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Showing 41 to 43 of 43 (0.033 seconds)Spelling suggestions: "subject:"hydroxylamine"" "subject:"2hydroxylamine""
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The synthesis of novel profluorescent nitroxide probesKeddie, Daniel Joseph January 2008 (has links)
A number of novel isoindoline nitroxides have been synthesised using a variety of synthetic techniques. Several carbon-carbon bond forming methodologies, including the first examples of Heck and Sonogashira coupling applied to the isoindoline nitroxide class, were utilised to give novel robust aromatic frameworks. Palladium-catalysed Heck coupling of brominated nitroxides and ester-substituted olefins generates novel nitroxides possessing extended conjugation. Hydrolysis of the nitroxide esters gave the corresponding carboxylic acids, which showed enhanced water solubility. Sonogashira coupling of an iodo-isoindoline nitroxide gave several novel alkynesubstituted nitroxides in high yield. Subsequent coupling of a deprotected ethynyl nitroxide with aromatic iodides gave acetylene-linked nitroxides and an acetylene linked nitroxide dimer. A butadiyne linked dinitroxide was successfully synthesised via Eglinton oxidative coupling of two ethynyl nitroxides. The synthesis of a novel water-soluble dicarboxy nitroxide was achieved by base hydrolysis of a dinitrile. Functional group interconversion furnished anhydride and imide substituted nitroxides from the diacid. Subjecting the imide to the Hofmann rearrangement gave an unexpected brominated amino-carboxy nitroxide. The dicarboxy nitroxide and the brominated amino-carboxy nitroxide were both shown to have a protective effect on Ataxia-Telangiectasia cells, indicating a possible role as antioxidants in the treatment of this disease. A fluorescein nitroxide was successfully synthesised through the condensation of the anhydride substituted nitroxide and resorcinol. After limited success using a variety of other techniques, Buchwald-Hartwig amination was able to furnish a rhodamine nitroxide, via a triflate-fluorescein nitroxide. The extended aromatic nitroxides possess suppressed fluorescence and we have described these systems as profluorescent. The profluorescent nitroxides were found to have significantly lower quantum yields than the non-radical analogues and displayed a substantial increase in fluorescence intensity upon radical trapping, making them useful probes for free radical reactions.
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| 42 |
Generation of 4,5-Dihydro-1,2,3-oxadiazole and Study of the Decomposition Products / Erzeugung von 4,5-Dihydro-1,2,3-oxadiazol und Untersuchung der ZersetzungsprodukteSingh, Neeraj 16 December 2015 (has links) (PDF)
4,5-Dihydro-1,2,3-oxadiazoles are postulated to be key intermediates in the synthesis of ketones from alkenes on an industrial scale, alkylation of DNA in vivo, decomposition of N-nitrosoureas (potent carcinogens), and are also a subject of great interest for theoretical chemists. In this thesis, formation of the parent compound and decay into secondary products has been studied by NMR monitoring analysis. The elusive properties and the intermediacy of the parent compound, 4,5-dihydro-1,2,3-oxadiazole, in the decomposition of suitably substituted N-nitrosoureas using Tl(I) alkoxides as bases, have been confirmed by the characterisation of its decay products viz., ethylene oxide, acetaldehyde, and especially diazomethane, at very low temperatures by 1H NMR, 13C NMR, 15N NMR, and relevant 2D NMR methods. Moreover, it has been shown that the methylation of nucleophilic molecules by 3-methyl-4,5-dihydro-1,2,3-oxadiazolium salts, which are considered to be activated forms of β−hydroxyalkylnitrosamines, does not involve 4,5-dihydro-1,2,3-oxadiazole as an intermediate, as has been reported in literature; instead, nucleophilic substitution leading to synthesis of open-chain products dominates the reaction. / 4,5-Dihydro-1,2,3-oxadiazole wurden als Schlüsselintermediate in der industriellen Synthese von Ketonen aus Alkenen, der in vivo Alkylierung von DNA und der Zersetzung von N-Nitrosoharnstoffen (potente Karzinogene) postuliert. Sie sind ebenso von großem Interesse in der theoretischen Chemie. Im Rahmen dieser Arbeit wurde die Bildung der Stammverbindung und deren Zersetzung in sekundäre Produkte mittels NMR-Verfolgung studiert. Die ausgesprochene Kurzlebigkeit der Stammverbindung 4,5-Dihydro-1,2,3-oxadiazol wurde durch die Charakterisierung der Produkte bei der Zersetzung geeignet substituierter N-Nitrosoharnstoffe mit Tl(I)-Alkoxiden bestätigt. Die Zersetzungsprodukte Ethylenoxid, Acetaldehyd und besonders Diazomethan wurden bei sehr niedrigen Temperaturen mittels 1H-NMR, 13C-NMR, 15N-NMR und relevanten 2D-NMR-Methoden charakterisiert.
