Browsing by Author "Kihampa, Charles"

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    Novel quinonoids and other natural products from mosquitoidal plant species.
    (University of Dar es Salaam, 2002) Kihampa, Charles
    In the phytochemical studies reported in this thesis, extracts from seven plant families collected from various parts of Tanzania and selected on the basis of their use as traditional insecticidal agents and/or belonging to families known to be potential sources of insecticidal compounds were tested against Anopheles gambiae mosquito larvae and adults. The majority of the extracts showed some activity at varying levels. The less and moderately polar extracts exhibited more promising results than the more polar extracts. Some of the constituents of Asteranthe lutea Scrnryfaelia ruffonammari and Uvaria scheffleri were isolated, identified spectroscopically and tested against mosquito larvae and adults. 2',3'-Epoxyasteranthine and 2',3'-dihydroxyasteranthine obtained from the pet ether extract of the root bark of A. lutea were active against the larvae, with LC50 values of 0.0023 and 0.0775, and 0.0005 and ~ 0.0338 mg/ml after 24 and 48 hours of exposure, respectively. Also the styrylpyrones (+)-G-styryl-7,8epoxy-4-methoxypyran-2-one and (-)-G-styryl-7,8-dihydroxy-4-methoxypyran-2-one were obtained from the chloroform extract of the root bark of S. ruffonammari but unfortunately they were not tested for insecticidal activity due to time limitations. Of the five compounds, 2',G'-dihydroxy-3'.4'-dimethoxychalcone, espintanol schefflone and the novel compounds scheffloquinone A and scheffloquinone B obtained from the chloroform extract of the root bark of U. scheffler, only espintanol showed the highest activity against the larvae and adult mosquitoes. The LC50 values against the larvae were 0.01 G4, 0.0049 and 0.002 mg/ml after 24, 48 and 72 hours of exposure, respectively, while it knocked down at a 100 % level adult mosquitoes, at a dose of 0.008 mg/cm2 showing a 100% mortality at a dose Of 0.012 mg/cm2 within 24 hours the computed LC50 being 0.004G mg/cm2. Schefflone was only active against the larvae (LCSp = 0.9305, 0.0183 and 0.0005 mg/ml after 48, 72 and 9G hours respectively), while 2',G'-dihydroxy-3',4'-dimethoxychalcone and the scheftloquinones were not assayed for insecticidal activity due to time limitations.