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Semenov VA, Larina LI. Stereochemical and Computational NMR Survey of 1,2,3-Triazoles: in Search of the Original Tauto-Conformers. J Phys Chem A 2024; 128:3231-3240. [PMID: 38512800 DOI: 10.1021/acs.jpca.3c08217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/23/2024]
Abstract
The conformational analysis of nine functionalized 1,2,3-triazoles was carried out by the correlation of calculated and experimental high-level nuclear magnetic resonance (NMR) chemical shifts. In solution, the studied triazoles are in exchange dynamic equilibrium caused by their prototropic tautomerism of the NH-proton. The experimentally unresolved NMR signals were assigned for most of the compounds. A more thorough survey was conducted for 4-t-butyl-1,2,3-triazole-5-carbaldehyde oxime. The analysis performed within the framework of the DP4+ formalism completely confirmed the hypothesis of the predominance of the 2H-tautomer. Thus, the methodology for estimating stereochemical structures in the absence of some experimental data allowed the most stable conformations for dynamic systems with different tautomeric ratios to be reliably identified.
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Affiliation(s)
- Valentin A Semenov
- A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky st. 1, Irkutsk 664033, Russia
| | - Lyudmila I Larina
- A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky st. 1, Irkutsk 664033, Russia
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2
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García-López J, Khomenko DM, Zakharchenko BV, Doroshchuk RO, Starova VS, Iglesias MJ, Lampeka RD, López-Ortiz F. Solvent- and functional-group-assisted tautomerism of 3-alkyl substituted 5-(2-pyridyl)-1,2,4-triazoles in DMSO-water. Org Biomol Chem 2023; 21:9443-9458. [PMID: 37997179 DOI: 10.1039/d3ob01651j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2023]
Abstract
The tautomerism of a series of 5-alkyl substituted 3-(2-pyridyl)-1,2,4-triazoles in DMSO-d6-containing water has been investigated by 1H, 13C and 15N NMR spectroscopy. The populations of the three possible regioisomers in the tautomeric equilibrium (A [3-alkyl-5-(2-pyridyl)-1H], B [5-alkyl-3-(2-pyridyl)-1H] and C [5-alkyl-3-(2-pyridyl)-4H]) were determined. Isomers A (17-40%) and B (54-79%) are the major components and their ratio is insensitive to the substitution pattern, except for the unsubstituted and the methoxymethyl substituted derivatives. The isomer C (3-5%) has been fully characterised for the first time by NMR spectroscopy. Activation energies of tautomerisation (14.74-16.78 kcal mol-1) were determined by EXSY experiments, which also supported the involvement of water in the tautomerisation. Substituent effects on the 15N chemical shifts are relatively small. The DFT study of the tautomerism in DMSO-water showed that both A/B and B/C interconversions are assisted by the pyridine substituent and catalysed by solvent molecules. The NH-A/NH-B tautomerisation takes place via a relayed quadruple proton transfer mediated by three water molecules in the hydrogen-bonded cyclic substructure of a triazole·4H2O complex. The equilibrium B ⇄ C involves three steps: NH-B transfer to the pyridyl nitrogen mediated by a water molecule in a 1 : 1 cyclic complex, rotamerisation to bring the pyridinium NH close to N4 of the triazole catalysed by complexation to a DMSO molecule and transfer of the NH from the pyridinium donor to the N4 acceptor via a 1 : 1 complex with a bridging water molecule. This mechanism of 1,3-prototropic shift in triazoles is unprecedented in the literature.
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Affiliation(s)
- Jesús García-López
- Área de Química Orgánica, Research Centre CIAIMBITAL, Universidad de Almería, Carretera de Sacramento s/n, Almería, 04120, Spain.
| | - Dmytro M Khomenko
- Department of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine.
| | - Borys V Zakharchenko
- Department of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine.
| | - Roman O Doroshchuk
- Department of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine.
| | - Viktoriia S Starova
- Department of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine.
| | - María José Iglesias
- Área de Química Orgánica, Research Centre CIAIMBITAL, Universidad de Almería, Carretera de Sacramento s/n, Almería, 04120, Spain.
| | - Rostyslav D Lampeka
- Department of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine.
| | - Fernando López-Ortiz
- Área de Química Orgánica, Research Centre CIAIMBITAL, Universidad de Almería, Carretera de Sacramento s/n, Almería, 04120, Spain.
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3
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Dobrikov GM, Nikolova Y, Slavchev I, Dangalov M, Deneva V, Antonov L, Vassilev NG. Structure and Conformational Mobility of OLED-Relevant 1,3,5-Triazine Derivatives. Molecules 2023; 28:molecules28031248. [PMID: 36770913 PMCID: PMC9921695 DOI: 10.3390/molecules28031248] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 01/24/2023] [Accepted: 01/25/2023] [Indexed: 01/31/2023] Open
Abstract
A series of OLED-relevant compounds, consisting of 1,3,5-triazine core linked to various aromatic arms by amino group, has been synthesized and characterized. The studied compounds exist in solution as a mixture of two conformers, a symmetric propeller and asymmetric conformer, in which one of the aromatic arms is rotated around the C-N bond. At temperatures below -40 °C, the VT NMR spectra in DMF-d7 are in a slow exchange regime, and the signals of two conformers can be elucidated. At temperatures above 100 °C, the VT NMR spectra in DMSO-d6 are in a fast exchange regime, and the averaged spectra can be measured. The ratio of symmetric and asymmetric conformers in DMF-d7 varies from 14:86 to 50:50 depending on the substituents. The rotational barriers of symmetric and asymmetric conformers in DMF-d7 were measured for all compounds and are in the interval from 11.7 to 14.7 kcal/mol. The ground-state energy landscapes of the studied compounds, obtained by DFT calculations, show good agreement with the experimental rotational barriers. The DFT calculations reveal that the observed chemical exchange occurs by the rotation around the C(1,3,5-triazine)-N bond. Although some of the compounds are potentially tautomeric, the measured absorption and emission spectra do not indicate proton transfer neither in the ground nor in the excited state.
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Affiliation(s)
- Georgi M. Dobrikov
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113 Sofia, Bulgaria
| | - Yana Nikolova
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113 Sofia, Bulgaria
| | - Ivaylo Slavchev
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113 Sofia, Bulgaria
| | - Miroslav Dangalov
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113 Sofia, Bulgaria
| | - Vera Deneva
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113 Sofia, Bulgaria
- Institute of Electronics, Bulgarian Academy of Sciences, 72 Tsarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
| | - Liudmil Antonov
- Institute of Electronics, Bulgarian Academy of Sciences, 72 Tsarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
| | - Nikolay G. Vassilev
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113 Sofia, Bulgaria
- Correspondence:
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4
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Deneva V, Slavova S, Kumanova A, Vassilev N, Nedeltcheva-Antonova D, Antonov L. Favipiravir-Tautomeric and Complexation Properties in Solution. Pharmaceuticals (Basel) 2022; 16:ph16010045. [PMID: 36678542 PMCID: PMC9864296 DOI: 10.3390/ph16010045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 12/16/2022] [Accepted: 12/23/2022] [Indexed: 12/31/2022] Open
Abstract
The tautomeric properties of favipiravir were investigated experimentally for the first time by using molecular spectroscopy (UV-Vis absorption, fluorescence and NMR), as well as DFT quantum-chemical calculations. According to the obtained results, the enol tautomer is substantially more stable in most of the organic solvents. In the presence of water, a keto form appears to be favored due to the specific solute-solvent interactions. Upon the addition of alkaline-earth-metal ions, deprotonation and complexation occurred simultaneously, giving the formation of 2 : 1 ligand : metal complexes. According to the theoretical simulations, the metal ion is captured between the carbonyl groups as a result of the size-fit effect.
