- Photoinduced oxidation of sterically hindered amines in acetonitrile solutions and titania suspensions (An EPR Study)
-
The reactions of sterically hindered amines (SHA) were investigated in acetonitrile solutions and TiO2 suspensions upon exposure to monochromatic radiation, λ = 365 nm, by means of in situ EPR spectroscopy. The formation of singlet oxygen, as one of the possible oxidation agents for SHA, in these systems is affected significantly by solvent used and the experimental conditions. Experiments in homogeneous media evidenced alternative pathways for the SHA oxidation with a variety reactive oxygen species involved. In anhydrous acetonitrile solutions containing KO2, the SHA oxidation was negligible not only in the dark but also on continuous exposure. However, the presence of water, even at low concentrations, led to the transformation of O2?- to singlet oxygen and hydrogen peroxide, which served as a source of hydroxyl radicals. These species participated in oxidation of SHA resulting in the generation of nitroxide radicals. To investigate the influence of different competitive reactions of SHA with other ROS formed upon TiO2 photoexcitation, a series of experiments using different additives (e.g. KO2, H2O 2, NaN3, dimethylsulfoxide, methanol as organic cosolvents) under air or argon were performed. The detailed analysis of paramagnetic intermediates formed upon the irradiation of the studied systems was accomplished using EPR spin trapping technique. The reactions of sterically hindered amines (SHA) were investigated in acetonitrile solutions and TiO 2 suspensions upon exposure to monochromatic radiation (λ = 365 nm) by in situ EPR spectroscopy. Experiments in homogeneous media using KO2 and H2O2 evidenced alternative pathways for the SHA oxidation with a variety reactive oxygen species (ROS) involved. The influence of competitive reactions of SHA with ROS formed upon TiO2 photoexcitation was investigated in a series of experiments using different additives (e.g. KO2, H2O2, NaN3, dimethylsulfoxide and methanol) under air or argon. The detailed analysis of paramagnetic intermediates formed upon the irradiation of the studied systems was accomplished using an EPR spin trapping technique. 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology
- Barbierikova, Zuzana,Mihalikova, Maria,Brezova, Vlasta
-
-
Read Online
- EPR Study of Membrane Partitioning, Orientation, and Membrane-Modulated Alkaline Hydrolysis of a Spin-Labeled Benzoic Acid Ester
-
The composite EPR spectra of a spin probe (Tempobenzoate, TB) that partitions between aqueous and egg phosphatidylcholine (EPC) membrane phases provide information about (1) its location and orientation in the membrane, (2) its partition coefficient and the thermodynamics of the process, and (3) the kinetics of its alkaline hydrolysis, a novel application of spin label spectra.The broad and narrow spectral components of the probe in the membrane and aqueous phase, respectively, are sufficiently resolved in the high-field region, to permit quantitative evaluation of the narrow line (h).The line shapes of membrane spectra, obtained by spectral subtraction, indicate that the nitroxide x axis (the probe long molecular axis) is aligned preferentially parallel to the bilayer normal.Spectral subtractions, as well as measurement of h, are used to calculate the probe's partition coefficient.Thermodynamic analysis indicated that binding of the probe is endothermic and driven by an increase in entropy suggesting that dehydration is the predominant step.At alkaline pH, TB undergoes hydrolysis.Although the narrow high-field lines of both reactant (TB) and product (Tempol) overlap, the pseudo-first-order rate constants can be calculated from the time-dependent height of this line.At high ionic strength, the reaction occurs essentially in the aqueous phase, and the decrease in rate with increasing membrane concentration is due to partition modulation of reagent concentration.TB-membrane binding was also evaluated from the kinetic data.The results are in excellent agreement with those obtained by direct measurements.
- Bianconi, M. Lucia,Schreier, Shirley
-
-
Read Online
- Reactions of nitroxides. Part XII [1]. - 2,2,6,6-tetramethyl-l-oxyl-4- piperidyl chloroformate - A new reactive nitroxyl radical. a one-pot synthesis of 2,2,6,6-tetramethyl-1-oxyl-4-piperidyl N,N-dialkyl-carbamates
-
The reactive nitroxides 2,2,6,6-tetramethyl-1-oxyl-4-piperidyl chloroformate and 2,2,6,6-tetramethyl-1-oxyl-4-piperidyl chlorothionoformate were synthesized from 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl and diphosgene (68percent) or thiophosgene (61 percent), respectively. The reactions of the chloroformate and chlorothionoformate with lower secondary amines lead to 2,2,6,6-tetramethyl-1-oxyl-4-piperidyl A,A-dialkylcarbamates (59-94percent) and thionocarbamates (35-65 percent), respectively. Unexpectedly, the same 2,2,6,6-tetramethyl-1-oxyl-4-piperidyl A,A-dialkylcarbamates were obtained directly in a one-pot reaction of 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl with diphosgene and lower tertiary alkylamines by dealkylation in 32-86 percent yield. The antifungal activity of the synthesized carbamates and thionocarbamates has been demonstrated.
