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Okamura T, Kikuchi T, Ogawa M, Zhang MR. Improved synthesis of 6-bromo-7-[ 11C]methylpurine for clinical use. EJNMMI Radiopharm Chem 2024; 9:10. [PMID: 38334858 PMCID: PMC10857989 DOI: 10.1186/s41181-024-00240-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Accepted: 01/25/2024] [Indexed: 02/10/2024] Open
Abstract
BACKGROUND Multidrug resistance-associated protein 1 (MRP1), an energy-dependent efflux pump, is expressed widely in various tissues and contributes to many physiological and pathophysiological processes. 6-Bromo-7-[11C]methylpurine ([11C]7m6BP) is expected to be useful for the assessment of MRP1 activity in the human brain and lungs. However, the radiochemical yield (RCY) in the synthesis of [11C]7m6BP was low, limiting its clinical application, because the methylation of the precursor with [11C]CH3I provided primarily the undesired isomer, 6-bromo-9-[11C]methylpurine ([11C]9m6BP). To increase the RCY of [11C]7m6BP, we investigated conditions for improving the [11C]7m6BP/[11C]9m6BP selectivity of the methylation reaction. RESULTS [11C]7m6BP was manually synthesized via the methylation of 6-bromopurine with [11C]CH3I in various solvents and at different temperatures in the presence of potassium carbonate for 5 min. Several less polar solvents, including tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), and ethyl acetate (AcOEt) improved the [11C]7m6BP/[11C]9m6BP selectivity from 1:1 to 2:1, compared with the conventionally used solvents for the alkylation of 6-halopurines, acetone, acetonitrile, and N,N-dimethylformamide. However, a higher temperature (140 °C or 180 °C) was needed to progress the 11C-methylation in the less polar solvents, and the manual conditions could not be directly translated to an automated synthesis. [11C]Methyl triflate ([11C]CH3OTf) was thus used as a methylating agent to increase the conversion at a lower temperature. The 11C-methylation using [11C]CH3OTf at 100 °C proceeded efficiently in THF, 2-MeTHF, and AcOEt with maintenance of the improved selectivity. Starting from 28 to 34 GBq [11C]CO2, [11C]7m6BP was produced with 2.3-2.6 GBq for THF, 2.7-3.3 GBq for AcOEt, and 2.8-3.9 GBq for 2-MeTHF at approximately 30 min after the end of bombardment (n = 3 per solvent). The isolated RCYs (decay corrected) for THF, 2-MeTHF, and AcOEt were 24-28%, 29-35%, and 22-31% (n = 3), respectively. CONCLUSIONS The use of THF, 2-MeTHF, and AcOEt improved the [11C]7m6BP/[11C]9m6BP selectivity in the methylation reaction, and the improved method provided [11C]7m6BP with sufficient radioactivity for clinical use.
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Affiliation(s)
- Toshimitsu Okamura
- Department of Advanced Nuclear Medicine Sciences, Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan.
| | - Tatsuya Kikuchi
- Department of Advanced Nuclear Medicine Sciences, Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan
| | - Masanao Ogawa
- Department of Advanced Nuclear Medicine Sciences, Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan
- SHI Accelerator Service, Ltd., 7-1-1 Nishigotanda, Shinagawa-ku, Tokyo, 141-0031, Japan
| | - Ming-Rong Zhang
- Department of Advanced Nuclear Medicine Sciences, Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan
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Jezuita A, Wieczorkiewicz PA, Krygowski TM, Szatylowicz H. Influence of the Solvent on the Stability of Aminopurine Tautomers and Properties of the Amino Group. Molecules 2023; 28:molecules28072993. [PMID: 37049758 PMCID: PMC10095612 DOI: 10.3390/molecules28072993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Revised: 03/23/2023] [Accepted: 03/24/2023] [Indexed: 03/30/2023] Open
Abstract
Amino derivatives of purine (2-, 6-, 8-, and N-NH2) have found many applications in biochemistry. This paper presents the results of a systematic computational study of the substituent and solvent effects in these systems. The issues considered are the electron-donating properties of NH2, its geometry, π-electron delocalization in purine rings and tautomeric stability. Calculations were performed in ten environments, with 1 < ε < 109, using the polarizable continuum model of solvation. Electron-donating properties were quantitatively described by cSAR (charge of the substituent active region) parameter and π-electron delocalization by using the HOMA (harmonic oscillator model of aromaticity) index. In aminopurines, NH2 proximity interactions depend on its position and the tautomer. The results show that they are the main factor determining how solvation affects the electron-donating strength and geometry of NH2. Proximity with the NH∙∙∙HN repulsive interaction between the NH2 and endocyclic NH group results in stronger solvent effects than the proximity with two attractive NH∙∙∙N interactions. The effect of amino and nitro (previously studied) substitution on aromaticity was compared; these two groups have, in most cases, the opposite effect, with the largest being in N1H and N3H purine tautomers. The amino group has a smaller effect on the tautomeric preferences of purine than the nitro group. Only in 8-aminopurine do tautomeric preferences change: N7H is more stable than N9H in H2O.
