 30602
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65
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Laroche C, Li J, Gonzales C, David WM, Kerwin SM. Cyclization kinetics and biological evaluation of an anticancer 1,2-dialkynylimidazole. Org Biomol Chem 2010; 8:1535-9. [DOI: 10.1039/b925261d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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66
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Liang ZX. Complexity and simplicity in the biosynthesis of enediyne natural products. Nat Prod Rep 2010; 27:499-528. [DOI: 10.1039/b908165h] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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67
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Baroudi A, Mauldin J, Alabugin IV. Conformationally Gated Fragmentations and Rearrangements Promoted by Interception of the Bergman Cyclization through Intramolecular H-Abstraction: A Possible Mechanism of Auto-Resistance to Natural Enediyne Antibiotics? J Am Chem Soc 2009; 132:967-79. [DOI: 10.1021/ja905100u] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Abdulkader Baroudi
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306
| | - Justin Mauldin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306
| | - Igor V. Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306
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68
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Adeuya A, Price JM, Jankiewicz BJ, Nash JJ, Kenttämaa HI. Gas-phase reactivity of protonated 2-, 3-, and 4-dehydropyridine radicals toward organic reagents. J Phys Chem A 2009; 113:13663-74. [PMID: 19902945 PMCID: PMC2804851 DOI: 10.1021/jp901380y] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
To explore the effects of the electronic nature of charged phenyl radicals on their reactivity, reactions of the three distonic isomers of n-dehydropyridinium cation (n = 2, 3, or 4) have been investigated in the gas phase by using Fourier-transform ion cyclotron resonance mass spectrometry. All three isomers react with cyclohexane, methanol, ethanol, and 1-pentanol exclusively via hydrogen atom abstraction and with allyl iodide mainly via iodine atom abstraction, with a reaction efficiency ordering of 2 > 3 > 4. The observed reactivity ordering correlates well with the calculated vertical electron affinities of the charged radicals (i.e., the higher the vertical electron affinity, the faster the reaction). Charged radicals 2 and 3 also react with tetrahydrofuran exclusively via hydrogen atom abstraction, but the reaction of 4 with tetrahydrofuran yields products arising from nonradical reactivity. The unusual reactivity of 4 is likely to result from the contribution of an ionized carbene-type resonance structure that facilitates nucleophilic addition to the most electrophilic carbon atom (C-4) in this charged radical. The influence of such a resonance structure on the reactivity of 2 is not obvious, and this may be due to stabilizing hydrogen-bonding interactions in the transition states for this molecule. Charged radicals 2 and 3 abstract a hydrogen atom from the substituent in both phenol and toluene, but 4 abstracts a hydrogen atom from the phenyl ring, a reaction that is unprecedented for phenyl radicals. Charged radical 4 reacts with tert-butyl isocyanide mainly by hydrogen cyanide (HCN) abstraction, whereas CN abstraction is the principal reaction for 2 and 3. The different reactivity observed for 4 (as compared to 2 and 3) is likely to result from different charge and spin distributions of the reaction intermediates for these charged radicals.
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Affiliation(s)
| | | | | | - John J. Nash
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
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69
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CIOSLOWSKI JERZY, SZARECKA AGNIESZKA, MONCRIEFF DAVID. Energetics, electronic structures and geometries of didehydroazines. Mol Phys 2009. [DOI: 10.1080/0026897021000034512] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- JERZY CIOSLOWSKI
- a Department of Chemistry and Biochemistry and School of Computational Science and Information Technology , Florida State University , Tallahassee , FL , 32306 , USA
| | - AGNIESZKA SZARECKA
- a Department of Chemistry and Biochemistry and School of Computational Science and Information Technology , Florida State University , Tallahassee , FL , 32306 , USA
| | - DAVID MONCRIEFF
- a Department of Chemistry and Biochemistry and School of Computational Science and Information Technology , Florida State University , Tallahassee , FL , 32306 , USA
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70
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Melikyan GG, Spencer R, Abedi E. Stereoselective Synthesis of meso-1,5-Cyclodecadiynes. J Org Chem 2009; 74:8541-6. [DOI: 10.1021/jo901404f] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Gagik G. Melikyan
- Department of Chemistry and Biochemistry, California State University Northridge, Northridge, California 91330-8262
| | - Ryan Spencer
- Department of Chemistry and Biochemistry, California State University Northridge, Northridge, California 91330-8262
| | - Edwin Abedi
- Department of Chemistry and Biochemistry, California State University Northridge, Northridge, California 91330-8262
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71
