Studies On Chemical Constituents And Antioxidant Activities Of Brown Alga Sargassum Fusiforme

In this thesis, the chemical compositions of the brown alga Sargassum Fusiforme as well as their antioxidant activities were studied. The ethanol extract of Sargassum was systematically studied by silica gel, reversed-phase C18 column, Sephadex LH-20 gel column and a variety of normal and reversed-phase chromatography, such as preparative column. Six compounds including one saturated fatty acid, three cholesterol and two firstly isolated unsaturated fatty acid amide were obtained from the extract. The structure of these compounds were determined by physicochemical and 1HNMR, 13 CNMR, GC-MS, LC-MS analysis. The antioxidant activity of these six compounds were tested using DPPH-HPLC method which showed that the IC50 of those six compounds(cholesterol, phytol, D-mannitol, oleic acid amide, erucic acid amide and palmitic acid) are between 11.8 μg/mL and 135.2 μg/m L, have a certain antioxidant activity.The methods of HPLC-DAD and derivatization-HPLC-MS for determinating the active ingredients of Melia azedarach L. were established. After comparison of two methods, the results show that the quantitative methods by peak area of HPLC require the component must be completely separated from the other components, using gradient elution, long separation time, baseline drift and other shortcomings. The results showed that by utilizing hydroxylamine hydrochloride as the derivative reagent, derivatization HPLC-MS which overcome low ionization efficiency of aldehyde compounds and greatly improve the sensitivity. Vanillin and coniferyl aldehyde derivatized by reaction of oxime compounds which is an N-containing compounds. N atom lone pair electrons and protons easily combined to form hydrogen [M+H]+ ions, which play a role in enhancing the ionization efficiency. Compared with the high-performance liquid chromatography, high performance liquid chromatography-tandem mass spectrometry is more suitable for the separation and analysis of trace components in natural products with the advantage of rapid, sensitive, low detection limit, and good reproducibility.