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Affiliation(s)
- Anna Jezuita
- Faculty of Science and Technology, Jan Dlugosz University in Czestochowa, Al. Armii Krajowej 13/15, 42-200 Czestochowa, Poland
| | - Paweł A. Wieczorkiewicz
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
- Correspondence: (P.A.W.); (H.S.)
| | | | - Halina Szatylowicz
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
- Correspondence: (P.A.W.); (H.S.)
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Osifová Z, Socha O, Mužíková Čechová L, Šála M, Janeba Z, Dračínský M. Hydrogen‐Bonding Interactions of Methylated Adenine Derivatives. European J Org Chem 2021. [DOI: 10.1002/ejoc.202100721] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Zuzana Osifová
- Institute of Organic Chemistry and Biochemistry ASCR Flemingovo nám. 2 16000 Prague Czech Republic
- Department of Organic Chemistry Faculty of Science Charles University Hlavova 2030 Prague 128 00 Czech Republic
| | - Ondřej Socha
- Institute of Organic Chemistry and Biochemistry ASCR Flemingovo nám. 2 16000 Prague Czech Republic
| | - Lucie Mužíková Čechová
- Institute of Organic Chemistry and Biochemistry ASCR Flemingovo nám. 2 16000 Prague Czech Republic
| | - Michal Šála
- Institute of Organic Chemistry and Biochemistry ASCR Flemingovo nám. 2 16000 Prague Czech Republic
| | - Zlatko Janeba
- Institute of Organic Chemistry and Biochemistry ASCR Flemingovo nám. 2 16000 Prague Czech Republic
| | - Martin Dračínský
- Institute of Organic Chemistry and Biochemistry ASCR Flemingovo nám. 2 16000 Prague Czech Republic
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4
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Solvent Effect on the Stability and Reverse Substituent Effect in Nitropurine Tautomers. Symmetry (Basel) 2021. [DOI: 10.3390/sym13071223] [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
The solvent effect on the stability and electron-accepting properties (EA) of the nitro group attached to the C2, C6, or C8 position of nitropurine NH tautomers is investigated. For this purpose, the density functional theory (DFT) and the polarizable continuum model (PCM) of solvation in a wide range of solvents (1 < ε < 109) are used. We show that the EA properties of the NO2 group, described by the charge of the substituent active region (cSAR) model, are linearly dependent on the reciprocal of the solvent dielectric constant; in all cases, solvation enhances the EA properties of this group. Furthermore, the sensitivity of EA properties of the nitro group to the solvent effect depends on the proximity effects. It has been shown that the proximity of two endocyclic N atoms (two repulsive interactions) results in higher sensitivity than the asymmetric proximity of the endocyclic N atom and NH group (one repulsive and one attractive interaction). To explain this phenomenon, the geometry of the nitro group in coplanar form and after forcing its rotation around the CN bond is discussed. Relative stabilities of nitropurine tautomers in different solvents are also presented. Differences in the stabilities and solvation energies are explained by aromaticity, electronic structure, and intramolecular interactions of the nitropurine tautomers.