- Zakrzewski, Jerzy,Krawczyk, Maria
-
-
Read Online
- Light-Sensitive Alkoxyamines as Versatile Spatially- and Temporally- Controlled Precursors of Alkyl Radicals and Nitroxides
-
The use of UV/visible light irradiation as a means to initiate organic syntheses is increasingly attractive due to the high spatial and temporal control conferred by photochemical processes. The aim of this work is thus to demonstrate that alkoxyamines be
- Baron, Marc,Morris, Jason C.,Telitel, Siham,Clément, Jean-Louis,Lalevée, Jacques,Morlet-Savary, Fabrice,Spangenberg, Arnaud,Malval, Jean-Pierre,Soppera, Olivier,Gigmes, Didier,Guillaneuf, Yohann
-
-
Read Online
- Synthesis of novel spin-labeled derivatives of 5-FU as potential antineoplastic agents
-
Chemotherapy is a general treatment option for various cancers, including lung cancer. In order to find compounds with superior bioactivity and less toxicity against lung cancer, novel spin-labeled 5-fluorouracil (5-FU) derivatives (3a-f) were synthesized and evaluated against four human tumor cell lines (A-549, DU-145, KB, and KBvin). Two promising compounds 3d and 3f exhibited IC50 values of 2.76 and 2.38 μM, respectively, against non-small cell lung carcinoma cell line A-549. These compounds were twofold more cytotoxic than 5-FU and less toxic against other tested cell lines. Compound 3f exhibited seven times more selective cytotoxicity against A-549 than 5-FU. Our results suggest that compounds 3d and 3f merit further investigation for development into clinical trial candidates for non-small cell lung cancer.
- Yang, Liu,Wang, Mei-Juan,Zhang, Zhi-Jun,Morris-Natschke, Susan L.,Goto, Masuo,Tian, Jing,Liu, Ying-Qian,Wang, Chih-Ya,Tian, Xuan,Yang, Xiao-Ming,Lee, Kuo-Hsiung
-
-
Read Online
- Chemistry and anti-herpes simplex virus type 1 evaluation of 4-substituted-1H-1,2,3-triazole-nitroxyl-linked hybrids
-
Abstract: HSV disease is distributed worldwide. Anti-herpesvirus drugs are a problem in clinical settings, particularly in immunocompromised individuals undergoing herpes simplex virus type 1 infection. In this work, 4-substituted-1,2,3-1H-1,2,3-triazole linked nitroxyl radical derived from TEMPOL were synthesized, and their ability to inhibit the in vitro replication of HSV-1 was evaluated. The nitroxide derivatives were characterized by infrared spectroscopy and elemental analysis, and three of them had their crystal structures determined by single-crystal X-ray diffraction. Four hybrid molecules showed important anti-HSV-1 activity with IC50 values ranged from 0.80 to 1.32?μM. In particular, one of the nitroxide derivatives was more active than Acyclovir (IC50 = 0.99?μM). All compounds tested were more selective inhibitors than the reference antiviral drug. Among them, two compounds were 4.5 (IC50 0.80?μM; selectivity index CC50/IC50 3886) and 7.7 times (IC50 1.10?μM; selectivity index CC50/IC50 6698) more selective than acyclovir (IC50 0.99?μM; selectivity index CC50/IC50: 869). These nitroxide derivatives may be elected as leading compounds due to their antiherpetic activities and good selectivity. Graphic abstract: [Figure not available: see fulltext.]
- Cunha, Anna C.,Ferreira, Vitor F.,Vaz, Maria G. F.,Cassaro, Rafael A. All?o,Resende, Jackson A. L. C.,Sacramento, Carolina Q.,Costa, Jéssica,Abrantes, Juliana L.,Souza, Thiago Moreno L.,Jord?o, Alessandro K.
-
-
Read Online
- Ultrafast and reversible multiblock formation by the SET-nitroxide radical coupling reaction
-
The single electron transfer-nitroxide radical coupling (SET-NRC) reaction has been used to produce multiblock polymers with high molecular weights in under 3 min at 50°C by coupling a difunctional telechelic polystyrene (Br-PSTY-Br) with a dinitroxide. The well known combination of dimethyl sulfoxide as solvent and Me6TREN as ligand facilitated the in situ disproportionation of CuIBr to the highly active nascent Cu 0 species. This SET reaction allowed polymeric radicals to be rapidly formed from their corresponding halide end-groups. Trapping of these carbon-centred radicals at close to diffusion controlled rates by dinitroxides resulted in high-molecular-weight multiblock polymers. Our results showed that the disproportionation of CuI was critical in obtaining these ultrafast reactions, and confirmed that activation was primarily through Cu 0. We took advantage of the reversibility of the NRC reaction at elevated temperatures to decouple the multiblock back to the original PSTY building block through capping the chain-ends with mono-functional nitroxides. These alkoxyamine end-groups were further exchanged with an alkyne mono-functional nitroxide (TEMPO-≡) and 'clicked' by a Cu I-catalyzed azide/alkyne cycloaddition (CuAAC) reaction with N 3-PSTY-N3 to reform the multiblocks. This final 'click' reaction, even after the consecutive decoupling and nitroxide-exchange reactions, still produced high-molecular-weight multiblocks efficiently. These SET-NRC reactions would have ideal applications in re-usable plastics and possibly as self-healing materials. CSIRO 2010.
- Kulis, Jakov,Bell, Craig A.,Micallef, Aaron S.,Monteiro, Michael J.