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Yang WY, Breiner B, Kovalenko SV, Ben C, Singh M, LeGrand SN, Sang QXA, Strouse GF, Copland JA, Alabugin IV. C-lysine conjugates: pH-controlled light-activated reagents for efficient double-stranded DNA cleavage with implications for cancer therapy. J Am Chem Soc 2009; 131:11458-70. [PMID: 19637922 PMCID: PMC2771568 DOI: 10.1021/ja902140m] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Double-stranded DNA cleavage of light-activated lysine conjugates is strongly enhanced at the slightly acidic pH (<7) suitable for selective targeting of cancer cells. This enhancement stems from the presence of two amino groups of different basicities. The first amino group plays an auxiliary role by enhancing solubility and affinity to DNA, whereas the second amino group, which is positioned next to the light-activated DNA cleaver, undergoes protonation at the desired pH threshold. This protonation results in two synergetic effects which account for the increased DNA-cleaving ability at the lower pH. First, lysine conjugates show tighter binding to DNA at the lower pH, which is consistent with the anticipated higher degree of interaction between two positively charged ammonium groups with the negatively charged phosphate backbone of DNA. Second, the unproductive pathway which quenches the excited state of the photocleaver through intramolecular electron transfer is eliminated once the donor amino group next to the chromophore is protonated. Experiments in the presence of traps for diffusing radicals show that reactive oxygen species do not contribute significantly to the mechanism of DNA cleavage at the lower pH, which is indicative of tighter binding to DNA under these conditions. This feature is valuable not only because many solid tumors are hypoxic but also because cleavage which does not depend on diffusing species is more localized and efficient. Sequence-selectivity experiments suggest combination of PET and base alkylation as the chemical basis for the observed DNA damage. The utility of these molecules for phototherapy of cancer is confirmed by the drastic increase in toxicity of five conjugates against cancer cell lines upon photoactivation.
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Affiliation(s)
- Wang-Yong Yang
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
| | - Boris Breiner
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
| | - Serguei V. Kovalenko
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
| | - Chi Ben
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
| | - Mani Singh
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
| | - Shauna N. LeGrand
- Department of Cancer Biology, Mayo Clinic Comprehensive Cancer Center, Jacksonville, Florida 32224
| | - Qing-Xiang Amy Sang
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
| | - Geoffrey F. Strouse
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
| | - John A. Copland
- Department of Cancer Biology, Mayo Clinic Comprehensive Cancer Center, Jacksonville, Florida 32224
| | - Igor V. Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
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72
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Pati K, Liu RS. Efficient syntheses of alpha-pyridones and 3(2H)-isoquinolones through ruthenium-catalyzed cycloisomerization of 3-en-5-ynyl and o-alkynylphenyl nitrones. Chem Commun (Camb) 2009:5233-5. [PMID: 19707630 DOI: 10.1039/b910773h] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a new catalytic synthesis of alpha-pyridones and 3(2H)-isoquinolones from readily available 3-en-5-ynyl nitrones and o-alkynylphenyl nitrones; the reaction mechanism is proposed to involve iminyl ketene species through an oxygen transfer process.
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Affiliation(s)
- Kamalkishore Pati
- Department of Chemistry, National Tsing-Hua University, Hsinchu, 30043, Taiwan, ROC
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73
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Sherer EC, Kirschner KN, Pickard FC, Rein C, Feldgus S, Shields GC. Efficient and accurate characterization of the Bergman cyclization for several enediynes including an expanded substructure of esperamicin A1. J Phys Chem B 2008; 112:16917-34. [PMID: 19053814 PMCID: PMC2854586 DOI: 10.1021/jp807341t] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Incorporation of enediynes into anticancer drugs remains an intriguing yet elusive strategy for the design of therapeutically active agents. Density functional theory was used to locate reactants, products, and transition states along the Bergman cyclization pathways connecting enediynes to reactive para-biradicals. Sum method correction to low-level calculations confirmed B3LYP/6-31G(d,p) as the method of choice in investigating enediynes. Herein described as MI:Sum, calculated reaction enthalpies differed from experiment by an average of 2.1 kcal x mol(-1) (mean unsigned error). A combination of strain energy released across the reaction coordinate and the critical intramolecular distance between reacting diynes explains reactivity differences. Where experimental and calculated barrier heights are in disagreement, higher level multireference treatment of the enediynes confirms lower level estimates. Previous work concerning the chemically reactive fragment of esperamcin, MTC, is expanded to our model system MTC2.