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Affiliation(s)
- Vera Deneva
- Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
- Correspondence: (V.D.); (L.A.)
| | - Sofia Slavova
- Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
- Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Alina Kumanova
- Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
| | - Nikolay Vassilev
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Daniela Nedeltcheva-Antonova
- Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Luidmil Antonov
- Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
- Correspondence: (V.D.); (L.A.)
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5
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Theoretical study on the origins of sildenafil tautomers’ relative stability. Z PHYS CHEM 2022. [DOI: 10.1515/zpch-2022-0090] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Abstract
Tautomers of sildenafil (5-{2-Ethoxy-5-[(4-methylpiperazin-1-yl)sulfonyl]phenyl}-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one), a drug commonly used for treating the erectile dysfunction and pulmonary arterial hypertension were studied computationally at the DFT (B3LYP/6-311++G**) level. Four possible structures of sildenafil tautomers structures were considered. The geometries and chemical shifts of carbon and nitrogen nuclei were calculated and compared with available experimental data. The theoretical calculations proved to be consistent with experimental data and indicate the same lowest energy sildenafil structure. The energies of the all considered sildenafil tautomers were determined and ranked according to their energy values. This article presents calculations of several properties (aromaticity, atomic charges, atomic energies, intramolecular hydrogen bonding) and discusses their influence on the relative energies of sildenafil tautomers.
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6
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3,6-Dihydro-5H-pyrazolo [4′,3′:5,6]pyrano[3,4-b]indol-5-one. MOLBANK 2022. [DOI: 10.3390/m1412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Pyrano [3,4-b]indol-1(9H)-ones and indolo [2,3-c]coumarins are important classes of heterocyclic compounds with versatile biological activities. Herein, we describe a straightforward and scalable synthesis of 3,6-dihydro-5H-pyrazolo [4′,3′:5,6]pyrano [3,4-b]indol-5-one, a pyrazolo-fused pyrano [3,4-b]indolone, via a three step approach including Fischer-indole synthesis and intramolecular esterification. The compound is fully characterized by means of 1H and 13C NMR spectra, using direct and long-range heteronuclear correlation experiments (HMBC and HMQC).
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7
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The Structure of Biologically Active Functionalized Azoles: NMR Spectroscopy and Quantum Chemistry. MAGNETOCHEMISTRY 2022. [DOI: 10.3390/magnetochemistry8050052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This review summarizes the data on the stereochemical structure of functionalized azoles (pyrazoles, imidazoles, triazoles, thiazoles, and benzazoles) and related compounds obtained by multipulse and multinuclear 1H, 13C, 15N NMR spectroscopy and quantum chemistry. The stereochemistry of functionalized azoles is a challenging topic of theoretical research, as the correct interpretation of their chemical behavior and biological activity depends on understanding the factors that determine the stereochemical features and relative stability of their tautomers. NMR spectroscopy, in combination with quantum chemical calculations, is the most convenient and reliable approach to the evaluation of the stereochemical behavior of, in particular, nitrogen-containing heteroaromatic and heterocyclic compounds. Over the last decade, 15N NMR spectroscopy has become almost an express method for the determination of the structure of nitrogen-containing heterocycles.
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Largy E, König A, Ghosh A, Ghosh D, Benabou S, Rosu F, Gabelica V. Mass Spectrometry of Nucleic Acid Noncovalent Complexes. Chem Rev 2021; 122:7720-7839. [PMID: 34587741 DOI: 10.1021/acs.chemrev.1c00386] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Nucleic acids have been among the first targets for antitumor drugs and antibiotics. With the unveiling of new biological roles in regulation of gene expression, specific DNA and RNA structures have become very attractive targets, especially when the corresponding proteins are undruggable. Biophysical assays to assess target structure as well as ligand binding stoichiometry, affinity, specificity, and binding modes are part of the drug development process. Mass spectrometry offers unique advantages as a biophysical method owing to its ability to distinguish each stoichiometry present in a mixture. In addition, advanced mass spectrometry approaches (reactive probing, fragmentation techniques, ion mobility spectrometry, ion spectroscopy) provide more detailed information on the complexes. Here, we review the fundamentals of mass spectrometry and all its particularities when studying noncovalent nucleic acid structures, and then review what has been learned thanks to mass spectrometry on nucleic acid structures, self-assemblies (e.g., duplexes or G-quadruplexes), and their complexes with ligands.
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Affiliation(s)
- Eric Largy
- Univ. Bordeaux, CNRS, INSERM, ARNA, UMR 5320, U1212, IECB, F-33600 Pessac, France
| | - Alexander König
- Univ. Bordeaux, CNRS, INSERM, ARNA, UMR 5320, U1212, IECB, F-33600 Pessac, France
| | - Anirban Ghosh
- Univ. Bordeaux, CNRS, INSERM, ARNA, UMR 5320, U1212, IECB, F-33600 Pessac, France
| | - Debasmita Ghosh
- Univ. Bordeaux, CNRS, INSERM, ARNA, UMR 5320, U1212, IECB, F-33600 Pessac, France
| | - Sanae Benabou
- Univ. Bordeaux, CNRS, INSERM, ARNA, UMR 5320, U1212, IECB, F-33600 Pessac, France
| | - Frédéric Rosu
- Univ. Bordeaux, CNRS, INSERM, IECB, UMS 3033, F-33600 Pessac, France
| | - Valérie Gabelica
- Univ. Bordeaux, CNRS, INSERM, ARNA, UMR 5320, U1212, IECB, F-33600 Pessac, France
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9
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Tang Y, Huang W, Chinnam AK, Singh J, Staples RJ, Shreeve JM. Energetic Tricyclic Polynitropyrazole and Its Salts: Proton-Locking Effect of Guanidium Cations. Inorg Chem 2021; 60:8339-8345. [PMID: 34014642 DOI: 10.1021/acs.inorgchem.1c01202] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An axisymmetric polynitro-pyrazole molecule, 3,5-di(3,5-dinitropyrazol-4-yl)]-4-nitro-1H-pyrazole (5), and its salts (6-12) were prepared and fully characterized. These compounds not only show promising energetic properties but also show a unique tautomeric switch via combining different cations with the axisymmetric compound (5). Its salts (6-9) remain axisymmetric when the cations are potassium, ammonium, or amino-1,2,4-triazolium. However, when the cations are guanidiums, the salts (10-12) dramatically become asymmetric owing to the fixed proton. The introduction of guanidium cations breaks the tautomeric equilibrium by blocking the prototropic transformations and results in the switch-off effect to tautomerism. The structural constraints of 1H NMR and 13C NMR spectra provide strong evidence for the unusual structural constraint phenomenon. These stabilized asymmetric tautomers are very important from the point of molecular recognition, and this research may promote further developments in synthetic and isolation methodologies for novel bioactive pyrazole-based compounds.