-
-
Read Online
- Kinetics of oxidation and comproportionation reactions involving an oxammonium ion, benzyl alcohol and methyltrioxorhenium(VII)
-
The reactions of 4-hydroxy-2,2,6,6-tetramethylpiperidinium N-oxide, an oxammonium ion abbreviated R2NO+, have been studied. The previously unreported triflate salt was used in this study because the anions of the usual chloride and bromide salts can themselves be oxidized. Reactions between R2NO+ and alcohols produce ketones and aldehydes; the rate constant for PhCH2OH is 4.4×10-3 L mol-1 s-1 in acetonitrile at 298 K. The immediate product is the hydroxylamine, R2NOH, but its further comproportionation reaction with R2NO+ yields the stable piperidinyl oxyl radical, R2NO·. The rate constant of this reaction is 1.78×103 L mol-1 s-1 at 298 K. The possibility of using R2NO+ and MTO as co-catalysts for the oxidation of alcohols was explored, but the competitive rates are such that the resultant is not particularly attractive.
- Zauche, Timothy H.,Espenson, James H.
-
-
Read Online
- Method for preparing hindered amine nitroxide free radical compound by alkaline heterogeneous catalysis system
-
The method comprises the following steps: dissolving a hindered amine compound in an organic solvent; adjusting pH by a carbonate aqueous solution; reacting with an aqueous hydrogen peroxide solution; and generating a hindered amine nitroxide free radical compound (IV). (V) Or (VI). The method is high in universality, and the hindered amine nitroxide free radical compound with various structures is prepared. The method is high in catalytic activity, short in reaction time, high in yield, simple in preparation process and convenient to operate; a high-purity target product can be obtained through simple phase separation, drying and concentration in the post-treatment process; meanwhile, the aqueous solution system and ethyl acetate can be recycled. Small by-products.
- -
-
Paragraph 0042-0045; 0058-0059
(2021/09/26)
-
- A cyanine dye based supramolecular photosensitizer enabling visible-light-driven organic reaction in water
-
We report the aggregation-induced photosensitizing activity of a cyanine dye in water and the mechanism. In addition, using the supramolecular assembly, visible-light-driven photooxidation of hydrophobic aromatic compounds in water was successfully performed. This journal is
- Fujitsuka, Mamoru,Kida, Toshiyuki,Mori, Tadashi,Ohkubo, Kei,Osakada, Yasuko,Shigemitsu, Hajime,Tamemoto, Tomoe
-
supporting information
p. 11217 - 11220
(2021/11/09)
-
- Synthesis and evaluation of β-galactosidase-targeting spin-label probe: 5-o-β-d-galactosyl-5-hydroxy-1,1,3,3-tetramethylisoindoline-2-oxyl
-
In this study, 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and 5-hydroxy-1,1,3,3-tetra-methylisoindoline-2-oxyl O-galactosides (PG, TG, and IG) were synthesized. Moreover, their reduction reactivi
- Ito, Tomohiro,Konno, Hiroyuki,Sato, Shingo,Sugawara, Koya
-
p. 1799 - 1815
(2020/11/19)
-
- 2′-Alkynylnucleotides: A Sequence- and Spin Label-Flexible Strategy for EPR Spectroscopy in DNA
-
Electron paramagnetic resonance (EPR) spectroscopy is a powerful method to elucidate molecular structure through the measurement of distances between conformationally well-defined spin labels. Here we report a sequence-flexible approach to the synthesis of double spin-labeled DNA duplexes, where 2′-alkynylnucleosides are incorporated at terminal and internal positions on complementary strands. Post-DNA synthesis copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions with a variety of spin labels enable the use of double electron-electron resonance experiments to measure a number of distances on the duplex, affording a high level of detailed structural information.
- Haugland, Marius M.,El-Sagheer, Afaf H.,Porter, Rachel J.,Pe?a, Javier,Brown, Tom,Anderson, Edward A.,Lovett, Janet E.
-
p. 9069 - 9072
(2016/08/05)
-
- Synthesis and properties of multifunctional nitroxyl radical hindered-amine light stabilizers
-
A series of novel nitroxyl radical hindered-amine light stabilizer monomers were designed and synthesized from 2,2,6,6-tetramethylpiperidine-N-oxyl-4-ol, cyanuric chloride, allylamine, and 2-hydroxyphenylbenzotriazole derivatives. Structures of the new stabilizers were confirmed by 1H NMR, 13C NMR, FT-IR, ESI-HRMS, and element analysis. The synthesized compounds 5a-f were evaluated for their antioxidant and antiaging properties, and a significant stabilizing effect against photodegradation was found.
- Zhang, Wen,Liu, Dong,Hua, Chengwen,Zhao, Junlong,Chen, Bang,Gou, Xiaofeng
-
-
- Reactions of nitroxides XIV. Analogs of phenoxy carboxylic herbicides based on the piperidine scaffold; Unexpected fungicidal activity of the 2-[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy] butanoic acid
-
Alkanoic acid derivatives bearing a nitroxyl moiety 3a-e were synthesized from 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (1) and the corresponding 2-bromoalkane carboxylic acids 2a-e. The herbicidal and antifungal activity of 3a-e was tested. No herbicidal activity of the tested compounds was found. The 2-[(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]butanoic acid 3c revealed a strong antifungal activity against the pathogenic fungus Phytophthora cactorum.
- Zakrzewski, Jerzy,Krawczyk, Maria
-
-
- A novel protecting group methodology for syntheses using nitroxides
-
The methoxyamine group represents an ideal protecting group for the nitroxide moiety. It can be easily and selectively introduced in high yield (typically >90%) to a range of functionalised nitroxides using FeSO 4·7H2O and H2O2 in DMSO. Its removal is readily achieved under mild conditions in high yield (70-90%) using mCPBA in a Cope-type elimination process.