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Affiliation(s)
| | | | - Frank C. Pickard
- Department of Chemistry Center for Molecular Design Hamilton College Clinton, NY 13323
| | - Chantelle Rein
- Department of Chemistry Center for Molecular Design Hamilton College Clinton, NY 13323
| | - Steven Feldgus
- Department of Chemistry Center for Molecular Design Hamilton College Clinton, NY 13323
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74
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Vicente J, Saura-Llamas I, García-López JA, Bautista D. Insertion of Isocyanides, Isothiocyanates, and Carbon Monoxide into the Pd−C Bond of Cyclopalladated Complexes Containing Primary Arylalkylamines of Biological and Pharmaceutical Significance. Synthesis of Lactams and Cyclic Amidinium Salts Related to the Isoquinoline, Benzo[g]isoquinoline, and β-Carboline Nuclei. Organometallics 2008. [DOI: 10.1021/om800951k] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- José Vicente
- Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
| | - Isabel Saura-Llamas
- Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
| | - José-Antonio García-López
- Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
| | - Delia Bautista
- SAI, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
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75
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Wang EB, Parish CA, Lischka H. An extended multireference study of the electronic states of para-benzyne. J Chem Phys 2008; 129:044306. [DOI: 10.1063/1.2955744] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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76
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Kraka E, Tuttle T, Cremer D. Design of a new warhead for the natural enediyne dynemicin A. An increase of biological activity. J Phys Chem B 2008; 112:2661-70. [PMID: 18269275 DOI: 10.1021/jp0773536] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A concept for designing nontoxic enediyne-based antitumor drugs that was previously suggested (J. Am. Chem. Soc. 2000, 122, 8245) is converted into reality by merging amidines with the natural enediyne dynemicin A. The dynemicin-amidines (DADs) resulting from this combination are biologically not active because they form extremely labile singlet biradicals that can no longer abstract H from DNA. However, if protonated in the acidic environment of the tumor cell, they possess increased biological activity, as is reflected by a lowering of the activation enthalpy for the Bergman cyclization from 16.7 (dynemicin A) to 11-12 kcal/mol (DADs), kinetic stability of the singlet biradicals formed in the cyclization reaction, increased H abstraction ability of the singlet biradicals, and improved docking properties in the minor groove of the duplex 10-mer B-DNA sequence d(CTACTACTGG).d(CCAGTAGTAG) throughout the triggering and Bergman reactions. The implications and the consequences of using DADs to exploit the differences between normal and tumor cells and to design a nontoxic antitumor drugs are discussed.
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Affiliation(s)
- Elfi Kraka
- Department of Chemistry and Department of Physics, University of the Pacific, 3601 Pacific Avenue, Stockton, California 95211-0110, USA
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77
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Papp P, Neogrady P, Mach P, Pittner J, Huba[cbreve] I, Wilson S. Many-body Brillouin–Wigner second-order perturbation theory: an application to the autoaromatisation of hex-3-ene-1,5-diyne (the Bergman reaction). Mol Phys 2008. [DOI: 10.1080/00268970701832355] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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78
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Kraka E, Tuttle T, Cremer D. The Reactivity of Calicheamicin γ1I in the Minor Groove of DNA: The Decisive Role of the Environment. Chemistry 2007; 13:9256-69. [PMID: 17694527 DOI: 10.1002/chem.200700504] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Triggering and Bergman cyclization of calicheamicin gamma(1) (I) outside and inside the minor groove of the duplex 9mer-B-DNA sequence d(CACTCCTGG).d(CCAGGAGTG) were investigated by using density functional theory and molecular mechanics (DFT and MM) descriptions in which the ligand is completely described at the DFT and the receptor at the MM level. The calculated docking energy of calicheamicin gamma(1) (I) (-12.5 kcal mol(-1)) is close to the measured value of -9.7 kcal mol(-1) and the site specificity is in line with experimental observations. Calicheamicin is triggered in the minor groove in such a way that out of a cyclohexenone by Michael addition an E rather than a Z form of a cyclohexanone is formed, which in turn adopts a chair rather than a twistboat form. Decisive for the stereochemistry of the Michael addition is the orientation of the carbamate substituent at the headgroup of calicheamicin. Triggered calicheamicin can undergo the Bergman cyclization at body temperature only if present in its E chair form (activation enthalpy 16.4 kcal mol(-1)). An intermediate biradical is formed (docking energy -13.6 kcal mol(-1)), which has a sufficient lifetime to abstract two hydrogen atoms. Hydrogen abstraction is a two- rather than one-step process and involves the C5(H5') atom first and then the T22(H4') atom in line with experimental observations. The decisive role of using a DFT rather than an MM description for the ligand is documented.