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Affiliation(s)
- Yongxing Tang
- School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China.,Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, United States
| | - Wei Huang
- School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China
| | - Ajay Kumar Chinnam
- Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, United States
| | - Jatinder Singh
- Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, United States
| | - Richard J Staples
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Jean'ne M Shreeve
- Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, United States
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Stachelska-Wierzchowska A, Wierzchowski J. Non-typical nucleoside analogs as fluorescent and fluorogenic indicators of purine-nucleoside phosphorylase activity in biological samples. Anal Chim Acta 2020; 1139:119-128. [PMID: 33190694 DOI: 10.1016/j.aca.2020.09.018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Revised: 09/07/2020] [Accepted: 09/09/2020] [Indexed: 12/12/2022]
Affiliation(s)
- A Stachelska-Wierzchowska
- Department of Physics and Biophysics, University of Warmia and Mazury in Olsztyn, 4 Oczapowskiego St., PL-10-710, Olsztyn, Poland.
| | - J Wierzchowski
- Department of Physics and Biophysics, University of Warmia and Mazury in Olsztyn, 4 Oczapowskiego St., PL-10-710, Olsztyn, Poland.
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11
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Mech P, Makowski M, Kawiak A, Chylewska A. When biomolecules meet 2-hydrazinopyrazine: from theory through experiment to molecular levels using a wide spectrum of techniques. RSC Adv 2020; 10:40673-40688. [PMID: 35519225 PMCID: PMC9059145 DOI: 10.1039/d0ra06239a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Accepted: 10/21/2020] [Indexed: 11/21/2022] Open
Abstract
The design of drug structures that are non-toxic, easily transported and permeable to cellular barriers is currently one of the most growing research trends. Indeed, the structural similarity of 2-hydrazinopyrazine (2HP) to pyrazinamide, which has been successfully used in anti-tuberculosis therapy, makes 2HP a promising research object. Thus, herein, a complete analysis of the structure of 2HP and its physicochemical and cytotoxic properties was performed. Calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) binding studies were conducted, which demonstrated the higher affinity of 2HP to BSA. Furthermore, cytotoxicity tests were performed, which proved that 2HP was non-toxic to human skin keratinocyte cells. Accordingly, 2HP was initially classified as a compound with potential application. Physicochemical investigations were performed using a wide range of experiments, which were supported by DFT calculations using the B3LYP functional and 6-311+G** basis set. The good correlation, high quality and correctness of the obtained parameters were proven although the data was obtained using independent techniques. Additionally, 42 tautomeric (prototrophic) forms of 2HP were found by searching the conformational hyperspace. The most energy stable 2HP conformer structure and the partial charge distribution were established. The preferred 2HP ionic forms preferred were presented, and models of the equilibrium occurring in aqueous solution were proposed. The hydrophilic character of 2HP was established based on the partition coefficient values determined by both experiment and theory. The PCM and SMD solvent models of water and n-octanol were used. Structure, ionic forms, hydrophilic and non-cytotoxic character of 2-hydrazinopyrazine with stronger affinity to BSA than DNA were proved.![]()
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Affiliation(s)
- Paulina Mech
- University of Gdańsk, Faculty of Chemistry, Department of Bioinorganic Chemistry ul. Wita Stwosza 63 80-308 Gdańsk Poland
| | - Mariusz Makowski
- University of Gdańsk, Faculty of Chemistry, Department of Bioinorganic Chemistry ul. Wita Stwosza 63 80-308 Gdańsk Poland
| | - Anna Kawiak
- Intercollegiate Faculty of Biotechnology of University of Gdańsk and Medical University of Gdańsk, Laboratory of Plant Protection and Biotechnology ul. Abrahama 58 80-307 Gdańsk Poland
| | - Agnieszka Chylewska
- University of Gdańsk, Faculty of Chemistry, Department of Bioinorganic Chemistry ul. Wita Stwosza 63 80-308 Gdańsk Poland
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Krzymiński K, Zadykowicz B, Storoniak P, Wera M, Żamojć K. Tautomerism of N-substituted acridin-9-amines in the context of dynamic NMR and matrix isolation-FT-IR spectroscopy supported by DFT calculations and structural analysis. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2020.128424] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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13
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Zhang J, Qi S, Zhang C, Fan Z, Ding Q, Mao S, Dong Z. Controlling Keto–Enol Tautomerism of Ureidopyrimidinone to Generate a Single-Quadruple AADD-DDAA Dimeric Array. Org Lett 2020; 22:7305-7309. [DOI: 10.1021/acs.orglett.0c02644] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jing Zhang
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Shuaiwei Qi
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Chenyang Zhang
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Zengming Fan
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Qinwen Ding
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Shizhong Mao
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Zeyuan Dong
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
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14
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Stereochemistry and tautomerism of silicon-containing 1,2,3-triazole: ab initio and NMR study. Struct Chem 2020. [DOI: 10.1007/s11224-020-01570-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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15
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Bomzon B, Khunger Y, Subramanian R. A dielectric and spectrophotometric study of the tautomerization of 2-hydroxypyridine and 2-mercaptopyridine in water. RSC Adv 2020; 10:2389-2395. [PMID: 35494609 PMCID: PMC9048638 DOI: 10.1039/c9ra08392h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Accepted: 12/17/2019] [Indexed: 11/21/2022] Open
Abstract
The basic ionization (pk1) and acidic ionization (pk2) constants and equilibrium constant (KT) of 2HPy and 2MPy were determined. The pk1(s) of their N- and X-methyl derivatives (X = O, S) were also determined. The equilibrium constant of 2MPy is approximately 60 times greater than its oxygen analog, 2HPy. The micro-ionization constants of the functional groups, –NH (pkA and pkC) and –XH (pkB and pkD), were determined to provide further insights into the ionization equilibria of these N-heteroaromatic XH compounds (2HPy and 2MPy). The relaxation time of water (τ) in aqueous solutions of 2HPy and 2MPy are collectively used with the KT values to determine the forward (kf) and backward (kb) rate constants of tautomerization. Subsequently, the kf and kb are used to provide the rationale for the KT and τ values. The basic ionization (pk1) and acidic ionization (pk2) constants and equilibrium constant (KT) of 2HPy and 2MPy were determined.![]()
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Affiliation(s)
- Biswadeep Bomzon
- Department of Chemistry, Indian Institute of Technology Patna 801106 India
| | - Yashita Khunger
- Department of Chemistry, Indian Institute of Technology Patna 801106 India
| | - Ranga Subramanian
- Department of Chemistry, Indian Institute of Technology Patna 801106 India
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Secrieru A, O’Neill PM, Cristiano MLS. Revisiting the Structure and Chemistry of 3(5)-Substituted Pyrazoles. Molecules 2019; 25:molecules25010042. [PMID: 31877672 PMCID: PMC6982847 DOI: 10.3390/molecules25010042] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 12/13/2019] [Accepted: 12/19/2019] [Indexed: 11/16/2022] Open
Abstract
Pyrazoles are known as versatile scaffolds in organic synthesis and medicinal chemistry, often used as starting materials for the preparation of more complex heterocyclic systems with relevance in the pharmaceutical field. Pyrazoles are also interesting compounds from a structural viewpoint, mainly because they exhibit tautomerism. This phenomenon may influence their reactivity, with possible impact on the synthetic strategies where pyrazoles take part, as well as on the biological activities of targets bearing a pyrazole moiety, since a change in structure translates into changes in properties. Investigations of the structure of pyrazoles that unravel the tautomeric and conformational preferences are therefore of upmost relevance. 3(5)-Aminopyrazoles are largely explored as precursors in the synthesis of condensed heterocyclic systems, namely pyrazolo[1,5-a]pyrimidines. However, the information available in the literature concerning the structure and chemistry of 3(5)-aminopyrazoles is scarce and disperse. We provide a revision of data on the present subject, based on investigations using theoretical and experimental methods, together with the applications of the compounds in synthesis. It is expected that the combined information will contribute to a deeper understanding of structure/reactivity relationships in this class of heterocycles, with a positive impact in the design of synthetic methods, where they take part.