- Chalmers, Benjamin A.,Morris, Jason C.,Fairfull-Smith, Kathryn E.,Grainger, Richard S.,Bottle, Steven E.
-
supporting information
p. 10382 - 10384
(2013/10/22)
-
- Synthesis and mechanistic studies of novel spin-labeled combretastatin derivatives as potential antineoplastic agents
-
Two series (14a-d and 21a-h) of novel spin-labeled combretastatin derivatives were synthesized and evaluated for cytotoxicity against four tumor cell lines (K562, SGC-7901, Hela and HepG-2). Simultaneously, a representative compound 21a was selected to investigate the antitumor mechanisms of these synthetic compounds. The results indicated that some of the compounds showed significant cytotoxicity against four tumor cell lines in vitro and were more active than etoposide, a clinically available anticancer drug. Among the newly synthesized compounds, 21a, 21b and 21c displayed the greatest cytotoxicity against three tested tumor cell lines (HEPG-2, BGC-832 and Hela), with IC 50 values ranging from 0.15 to 1.05 μM, compared with values of 0.014-0.403 μM for 3-amino-deoxycombretastatin A-4 (3). In addition, the mechanistic analysis revealed that compound 21a effectively interfered with tubulin dynamics to prevent mitosis in cancer cells, leading to cell cycle arrest and, eventually, dose dependent apoptosis.
- Liu, Ying-Qian,Li, Xiao-Jing,Zhao, Chun-Yan,Nan, Xiang,Tian, Jing,Morris-Natschke, Susan L.,Zhang, Zhi-Jun,Yang, Xiao-Ming,Yang, Liu,Li, Lin-Hai,Zhou, Xing-Wen,Lee, Kuo-Hsiung
-
p. 1248 - 1256
(2013/03/14)
-
- Reactions of nitroxides XIII: Synthesis of the Morita-Baylis-Hillman adducts bearing a nitroxyl moiety using 4-acryloyloxy-2,2,6,6- tetramethylpiperidine-1-oxyl as a starting compound, and DABCO and quinuclidine as catalysts
-
The Morita-Baylis-Hillman adducts bearing a nitroxyl moiety were synthesized from 4-acryloyloxy-2,2,6,6-tetramethylpiperidine- 1-oxyl and aliphatic, aryl and heterocyclic aldehydes.
- Zakrzewski, Jerzy
-
p. 1515 - 1522
(2012/11/07)
-
- Tacticity influence on the electrochemical reactivity of group transfer polymerization-synthesized PTMA
-
Spectroscopic, thermal, and electrochemical characterization results are presented for the redox active polymer poly(2,2,6,6-tetramethyl-1- piperinidyloxy-4-yl methacrylate) or PTMA, synthesized by group transfer polymerization (GTP), and its precursors 4-hydroxy-tetramethylpiperidine-N-oxyl (HO-TEMPO) and 4-methacryloyloxy-tetramethylpiperidine-N-oxyl (MO-TEMPO). DSC analysis of synthesized PTMA showed that the glass transition temperature (Tg) of the polymer structure occurs at 155 °C, corroborated by dynamic mechanical analysis (DMA), which is higher when compared with T g data for PTMA synthesized by other methods. Also, the amount of radical species present in PTMA synthesized by GTP reactions (100%) is higher than the values typically upon synthesizing PTMA by radical polymerization. Electrochemical and spectroelectrochemical-electron spin resonance studies in acetonitrile revealed two redox events in the PTMA polymer, one of which is reversible, accounting for ca. 80% of the spins in the polymer and giving rise to the battery behavior. The other redox event is irreversible, accounting for the remaining ca. 20% of spins, which has not previously been reported. These two redox events are linked to a structural property associated with the tacticity of the polymer, where the reversible feature (responsible for cathode behavior) is the dominant species. This corresponds to a number of isotactic domains of the polymer (determined by high temperature 1H NMR). The second feature accounts for the three-line impurity observed in the ESR, which has been reported previously but poorly explained, associated to the number of heterotactic/syndiotactic triads.
- Lopez-Penna, Hugo A.,Hernandez-Munnoz, Lindsay S.,Frontana-Uribe, Bernardo A.,Gonzalez, Felipe J.,Gonzalez, Ignacio,Frontana, Carlos,Cardoso, Judith
-
experimental part
p. 5542 - 5550
(2012/07/31)
-
- MODIFIED ZNO NANOPARTICLES
-
Process for the preparation of modified zinc oxide nanoparticles, which comprises reacting zinc oxide nanoparticles, which are dissolved in a solvent, in the presence of ammonia or amines with a tetraalkyl orthosilicate and optionally with an organosilane, with the proviso that the reaction takes place at a content of less than 5% by weight of water, based on the total amount of solvent and water. Modified zinc oxide nanoparticles which have Si—O-alkyl groups and are soluble in organic solvents, obtainable by this process for the preparation. Liquid or solid formulations which comprise modified ZnO nanoparticles. Inanimate organic materials, for example plastics or coatings, which comprise modified ZnO nanoparticles. Method of stabilizing inanimate organic materials against the effect of light, free radicals or heat, where modified ZnO nanoparticles, which optionally comprise UV absorbers and/or stabilizers as further additives, are added to the materials.