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Parshotam S, Joy M, Rossano-Tapia M, Mora-Gomez VA, Brown A. The thermochemical, structural, and spectroscopic analyses of the tautomers of sulfur and selenium modified emissive nucleobases. CAN J CHEM 2021. [DOI: 10.1139/cjc-2020-0294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In this study, density functional theory (DFT) and time dependent density functional theory (TD-DFT) are used to investigate the stabilities and spectral properties [IR, UV–vis, and two-photon absorption (2PA)] of two sets of modified RNA nucleobase tautomers. The modifications introduce either a sulfur or selenium atom to form an isothiazolo[4,3-d]pyrimidine or isoselenazolo[4,3-d]pyrimidine heterocyclic core, respectively. The relative stabilities of both sets of modified tautomers determined with B3LYP/6-31++G(d,p) reveal that in water (with a polarizable continuum model), the 6-keto-2-amino tautomer of guanine and the rare 4-imino-2-keto tautomer of cytosine may be present at significant populations, whereas the 6-enol-2-amino tautomer of guanine is more common in the gas phase. The identification of these modified tautomers is possible due to the natural differences in their vibrational modes and hence IR spectra. Furthermore, the photophysical properties of both these sets of modified tautomers indicate that excitation and emission energies are shifted relative to their more abundant form in both one photon absorption and emission and 2PA spectra, as determined at the B3LYP/6-31++G(d,p) and CAM-B3LYP/aug-cc-pVDZ levels of theory, respectively. Even though the 2PA cross sections in water for all of the species are small (0.3–2.3 GM), the modified cytosine tautomer shows promise, as its cross section is larger than the more dominant form. The spectral separation between the dominant form and the tautomers of isoselenazole and isothiazole modified cytosine and guanine are relatively similar, suggesting both modifications could be useful in elucidating the tautomers from their more abundant counterparts.
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Affiliation(s)
- Shyam Parshotam
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
| | - Megan Joy
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
| | - Maria Rossano-Tapia
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
| | - V. A. Mora-Gomez
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
| | - Alex Brown
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
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Ji X, Gonnella NC, Xin D. Deconvolution of fast exchange equilibrium states in NMR spectroscopy using virtual reference standards and probability theory. Org Biomol Chem 2020; 18:6927-6934. [PMID: 32936188 DOI: 10.1039/d0ob01459a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A methodology for deconvolution of fast exchange equilibrium states in NMR spectroscopy (DFEQNMR) was developed based on DFT-GIAO NMR chemical shift prediction and a probability theory algorithm. Proof-of-concept studies were performed to estimate the protonation state of N-containing organic molecules involving fast proton exchange equilibrium and evaluate the solution tautomerism of a purine derivative. DFT-GIAO calculations were optimized to achieve good accuracy in 13C, 1H and 15N chemical shift prediction for protonated species. The probability theory algorithm enabled the determination of solution species ratios and yielded 95% confidence regions by comparing experimental and simulated chemical shift data sets. The calculation showed good accuracy for model partial salts with various functionalities and application in structure elucidation of complex natural product partial salts was also demonstrated. This method showed promising potential in acquisition of important insight into fast exchange equilibrium systems with only one experimental NMR chemical shift data set.
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Affiliation(s)
- Xiaozhou Ji
- Department of Chemistry, Texas A&M University, College Station, TX, USA
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7
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Oh J, Quan KT, Lee JS, Park I, Kim CS, Ferreira D, Thuong PT, Kim YH, Na M. NMR-Based Investigation of Hydrogen Bonding in a Dihydroanthracen-1(4 H)one from Rubia philippinensis and Its Soluble Epoxide Hydrolase Inhibitory Potential. JOURNAL OF NATURAL PRODUCTS 2018; 81:2429-2435. [PMID: 30354105 DOI: 10.1021/acs.jnatprod.8b00441] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Hydrogen bonding is a vital feature of a large ensemble of chemical structures. Soluble epoxide hydrolase (sEH) has been targeted for development of the treatment for inflammation-associated diseases. Compounds 1 and 2 were purified from Rubia philippinensis, and their structures were established via physical data analysis. Compound 1 possesses intramolecular hydrogen bonding, sufficiently robust to transfer heteronuclear magnetization via a nonbonded interaction. The bonding strength was assessed using the 1H NMR chemical shift temperature coefficients (-1.8 ppb/K), and the heteronuclear coupling constants were measured. The stereochemical details were investigated using interproton distance analysis and ECD. Purified compounds displayed moderate sEH-inhibitory activity.