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Affiliation(s)
- Alina Secrieru
- Center of Marine Sciences, CCMAR, Gambelas Campus, University of Algarve, UAlg, 8005-139 Faro, Portugal;
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK;
- Department of Chemistry and Pharmacy, Faculty of Sciences and Technology, FCT, Gambelas Campus, University of Algarve, UAlg, 8005-139 Faro, Portugal
| | | | - Maria Lurdes Santos Cristiano
- Center of Marine Sciences, CCMAR, Gambelas Campus, University of Algarve, UAlg, 8005-139 Faro, Portugal;
- Department of Chemistry and Pharmacy, Faculty of Sciences and Technology, FCT, Gambelas Campus, University of Algarve, UAlg, 8005-139 Faro, Portugal
- Correspondence: ; Tel.: +351-289-800-953
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17
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DFT investigation on the intramolecular and intermolecular proton transfer processes in 2-aminobenzothiazole (ABT) in the gas phase and in different solvents. Struct Chem 2019. [DOI: 10.1007/s11224-019-01395-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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18
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Alkorta I, Elguero J. Prototropic tautomerism of the addition products of N-heterocyclic carbenes to CO2, CS2, and COS. Struct Chem 2019. [DOI: 10.1007/s11224-019-01381-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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19
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Antonov L. Tautomerism in Azo and Azomethyne Dyes: When and If Theory Meets Experiment. Molecules 2019; 24:molecules24122252. [PMID: 31212924 PMCID: PMC6631587 DOI: 10.3390/molecules24122252] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 06/13/2019] [Accepted: 06/14/2019] [Indexed: 12/15/2022] Open
Abstract
The performance of 26 hybrid density functionals was tested against a tautomeric dataset (TautData), containing experimental information for the keto-enol tautomeric equilibrium in 16 tautomeric azodyes and Schiff bases in cyclohexane, carbon tetrachloride and acetonitrile. The results have shown that MN12-SX, BHandH and M06-2X can be used to describe the tautomeric state of the core structures in the frame of ~0.5 kcal/mol error and correctly predict the tautomeric state in respect of dominating tautomeric form. Among them MN12-SX is the best performer, although it fails to describe the nonplanarity of some of the enol tautomers. The same experimental dataset was used to develop and test a special DFT functional (TautLYP) aimed at describing the tautomeric state in azo- and azomethyne compounds in solution when nonspecific solvents are used.
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Affiliation(s)
- Liudmil Antonov
- Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria.
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20
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Pagacz-Kostrzewa M, Sałdyka M, Bil A, Gul W, Wierzejewska M, Khomenko DM, Doroschuk RO. Phototransformations of 2-(1,2,4-Triazol-3-yl)benzoic Acid in Low Temperature Matrices. J Phys Chem A 2019; 123:841-850. [DOI: 10.1021/acs.jpca.8b10762] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. Pagacz-Kostrzewa
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
| | - M. Sałdyka
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
| | - A. Bil
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
| | - W. Gul
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
| | - M. Wierzejewska
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
| | - D. M. Khomenko
- Department of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine
| | - R. O. Doroschuk
- Department of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine
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21
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Oyarzo J, Bosque R, Toro P, Silva CP, Arancibia R, Font-Bardía M, Artigas V, Calvis C, Messeguer R, Klahn AH, López C. A novel type of organometallic 2-R-2,4-dihydro-1H-3,1-benzoxazine with R = [M(η5-C5H4)(CO)3] (M = Re or Mn) units. Experimental and computational studies of the effect of substituent R on ring-chain tautomerism. Dalton Trans 2019; 48:1023-1039. [DOI: 10.1039/c8dt03265c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Novel 2-cyrhetrenyl and cymantrenyl-2,4-dihydro-1H-3,1-benzoxazines.
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22
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Experimental and pK a prediction aspects of tautomerism of drug-like molecules. DRUG DISCOVERY TODAY. TECHNOLOGIES 2018; 27:59-64. [PMID: 30103864 DOI: 10.1016/j.ddtec.2018.06.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 06/13/2018] [Accepted: 06/14/2018] [Indexed: 11/20/2022]
Abstract
Molecules that can tautomerize are a challenge to scientists because one must consider the possible tautomers in most tasks involving chemical structures: for example, searching databases, interpreting experimental property measurements, calculating properties, virtual screening, and analyzing structure-bioactivity relationships. The challenge in interpreting property measurements such as pKa values feeds into the general lack of extensive information not only of the relative tautomer stability in water but also the properties of the individual tautomers. This lack of information results in the lack of reliability of computational predictions of tautomer stability or properties. In spite of these problems, pKa calculations are reliable enough that they can be used to filter out high-energy tautomers from databases used for virtual screening. Continuous improvements in both pKa prediction software and theoretical calculations promise further improvements in solving the challenges of tautomers. The expected availability of high-resolution structures of many more tautomer-protein complexes will help guide the selection of the bioactive tautomer when the structure of the complex is not known.
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23
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Liu LL, Zhou J, Andrews R, Stephan DW. A Room-Temperature-Stable Phosphanorcaradiene. J Am Chem Soc 2018; 140:7466-7470. [PMID: 29860832 DOI: 10.1021/jacs.8b04930] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A room-temperature-stable crystalline phosphanorcaradiene 2 has been synthesized via a C-C bond forming strategy induced by the demetalation of a phosphepine-Au complex 1 using a Lewis base (Ph3P, IDipp or CyNC). Compound 2 undergoes photolysis to afford a 2 H-phosphirene 4. Ru(PPh3)3Cl2 is shown to catalyze the equilibration of 2 and 4 in solution. In addition, the transformation of 2 to 4 can be achieved by a two-step strategy, namely cyclopropenylidene-induced ring opening to give cyclopropenylidene-stabilized vinylphosphinidene 7 followed by elimination of cyclopropenylidene by an electrophile including TMSOTf and Me2SBH3.
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Affiliation(s)
- Liu Leo Liu
- Department of Chemistry , University of Toronto , 80 St. George Street , Toronto , Ontario M5S3H60 , Canada
| | - Jiliang Zhou
- Department of Chemistry , University of Toronto , 80 St. George Street , Toronto , Ontario M5S3H60 , Canada
| | - Ryan Andrews
- Department of Chemistry , University of Toronto , 80 St. George Street , Toronto , Ontario M5S3H60 , Canada
| | - Douglas W Stephan
- Department of Chemistry , University of Toronto , 80 St. George Street , Toronto , Ontario M5S3H60 , Canada
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24
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Safi ZS, Al Hasanat SJ, Wazzan NA. DFT investigation of the amino/imino proton transfer process of 2-amino-2-oxazolin-4-one in gas phase and solution. JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2018. [DOI: 10.1142/s0219633618500049] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Density functional theory (DFT) at the B3LYP-6-311[Formula: see text]G(3df,2p)//6-311[Formula: see text]G(d,p) level of theory in the gas phase and solution was performed to investigate the relative stabilities of all possible tautomers of 2-amino-2-oxazolin-4-one. Five different paths have been proposed to investigate the amino/oxo [Formula: see text] imino/oxo proton transfer (PT) process. These paths are direct, mono-, di- and tri-water-assisted and self-assistance (dimerization) PT process. A clear catalytic effect has been observed when the introduction of water molecules and self-dimerization are taken place. Furthermore, barrier energies, equilibrium constants and reaction rate constants of the PT process between amine/oxo and imine/oxo tautomers of the self-assistance and in the presence of one, two and three water-assisted molecules were calculated. The computed activation barriers in the presence of water molecules are about 35–45 kcal/mol lower than those in the isolated case. In addition, the effective rate of the T1 [Formula: see text] T2 processes were also recorded, compared and discussed. Finally, time-dependent–DFT (TD–DFT) was performed to determine the electronic absorption spectra of all species under probe. A reasonable agreement with the available experiments was also achieved.