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Affiliation(s)
- Elfi Kraka
- Department of Chemistry and Department of Physics, University of the Pacific, Stockton, CA 95211-0110, USA.
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79
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Poloukhtine A, Popik VV. Synthesis and unusual reactivity of N-tosyl-4,5-benzoazacyclodeca-2,6-diyne, yneamino-containing enediyne. J Am Chem Soc 2007; 129:12062-3. [PMID: 17877347 DOI: 10.1021/ja073614d] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Andrei Poloukhtine
- Department of Chemistry, The University of Georgia, Athens, Georgia 30602, USA
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80
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Tuttle T, Kraka E, Thiel W, Cremer D. A QM/MM Study of the Bergman Reaction of Dynemicin A in the Minor Groove of DNA. J Phys Chem B 2007; 111:8321-8. [PMID: 17585802 DOI: 10.1021/jp072373t] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The Bergman cyclization of the natural enediyne dynemicin A in its triggered form (2) bound to the minor groove of DNA is compared with the corresponding reaction of its open isomer (4) utilizing QM/MM methodology. The two isomers are typical representatives of 10-membered cyclic (2) and acyclic (4) enediynes, which possess significantly different barriers for the Bergman reaction in the gas phase (2, 20.4 kcal/mol; 4, 31.3 kcal/mol). In the case of the cyclic enediyne (2) the explicit consideration of environmental factors such as the receptor DNA, the solvent water, and charge neutralization by counterions has only minor effects on the energy profile of the cyclization reaction and the corresponding optimized structures when compared with the gas phase. The energetics of the reaction is predominantly determined by QM (electronic) effects. This makes it possible to replace the explicit description of the environment by an implicit one, thus avoiding costly QM/MM calculations and using instead a decoupled QM+MM approach. A conformationally driven hinge mechanism is identified for 2 that makes it possible for the ligand to adjust to the dimensions of the minor groove without significant energy loss. In the case of the acyclic enediyne 4 a QM/MM treatment is necessary to describe the Bergman cyclization in the minor groove. QM/MM corrects the cyclization barrier from 31.3 to 23.7 kcal/mol, which makes the reaction feasible under physiological conditions. The reduction of the barrier is a result of transition-state stabilization, which is caused by an increased dipole moment and hence stronger electrostatic interactions with the environment. In both cases the anionic charge of dynemicin A is largely shielded by water solvation and ion pair formation so that it does not significantly affect the energetics of the Bergman cyclization.
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Affiliation(s)
- Tell Tuttle
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470, Mülheim an der Ruhr, Germany
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81
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Cycloaromatization reactions: the testing ground for theory and experiment. ADVANCES IN PHYSICAL ORGANIC CHEMISTRY 2007. [DOI: 10.1016/s0065-3160(07)42001-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
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82
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Liu HC, Zhang XH, Wang C, Wu YD, Yang S. Pyridyne radical cations produced by photodissociation of Mg˙+(multifluoro-pyridine) complexes: A combined experimental and theoretical study. Phys Chem Chem Phys 2007; 9:607-15. [PMID: 17242742 DOI: 10.1039/b614445d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Gas phase complexes Mg*+ (2,6-difluoropyridine) (1) and Mg*+ (pentafluoropyridine) (2) have been subjected to photodissociation in the spectral range of approximately 230-440 nm. Except for the evaporative photofragment Mg*+ , the primary photoproduct for is C(5)H(3)N*(+), which is associated with the rupture of two C-F bonds by the photoexcited Mg*+ , forming very stable MgF(2). In contrast, the direct loss of MgF(+) is more favorable for due to fluorine substitution. Given enough energy, C(5)H(3)N*(+) can undergo decomposition to form C(4)H(2)*(+) and HCN. These results are very different from those for Mg*+ (2-fluoropyridine), highlighting the significance of the additional F at C6 of and . Density functional theory (DFT) calculations have been employed to examine the geometries and energetics of the complexes as well as relevant reaction mechanisms. All of the complexes feature the direct attachment of Mg*+ to the N atom. The key intermediate is found to be FMg(+) (C(5)H(x)F(4-x)N) (x = 3 or 0), which can lead to the formation of MgF(+) directly or MgF(2) through activation of another C-F bond adjacent to N, producing the pyridyne radical cations. However, hydrogen-transfer prior to the rupture of the second C-F bond followed by ring-opening of C(5)H(3)N*(+) may result in the formation of chain forms of C(5)H(3)N*(+). The influence of the fluorine substitution on the competition of the two routes have been demonstrated.