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Affiliation(s)
- Joonseok Oh
- Department of Chemistry , Yale University , New Haven , Connecticut 06520 , United States
- Chemical Biology Institute , Yale University , West Haven , Connecticut 06516 , United States
| | - Khong Trong Quan
- College of Pharmacy , Chungnam National University , Daejeon 34134 , Republic of Korea
- Department of Herbal Analysis and Standardization , National Institute of Medicinal Materials , Hanoi , Vietnam
| | - Ji Sun Lee
- College of Pharmacy , Chungnam National University , Daejeon 34134 , Republic of Korea
| | - InWha Park
- College of Pharmacy , Chungnam National University , Daejeon 34134 , Republic of Korea
| | - Chung Sub Kim
- Department of Chemistry , Yale University , New Haven , Connecticut 06520 , United States
- Chemical Biology Institute , Yale University , West Haven , Connecticut 06516 , United States
| | - Daneel Ferreira
- Department of BioMolecular Sciences, Division of Pharmacognosy, Research Institute of Pharmaceutical Sciences, School of Pharmacy , The University of Mississippi , University , Mississippi 38677, United States
| | - Phuong Thien Thuong
- Department of Herbal Analysis and Standardization , National Institute of Medicinal Materials , Hanoi , Vietnam
| | - Young Ho Kim
- College of Pharmacy , Chungnam National University , Daejeon 34134 , Republic of Korea
| | - MinKyun Na
- College of Pharmacy , Chungnam National University , Daejeon 34134 , Republic of Korea
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8
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Krasnov VP, Vigorov AY, Gruzdev DA, Levit GL, Demin AM, Nizova IA, Tumashov AA, Sadretdinova LS, Gorbunov EB, Charushin VN. Synthesis of enantiomers of N-(2-aminopurin-6-yl)amino acids. Russ Chem Bull 2016. [DOI: 10.1007/s11172-015-1125-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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9
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Structure, stability, energy barrier and ionization energies of chemically modified DNA-bases: Quantum chemical calculations on 37 favored and rare tautomeric forms of tetraphosphoadenine. COMPUT THEOR CHEM 2015. [DOI: 10.1016/j.comptc.2014.11.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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10
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Tautomerism provides a molecular explanation for the mutagenic properties of the anti-HIV nucleoside 5-aza-5,6-dihydro-2'-deoxycytidine. Proc Natl Acad Sci U S A 2014; 111:E3252-9. [PMID: 25071207 DOI: 10.1073/pnas.1405635111] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Viral lethal mutagenesis is a strategy whereby the innate immune system or mutagenic pool nucleotides increase the error rate of viral replication above the error catastrophe limit. Lethal mutagenesis has been proposed as a mechanism for several antiviral compounds, including the drug candidate 5-aza-5,6-dihydro-2'-deoxycytidine (KP1212), which causes A-to-G and G-to-A mutations in the HIV genome, both in tissue culture and in HIV positive patients undergoing KP1212 monotherapy. This work explored the molecular mechanism(s) underlying the mutagenicity of KP1212, and specifically whether tautomerism, a previously proposed hypothesis, could explain the biological consequences of this nucleoside analog. Establishing tautomerism of nucleic acid bases under physiological conditions has been challenging because of the lack of sensitive methods. This study investigated tautomerism using an array of spectroscopic, theoretical, and chemical biology approaches. Variable temperature NMR and 2D infrared spectroscopic methods demonstrated that KP1212 existed as a broad ensemble of interconverting tautomers, among which enolic forms dominated. The mutagenic properties of KP1212 were determined empirically by in vitro and in vivo replication of a single-stranded vector containing a single KP1212. It was found that KP1212 paired with both A (10%) and G (90%), which is in accord with clinical observations. Moreover, this mutation frequency is sufficient for pushing a viral population over its error catastrophe limit, as observed before in cell culture studies. Finally, a model is proposed that correlates the mutagenicity of KP1212 with its tautomeric distribution in solution.