- -
-
-
- Design, synthesis and cytotoxic activity of novel spin-labeled rotenone derivatives
-
Three series of novel spin-labeled rotenone derivatives were synthesized and evaluated for cytotoxicity against four tumor cell lines, A-549, DU-145, KB and KBvin. All of the derivatives showed promising in vitro cytotoxic activity against the tumor cell lines tested, with IC50 values ranging from 0.075 to 0.738 μg/mL. Remarkably, all of the compounds were more potent than paclitaxel against KBvin in vitro, and compounds 3a and 3d displayed the highest cytotoxicity against this cell line (IC50 0.075 and 0.092 μg/mL, respectively). Based on the observed cytotoxicity, structure-activity relationships have been described.
- Liu, Ying-Qian,Ohkoshi, Emika,Li, Lin-Hai,Yang, Liu,Lee, Kuo-Hsiung
-
body text
p. 920 - 923
(2012/03/26)
-
- Reactions of nitroxides, part XI: O-Aryl phenylselenophosphonates bearing a nitroxyl moiety
-
O-Aryl phenylselenophosphonates bearing a nitroxyl moiety were synthesized in the presence of pyridine in diethyl ether from 4-hydroxy-2,2,6,6- tetramethylpiperidine-1-oxyl, and either phenyldichlorophosphine and elemental selenium in 9-35% yield or phenyldichlorophosphine selenide in 36-62% yield. O,O-Diaryl phenylselenophosphonates and O,O-bis(2,2,6,6-tetramethyl-1-oxyl-4- piperidyl)phenylselenophosphonates were obtained as by-products. O,O-Diaryl phenylselenophosphonates were obtained from phenyldichlorophosphine selenide and 2 mol of phenols in 55-86% yield. Antifungal activity of some synthesized selenophosphonates was found.
- Huras, Bogumila,Zakrzewski, Jerzy,Krawczyk, Maria
-
experimental part
p. 137 - 147
(2011/10/08)
-
- First synthesis and biological evaluation of novel spin-labeled derivatives of deoxypodophyllotoxin
-
Deoxypodophyllotoxin inhibits tubulin polymerization and induces cell cycle arrest at G2/M, followed by apoptosis. In order to find compounds with superior bioactivity and less toxicity, a series of spin-labeled derivatives of deoxypodophyllotoxin were synthesized by reacting 4′-demethyl-4-deoxypodophyllotoxin (DPPT) with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyloxycarbonyl) amino acids. The cytotoxic activities against three tumor cell lines (HL-60, RPMI-8226, A-549) in vitro and the antioxidative activities in tissues of Sprague Dawley (SD) rats of target compounds were evaluated, and the results indicated that compounds 11a-h were more potent in terms of cytotoxicities and antioxidative activities than either parent compound DPPT or anticancer drug VP-16.
- Zhang, Zhi-Wei,Zhang, Jia-Qiang,Hui, Ling,Chen, Shi-Wu,Tian, Xuan
-
scheme or table
p. 1673 - 1677
(2010/05/18)
-
- Novel semisynthetic spin-labeled derivatives of podophyllotoxin with cytotoxic and antioxidative activity
-
A series of novel spin-labeled podophyllotoxin derivatives were synthesized by reacting the corresponding N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyloxy carbonyl)-amino acids with 4β-amino-4′-demethylepipodophyllotoxin. The synthesized derivatives 12a-g were evaluated for the partition coefficients, cytotoxicities in vitro against three tumor cell lines (A-549, HL-60, and RPMI-8226) and antioxidative activities in tissues of SD rats by the TBA method. The vast majority of target compounds have shown superior or comparable activities against A-549, HL-60, and RPMI-8226 compared to VP-16, and they have shown more significant antioxidative activities and superior water solubility than VP-16.
- Zhang, Jia-Qiang,Zhang, Zhi-Wei,Hui, Ling,Chen, Shi-Wu,Tian, Xuan
-
scheme or table
p. 983 - 986
(2010/06/13)
-
- Synthesis and spectral properties of polymethine-cyanine dye-nitroxide radical hybrid compounds for use as fluorescence probes to monitor reducing species and radicals
-
Various hybrid compounds comprised of two types of nitroxide radicals and either a pentamethine (Cy5) or trimethine cyanine (Cy3) were synthesized. The nitroxide radicals were linked either via an ester-bond to one or two N-alkyl carboxyl-terminated groups of Cy5, or via two amido-bonds (aminocarbonyl or carbonylamino group) to the 5-position of the indolenine moieties of Cy5 and Cy3. Changes in fluorescence and ESR intensities of the hybrid compounds were measured before and after addition of Na ascorbate in PBS (pH 7.0) to reduce the radicals. Among the hybrid compounds synthesized, those that linked the nitroxide radicals via an aminocarbonyl residue at the 5-position of the indolenine moieties on Cy5 and Cy3 exhibited a 1.8- and 5.1-fold increase in fluorescence intensity with the reduction of the nitroxide segment by the addition of Na ascorbate, respectively. In contrast, fluorescence intensity was not enhanced in the other hybrid compounds. Thus, the hybrid compounds which exhibited an increase in fluorescent intensity with radical reduction can be used in the quantitative measurement of reducing species such as Fe2+ and ascorbic acid, and hydroxyl radicals. Because these hybrid compounds have the advantage of fluorescing at longer wavelengths-661 (Cy5) or 568 (Cy3) nm, respectively, they can be used to measure radical-reducing species or radicals either in solution or in vivo.