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Affiliation(s)
- Hai-Chuan Liu
- Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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83
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Theoretical study of the regioselectivity of the cycloaddition reaction between cyclopentadiene and methyleneketene. Tetrahedron 2006. [DOI: 10.1016/j.tet.2006.04.067] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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84
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Feng L, Zhang A, Kerwin SM. Enediynes from Aza-Enediynes: C,N-Dialkynyl Imines Undergo Both Aza-Bergman Rearrangement and Conversion to Enediynes and Fumaronitriles. Org Lett 2006; 8:1983-6. [PMID: 16671762 DOI: 10.1021/ol0600638] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction; see text] Aza-enediynes (C,N-dialkynyl imines) undergo thermal aza-Bergman rearrangement to beta-alkynyl acrylonitriles through 2,5-didehydropyridine (2,5-ddp) intermediates. Certain aza-enediynes also undergo an alternative process affording enediynes and fumaronitriles. Studies employing a specifically (l3)C-labeled aza-enediyne show that the conversion to enediyne is second order in aza-enediyne, proceeds by a "head-to-tail" coupling, and affords the (Z)-enediyne.
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Affiliation(s)
- Liping Feng
- Division of Medicinal Chemistry, College of Pharmacy and Institute for Cellular and Molecular Biology, The University of Texas at Austin, 78712, USA
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85
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Nadipuram AK, Kerwin SM. Thermal cyclization of 1,2-dialkynylimidazoles to imidazo[1,2-a]pyridines. Tetrahedron 2006. [DOI: 10.1016/j.tet.2005.11.084] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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86
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Pickard FC, Shepherd RL, Gillis AE, Dunn ME, Feldgus S, Kirschner KN, Shields GC, Manoharan M, Alabugin IV. Ortho Effect in the Bergman Cyclization: Electronic and Steric Effects in Hydrogen Abstraction by 1-Substituted Naphthalene 5,8-Diradicals. J Phys Chem A 2006; 110:2517-26. [PMID: 16480313 DOI: 10.1021/jp0562835] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a detailed theoretical study of geometries, electronic structure, and energies of transition states and intermediates completing the full Bergman cycloaromatization pathway of ortho-substituted enediynes with a focus on polar and steric contributions to the kinetics and thermodynamics of hydrogen abstraction. This study provides a rare unambiguous example of remote substitution that affects reactivity of a neutral reactive intermediate through an sigma framework.
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Affiliation(s)
- Frank C Pickard
- Department of Chemistry, Hamilton College, Clinton, New York 13323, USA
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87
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Zeidan TA, Manoharan M, Alabugin IV. Ortho Effect in the Bergman Cyclization: Interception of p-Benzyne Intermediate by Intramolecular Hydrogen Abstraction. J Org Chem 2006; 71:954-61. [PMID: 16438507 DOI: 10.1021/jo051857n] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intramolecular hydrogen atom (H-atom) abstraction from the o-OCH3 group effectively intercepts the p-benzyne intermediate in the Bergman cycloaromatization of 2,3-diethynyl-1-methoxybenzene (1) before this intermediate undergoes either retro-Bergman ring opening or external H-atom abstraction. This process leads to the formation of a new diradical and renders the cyclization step essentially irreversible. Chemical and kinetic consequences of this phenomenon were investigated through the combination of computational and experimental studies.
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Affiliation(s)
- Tarek A Zeidan
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
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88
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Tuttle T, Kraka E, Cremer D. Docking, triggering, and biological activity of dynemicin A in DNA: a computational study. J Am Chem Soc 2005; 127:9469-84. [PMID: 15984874 DOI: 10.1021/ja046251f] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The triggering and biological activity of the naturally occurring enediyne dynemicin A (1) was investigated, both inside and outside the minor groove of the duplex 10-mer B-DNA sequence d(CTACTACTGG).d(CCAGTAGTAG), using density functional theory (B3LYP with the 3-21G and 6-31G(d) basis set), BD(T)/cc-pVDZ (Brueckner doubles with a perturbative treatment of triple excitations), and the ONIOM approach. Enediyne 1 is triggered by NADPH in a strongly exothermic reaction (-88 kcal/mol), which involves a number of intermediate steps. Untriggered 1 has a high barrier for the Bergman cyclization (52 kcal/mol) that is lowered after triggering to 16.7 kcal/mol due to an epoxide opening and the accompanying strain relief. The Bergman reaction of triggered 1 is slightly exothermic by 2.8 kcal/mol. The singlet biradical formed in this reaction is kinetically stable (activation enthalpies of 19.5 and 21.8 kcal/mol for retro-Bergman reactions) and is as reactive as para-benzyne. The activity-relevant docking mode is an edge-on insertion into the minor groove, whereas the intercalation between base pairs, although leading to larger binding energies, excludes a triggering of 1 and the development of its biological activity. Therefore, an insertion-intercalation model is developed, which can explain all known experimental observations made for 1. On the basis of the insertion-intercalation model it is explained why large intercalation energies suppress the biological activity of dynemicin and why double-strand scission can be achieved only in a two-step mechanism that involves two enediyne molecules, explaining thus the high ratio of single-strand to double-strand scission observed for 1.