Des Weiteren konnte gezeigt werden, dass die Methylierung nucleophiler Spezies mit 3-Methyl-4,5-dihydro-1,2,3-oxadiazoliumsalzen, welchen als aktivierte Äquivalente der β−Hydroxyalkylnitrosamine verstanden werden, nicht zur Bildung von 4,5-Dihydro-1,2,3-oxadiazol als Intermediat führt, so wie dies in der Literatur berichtet wurde. Stattdessen wird die Bildung offenkettiger Produkte durch nukleophile Substitution bevorzugt.
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| 43 |
Generation of 4,5-Dihydro-1,2,3-oxadiazole and Study of the Decomposition ProductsSingh, Neeraj 24 November 2015 (has links)
4,5-Dihydro-1,2,3-oxadiazoles are postulated to be key intermediates in the synthesis of ketones from alkenes on an industrial scale, alkylation of DNA in vivo, decomposition of N-nitrosoureas (potent carcinogens), and are also a subject of great interest for theoretical chemists. In this thesis, formation of the parent compound and decay into secondary products has been studied by NMR monitoring analysis. The elusive properties and the intermediacy of the parent compound, 4,5-dihydro-1,2,3-oxadiazole, in the decomposition of suitably substituted N-nitrosoureas using Tl(I) alkoxides as bases, have been confirmed by the characterisation of its decay products viz., ethylene oxide, acetaldehyde, and especially diazomethane, at very low temperatures by 1H NMR, 13C NMR, 15N NMR, and relevant 2D NMR methods. Moreover, it has been shown that the methylation of nucleophilic molecules by 3-methyl-4,5-dihydro-1,2,3-oxadiazolium salts, which are considered to be activated forms of β−hydroxyalkylnitrosamines, does not involve 4,5-dihydro-1,2,3-oxadiazole as an intermediate, as has been reported in literature; instead, nucleophilic substitution leading to synthesis of open-chain products dominates the reaction. / 4,5-Dihydro-1,2,3-oxadiazole wurden als Schlüsselintermediate in der industriellen Synthese von Ketonen aus Alkenen, der in vivo Alkylierung von DNA und der Zersetzung von N-Nitrosoharnstoffen (potente Karzinogene) postuliert. Sie sind ebenso von großem Interesse in der theoretischen Chemie. Im Rahmen dieser Arbeit wurde die Bildung der Stammverbindung und deren Zersetzung in sekundäre Produkte mittels NMR-Verfolgung studiert. Die ausgesprochene Kurzlebigkeit der Stammverbindung 4,5-Dihydro-1,2,3-oxadiazol wurde durch die Charakterisierung der Produkte bei der Zersetzung geeignet substituierter N-Nitrosoharnstoffe mit Tl(I)-Alkoxiden bestätigt. Die Zersetzungsprodukte Ethylenoxid, Acetaldehyd und besonders Diazomethan wurden bei sehr niedrigen Temperaturen mittels 1H-NMR, 13C-NMR, 15N-NMR und relevanten 2D-NMR-Methoden charakterisiert.
Des Weiteren konnte gezeigt werden, dass die Methylierung nucleophiler Spezies mit 3-Methyl-4,5-dihydro-1,2,3-oxadiazoliumsalzen, welchen als aktivierte Äquivalente der β−Hydroxyalkylnitrosamine verstanden werden, nicht zur Bildung von 4,5-Dihydro-1,2,3-oxadiazol als Intermediat führt, so wie dies in der Literatur berichtet wurde. Stattdessen wird die Bildung offenkettiger Produkte durch nukleophile Substitution bevorzugt.
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