- Sato, Shingo,Tsunoda, Minoru,Suzuki, Minoru,Kutsuna, Masahiro,Takido-uchi, Kiyomi,Shindo, Mitsuru,Mizuguchi, Hitoshi,Obara, Heitaro,Ohya, Hiroaki
-
experimental part
p. 2030 - 2039
(2009/03/12)
-
- Steric and polar effects of the cyclic nitroxyl fragment on the C-ON bond homolysis rate constant
-
Alkoxyamines and persistent nitroxyl radicals are important regulators of nitroxide mediated radical polymerization (NMP). Because polymerization times decrease with increasing rate constant of the homolysis of the C-ON bond between the polymer chain and the nitroxyl moiety, the factors influencing the cleavage rate constant are of considerable interest. Here, we present the measurements of the rate constants (kd) of the C-ON bond cleavage in new cyclic alkoxyamine models. The homolysis rate constants of 9 new alkoxyamines and 33 others given by the literature are analyzed with regards to the contributions of the polar inductive/field (σI) effect, the steric (E s) effect and the intramolecular hydrogen bonding (IHB) effect of the nitroxyl moieties, using the multiparameter equation established by Marque, i.e., log(kd/kd,0) = -3.07σI - 0.88E s - 5.88. Cyclic steric constants r(Ri) for seven- and eight-membered rings are developed. Analysis of the results provides new insight on the importance of the conformation of the alkoxyamine on the values of kd.
- Fischer, Hanns,Kramer, Andreas,Marque, Sylvain R. A.,Nesvadba, Peter
-
p. 9974 - 9984
(2008/02/01)
-
- Synthesis of novel spin-labeled derivatives of podophyllotoxin as potential antineoplastic agents
-
Five novel nitroxyl spin-labeled ester derivatives of podophyllotoxin have been prepared by reacting the corresponding N-(1-oxyl-2,2,6,6-tetramethyl-4- piperidinyloxy-carbonyl) amino acids with the hydroxy group of podophyllotoxin in the presence of dimethylaminopyridine and N,N-dicyclohexylcarbodiimide and evaluated as potential antitumor agents. All of the target compounds showed more significant cytotoxicity against P-388 murine leukemia and A-549 human lung carcinoma in vitro than etoposide. Copyright Taylor & Francis, Inc.
- Liu, Ying-Qian,Tian, Xuan
-
p. 2749 - 2758
(2007/10/03)
-
- New seven- and eight-membered cyclic alkoxyamines for the living free radical polymerization
-
A straightforward synthesis of new seven- and eight-membered cyclic alkoxyamines from the corresponding lower homologous keto-alkoxyamines via ring-enlargement using TMS-diazomethane is described. The use of these ring-enlarged cyclic alkoxyamines as regulators/initiators for the radical polymerization of styrene and n-butyl acrylate is presented. Efficient controlled and living styrene polymerization (molecular weight of up to 40 000) can be obtained using the seven- and eight-membered alkoxyamine initiators. The influence of the ring-enlargement on the quality of the polymerization process (polymerization time, livingness, PDI) is discussed. The rate constant of the C-O bond cleavage of these new alkoxyamines has been measured. In addition, the thermal decomposition of the alkoxyamines has been studied. Furthermore, EPR data of the corresponding new nitroxides are presented.
- Schulte, Tobias,Studer, Armido
-
p. 3078 - 3084
(2007/10/03)
-
- Comparative study on decomposition rate constants for some alkoxyamines
-
The decomposition rate constants kdec as well as the activation rate constants kact of some alkoxyamines were determined and compared with regard to their structures. The results showed that decomposition depends predominantly on ste
- Goto, Atsushi,Kwak, Yungwan,Yoshikawa, Chiaki,Tsujii, Yoshinobu,Sugiura, Yukio,Fukuda, Takeshi
-
p. 3520 - 3525
(2007/10/03)
-
- Synthesis of 2,2,6,6-tetramethylpiperidine derivatives
-
Diazotization of 4-amino-2,2,6,6-tetramethylpiperidine in acetic or sulfuric acid affords 2,2,6,6-tetramethyl-1,2,3,6-tetrahydropyridine in high yield. Under the same conditions, the corresponding nitroxyl radical transforms into 4-hydroxy-2,2,6,6-tetrame
- Kashparova,Kagan,Kashparov,Zhukova
-
p. 667 - 668
(2007/10/03)
-
- Chemoselective electrophilic oxidation of heteroatoms by hydroperoxy sultamst
-
The synthesis of novel hydroperoxy sultams 1b-d and their potential as renewable chemoselective electrophilic oxidants for a wide range of nitrogen, sulfur, and phosphorus heteroatoms in nonaqueous media is described. Reactions of 1b,c with secondary amines 10f,g yielded the hydroxysultams 2b,c and nitrone 11f or radical 11g depending on the substrate and stoichiometry, while tertiary amines 10a-d gave amine oxides 11a-d. Compounds 1c,d oxidized various thioethers 12a-g to sulfoxides 13a-g smoothly that were isolated by chromatography in nearly quantitative yields. 1c was regenerated from 2c by treatment of the latter with acidified H2O2. Kinetic studies of the reaction of 1c with 1,4-thioxane 12f suggest that the reaction follows the second-order kinetics, first order in substrate and first order in oxidant with the second-order rate constant several orders of magnitude larger than that of the corresponding reaction with hydrogen peroxide and tert-butyl hydroperoxide without the need for any acid or heavy metal catalysts. The phosphines 14a,b were also oxidized by 1c to the respective phosphine oxides 15a,b readily in quantitative yields. The reactions may be conducted at ambient temperature or lower and appear to proceed via a nonradical mechanism. Reactions are sensitive to steric as well as electronic factors.