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11
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Kadam SS, Maier L, Kostakis I, Pouli N, Toušek J, Nečas M, Marakos P, Marek R. Synthesis and Tautomerism of Substituted Pyrazolo[4,3-c]pyrazoles. European J Org Chem 2013. [DOI: 10.1002/ejoc.201300606] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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12
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Detection of tautomer proportions of dimedone in solution: a new approach based on theoretical and FT-IR viewpoint. J Comput Aided Mol Des 2013; 27:681-8. [DOI: 10.1007/s10822-013-9669-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 07/31/2013] [Indexed: 11/26/2022]
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Chiavarino B, Crestoni ME, Fornarini S, Scuderi D, Salpin JY. Interaction of Cisplatin with Adenine and Guanine: A Combined IRMPD, MS/MS, and Theoretical Study. J Am Chem Soc 2013; 135:1445-55. [DOI: 10.1021/ja309857d] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Barbara Chiavarino
- Dipartimento di Chimica e Tecnologie
del Farmaco, Università di Roma “La Sapienza”, P.le A. Moro 5, I-00185 Roma, Italy
| | - Maria Elisa Crestoni
- Dipartimento di Chimica e Tecnologie
del Farmaco, Università di Roma “La Sapienza”, P.le A. Moro 5, I-00185 Roma, Italy
| | - Simonetta Fornarini
- Dipartimento di Chimica e Tecnologie
del Farmaco, Università di Roma “La Sapienza”, P.le A. Moro 5, I-00185 Roma, Italy
| | - Debora Scuderi
- Laboratoire de Chimie-Physique, Université Paris Sud Orsay, Avenue Georges Clémenceau,
91405 Orsay Cedex, France
- CNRS-UMR 8000
| | - Jean-Yves Salpin
- Université d'Evry Val d'Essonne, Laboratoire Analyse et Modélisation
pour la Biologie et l’Environnement, Boulevard François
Mitterrand, 91025 Evry, France
- CNRS-UMR 8587
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14
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O'Donovan DH, Kelly B, Diez-Cecilia E, Kitson M, Rozas I. A structural study of N,N′-bis-aryl-N′′-acylguanidines. NEW J CHEM 2013. [DOI: 10.1039/c3nj00285c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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15
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Das RS, Samaraweera M, Morton M, Gascón JA, Basu AK. Stability of N-glycosidic bond of (5'S)-8,5'-cyclo-2'-deoxyguanosine. Chem Res Toxicol 2012; 25:2451-61. [PMID: 23025578 DOI: 10.1021/tx300302a] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
8,5'-Cyclopurine deoxynucleosides are unique tandem lesions containing an additional covalent bond between the base and the sugar. These mutagenic and genotoxic lesions are repaired only by nucleotide excision repair. The N-glycosidic (or C1'-N9) bond of 2'-deoxyguanosine (dG) derivatives is usually susceptible to acid hydrolysis, but even after cleavage of this bond of the cyclopurine lesions, the base would remain attached to the sugar. Here, the stability of the N-glycosidic bond and the products formed by formic acid hydrolysis of (5'S)-8,5'-cyclo-2'-deoxyguanosine (S-cdG) were investigated. For comparison, the stability of the N-glycosidic bond of 8,5'-cyclo-2',5'-dideoxyguanosine (ddcdG), 8-methyl-2'-deoxyguanosine (8-Me-dG), 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-Oxo-dG), and dG was also studied. In various acid conditions, S-cdG and ddcdG exhibited similar stability to hydrolysis. Likewise, 8-Me-dG and dG showed comparable stability, but the half-lives of the cyclic dG lesions were at least 5-fold higher than those of dG or 8-Me-dG. NMR studies were carried out to investigate the products formed after the cleavage of the C1'-N9 bond. 2-Deoxyribose generated α and β anomers of deoxyribopyranose and deoxyribopyranose oligomers following acid treatment. S-cdG gave α- and β-deoxyribopyranose linked guanine as the major products, but α and β anomers of deoxyribofuranose linked guanine and other products were also detected. The N-glycosidic bond of 8-Oxo-dG was found exceptionally stable in acid. Computational studies determined that both the protonation of the N7 atom and the rate constant in the bond breaking step control the overall kinetics of hydrolysis, but both varied for the molecules studied indicating a delicate balance between the two steps. Nevertheless, the computational approach successfully predicted the trend observed experimentally. For 8-Oxo-dG, the low pK(a) of O(8) and N3 prevented appreciable protonation, making the free energy for N-glycosidic bond cleavage in the subsequent step very high.