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Affiliation(s)
- Zaki S. Safi
- Department of Chemistry, Faculty of Science, Al Azhar University-Gaza, Gaza City, P. O. Box 1277, Palestine
| | - Subhia J. Al Hasanat
- Department of Chemistry, Faculty of Science, Al Azhar University-Gaza, Gaza City, P. O. Box 1277, Palestine
| | - Nuha A. Wazzan
- Department of Chemistry, Faculty of Science, King Abdulaziz University, P. O. Box 42805, Jeddah 21589, Saudi Arabia
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25
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Ofoegbu SU, Galvão TLP, Gomes JRB, Tedim J, Nogueira HIS, Ferreira MGS, Zheludkevich ML. Corrosion inhibition of copper in aqueous chloride solution by 1H-1,2,3-triazole and 1,2,4-triazole and their combinations: electrochemical, Raman and theoretical studies. Phys Chem Chem Phys 2018; 19:6113-6129. [PMID: 28191580 DOI: 10.1039/c7cp00241f] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Triazoles are well-known organic corrosion inhibitors of copper. 1H-1,2,3-Triazole and 1,2,4-triazole, two very simple molecules with the only difference being the positions of the nitrogen atoms in the triazole ring, were studied in this work as corrosion inhibitors of copper in 50 mM NaCl solution using a set of electrochemical and analytical techniques. The results of electrochemical tests indicate that 1H-1,2,3-triazole exhibited superior inhibitor properties but could not suppress anodic copper dissolution at moderate anodic potentials (>+300 mV SCE), while 1,2,4-triazole, although it exhibited higher anodic currents, suppressed anodic copper dissolution at very anodic potentials. Density functional theory calculations were also performed to interpret the measured data and trends observed in the electrochemical studies. The computational studies considered either the inhibitors isolated in the gaseous phase or adsorbed onto Cu(111) surface models. From the calculations, the mechanisms of the inhibitive effects of both triazoles were established and plausible mechanisms of formation of the protective films on the Cu surface were proposed. The results of this study hold positive implications for research in the areas of catalysis, and copper content control in water purification systems.
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Affiliation(s)
- Stanley Udochukwu Ofoegbu
- Department of Materials and Ceramic Engineering, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
| | - Tiago L P Galvão
- Department of Materials and Ceramic Engineering, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
| | - José R B Gomes
- Department of Chemistry, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
| | - João Tedim
- Department of Materials and Ceramic Engineering, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
| | - Helena I S Nogueira
- Department of Chemistry, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
| | - M G S Ferreira
- Department of Materials and Ceramic Engineering, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
| | - M L Zheludkevich
- Department of Materials and Ceramic Engineering, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal. and MagIC, Institute of Materials Research, Helmholtz-ZentrumGeesthacht, Max-Planck-Strasse1, 21502 Geesthacht, Germany
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26
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On the Tautomerism of N-Substituted Pyrazolones: 1,2-Dihydro-3H-pyrazol-3-ones versus 1H-Pyrazol-3-ols. Molecules 2018; 23:molecules23010129. [PMID: 29315238 PMCID: PMC6017633 DOI: 10.3390/molecules23010129] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 12/28/2017] [Accepted: 12/30/2017] [Indexed: 11/24/2022] Open
Abstract
The tautomerism of 1-phenyl-1,2-dihydro-3H-pyrazol-3-one was investigated. An X-ray crystal structure analysis exhibits dimers of 1-phenyl-1H-pyrazol-3-ol units. Comparison of NMR (nuclear magnetic resonance) spectra in liquid state (1H, 13C, 15N) with those of “fixed” derivatives, as well as with the corresponding solid state NMR spectra reveal this compound to exist predominantly as 1H-pyrazol-3-ol molecule pairs in nonpolar solvents like CDCl3 or C6D6, whereas in DMSO-d6 the corresponding monomers are at hand. Moreover, the NMR data of different related 1H-pyrazol-3-ol derivatives are presented.
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27
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Tautomerism of N-(3,4-dichlorophenyl)-1H-indazole-5-carboxamide – A new selective, highly potent and reversible MAO-B inhibitor. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2017.07.108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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28
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Neralkar M, Mishra B, Hotha S. Nucleofuge Generating Glycosidations by the Remote Activation of Hydroxybenzotriazolyl Glycosides. J Org Chem 2017; 82:11494-11504. [DOI: 10.1021/acs.joc.7b02027] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Mahesh Neralkar
- Department of Chemistry, Indian Institute of Science Education and Research, Pune, 411 008 MH, India
| | - Bijoyananda Mishra
- Department of Chemistry, Indian Institute of Science Education and Research, Pune, 411 008 MH, India
| | - Srinivas Hotha
- Department of Chemistry, Indian Institute of Science Education and Research, Pune, 411 008 MH, India
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29
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Jordaan MA, Shapi M. Investigation of the solvent-dependent photolysis of a nonnucleoside reverse-transcriptase inhibitor, antiviral agent efavirenz. Antivir Chem Chemother 2017; 25:94-104. [PMID: 28893089 PMCID: PMC5890511 DOI: 10.1177/2040206617730170] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
This study sought to investigate the solvent-dependency on the photolysis of efavirenz to gain insight into the photoprocesses involved. The primary mechanisms were firstly the excited-state intramolecular proton transfer (i.e. phototautomerization), which generated the imidic acid phototautomer observed as [M-H]- quasimolecular ion at m/z 314.0070 in the high-performance liquid chromatography-electrospray ionization-time-of-flight mass spectrometry in the negative mode. Secondly, the photoinduced α-cleavage with the loss of a carbonyl group occurred (i.e. photodecarbonylation) to form the photoproduct at m/z 286.0395. The ultraviolet-visible spectra illustrated a large, hyperchromic, and slight bathochromic effect in both the π→π* and n→π* electronic transitions. The largest bathochromic effect was prevalent in the chloroform solvent, i.e. chloroform (π* = 0.58; β = 0.00; α = 0.44) > methanol (π* = 0.60; β = 0.66; α = 0.98) > acetonitrile (π* = 0.75; β = 0.40; α = 0.19). This is due to the significant interaction of the amino group with the excited carbonyl moiety which is attributed to intramolecular phototautomerization resulting in a larger energy shift of the electronic state. A plausible explanation is due to the hydrogen bond donor ability of the polar methanol and nonpolar chloroform solvents, which stabilized the polarized imidic acid phototautomer by means of hydrogen bonding interactions, as opposed to the aprotic acetonitrile which exhibits no hydrogen bonding interactions. The study would form the basis for further photolytic analyses and syntheses to generate a plethora of novel photoproducts with anti-HIV activity based on the biologically active benzoxazinone framework of efavirenz.