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Affiliation(s)
- Tell Tuttle
- Department of Chemistry and Department of Physics, University of the Pacific, 3601 Pacific Avenue, Stockton, California 95211-0110, USA
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89
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Kar M, Basak A, Bhattacharjee M. Photoisomerization as a trigger for Bergman cyclization: Synthesis and reactivity of azoenediynes. Bioorg Med Chem Lett 2005; 15:5392-6. [PMID: 16236507 DOI: 10.1016/j.bmcl.2005.09.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2005] [Revised: 08/27/2005] [Accepted: 09/02/2005] [Indexed: 10/25/2022]
Abstract
Cyclic enediynes 1a and 2a containing stable E-azo moiety (azoenediynes) have been synthesized. These compounds upon irradiation with long wavelength UV isomerize to the Z-compounds 1b and 2b, which can be thermally reisomerized to the Z compounds. Reactivity studies toward BC using DSC predictably indicate higher reactivity for the Z-isomers. Our studies may provide a novel way to modulate the reactivity of enediynes under thermal or photochemical conditions.
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Affiliation(s)
- Moumita Kar
- Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India
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90
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Nash JJ, Kenttämaa HI, Cramer CJ. Quantum Chemical Characterization of the Structures, Thermochemical Properties, and Singlet−Triplet Splittings of Didehydroquinolinium and Didehydroisoquinolinium Ions. J Phys Chem A 2005; 109:10348-56. [PMID: 16833330 DOI: 10.1021/jp053774g] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Structural and energetic properties are predicted for the 21 didehydroquinolinium ion isomers and 21 didehydroisoquinolinium ion isomers in their lowest-energy singlet and triplet states by using density functional and multireference second-order perturbation theories. Singlet-triplet splittings and biradical stabilization energies are examined to gain insight into the degree of interaction between the biradical centers, with comparison being made to analogous didehydronaphthalenes and didehydropyridines.
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Affiliation(s)
- John J Nash
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
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91
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Alabugin IV, Manoharan M. Thermodynamic and Strain Effects in the Competition between 5-Exo-dig and 6-Endo-dig Cyclizations of Vinyl and Aryl Radicals. J Am Chem Soc 2005; 127:12583-94. [PMID: 16144406 DOI: 10.1021/ja052677y] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Electronic and structural factors controlling the competition between 5-exo-dig and 6-endo-dig cyclizations of sp2-radicals were analyzed using a combination of available experimental data and computation. Although the stereoelectronically favored 5-exo pathways usually has the lower activation energy, formation of a new aromatic ring not only makes the 6-endo process favorable thermodynamically in conjugated systems but also lowers its activation barrier to the extent where the 5-exo/6-endo selectivity is controlled by subtle factors such as the different sensitivity of the two pathways to strain effects in polycyclic systems. In particular, the stronger sensitivity of the 5-exo pathway to strain leads to a crossover in selectivity. The 6-endo cyclization is kinetically favored in smaller (and strained) cycles, whereas the 5-exo cyclization has lower barriers in the larger rings.
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Affiliation(s)
- Igor V Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.
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92
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Kinal A, Piecuch P. Is the Mechanism of the [2+2] Cycloaddition of Cyclopentyne to Ethylene Concerted or Biradical? A Completely Renormalized Coupled Cluster Study. J Phys Chem A 2005; 110:367-78. [PMID: 16405307 DOI: 10.1021/jp0513216] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The mechanism of the [2+2] cycloaddition reaction of cyclopentyne to ethylene has been studied using the completely renormalized coupled cluster method with singles, doubles, and noniterative triples (CR-CCSD(T)). In agreement with the experimentally observed stereochemistry, the CR-CCSD(T) method favors the concerted pathway involving a [2+1] transition state, whereas the popular CCSD(T) method, which is often regarded as the "gold standard" of electronic structure theory, and low-order multireference methods support the less probable biradical mechanism. In addition, the CCSD(T) approach produces an erroneous description of some transition states and intermediates, particularly those which have a significant biradical character. The CR-CCSD(T) calculations indicate that the reaction is a highly exothermic (deltaG(r)298 = -68 kcal/mol), predominantly concerted process with a relatively low activation barrier on the order of 13-16 kcal/mol which permits its thermal occurrence.