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Affiliation(s)
- Rajat S Das
- Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA
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16
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Karabulut S, Namlı H. An FT-IR and DFT based new approach for the detection of tautomer proportions in solution. J Mol Struct 2012. [DOI: 10.1016/j.molstruc.2012.05.029] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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17
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Vícha J, Demo G, Marek R. Platinum-Modified Adenines: Unprecedented Protonation Behavior Revealed by NMR Spectroscopy and Relativistic Density-Functional Theory Calculations. Inorg Chem 2012; 51:1371-9. [DOI: 10.1021/ic201595e] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Affiliation(s)
- Jan Vícha
- National Center for Biomolecular Research, Faculty
of Science and Central European Institute of Technology-CEITEC, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech
Republic
| | - Gabriel Demo
- National Center for Biomolecular Research, Faculty
of Science and Central European Institute of Technology-CEITEC, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech
Republic
| | - Radek Marek
- National Center for Biomolecular Research, Faculty
of Science and Central European Institute of Technology-CEITEC, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech
Republic
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18
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Liang Y, Hnatiuk N, Rowley JM, Whiting BT, Coates GW, Rablen PR, Morton M, Howell AR. Access to Oxetane-Containing psico-Nucleosides from 2-Methyleneoxetanes: A Role for Neighboring Group Participation? J Org Chem 2011; 76:9962-74. [DOI: 10.1021/jo201565h] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Yanke Liang
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060,
United States
| | - Nathan Hnatiuk
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060,
United States
| | - John M. Rowley
- Department
of Chemistry and
Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
| | - Bryan T. Whiting
- Department
of Chemistry and
Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
| | - Geoffrey W. Coates
- Department
of Chemistry and
Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
| | - Paul R. Rablen
- Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, Pennsylvania 19081-1397,
United States
| | - Martha Morton
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060,
United States
| | - Amy R. Howell
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060,
United States
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Franco-Pérez M, Moya-Hernández R, Rojas-Hernández A, Gutiérrez A, Gómez-Balderas R. Tautomeric Ratio and Prototropic Equilibrium Constants of Tenoxicam, a 1H and 13C NMR Theoretical and Experimental Study. J Phys Chem B 2011; 115:13593-8. [DOI: 10.1021/jp204902t] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Marco Franco-Pérez
- Laboratorio de Fisicoquímica Analítica, Unidad de Investigación Multidisciplinaria, FES Cuautitlán, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, Estado de México, 54714, México
| | - Rosario Moya-Hernández
- Laboratorio de Fisicoquímica Analítica, Unidad de Investigación Multidisciplinaria, FES Cuautitlán, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, Estado de México, 54714, México
| | - Alberto Rojas-Hernández
- Departamento de Química, Área de Química Analítica, Universidad Autónoma Metropolitana-Iztapalapa, Apartado Postal 55-534, 09340 México, D.F., México
| | - Atilano Gutiérrez
- Departamento de Química, Área de Química Analítica, Universidad Autónoma Metropolitana-Iztapalapa, Apartado Postal 55-534, 09340 México, D.F., México
| | - Rodolfo Gómez-Balderas
- Laboratorio de Fisicoquímica Analítica, Unidad de Investigación Multidisciplinaria, FES Cuautitlán, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, Estado de México, 54714, México
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20
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Cuñat AC, Flores S, Oliver J, Fustero S. Synthesis of Fluorinated and Non-Fluorinated Bicyclic Amidines through Ring-Closing Metathesis. European J Org Chem 2011. [DOI: 10.1002/ejoc.201101091] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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21
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Dybiec K, Molchanov S, Gryff-Keller A. Structure of Neutral Molecules and Monoanions of Selected Oxopurines in Aqueous Solutions As Studied by NMR Spectroscopy and Theoretical Calculations. J Phys Chem A 2011; 115:2057-64. [DOI: 10.1021/jp110888m] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Katarzyna Dybiec
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw
| | - Sergey Molchanov
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw
| | - Adam Gryff-Keller
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw
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22
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Standara S, Bouzková K, Straka M, Zacharová Z, Hocek M, Marek J, Marek R. Interpretation of substituent effects on 13C and 15N NMR chemical shifts in 6-substituted purines. Phys Chem Chem Phys 2011; 13:15854-64. [DOI: 10.1039/c1cp20680j] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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23
