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ABSTRACT: In the present study, five cyclic nitrone superoxide spin adducts, i.e. DMPO-OOH, M(3)PO-OOH, EMPO-OOH, DEPMPO-OOH and DEPDMPO-OOH, were chosen as model compounds to investigate the effect of 2,5-subsitituents on their stability, through structural analysis and decay thermodynamics using density functional theory (DFT) calculations. Analysis of the optimized geometries reveals that none of the previously proposed stabilizing factors, including intramolecular H-bonds, intramolecular non-bonding interactions, bulky steric protection nor the C(2)-N(1) bond distance can be used to clearly explain the effect of 2,5-substituents on the stability of the spin adducts. Subsequent study found that spin densities on the nitroxyl nitrogen and oxygen are well correlated with the half-lives of the spin adducts and consequently are the proper parameters to characterize the effect of 2,5-substituents on their stability. Examination of the decomposition thermodynamics further supports the effect of the substituents on the persistence of cyclic nitrone superoxide spin adducts.
Free radical research 04/2010; 44(7):751-78. · 2.22 Impact Factor
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ABSTRACT: Bioactivity guided fractionation of the ethanolic extract of the whole plants of Lespedeza virgata (Thunb.) DC. resulted in the isolation of a novel flavonoid (1) along with five known compounds 2-6. The molecular and structural formula as well as the stereochemistry of compound 1 were determined using data obtained from (1)H and (13)C NMR spectra, DEPT135 and by 2D HSQC, HMBC, (1)H-(1)H correlated spectroscopy ((1)H-(1)H COSY), and nuclear overhauser effect spectroscopy (NOESY) experiments. The superoxide anion scavenging activities of all isolated compounds were evaluated by the hypoxanthine nitro blue tetrazolium and ESR methods and the new compound 1 showed the strongest antioxidative activity 95.79% (IC(50)=0.14 mg/ml).
Bioorganic & Medicinal Chemistry Letters 12/2007; 17(22):6311-5. · 2.55 Impact Factor
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ABSTRACT: The effects of three diosgenyl saponins isolated from Paris polyphylla on the immuno-stimulating activity in relation to phagocytosis, respiratory burst, and nitric oxide production in mouse macrophage cells RAW 264.7 have been investigated. Our results showed that all three diosgenyl saponins significantly enhanced phagocytic activity that increased with the concentration of saponins to reach a maximum, and then tended to decrease with higher concentrations. Saponins with sugar moiety directly induced respiratory burst response in RAW 264.7 cells that increased with the concentrations and reached a maximum, then decreased with higher concentrations after 2-h incubations, however, diosgenin had no PMA-triggered respiratory burst response. Treatment of RAW 264.7 cells with saponins with sugar moiety for 24-h caused a significant increase in the production of nitric oxide, while diosgenin had no effect at all. Consequently, relationship between molecular structures of three diosgenyl saponins and their immunomodulatory activities was discussed, and a possible mechanism of immuno-stimulating function of diosgenyl saponins was accordingly explored.
Bioorganic & Medicinal Chemistry Letters 06/2007; 17(9):2408-13. · 2.55 Impact Factor
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Bioorganic & Medicinal Chemistry Letters 01/2007; 17:2408-2413. · 2.55 Impact Factor
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Bioorganic & Medicinal Chemistry Letters 01/2007; 17:6311-6315. · 2.55 Impact Factor
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ABSTRACT: A new phosphorylated linear nitrone N-(4-hydroxybenzyliene)-1-diethoxyphosphoryl-1-methylethylamine N-oxide (4-HOPPN) was synthesized, and its X-ray structure was determined. The spin trapping ability of various kinds of free radicals by 4-HOPPN was evaluated. Kinetic study of decay of the superoxide spin adduct (4-HOPPN-OOH) shows the half-life time of 8.8 min. On the basis of the X-ray structural coordinates, theoretical analyses using density functional theory (DFT) calculations at the B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level were performed on spin-trapping reactions of superoxide radical with 4-HOPPN and PBN and three possible decay routes for their corresponding superoxide adducts. The comparative calculations on the spin-trapping reactions with superoxide radical predicted that both spin traps share an identical reaction type and have comparable potency when spin trapping superoxide radical. Analysis of the optimized geometries of 4-HOPPN-OOH and PBN-OOH reveals that an introduction of the phosphoryl group can efficiently stabilize the spin adduct through the intramolecular H-bonds, the intramolecular nonbonding attractive interactions, as well as the bulky steric protection. Examination of the decomposition thermodynamics of 4-HOPPN-OOH and PBN-OOH further supports the stabilizing role of the phosphoryl group to a linear phosphorylated spin adduct.
The Journal of Organic Chemistry 10/2006; 71(20):7753-62. · 4.45 Impact Factor
