| Firstly, two novel flavonoids compounds, namely, 6’’,6’’-dimethyl-4’’,5’’-dihydropyrano[2’’,3’’:7,6]-6’ ",6’"-dimethyl-prenyl-4’ ",5’"-dihydropyrano [2’ ",3’" : 2’,3’]Apigenin and(E)-5, 7-dihydroxy-2-(4-hydroxyphenyl)-8-(3-methylbut-1-enyl)-4H-chromen-4-one from the ethanol extract of allium chrysanthum were isolated together with seven known compounds 1-4 & 7-9. All of them have a nucleus of flavonoids except for conpound 9. The structures of these two novel phenolic compounds were established via extensive 1D-and 2D-nuclear magnetic resonance spectroscopy experiments.In addition, metal ion chelation, DPPH radical scavenging and potassium ferricyanide reduction experiments were taken to evaluate the in vitro antioxidant activity of the eight flavonoids above. The results showed that in these three experiments all the flavonoids possessed strong antioxidant activities, but the the sequence of antioxidation abilities corresponding to the above three methods was not completely consistent. In metal ion chelation experiments, 1, 2, 6, 3showed comparatively higher activity, respectively 0.516±0.013、0.478±0.0082、0.461±0.0076 and 0.453±0.0070 EDTA equivalents; in DPPH radical scavenging tests, 1, 2, 3 were far more active than the others, namely 7.15±016, 6.06±0.17 and 3.73±0.14 ascorbic acid equivalents; in potassium ferricyanide reduction experiments, 1, 2, 3 showed high reducing power, respectively7.87±0.11, 6.73±0.10 and 2.65±0.056 ascorbic acid equivalents. By comparing their relative activity and structure of these compounds, the structure-activity relationship between them was analyzed.Furthermore, the major type of force between 1, 2, 3, 6 and bovine serum albumin(BSA)were studied and identified by fluorescence spectroscopy method. The results showed that compounds 1, 2, 3, 6 could lead to the quenching of BSA intrinsic fluorescence. The higher the concentration of these compounds, the stronger the quenching of BSA were. It was found that fluorescence quenching occured via static mechanisms and at the experimental temperature there was an approximate 1:1 complex formed between them and BSA. With further calculation and analyses, it suggested that hydrophobic force was the major force between BSA and 1, 2, 3, 6while a certain degree of hydrogen bonding were also showed between 1, 3, 6 and BSA.Ultimately, the kinetic parameters for the decomposition of alliin in H2 O were determined.The activation energy was 80.5 kJ·mol-1 and the pre-exponential was 1.27×107. Via analyzing the thermal decomposition products with GC-MS, it’s found that as the temperature rose,diallyl disulfide continued to drop from the 91.59 to 53.62 percent, diallyl trisulfide content first increased and then decreased while the content of diallyl thioether continued to increase. Thechanging content of sulfur compounds illustrates that high temperature promotes their fracture and rearrangement. Through applying mass spectrometry and 2, 4 dinitrophenylhydrazine method, S-allyl-L-cysteine sodium and pyruvic acid were detected among the liquid products. At the B3LYP/3-21+G(d, p) leve1, the structure of the reactants and products were optimized,decomposition transition state of alliin was calculated theoretically. Combined with decomposition kinetics and thermal decomposition product analysis, we concluded that alliin will form five-membered ring intermediate in the decomposition process. After the COPE elimination, hyposulfurous acid and pyruvic acid were generated. Diallyl disulfide and diallyl trisulfide are conformed from hyposulfurous acid during the further reaction. |
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