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Maliňáková K, Novosadová L, Pipíška M, Marek R. Chemical Shift Tensors in Isomers of Adenine: Relation to Aromaticity of Purine Rings? Chemphyschem 2010; 12:379-88. [DOI: 10.1002/cphc.201000657] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2010] [Revised: 10/18/2010] [Indexed: 11/11/2022]
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24
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Marek R, Křístková A, Maliňáková K, Toušek J, Marek J, Hocek M, Malkina OL, Malkin VG. Interpretation of Indirect Nuclear Spin−Spin Couplings in Isomers of Adenine: Novel Approach to Analyze Coupling Electron Deformation Density Using Localized Molecular Orbitals. J Phys Chem A 2010; 114:6689-700. [DOI: 10.1021/jp102186r] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Radek Marek
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
| | - Anežka Křístková
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
| | - Kateřina Maliňáková
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
| | - Jaromír Toušek
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
| | - Jaromír Marek
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
| | - Michal Hocek
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
| | - Olga L. Malkina
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
| | - Vladimir G. Malkin
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava, Slovak Republic, Laboratory of Functional Genomics and Proteomics, Masaryk University, Kamenice 5/A2, CZ-62500 Brno, Czech Republic, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague, Czech Republic
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25
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Vícha J, Malon M, Veselá P, Humpa O, Strnad M, Marek R. 1H-, 13C-, and 15N-NMR chemical shifts for selected glucosides and ribosides of aromatic cytokinins. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2010; 48:318-322. [PMID: 20198611 DOI: 10.1002/mrc.2575] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The (1)H and (13)C NMR resonances of 16 purine glucosides were assigned by a combination of one- and two-dimensional NMR experiments, including gs-COSY, gs-HSQC, and gs-HMBC, in order to characterize the effect of substituent and the position of glucose unit on the NMR chemical shifts. In addition, (15)N NMR chemical shifts for selected derivatives were investigated by using (1)H-(15)N chemical shift correlation techniques. To map the influence of sugar moiety on the directly bonded nitrogen atom, selected N(9)-glucosides and their ribose analogs were compared. Characteristic long-range (1)H-(15)N coupling constants, measured by using (1)H-(15)N gradient-selected single-quantum multiple bond correlation (GSQMBC), are also reported and discussed. All compounds investigated here belong to cytokinins, an important group of plant hormones.
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Affiliation(s)
- Jan Vícha
- National Center for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5/A4, CZ-625 00 Brno, Czech Republic
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26
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Maliňáková K, Novosadová L, Lahtinen M, Kolehmainen E, Brus J, Marek R. 13C Chemical Shift Tensors in Hypoxanthine and 6-Mercaptopurine: Effects of Substitution, Tautomerism, and Intermolecular Interactions. J Phys Chem A 2010; 114:1985-95. [DOI: 10.1021/jp9100619] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kateřina Maliňáková
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Department of Chemistry, University of Jyväskylä, P. O. Box 35, FIN-40014, Finland, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Prague, Czech Republic
| | - Lucie Novosadová
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Department of Chemistry, University of Jyväskylä, P. O. Box 35, FIN-40014, Finland, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Prague, Czech Republic
| | - Manu Lahtinen
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Department of Chemistry, University of Jyväskylä, P. O. Box 35, FIN-40014, Finland, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Prague, Czech Republic
| | - Erkki Kolehmainen
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Department of Chemistry, University of Jyväskylä, P. O. Box 35, FIN-40014, Finland, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Prague, Czech Republic
| | - Jiří Brus
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Department of Chemistry, University of Jyväskylä, P. O. Box 35, FIN-40014, Finland, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Prague, Czech Republic
| | - Radek Marek
- National Center for Biomolecular Research, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic, Department of Chemistry, University of Jyväskylä, P. O. Box 35, FIN-40014, Finland, and Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Prague, Czech Republic
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27
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Mukano Y, Momochi M, Takanashi Y, Suzuki M, Wakabayashi H, Teramae H, Kobayashi K. Imino–enamine tautomerism and dynamic prototropy in 1-imino-3-amino-1H-indens. Tetrahedron 2010. [DOI: 10.1016/j.tet.2009.11.076] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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28
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Novotná R, Trávníček Z, Popa I. X-ray crystallographic and NMR study of the tautomerism in kinetin, kinetin riboside and their derivatives: A comparison between the solid state and solution. J Mol Struct 2010. [DOI: 10.1016/j.molstruc.2009.10.036] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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29