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Affiliation(s)
- Maryam A Jordaan
- Department of Chemistry, Faculty of Natural Sciences, 70688 Mangosuthu University of Technology , Durban, South Africa
| | - Michael Shapi
- Department of Chemistry, Faculty of Natural Sciences, 70688 Mangosuthu University of Technology , Durban, South Africa
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30
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Centore R, Manfredi C, Capobianco A, Volino S, Ferrara MV, Carella A, Fusco S, Peluso A. Solid State Separation and Isolation of Tautomers of Fused-Ring Triazolotriazoles. J Org Chem 2017; 82:5155-5161. [PMID: 28452478 DOI: 10.1021/acs.joc.7b00380] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Fine control of the tautomeric forms of [1,2,4]triazolo[3,2-c][1,2,4]triazole derivatives in acidic conditions has been achieved by acting on the electronic character of the substituent at position 7 of the heterobicycle and on the counterion. Strong electron releasing or electron withdrawing substituents lead almost exclusively to a single tautomeric form, the 1H-3H or the 2H-3H, respectively. In the case of the phenol substituent, both tautomeric forms are present in comparable amount in solution; the two tautomers can also be selectively precipitated in different crystalline salts using suitable counterions.
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Affiliation(s)
- Roberto Centore
- Department of Chemical Sciences, University of Naples Federico II , Via Cintia, I-80126 Naples, Italy
| | - Carla Manfredi
- Department of Chemical Sciences, University of Naples Federico II , Via Cintia, I-80126 Naples, Italy
| | - Amedeo Capobianco
- Department of Chemistry and Biology, University of Salerno , Via Giovanni Paolo II, 132, I-84084 Fisciano, Salerno, Italy
| | - Sabato Volino
- Department of Chemical Sciences, University of Naples Federico II , Via Cintia, I-80126 Naples, Italy
| | - Maria Vittoria Ferrara
- Department of Chemical Sciences, University of Naples Federico II , Via Cintia, I-80126 Naples, Italy
| | - Antonio Carella
- Department of Chemical Sciences, University of Naples Federico II , Via Cintia, I-80126 Naples, Italy
| | - Sandra Fusco
- Department of Chemical Sciences, University of Naples Federico II , Via Cintia, I-80126 Naples, Italy
| | - Andrea Peluso
- Department of Chemistry and Biology, University of Salerno , Via Giovanni Paolo II, 132, I-84084 Fisciano, Salerno, Italy
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31
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Hayashi D, Igura Y, Masui Y, Onaka M. Stabilization and activation of unstable propynal in the zeolite nanospace and its application to addition reactions. Catal Sci Technol 2017. [DOI: 10.1039/c7cy01161j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Propynal is stabilized in the Na-Y zeolite at ambient temperature and simultaneously activated to form pyrazoles, cinnamaldehydes, and cyclobutenes.
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Affiliation(s)
- Daijiro Hayashi
- Graduate School of Arts and Sciences
- The University of Tokyo
- Tokyo 153-8902
- Japan
| | - Yuta Igura
- Graduate School of Arts and Sciences
- The University of Tokyo
- Tokyo 153-8902
- Japan
| | - Yoichi Masui
- Graduate School of Arts and Sciences
- The University of Tokyo
- Tokyo 153-8902
- Japan
| | - Makoto Onaka
- Graduate School of Arts and Sciences
- The University of Tokyo
- Tokyo 153-8902
- Japan
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32
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Pulst M, Elgabarty H, Sebastiani D, Kressler J. The annular tautomerism of lithium 1,2,3-triazolate. NEW J CHEM 2017. [DOI: 10.1039/c6nj03732a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The tautomeric equilibrium of 1-lithium-1,2,3-triazolate (1Li-TR) and 2-lithium-1,2,3-triazolate (2Li-TR) is studied by X-ray diffraction, NMR spectroscopy and molecular dynamics simulations.
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Affiliation(s)
- Martin Pulst
- Department of Chemistry
- Martin Luther University Halle-Wittenberg
- D-06099 Halle
- Germany
| | - Hossam Elgabarty
- Department of Chemistry
- Martin Luther University Halle-Wittenberg
- D-06099 Halle
- Germany
| | - Daniel Sebastiani
- Department of Chemistry
- Martin Luther University Halle-Wittenberg
- D-06099 Halle
- Germany
| | - Jörg Kressler
- Department of Chemistry
- Martin Luther University Halle-Wittenberg
- D-06099 Halle
- Germany
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33
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Pairas GN, Tsoungas PG. H-Bond: Τhe Chemistry-Biology H-Bridge. ChemistrySelect 2016; 1:4520-4532. [PMID: 32328512 PMCID: PMC7169486 DOI: 10.1002/slct.201600770] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2016] [Accepted: 07/29/2016] [Indexed: 12/19/2022]
Abstract
H-bonding, as a non covalent stabilizing interaction of diverse nature, has a central role in the structure, function and dynamics of chemical and biological processes, pivotal to molecular recognition and eventually to drug design. Types of conventional and non conventional (H-H, dihydrogen, H- π, CH- π, anti- , proton coordination and H-S) H-bonding interactions are discussed as well as features emerging from their interplay, such as cooperativity (σ- and π-) effects and allostery. Its utility in many applications is described. Catalysis, proton and electron transfer processes in various materials or supramolecular architectures of preorganized hosts for guest binding, are front-line technology. The H-bond-related concept of proton transfer (PT) addresses energy issues or deciphering the mechanism of many natural and synthetic processes. PT is also of paramount importance in the functions of cells and is assisted by large complex proteins embedded in membranes. Both intermolecular and intramolecular PT in H-bonded systems has received attention, theoretically and experimentally, using prototype molecules. It is found in rearrangement reactions, protein functions, and enzyme reactions or across proton channels and pumps. Investigations on the competition between intra- and intermolecular H bonding are discussed. Of particular interest is the H-bond furcation, a common phenomenon in protein-ligand binding. Multiple H-bonding (H-bond furcation) is observed in supramolecular structures.
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Affiliation(s)
- George N. Pairas
- Department of PharmacyLaboratory of Medicinal ChemistryUniversity of PatrasGR-265 04PatrasGreece
| | - Petros G. Tsoungas
- Laboratory of BiochemistryHellenic Pasteur Institute127 Vas. Sofias Ave.GR-115 21AthensGreece
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34
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Tautomerism in some pyrimidine nucleoside analogues used in the treatment of cancer: an ab initio study. Theor Chem Acc 2016. [DOI: 10.1007/s00214-016-1985-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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35
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The kinetics of water-assisted tautomeric 1,2-proton transfer in azoles: a computational approach. Struct Chem 2016. [DOI: 10.1007/s11224-016-0813-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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36
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Polyfunctional 4-quinolinones. Synthesis of 2-substituted 3-hydroxy-4-oxo-1,4-dihydroquinolines. Tetrahedron Lett 2016. [DOI: 10.1016/j.tetlet.2016.01.077] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Głębocka A, Raczyńska ED, Chylewska A, Makowski M. Experimental (FT-IR) and theoretical (DFT) studies on prototropy and H-bond formation for pyrazine-2-amidoxime. J PHYS ORG CHEM 2016. [DOI: 10.1002/poc.3538] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Angelika Głębocka
- Laboratory of Intermolecular Interactions, Faculty of Chemistry; University of Gdańsk; Wita Stwosza 63 80-308 Gdańsk Poland
| | - Ewa D. Raczyńska
- Department of Chemistry; Warsaw University of Life Sciences; Nowoursynowska 159c 02-776 Warszawa Poland
| | - Agnieszka Chylewska
- Laboratory of Intermolecular Interactions, Faculty of Chemistry; University of Gdańsk; Wita Stwosza 63 80-308 Gdańsk Poland
| | - Mariusz Makowski
- Laboratory of Intermolecular Interactions, Faculty of Chemistry; University of Gdańsk; Wita Stwosza 63 80-308 Gdańsk Poland
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Trujillo C, Sánchez-Sanz G, Alkorta I, Elguero J. Computational Study of Proton Transfer in Tautomers of 3- and 5-Hydroxypyrazole Assisted by Water. Chemphyschem 2015; 16:2140-50. [PMID: 26033797 DOI: 10.1002/cphc.201500317] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Indexed: 11/12/2022]
Abstract
The tautomerism of 3- and 5-hydroxypyrazole is studied at the B3LYP, CCSD and G3B3 computational levels, including the gas phase, PCM-water effects, and proton transfer assisted by water molecules. To understand the propensity of tautomerization, hydrogen-bond acidity and basicity of neutral species is approached by means of correlations between donor/acceptor ability and H-bond interaction energies. Tautomerism processes are highly dependent on the solvent environment, and a significant reduction of the transition barriers upon solvation is seen. In addition, the inclusion of a single water molecule to assist proton transfer decreases the barriers between tautomers. Although the second water molecule further reduces those barriers, its effect is less appreciable than the first one. Neutral species present more stable minima than anionic and cationic species, but relatively similar transition barriers to anionic tautomers.
