Tandem mass spectrometry study of C-phenyl-N-tert-butyl nitrone spin adducts from in vitro rat liver microsomal metabolism of bromotrichloromethane and carbon tetrachloride
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Electron ionization and thermospray were used in conjunction with tandem mass spectrometry methods to identify trichloromethyl/C-phenyl-N-tert-butyl nitrone (PBN) spin adducts produced in rat liver microsomal dispersions that had been treated with reduced nicotinamide adenine dinucleotide phosphate (NADPH)-generating system and BrCCl3 (or CCl4). In the identification of PBN spin adducts, a scan of precursors of m / z 57 was utilized to confirm the presence of PBN spin adducts, because PBN spin adducts produce m / z 57 from tert-butyl as a characteristic fragment. Use of deuterated PBN (PBN-d9 deuterated at tert-butyl; PBN-d14 deuterated at both phenyl and tert-butyl) improved the recognition of PBN adducts in mixtures by precursor ion scans, because m / z 66 (which corresponds to the deuterated tert-butyl group) is characteristic and, unlike m / z 57, it is not a common fragment for any other compounds. Two new PBN spin adducts that were not detected before by electron paramagnetic resonance or mass spectrometry were identified by these methods for the first time.Keywords:
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Abstract The remarkable catalysis of Bu2SnO for nitrone formation in the nitrone-olefin cycloaddition reaction has been discovered, and has led to the development of a general method for the synthesis of N-unsubstituted isoxazolidine derivatives.
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Ester-containing nitrones, including 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide 5, have been reported to be robust spin traps for superoxide (O2•-). Using a chiral column, we have been able to isolate the two enantiomers of nitrone 5. With enantiomerically pure nitrone 5a and 5b we explored whether one of these isomers was solely responsible for the EPR spectrum of aminoxyl 6. Data obtained demonstrate that the spin trapping of O2•- by nitrone 5a and nitrone 5b affords the identical EPR spectra and lifetimes in homogeneous aqueous solution and exhibits the same ratio of cis and trans isomers. Quantum chemical modeling in vacuo also finds no difference, aside from the expected optical activity, arising from the difference in stereochemistry.
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Syn- and anti-β-substituted α-amino acids 1 and 2 were synthesized by employing nitrone-cycloaddition. The stereochemistries required were controlled via a (Z)-nitrone-exo transition state for syn-amino acid 1 and via an (E)-nitrone-exo transition state for anti-amino acid 2, respectively.
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Solutions in both chloroform and water of 4-hydroxymorpholine, when treated with a variety of oxidising agents, yielded 2,3-dihydro-1,4-oxazine 4-oxide (IV) as established by spectral and cycloaddition studies. When the solvent was removed, the heterocyclic nitrone (IV) yielded polymers, believed to have a chain-type structure (X). The nitrone (IV) behaved as a typical nitrone towards reducing agents. It was oxidised by arylhydrazines and by ferric chloride. With reactive π-bond systems it formed 1,3-cycloaddition products, the structures of which have been established by analysis and spectral data.
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Abstract For the first time, synthetic polyoxoaluminium Keggin ion pillared Buserite (KPB), has been used as an effective catalytic material gffor the 1,3-dipolar cycloaddition reaction of α-N-diaryl nitrone such as αphenyl-N-(p-methylphenyl) nitrone with some electron deficient olefins resulting in the exclusive formation of trans-4-substituted isoxazolidines.
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The adducts of phenylglycidyl ether with 2'-deoxyadenosine (dAdo) and 2'-deoxycytidine (dCyd) exhibit structural modifications. The N-1 adduct of dAdo underwent rearrangement to the N-6 adduct; the N-3 adduct of dCyd was deaminated to the corresponding 2'-deoxyuridine adduct. These structural modifications were studied by using liquid chromatography-electrospray tandem mass spectrometry, and kinetic data for both reactions are presented. The low energy (+) collision-activated dissociation spectra of the dAdo adducts allow the two positional isomers N-1 versus N-6 to be distinguished. The structure of the latter is independently proven by an extended NMR study. For the dCyd and 2'-deoxyuridine adducts, information about the alkylation site is found in the (-) collision-activated dissociation spectra. These spectra show the presence of an unexpected N-4-alkylated dCyd in addition to the two epimeric N-3 adducts.
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This chapter contains sections titled: Introduction Synthesis of Nitrones Structure and Spectra of Nitrones Electrochemical Properties and Electron Paramagnetic Resonance (EPR)-Spectra of Nitrone Radical Ions Nitrone Complexes Nitrone Reactions Nitrone Application in Radical Polymerization Reactions of Dipolar 1,3-Cycloaddition ([3 + 2] Cycloaddition) Kinugasa Reaction ([2 + 2] Cycloaddition) 1,7- Dipolar Cyclization Reactions Reactions with Cyclopropanes Conclusion Acknowledgment References
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