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Standara S, Maliňáková K, Marek R, Marek J, Hocek M, Vaara J, Straka M. Understanding the NMR chemical shifts for 6-halopurines: role of structure, solvent and relativistic effects. Phys Chem Chem Phys 2010; 12:5126-39. [DOI: 10.1039/b921383j] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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30
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X-ray structures of five variably tert-butoxycarbonyl-substituted adenines and their liquid and solid state NMR investigations. J Mol Struct 2009. [DOI: 10.1016/j.molstruc.2009.05.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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31
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Bartl T, Zacharová Z, Sečkářová P, Kolehmainen E, Marek R. NMR Quantification of Tautomeric Populations in Biogenic Purine Bases. European J Org Chem 2009. [DOI: 10.1002/ejoc.200801016] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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32
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Tsikouris O, Bartl T, Tousek J, Lougiakis N, Tite T, Marakos P, Pouli N, Mikros E, Marek R. NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2008; 46:643-649. [PMID: 18383434 DOI: 10.1002/mrc.2226] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Substituted pyrazolopyridines are potent inhibitors of phosphodiesterases and cyclin-dependent kinases. In this study, NMR was used to investigate the potential N1-H and N2-H tautomerism of 5-substituted pyrazolo[3,4-c]pyridine derivatives. Six compounds were fully characterized by using (1)H, (13)C, and (15)N chemical shifts and indirect (1)H--(13)C and (1)H--(15)N coupling constants. The (1)H NMR spectra were measured over a broad range of temperatures. All of the compounds were shown to exist predominantly in the N1-H tautomeric form. Complementary quantum-chemical calculations of the chemical shieldings and indirect spin-spin couplings support the structural conclusions drawn.
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Affiliation(s)
- Orestis Tsikouris
- Department of Pharmacy, Division of Pharmaceutical Chemistry, University of Athens, Panepistimiopolis Zografou, Athens GR-15771, Greece
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33
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Wagner G, Garland T. Synthesis of 5-trichloromethyl-Δ4-1,2,4-oxadiazolines and their rearrangement into formamidine derivatives. Tetrahedron Lett 2008. [DOI: 10.1016/j.tetlet.2008.04.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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34
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Fonseca Guerra C, Bickelhaupt FM, Saha S, Wang F. Adenine tautomers: relative stabilities, ionization energies, and mismatch with cytosine. J Phys Chem A 2007; 110:4012-20. [PMID: 16539424 DOI: 10.1021/jp057275r] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study, we have investigated 12 tautomers of the DNA base adenine at the BP86/TZ2P and BP86/QZ4P levels of density functional theory. The vertical and adiabatic ionization energies of all tautomers were determined as the difference in energy between the radical cation and the corresponding neutral system. Furthermore, an evaluation is made for the eigenvalue spectra calculated with the SAOP functional, which is shown to lead to substantial improvements for orbital energies compared to BP86. We have also explored the correlations between the Kohn-Sham orbitals of the different tautomers at the BP86/QZ4P and SAOP/QZ4P levels. Finally, we discuss implications of the existence of the tautomeric forms of adenine for the DNA replication.
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Affiliation(s)
- C Fonseca Guerra
- Theoretische Chemie, Scheikundig Laboratorium der Vrije Universiteit, De Boelelaan 1083, NL-1081 HV Amsterdam, The Netherlands
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35
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Díaz-Gavilán M, Choquesillo-Lazarte D, González-Pérez JM, Gallo MA, Espinosa A, Campos JM. Synthesis and reactivity of (RS)-6-chloro-7- or 9-(1,2,3,5-tetrahydro-4,1-benzoxazepin-3-yl)-7H- or 9H-purines bearing a nitrobenzenesulfonyl group on the nitrogen atom. Tetrahedron 2007. [DOI: 10.1016/j.tet.2007.03.155] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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36
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Conformational study and electron density analysis of 9-[tetrahydropyran-3-yl]purine derivatives. Tetrahedron 2007. [DOI: 10.1016/j.tet.2006.10.084] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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37
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38
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The studies of tautomerism in 6-mercaptopurine derivatives by 1H–13C, 1H–15N NMR and 13C, 15N CPMAS-experimental and quantum chemical approach. J Mol Struct 2006. [DOI: 10.1016/j.molstruc.2005.10.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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39
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Raczyńska ED, Kosińska W, Ośmiałowski B, Gawinecki R. Tautomeric Equilibria in Relation to Pi-Electron Delocalization. Chem Rev 2005; 105:3561-612. [PMID: 16218561 DOI: 10.1021/cr030087h] [Citation(s) in RCA: 248] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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