- Gelalcha, Feyissa Gadissa,Schulze, Baerbel
-
p. 8400 - 8406
(2007/10/03)
-
- Application of 4-hydroxy-, 4-Oxo-, and 4-hydroxyimino derivatives of stable 2,2,6,6-tetramethylpiperidine N-oxyl radical for the measurements of lewis acidity of solvents
-
UV-VIS spectra of 2,2,6,6-tetramethylpiperidine N-oxyl (TMPNO) stable radical measured in 18 solvents were compared with the spectra of its derivatives functionalized in the 4 position (4-hydroxy-(h-TMPNO), 4-oxo-(o-TMPNO) and 4-hydroxyimino-(i-TMPNO)). The results obtained proved, that the λmax values corresponding to the n → π* transition in the N-O? chromophore are for all TMPNO derivatives intercorrelated, and they also correlate very well with other acidity parameters (Z, E"T" and AN). Thus, all these compounds could be used as standard bases for determination of the experimental acidity of solvents. Detailed analysis of the spectral characteristics of all compounds leads to the conclusion, that the molar absorptivities (ε) of TMPNO and h-TMPNO corresponding to the n → π* transition are of the order of 10 dm3 mol-1 cm-1, whereas those of the o-TMPNO and i-TMPNO are two times lower. In the case of the π → π* transition we observed an opposite behaviour - the molar absorptivities (ε) of TMPNO and h-TMPNO are close to 2×103 dm3 mol-1 cm-1, whereas those of the oxo and hydroxyimino derivatives are equal to ~4.4×103 dm3 mol-1 cm-1. The integral intensities of both bands behave accordingly. These differences were attributed to the formation of the head-to-tail dimers, in which the N-O? chromophore interacts with the exocyclic double bond in the 4-position of the piperidine.
- Glowacka,Szczepek,Wrona
-
p. 1341 - 1348
(2007/10/03)
-
- A novel steroidal spin label for membrane structure studies: Synthesis and applications
-
2,2,6,6-Tetramethyl piperidine-N-oxyl nitroxyls are known to partition between aqueous and lipid phases, thus serving as probes to study membrane dynamics. The synthesis of a novel steroidal spin label, 3α-hydroxycholan- 24-yl-(2'',2'',6'',6''-tetramethyl-N-oxyl)piperidyl butan-1',4'-dioate, containing 2,2,6,6-tetramethylpiperidine-N-oxyl moiety covalently bonded to the side chain in 3,24-caprostan-diol has been described. The localization of this spin label in model biomembranes has been studied by using electron spin resonance, differential scanning calorimetry, and 1H and 31P NMR spectroscopic techniques. Its applicability in studying the phase transition properties of model membrane L-α-dipalmitoyl phosphatidyl choline in the presence and absence of drugs has been described by using electron spin resonance. The label has also been used to study the permeability of epinephrine into membrane. The results have shown the applicability of the spin label as a potential spin probe in the study of biomembranes.
- Katoch, Rita,Trivedia, Girish K.,Phadke, Ratna S.
-
p. 849 - 855
(2007/10/03)
-
- The formation of nitroxyl radicals in reactions of dimethyldioxirane with 2,2,6,6-tetramethylpiperidine and 2,2,5,5-tetramethyl-3-imidazoline-3-oxide derivatives
-
The oxidation of secondary and tertiary amines, derivatives of 2,2,6,6-tetramethylpiperidine and 2,2,5,5-tetramethyl-3-imidazoline-3-oxide, by dimethyldioxirane results in the formation of nitroxyl radicals, which induce the decomposition of dimethyldioxirane. Chemiluminescence in the IR and visible regions during the reaction of dimethyldioxirane with 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl was observed.
- Kabal'nova,Grabovsky,Shishlov,Shereshovets,Volodarskii,Tolstikov
-
p. 2419 - 2421
(2007/10/03)
-
- Carbonate-mediated hydrogen peroxide oxidations of 4-hydroxy-2,2,6,6-tetramethylpiperidine
-
An environmentally friendly process is described for the preparation of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl by the carbonate-mediated hydrogen peroxide oxidation of 4-hydroxy-2,2,6,6-tetramethylpiperidine.
- -
-
-
- Sulfonic peracids - III. Heteroatom oxidation and chemoselectivity
-
We have investigated the p-toluenesulfonic peracid (2) generated in situ in the oxidation of different types of compounds containing nitrogen and/or sulfur. The sulfonic peracid 2 shows a remarkable chemoselectivity characterized by a preferred oxidation of sulfides to the sulfones in the presence of amines or olefins and a strong dependence on the nature of the amine in the competitive oxidation of olefins and amines.