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Affiliation(s)
- Armagan Kinal
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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93
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Alabugin IV, Manoharan M. 5-Endo-Dig Radical Cyclizations: “The Poor Cousins” of the Radical Cyclizations Family. J Am Chem Soc 2005; 127:9534-45. [PMID: 15984880 DOI: 10.1021/ja050976h] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Kinetics and thermodynamics of 5-endo-dig radical cyclizations were studied using a combination of DFT computations and Marcus theory. When the reactant is stabilized by conjugation of the radical center with the bridge pi-system, the cyclization starts with reorientation of the radical orbital needed to reach the in-plane acetylene pi-orbital in the bond-forming step. This reorientation leads to loss of the above conjugative stabilization, increases the activation energy, and renders such cyclizations less exothermic. As a result, even when the radical needed for the 5-endo cyclization is formed efficiently, it undergoes either H-abstraction or equilibration with an isomeric radical. Only when the bridging moiety is saturated or when intramolecular constraints prevent the overlap of the bridge pi-orbital and the radical center, 5-endo cyclizations may be able to proceed with moderate efficiency under conditions when H-abstraction is slow. The main remaining caveat in designing such geometrically constrained 5-endo-dig cyclizations is their sensitivity to strain effects, especially when polycyclic systems are formed. The strain effects can be counterbalanced by increasing the stabilization of the product (e.g., by introducing heteroatoms into the bridging moiety). Electronic effects of such substitutions can be manifested in various ways, ranging from aromatic stabilization to a hyperconjugative beta-Si effect. The 4-exo-dig cyclization is kinetically competitive with the 5-endo-dig process but less favorable thermodynamically. As a result, by proper design of reaction conditions, 5-endo-dig radical cyclizations should be experimentally feasible.
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Affiliation(s)
- Igor V Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.
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94
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Marsella MJ, Yoon K, Estassi S, Tham FS, Borchardt DB, Bui BH, Schreiner PR. 1,4-Addition of Benzene to a Dihydrocyclopent[a]indene Diradical: Synthesis and DFT Study. J Org Chem 2005; 70:1881-4. [PMID: 15730313 DOI: 10.1021/jo0485132] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Photochemical cyclization of compound 1, a homoenediyne (-CCC=CCH2CC-) bearing two ethynylanthracene chromophores, yields two isomeric dihydrocyclopent[a]indene ring systems, spiro-fused to the 9-position of a 9,10-dihydroanthracene moiety. Evidence of a photochemically initiated diradical cyclization pathway is proposed on the basis of (i) hydrogen abstraction from reaction with 1,4-cyclohexadiene (1,4-CHD) and (ii) the observation of 1,4-addition of benzene (solvent). The reaction was further analyzed by a complete density functional theory (DFT) study, using an unrestricted approach (UBLYP) with a 6-31G* basis set for the open-shell triplet states of the reactants, products, and diradical intermediates to model the photochemical nature of observed transformation. A mechanism detailing the observed cyclization/addition reaction is proposed.
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Affiliation(s)
- Michael J Marsella
- Department of Chemistry, University of California at Riverside, Riverside, California 92506-0403, USA.
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95
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Stampfuss P, Wenzel W. Improved implementation and application of the individually selecting configuration interaction method. J Chem Phys 2005; 122:024110. [PMID: 15638575 DOI: 10.1063/1.1829045] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report on the progress of our implementation of the configuration-selecting multireference configuration interaction method on massively parallel architectures with distributed memory, which now permits the treatment of Hilbert spaces of dimension O(10(12)). Of these about 50,000,000 can be selected in the variational subspace. We provide scaling data for the running time of the code for the IBM/SP3 and the CRAY-T3E. We present benchmark results for two selected applications: the energetics of the isomers of dinitrosoethylene and the benchmark results for the ring closure reaction of enediyene.
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Affiliation(s)
- P Stampfuss
- Forschungszentrum Karlsruhe, Institut für Nanotechnologie, Postfach 3640, 76021 Karlsruhe, Germany
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96
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Schreiner PR, Navarro-Vázquez A, Prall M. Computational studies on the cyclizations of enediynes, enyne-allenes, and related polyunsaturated systems. Acc Chem Res 2005; 38:29-37. [PMID: 15654734 DOI: 10.1021/ar020270h] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Quantum chemical studies of cyclizations of enediynes and enyne-allenes have proven to be computationally tractable thanks to the success of the unrestricted broken spin symmetry (UBS) approach using GGA functionals for the description of open-shell biradicals; the results can further be improved through single-point energy coupled-cluster computations [CCSD(T), BD(T)]. This made comprehensive computational studies on substituent effects and heterosubstituted systems possible. For convenience and predicting new reactions, these transformations can be grouped within larger "families". Alternative cyclization modes are predicted and await experimental realization.