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Affiliation(s)
- Cristina Trujillo
- School of Chemistry, Trinity Biomedical Sciences Institute, Trinity College Dublin, 152-160 Pearse St. Dublin 2 (Ireland).
| | - Goar Sánchez-Sanz
- School of Physics & Complex and Adaptive Systems Laboratory, University College Dublin, Belfield, Dublin 4 (Ireland)
| | - Ibon Alkorta
- Instituto de Química Médica, CSIC, Juan de la Cierva, 3, 28006 Madrid (Spain)
| | - José Elguero
- Instituto de Química Médica, CSIC, Juan de la Cierva, 3, 28006 Madrid (Spain)
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Wierzchowski J. Excited-state proton transfer and phototautomerism in nucleobase and nucleoside analogs: a mini-review. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2015; 33:626-44. [PMID: 25105453 DOI: 10.1080/15257770.2014.913065] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Intermolecular excited-state proton transfer (ESPT) has been observed in several fluorescent nucleobase and/or nucleoside analogs. In the present work, some new examples of ESPT in this class of compounds are presented together with a brief recapitulation of the previously published data. The nucleobases, nucleosides, and their analogs contain many basic and acidic centers and therefore their ESPT behavior may be complex. To interpret the complex data, it is usually necessary to determine the microscopic pK* values for each (or most) of the possible ESPT centers. Typical approach to solve this problem is by analysis of the alkyl derivatives, in which the possibility of the ESPT is reduced. Of particular interest are examples of "phototautomerization via the cation," observed in several systems, which in the neutral media do not undergo ESPT. Protonation of the molecule in the ground state facilitates the two-step phototautomerism in several systems, including formycin A and 2-amino-8-azadenine. Fluorescence of the nucleobase and nucleoside analogs undergoing ESPT is usually solvent-, isotope-, and buffer-ion sensitive, and in some systems the ESPT can be promoted by environmental factors, e.g., the presence of buffer ions. This sensitivity to the microenvironment parameters makes the ESPT systems potentially useful for biological applications.
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Affiliation(s)
- Jacek Wierzchowski
- a Department of Biophysics , University of Varmia & Masuria in Olsztyn , Olsztyn , Poland
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41
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Alkorta I, Elguero J, Pérez-Torralba M, López C, Claramunt RM. A theoretical and experimental study of the NMR spectra of 4,5,6,7-tetrafluorobenzazoles with special stress on PCM calculations of chemical shifts. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2015; 53:353-362. [PMID: 25615404 DOI: 10.1002/mrc.4203] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 12/04/2014] [Indexed: 06/04/2023]
Abstract
The chemical shifts and several (19)F-(19)F, (13)C-(19) F and (1)H-(19)F spin-spin coupling constants (SSCSs) of eight 4,5,6,7-tetraflurobenzazoles (three benzimidazoles, three benzimidazolinones and two indazoles) have been determined. The chemical shifts were discussed using gauge including atomic orbital-density functional theory calculations taking into account solvent effects (polarizable continuum model) and, for the solid state, hydrogen bonds (clusters up to three molecules).
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Affiliation(s)
- Ibon Alkorta
- Instituto de Química Médica, CSIC, Juan de la Cierva 3, E-28006, Madrid, Spain
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42
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Verdejo B, Acosta-Rueda L, Clares MP, Aguinaco A, Basallote MG, Soriano C, Tejero R, García-España E. Equilibrium, kinetic, and computational studies on the formation of Cu2+ and Zn2+ complexes with an indazole-containing azamacrocyclic scorpiand: evidence for metal-induced tautomerism. Inorg Chem 2015; 54:1983-91. [PMID: 25635469 DOI: 10.1021/ic5029004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cu(2+) and Zn(2+) coordination chemistry of a new member of the family of scorpiand-like macrocyclic ligands derived from tris(2-aminoethyl)amine (tren) is reported. The new ligand (L1) contains in its pendant arm not only the amine group derived from tren but also a 6-indazole ring. Potentiometric studies allow the determination of four protonation constants. UV-vis and fluorescence data support that the last protonation step occurs on the indazole group. Equilibrium measurements in the presence of Cu(2+) and Zn(2+) reveal the formation of stable [ML1](2+), [MHL1](3+), and [ML1(OH)](+) complexes. Kinetic studies on the acid-promoted decomposition of the metal complexes were carried out using both absorbance and fluorescence detection. For Zn(2+), both types of detection led to the same results. The experiments suggest that [ZnL1](2+) protonates upon addition of an acid excess to form [ZnHL1](3+) within the mixing time of the stopped-flow instrument, which then decomposes with a first-order dependence on the acid concentration. The kinetic behavior is more complex in the case of Cu(2+). Both [CuL1](2+) and [CuHL1](3+) show similar absorption spectra and convert within the mixing time to a new intermediate species with a band at 750 nm, the process being reverted by addition of base. The intermediate then decomposes with a second-order dependence on the acid concentration. However, kinetic experiments with fluorescence detection showed the existence of an additional faster step. With the help of DFT calculations, an interpretation is proposed in which protonation of [CuL1](2+) to form [CuHL1](3+) would involve dissociation of the tren-based NH group in the pendant arm and coordination of a 2H-indazole group. Further protonation would lead to dissociation of coordinated indazole, which then will convert to the more stable 1H tautomer in a process signaled by fluorescence changes that would not be affecting to the d-d spectrum of the complex.
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Affiliation(s)
- Begoña Verdejo
- Instituto de Ciencia Molecular , C/Catedrático José Beltrán 2, 46980 Paterna, Valencia, Spain
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43
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Iglesias DA, Ruiz DL, Allegretti PE. 2-Cyanobenzoic Acids: Tautomeric Equilibria Study. Aust J Chem 2015. [DOI: 10.1071/ch14273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Evidence of ring–chain tautomerism in the gas phase from mass spectrometry and in solution determined by means of 1H NMR and 13C NMR is reported for 2-cyanobenzoic acids. The analysis of the corresponding spectra has allowed specific assignment of fragment ions to tautomers. The predictive value of this methodology is supported by the influence of the substitution pattern of these compounds on this equilibrium.