- Kluge,Schulz,Liebsch
-
p. 5773 - 5782
(2007/10/03)
-
- Oxidation of organic amide ions by dioxygen 2. Stable and intermediate products
-
The products of base-catalysed oxidation of secondary amines were identified by the GC-MS and EPR techniques as nitroxyls, quinone nitrones, quinone imines, and for diarylamines also as the products of C-N bond cleavage/substituted nitrobenzenes, anilines and phenols.It was shown that nitroxyl radicals are the primary paramagnetic products of the reaction and do not form by the interaction of aminyl radicals with dioxygen.A mechanism of the amide ion oxidation through the nonradical addition of dioxygen to the amide ion at the rate-limiting stage is suggested and discussed. - Key words: aromatic amines, amide ions, oxidation, dioxygen, mechanism, nitroxyl radicals, synthesis.
- Shashin, S. S.,Emanuel', O. N.,Skibida, I. P.
-
p. 1651 - 1656
(2007/10/02)
-
- THE OXIDATION OF SECONDARY AMINES BY ALKANESULFONIC PERACIDS
-
Alkanesulfonic peracids are efficient oxidation agents for the conversion of secondary amines to the corresponding nitroxyl radicals.
- Safiullin, R. L.,Enikeeva, L. R.,Bukin, I. I.,Mukhametova, G. A.,Shishlov, N. M.,et al.
-
p. 1045 - 1047
(2007/10/02)
-
- A Reaction of Nitroxides with Ethyl Mercaptane: A Mild Method for the Conversion of Nitroxides into Their Corresponding Amines
-
The mild reduction of the nitroxides 1a-j to the corresponding sterically hindered amines 2a-j by means of ethyl mercaptane is reported.The reaction mixtures of 1a,b,g were analyzed by glc/ms.
- Zakrzewski, Jerzy
-
p. 803 - 808
(2007/10/02)
-
- A CONVENIENT HIGH YIELD SYNTHESIS OF NITROXIDES
-
Appropriate secondary amines are readily converted to nitroxides by dimethyldioxirane in a rapid, convenient, and essentially quantitative process.
- Murray, Robert W.,Singh, Megh
-
p. 4677 - 4680
(2007/10/02)
-
- Process for preparing nitroxyls of sterically hindered amines
-
Nitroxyls of the formula STR1 where E1, E2, E3 and E4 are independently an organic radical so that the carbon atoms to which they are attached are each a quaternary carbon and T is a divalent radical are prepared by the oxidation of the corresponding amine in an inert organic solvent with a hydroperoxide in the presence of a metal carbonyl, metal oxide or metal alkoxide catalyst in high yield and purity. The nitroxyls may be directly reduced to the corresponding hydroxylamines by catalytic hydrogenation. The nitroxyls are useful as polymerization inhibitors and the hydroxylamines as polymer stabilizers.
- -
-
-
- Structure and function of bile. I. Relation between the structure of artificial bile and activity of pancreatic lipase
-
An aqueous solution of lecithin, bile salts, and cholesterol (artificial bile) which resembles human bile was studied by means of polarizing microscopy, electron microscopy, spin-probe electron spin resonance (ESR) spectroscopy, and pancreatic lipase treatment to digest fatty esters. The relation between the structure of artificial bile and the digestion of fatty esters by pancreatic lipase was investigated, and the following results were obtained. Artificial bile consists of bile salt micelles and bile salt-lecithin-cholesterol mixed micelles. Fatty esters are solubilized in these micelles. Lipase hydrolyzes fatty esters solubilized in bile salt micelles but not in bile salt-lecithin-cholesterol mixed micelles. Ranging from 0.1 to 0.4 μ in size, the macromolecular complex of bile salt-lecithin-cholesterol can be observed by electron microscopy.
- Uematsu,Unno,Niikura,Sawaumi,Akahori
-
p. 3327 - 3336
(2007/10/02)
-
- Synthesis of alpha- and beta-glycosides containing spin labels, as probes for studies of carbohydrate-protein interaction.
-
Nitroxide spin-labeled alpha-D-glycopyranosides were synthesized in good yield and in a highly stereoselective manner by reaction of per-O-benzyl-alpha-D-glycopyranosyl bromides with 2,2,6,6-tetramethyl-4-piperidinol under the bromide ion-catalyzed conditions devised by Lemieux et al. After hydrogenolysis, the deblocked intermediates were oxidized to give the desired, spin-labeled alpha-D-glycopyranosides. Nitroxide spin-labeled beta-D-glycopyranosides, as well as a beta-maltoside, were synthesized by standard methods. The synthesis is also described of 2-amino-2-deoxy-D-glucose and -D-galactose derivatives having a spin label at C-2, and of the spin-labeled compound 1-[4-(beta-D-galactopyranosyloxy)phenyl]-3-(2,2,6,6-tetramethylpiperidin-1-oxyl -4-yl)-2-thiourea.
- Plessas,Goldstein
-
p. 211 - 220
(2007/10/02)
-
- 148. Formation of N-Hydroxy-amines of Spin Labeled Nucleosides for 1H-NMR. Analysis
-
Amine-oxide radical 1a was efficiently converted to the corresponding N-hydroxy-amine 2a with sodium dithionite in acetone/water.This reaction was used to develop a procedure for monitoring the NMR. spectra of sodium dithionite reduced amine-oxide radicals and of novel reduced amine-oxide-labeled nucleosides.
- Ozinskas, Alvydas J.,Bobst, Albert M.
-
p. 1407 - 1411
(2007/10/02)
-