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Affiliation(s)
- Peter R Schreiner
- Institute of Organic Chemistry, Justus-Liebig-University, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany.
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97
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Feng L, Kumar D, Birney DM, Kerwin SM. α,5-Didehydro-3-picoline Diradicals from Skipped Azaenediynes: Computational and Trapping Studies of an Aza-Myers−Saito Cyclization. Org Lett 2004; 6:2059-62. [PMID: 15176818 DOI: 10.1021/ol049266r] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] On the basis of density functional calculations, the isomerization of skipped azaenediynes (C-alkynyl-N-propargylimines) to azaenyne allenes and subsequent rapid aza-Myers-Saito cyclization to alpha,5-didehydro-3-picoline were predicted. We prepared the N-propargylimine of 1-phenyl-3-tri(isopropyl)silylprop-2-yn-1-one, which undergoes proto-desilylation and isomerization to an azaenyne allene when treated with tetrabutylammonium fluoride. In the presence of 1,4-cyclohexadiene, this azaenyne allene affords 6-phenyl-3-picoline and other products corresponding to the trapping of an alpha,5-didehydro-3-picoline diradical.
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Affiliation(s)
- Liping Feng
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, Texas 78712, USA
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98
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Banfi L, Basso A, Gandolfo V, Guanti G, Riva R. Asymmetric synthesis of a new simplified dynemicin analogue equipped with a handle. Tetrahedron Lett 2004. [DOI: 10.1016/j.tetlet.2004.04.029] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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99
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Winkler M, Cakir B, Sander W. 3,5-PyridyneA Heterocyclic meta-Benzyne Derivative. J Am Chem Soc 2004; 126:6135-49. [PMID: 15137779 DOI: 10.1021/ja039142u] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
3,5-Pyridyne (3) has been generated by flash vacuum pyrolysis of 3,5-diiodopyridine (20) and 3,5-dinitropyridine (21) and characterized by IR spectroscopy in cryogenic argon matrices. The aryne can clearly be distinguished from other side products by its photolability at 254 nm, inducing a rapid ring-opening presumably to (Z)-1-aza-hex-3-ene-1,5-diyne. As byproducts of the pyrolysis, HCN and butadiyne were identified, together with traces of acetylene, cyanoacetylene, (E)-1-aza-hex-3-ene-1,5-diyne, and the 3-iodo-5-pyridyl radical (from 20). Several pathways for rearrangements and fragmentations of 3 and of the parent meta-benzyne (1) have been explored computationally by density functional theory and ab initio quantum chemical methods. The lowest energy decomposition pathway of biradicals 1 and 3 is a ring-opening process accompanied by hydrogen migration, leading to (Z)-hex-3-ene-1,5-diyne [(Z)-10] and (Z)-3-aza-hex-3-ene-1,5-diyne [(Z)-24], respectively. Both reactions require activation energies of 45-50 kcal mol(-1). Mechanisms leading from (Z)-24 or directly from 3 to the experimentally observed byproducts are discussed. Upon replacement of the C(5)H moiety by N in meta-benzyne, high-level calculations predict a modest shortening of the interradical distance by 5-7 pm and a reduction of the singlet-triplet energy splitting by 3 kcal mol(-1), in good agreement with isodesmic equations, according to which the singlet ground state of 3 is destabilized relative to 1 by 3-4 kcal mol(-1). In contrast to 3,5-borabenzyne (2), which is found to be doubly aromatic, nucleus-independent chemical shifts of 3 are almost identical to that of pyridine, indicating the absence of paramagnetic ring current effects that may be associated with "in-plane antiaromaticity". As compared with 1, the overall perturbation caused by the nitrogen atom in 3 is weak, and four electron, three center interaction is of minor importance in this molecule.
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Affiliation(s)
- Michael Winkler
- Lehrstuhl für Organische Chemie II der Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
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Liu H, Zhang X, Wang C, Guo W, Wu Y, Yang S. Effects of Aromatic Substitutions on the Photoreactions in Mg•+(C6HnF2X4-n) (X = F, CH3) Complexes: Formation and Decomposition of Benzyne Radical Cations. J Phys Chem A 2004. [DOI: 10.1021/jp037535+] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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