Antioxidant activity test using two different methods namely 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azinobis(3-ethylbenzothialozinesulfonate) diammonium salt free radical scavenging test has been carried out on three Cameroonian plant extracts used in the treatment of intestinal and infectious diseases: Pittosporum mannii Hook f. (Pittosporaceae), Vepris heterophylla R. Letouzey (Rutaceae) and Ricinodendron heudelotii (Baill) Pierre ex Pax (Euphorbiaceae). Results of this study in the 2,2-diphenyl-1-picrylhydrazyl scavenging test show that the ethyl acetate extract of P. mannii and the methanol extract of V. heterophylla exhibit high free radical scavenging activities with IC50 values of 177.74 and 204.69 μg/ml, respectively while the methanol/dichloromethane (1+1) extract of R. heudelotii showed weak free radical scavenging activities as compared to Trolox (939.19 μg/ml) used as standard. In the same manner, 2,2'-azinobis(3-ethylbenzothialozinesulfonate) diammonium salt radical scavenging test of these extracts was in accordance of the result of 2,2-diphenyl-1-picrylhydrazyl test. The antioxidant properties of these extracts probably explain partly, the use of these plants in traditional medicine for the treatment of infectious diseases and inflammations.
Phytochemical studies and antioxidant activities were carried out on n-hexane, ethyl acetate, ethanol and methanol extracts of the leaves of Lippia rugosa A. Chev (Verbenaceae), a medicinal plant used traditionally in the Cameroonian savannah's region to protect foodstuffs and to cure degenerative diseases. Results indicated that theses extracts contain terpenoids, phenolic and flavonoid compounds. Except the n-hexane extract, all of the obtained extracts exhibit antioxidant activities with the ethanol extract being the most effective with an inhibition percentage of 85.668% ± 1.233% and an inhibition concentration (IC 50) of 58 µg/ml (R 2 = 0.987, P < 0.01) at a concentration of 100 mg/ml. Chromatographic separation on silica gel of the ethanol extract led to the isolation of a pure organic compound which was characterized as 7-hydroxy-5,6,4'-trimethoxyflavone by extensive 1D and 2D NMR spectroscopy, a flavonoid exhibiting antioxidative activity with an inhibitory percentage of 25.506% ± 0.205% and inhibition concentration (IC 50) of 221 µg/ml (R 2 = 0.966, P < 0.01). This is the first time that 7-hydroxy-5,6,4'-trimethoxyflavone is being isolated from L. rugosa and its antioxidant activity evaluated.
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