RP-Department of Chemistry

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Browsing RP-Department of Chemistry by Author "Ahmed, Hassanali"

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    Influence of Host-Plant Surface Chemicals on the Oviposition of the Cereal Stemborer Busseola Fusca
    (2016) Juma, Gerald; Clément, Gilles; Ahuya, Peter; Ahmed, Hassanali; Derridj, Sylvie; Gaertner, Cyrile; Linard, Romain; Bruno, Le Ru; Frérot, Brigitte; Calatayud, Paul-André
    The chemical composition of plant surfaces plays a role in selection of host plants by herbivorous insects. Once the insect reaches the plant, these cues determine host acceptance. Laboratory studies have shown that the stem borer Busseola fusca (Lepidoptera: Noctuidae), an important pest of sorghum and maize in sub-Saharan Africa, is able to differentiate between host and non-host plant species. However, no information is available on the cues used by this insect to seek and accept the host plant. Thus, the role of surface phytochemical stimuli on host selection and oviposition by B. fusca was studied in the laboratory using two host plants, sorghum, Sorghum bicolor, and maize, Zea mays, and one non-host plant, Napier grass, Pennisetum purpureum. The numbers of eggs and egg masses deposited on the three plant species were compared first under no-choice and choice conditions. In both cases, more eggs and egg masses were laid on maize and sorghum than on the non-host. