- Preparation of Some Homologous TEMPO Nitroxides and Oxoammonium Salts; Notes on the NMR Spectroscopy of Nitroxide Free Radicals; Observed Radical Nature of Oxoammonium Salt Solutions Containing Trace Amounts of Corresponding Nitroxides in an Equilibrium Relationship
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Three new homologous TEMPO oxoammonium salts and three homologous nitroxide radicals have been prepared and characterized. The oxidation properties of the salts have been explored. The direct 13C NMR and EPR spectra of the nitroxide free radicals and the oxoammonium salts, along with TEMPO and its oxoammonium salt, have been successfully measured with little peak broadening of the NMR signals. In the spectra of all ten compounds (nitroxides and corresponding oxoammonium salts), the carbons in the 2,2,6,6-tetramethylpiperidine core do not appear, implying paramagnetic properties. This unpredicted overall paramagnetism in the oxoammonium salt solutions is explained by a redox equilibrium as shown between oxoammonium salts and trace amounts of corresponding nitroxide. This equilibrium is confirmed by electron interchange reactions between nitroxides with an N-acetyl substituent and oxoammonium salts with longer acyl side chains.
- Bobbitt, James M.,Eddy, Nicholas A.,Cady, Clyde X.,Jin, Jing,Gascon, Jose A.,Gelpí-Dominguez, Svetlana,Zakrzewski, Jerzy,Morton, Martha D.
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p. 9279 - 9290
(2017/09/22)
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- Synthesis and fluorescence properties of six fluorescein-nitroxide radical hybrid-compounds
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Six fluorescein-nitroxide radical hybrid-compounds (2ab, 3ab, 4, and 5) were synthesized by the condensation of 5- or 6-carboxy-fluorescein and 4-amino-TEMPO (2ab), 5- or 6-aminofluorescein and 4-carboxy-TEMPO (3ab), and fluorescein and 4-carboxy-TEMPO (4), or by reaction of the 3-hydroxyl group of fluorescein with DPROXYL-3-ylmethyl methanesulfonate (5). Fluorescence intensities (around 520 nm) after reduction of the radical increased to 1.43-, 1.38-, and 1.61-folds for 2a, 2b and 3b respectively; 3a alone exhibited a decrease in intensity on reduction. Since 4 was readily solvolyzed in PBS or even methanol to afford fluorescein and 4-carboxy-TEMPO, its fluorescence change could not be measured. Hybrid compound 5 containing an ether-linkage between the fluorescein phenol and 3-hydroxymethyl-DPROXYL hydroxyl centers, was stable and on reduction, showed a maximum increase (3.21-fold) in relative fluorescence intensity in PBS (pH 5.0), despite its remarkably low absolute fluorescence intensity.
- Sato, Shingo,Endo, Susumu,Kurokawa, Yusuke,Yamaguchi, Masaki,Nagai, Akio,Ito, Tomohiro,Ogata, Tateaki
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supporting information
p. 66 - 71
(2016/07/06)
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- Selective Aromatic C-H Hydroxylation Enabled by η6-Coordination to Iridium(III)
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We report an aromatic C-H hydroxylation protocol in which the arene is activated through η6-coordination to an iridium(III) complex. η6-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate η5-cyclohexadienyl adducts and arene exchange reactions, we evaluate incorporation of arene π-activation into a catalytic cycle for C-H functionalization.
- D'Amato, Erica M.,Neumann, Constanze N.,Ritter, Tobias
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p. 4626 - 4631
(2015/10/06)
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- Kinetics and thermodynamics of reversible disproportionation-comproportionation in redox triad oxoammonium cations - Nitroxyl radicals - Hydroxylamines
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Kinetics and equilibrium of the acid-catalyzed disproportionation of cyclic nitroxyl radicals R2NO· to oxoammonium cations R2NO+ and hydroxylamines R2NOH is defined by redox and acid-base properties of these compounds. In a recent work (J. Phys. Org. Chem. 2014, 27, 114-120), we showed that the kinetic stability of R2NO· in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R2NO+ and R2NOH to R2NO· and found that increasing in -I-effects of substituents greatly reduces the overall equilibrium constant of the reaction K4. This occurs because of both the increase of acidity constants of hydroxyammonium cations K3H+ and the difference between the reduction potentials of oxoammonium cations ER2NO+/R2NO· and nitroxyl radicals ER2NO·/R2NOH. pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E1/3σ and bond dissociation energies D(O-H) for hydroxylamines R2NOH inwater were determined. For a wide variety of piperidine- and pyrrolidine-1-oxyls values of pK3H+ and ER2NO+/R2NO· correlate with each other, as well aswith the equilibriumconstants K4 and the inductive substituent constants ωI. The correlations obtained allowprediction of the acid-base and redox characteristics of redox triads R2NO·-R2NO+-R2NOH.
- Sen, Vasily D.,Tikhonov, Ivan V.,Borodin, Leonid I.,Pliss, Evgeny M.,Golubev, Valery A.,Syroeshkin, Mikhail A.,Rusakov, Alexander I.
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- Photolabile protecting groups for nitroxide spin labels
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Nitroxide spin labels can be protected against critical conditions of DNA/RNA or peptide synthesis by reduction and alkylation with light-sensitive groups such as nitrobenzyl- or aminocoumarins. High chemical stability qualifies tetraethylisoindoline 5 an
- Seven, Ibrahim,Weinrich, Timo,Graenz, Markus,Gruenewald, Christian,Bruess, Silke,Krstic, Ivan,Prisner, Thomas F.,Heckel, Alexander,Goebel, Michael W.
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p. 4037 - 4043
(2014/07/08)
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- A revised preparation of (4-Acetamido-2,2,6,6-tetramethylpiperidin-1-yl) oxyl and 4-acetamido-2,2,6,6-tetramethyl-1-oxopiperidinium tetrafluoroborate: Reagents for stoichiometric oxidations of alcohols
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Revised preparations of (4-acetamido-2,2,6,6-tetramethylpiperidin-1-yl)oxyl and the corresponding oxoammonium salt, 4-acetamido-2,2,6,6-tetramethyl-1- oxoammonium tetrafluoroborate are presented together with some of the important properties of these two oxidizing reagents. Georg Thieme Verlag Stuttgart New York.
- Tilley, Leon J.,Bobbitt, James M.,Murray, Stephanie A.,Camire, Casey E.,Eddy, Nicholas A.
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p. 326 - 329
(2013/03/14)
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- Oxidation of α-trifluoromethyl alcohols using a recyclable oxoammonium salt
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A simple, mild method for the oxidation of α-trifluoromethyl alcohols to trifluoromethyl ketones (TFMKs) using the oxoammonium salt 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) is described. Under basic conditions, oxidation proceeds rapidly and affords good to excellent yields of TFMKs, without concomitant formation of the hydrate. The byproduct of the oxidation, 4-acetylamino-2,2,6,6-tetramethyl-1- piperidinyloxy (1c), is easily recovered and can be conveniently reoxidized to regenerate the oxoammonium salt.
- Kelly, Christopher B.,Mercadante, Michael A.,Hamlin, Trevor A.,Fletcher, Madison H.,Leadbeater, Nicholas E.
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p. 8131 - 8141
(2013/01/15)
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- Electron paramagnetic resonance (EPR) study of spin-labeled camptothecin derivatives: A different look of the ternary complex
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Camptothecin (CPT) derivatives are clinically effective poisons of DNA topoisomerase I (Top1) able to form a ternary complex with the Top1-DNA complex. The aim of this investigation was to examine the dynamic aspects of the ternary complex formation by means of site-directed spin labeling electron paramagnetic resonance (SDSL-EPR). Two semisynthetic CPT derivatives bearing the paramagnetic moiety were synthesized, and their biological activity was tested. A 22-mer DNA oligonucleotide sequence with high affinity cleavage site for Top1 was also synthesized. EPR experiments were carried out on modified CPT in the presence of DNA, of Top1, or of both. In the last case, a slow motion component in the EPR signal appeared, indicating the formation of the ternary complex. Deconvolution of the EPR spectrum allowed to obtain the relative drug amounts in the complex. It was also possible to demonstrate that the residence time of CPT "trapped" in the ternary complex is longer than hundreds of microseconds.
- Ricci, Antonio,Marinello, Jessica,Bortolus, Marco,Sánchez, Albert,Grandas, Anna,Pedroso, Enrique,Pommier, Yves,Capranico, Giovanni,Maniero, Anna Lisa,Zagotto, Giuseppe
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supporting information; experimental part
p. 1003 - 1009
(2011/04/25)
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- Amination of benzoxazoles and 1,3,4-oxadiazoles using 2,2,6,6- tetramethylpiperidine-N-oxoammonium tetrafluoroborate as an organic oxidant
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No transition metals are necessary to convert benzoxazoles and 1,3,4-oxadiazoles into the corresponding pharmacologically interesting 2-aminated heterocycles by formal direct C(2)-amination using tetramethylpiperidine-N-oxoammonium tetrafluoroborate (TEMPO+BF 4-) as an oxidant (see scheme; TEMP=2,2,6,6- tetramethylpiperidine; TfOH=trifluoromethanesulfonic acid).