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Nieto CI, Cabildo P, García MÁ, Claramunt RM, Alkorta I, Elguero J. An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism. Beilstein J Org Chem 2014; 10:1620-9. [PMID: 25161719 PMCID: PMC4142846 DOI: 10.3762/bjoc.10.168] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Accepted: 06/18/2014] [Indexed: 11/23/2022] Open
Abstract
This paper reports the 1H, 13C and 15N NMR experimental study of five benzimidazoles in solution and in the solid state (13C and 15N CPMAS NMR) as well as the theoretically calculated (GIAO/DFT) chemical shifts. We have assigned unambiguously the "tautomeric positions" (C3a/C7a, C4/C7 and C5/C6) of NH-benzimidazoles that, in some solvents and in the solid state, appear different (blocked tautomerism). In the case of 1H-benzimidazole itself we have measured the prototropic rate in HMPA-d18.
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Affiliation(s)
- Carla I Nieto
- Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED Senda del Rey 9, E-28040 Madrid, Spain
| | - Pilar Cabildo
- Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED Senda del Rey 9, E-28040 Madrid, Spain
| | - M Ángeles García
- Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED Senda del Rey 9, E-28040 Madrid, Spain
| | - Rosa M Claramunt
- Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED Senda del Rey 9, E-28040 Madrid, Spain
| | - Ibon Alkorta
- Instituto de Química Médica, CSIC, Juan de la Cierva, 3, E-28006 Madrid, Spain
| | - José Elguero
- Instituto de Química Médica, CSIC, Juan de la Cierva, 3, E-28006 Madrid, Spain
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Koyioni M, Manoli M, Manos MJ, Manolis MJ, Koutentis PA. Reinvestigating the reaction of 1H-pyrazol-5-amines with 4,5-dichloro-1,2,3-dithiazolium chloride: a route to pyrazolo[3,4-c]isothiazoles and pyrazolo[3,4-d]thiazoles. J Org Chem 2014; 79:4025-37. [PMID: 24734990 DOI: 10.1021/jo500509e] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The reaction of Appel salt 1 with 1H-pyrazol-5-amines 2 gives main products N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-1H-pyrazol-5-amines 3, and 6H-pyrazolo[3,4-c]isothiazole-3-carbonitriles 5, together with several minor side products. When the pyrazoles are N-1 methylated, the product ratio 3:5 can be modified by adjusting the pH of the reaction medium: acidic conditions favor formation of the dithiazolylidenes 3, while basic conditions favor formation of pyrazolo[3,4-c]isothiazoles 5. Furthermore, thermolysis of N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-1H-pyrazol-5-amines 3 gives 1H-pyrazolo[3,4-d]thiazole-5-carbonitriles 4. Single crystal X-ray crystallography supports the structure of 4,6-dimethyl-6H-pyrazolo[3,4-c]isothiazole-3-carbonitrile (5a) and helps resolve a previous incorrect structural assignment of 1H-pyrazolo[3,4-d]thiazole-5-carbonitriles 4.
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Affiliation(s)
- Maria Koyioni
- Department of Chemistry, University of Cyprus , P.O. Box 20537, 1678 Nicosia, Cyprus
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Belmar J, Ortiz L, Quezada J, Parra M, Jiménez CA. Synthesis and Characterization of Phenylene-bis-pyrazolones and Nitrosation Derivatives. J Heterocycl Chem 2014. [DOI: 10.1002/jhet.1843] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- J. Belmar
- Department of Organic Chemistry, Faculty of Chemical Sciences; University of Concepción; Casilla 160-C Concepción Chile
| | - L. Ortiz
- Department of Organic Chemistry, Faculty of Chemical Sciences; University of Concepción; Casilla 160-C Concepción Chile
| | - J. Quezada
- Department of Organic Chemistry, Faculty of Chemical Sciences; University of Concepción; Casilla 160-C Concepción Chile
| | - M. Parra
- Department of Organic Chemistry, Faculty of Chemical Sciences; University of Concepción; Casilla 160-C Concepción Chile
| | - C. A. Jiménez
- Department of Organic Chemistry, Faculty of Chemical Sciences; University of Concepción; Casilla 160-C Concepción Chile
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Raczyńska ED. Effects of positive and negative ionization for 2-aminopyrimidine in the gas phase and in water solution. COMPUT THEOR CHEM 2014. [DOI: 10.1016/j.comptc.2014.01.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Williams JK, Tietze D, Wang J, Wu Y, DeGrado WF, Hong M. Drug-induced conformational and dynamical changes of the S31N mutant of the influenza M2 proton channel investigated by solid-state NMR. J Am Chem Soc 2013; 135:9885-97. [PMID: 23758317 DOI: 10.1021/ja4041412] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The M2 protein of influenza A viruses forms a tetrameric proton channel that is targeted by the amantadine class of antiviral drugs. A S31N mutation in the transmembrane (TM) domain of the protein has caused widespread amantadine resistance in most of the currently circulating flu viruses. Recently, a new family of compounds based on amantadine- and aryl-substituted isoxazole were discovered to inhibit the S31N channel activity and reduce replication of S31N-harboring viruses. We now use solid-state NMR spectroscopy to investigate the effects of one of these isoxazole compounds, WJ352, on the conformation of the S31N TM segment and the dynamics of the proton-selective residue, His37. Chemical shift perturbations show that WJ352 changes the conformational equilibrium of multiple TM residues, with the maximal perturbation occurring at the crucial Asn31. (13)C-(2)H distance measurements and (1)H-(1)H NOE cross peaks indicate that the adamantane moiety of the drug is bound in the spacious pore between Asn31 and Gly34 while the phenyl tail is located near Val27. Thus, the polar amine points to the channel exterior rather than to His37, in contrast to amantadine and rimantadine in the wild-type channel, suggesting that the drug is significantly stabilized by hydrophobic interactions between the adamantane and the TM peptide. (15)N and (13)C chemical shifts indicate that at low pH, His37 undergoes fast exchange among the τ tautomer, the π tautomer, and the cationic state due to proton transfer with water. The exchange rate is higher than the wild-type channel, consistent with the larger single-channel conductance of the mutant. Drug binding at acidic pH largely suppresses this exchange, reverting the histidines to a similar charge distribution as that of the high-pH closed state.
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Padalkar VS, Ramasami P, Sekar N. A combined experimental and DFT-TDDFT study of the excited-state intramolecular proton transfer (ESIPT) of 2-(2'-hydroxyphenyl) imidazole derivatives. J Fluoresc 2013; 23:839-51. [PMID: 23613133 DOI: 10.1007/s10895-013-1201-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Accepted: 02/24/2013] [Indexed: 10/26/2022]
Abstract
We report a combined experimental and computational study of the effect of electron donor and acceptor groups on the excited state intramolecular proton transfer of 2-(2'-hydroxyphenyl) imidazole derivatives in solvents of different polarities. The changes in fluorescence properties, electronic transitions and energy levels are analyzed and discussed. The study was complemented using the Density Functional Theory (DFT)-Time Dependent DFT [B3LYP/6-31G(d)] computations. The calculated absorption and emission spectra of the imidazole derivatives are in good agreement with the experiments, thus allowing an assignment of the UV-vis spectra.
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Affiliation(s)
- Vikas S Padalkar
- Tinctorial Chemistry Group, Institute of Chemical Technology, Matunga, Mumbai, 400019, India,
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