- Wertz, Sebastian,Kodama, Shintaro,Studer, Armido
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supporting information; experimental part
p. 11511 - 11515
(2012/01/11)
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- Oxidation of primary and secondary alcohols by 4-acetylamino-2,2,6,6- tetramethylpiperidine-1-oxoammonium tetrafluoroborate in aqueous media
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water soluble oxidant 4-acetylamino-2,2,6,6-tetramethylpiperidine-1- oxoammonium tetrafluoroborate 1 oxidizes primary and secondary aliphatic, primary allylic, and primary and secondary benzylic alcohols to their corresponding aldehydes and ketones in aqueous media in good to excellent yields. ARKAT-USA, Inc.
- Mamros, Audrey N.,Sharrow, Phillip R.,Weller, William E.,Luderer, Mark R.,Fair, Justin D.,Pazehoski, Kristina O.,Luderer, Matthew R.
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- Reaction of Nitroxides with Sulfur Containing Compounds II [1]. Preparation of Nitroxides Bearing an Isothiocyanate Substituent in View of the Nitroxyl Group Reduction with Thiophosgene
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The reaction of thiophosgene with 2,2,6,6-tetramethylpiperidine-1-oxyl (used as a model nitroxyl radical) was examined. 2,2,6,6-Tetramethylpiperidine and 2,2,6,6-tetramethyl-1-hydroxypiperidine were identified as products. The reaction is not competitive with the reaction of thiophosgene with an amino group. Thus, three nitroxides with an isothiocyanate group were synthesized from thiophosgene and the nitroxides containing the amino substituent.
- Zakrzewski, Jerzy,Hupko, Jarosllaw,Kryczka, Krzysztof
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p. 843 - 850
(2007/10/03)
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- Synthesis of 2,2,6,6-tetramethylpiperidine derivatives
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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
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p. 667 - 668
(2007/10/03)
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- Carbonate-mediated hydrogen peroxide oxidation of 4-acylamino-2,2,6,6-tetramethylpiperidine
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An environmentally friendly process is described for the preparation of 4-acyl-amino-2,2,6,6-tetramethylpiperidine-N-oxyl by the carbonate-mediated hydrogen peroxide oxidation of 4-acylamino-2,2,6,6-tetramethylpiperidine. The reaction can also be run in the absence of any catalyst.
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- Oxoammonium salts. 6. 4-Acetylamino-2,2,6,6-tetramethylpiperidine-1- oxoammonium perchlorate: A stable and convenient reagent for the oxidation of alcohols. Silica gel catalysis
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4-Acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium perchlorate, 1, is a stable, nonhygroscopic oxoammonium salt that is easily prepared and can be used for the oxidation of alcohols to ketones or aldehydes in near quantitative yields. The reaction is colorimetric, does not require anhydrous conditions, does not involve heavy metals, and can be carried out conveniently. Furthermore, the oxidant can be easily regenerated. The oxidation is somewhat specific in that the relative reactivities of an allyl alcohol (geraniol), benzaldehyde, and 1-decanol are about 100:1:0.1. The reaction is catalyzed by silica gel.
- Bobbitt, James M.
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p. 9367 - 9374
(2007/10/03)
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- Organic Oxoammonium Salts. 3. A New Convenient Method for the Oxidation of Alcohols to Aldehydes and Ketones
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A new method for the selective oxidation of alcohols using organic oxoammonium salts generated by acid-promoted disproportionation of nitroxides in solution has been developed.Major advantages are high yields, ease of product isolation, and a high degree of selectivity in the presence of other functional groups.
- Ma, Zhenkun,Bobbitt, James M.
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p. 6110 - 6114
(2007/10/02)
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- Synthesis of alpha- and beta-glycosides containing spin labels, as probes for studies of carbohydrate-protein interaction.
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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
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p. 211 - 220
(2007/10/02)
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- Magnetic Resonance Study of 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl and Its Deuterated Derivatives
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4-Amino-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMP-NH2) is a spin label suitable for the investigation of polymer sytems.The analysis of EPR spectra of spin-labeled samples intended for the determination of the type and correlation time of spin-label rotational reorientation in the system under study requires the knowledge of the proton splitting constants, the hyperfine interactions tensor AN, and the g tensor of thisnitroxide.The splitting constants were determined by the NMR method from differences in the shifts of protons in the spectra of nitroxide and of its diamagnetic analod, 4-amino-2,2,6,6-tetramethylpiperidine. by analyzing the rigid-limit EPR spectrum of 4-acetamino-perdeutero-2,2,6,6-tetramethylpiperidine-N-oxyl recorded in CD3OD, we determined the tensors AN and g in this solvent
- Labsky, J.,Pilar, J.,Loevy, J.
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p. 515 - 522
(2007/10/02)
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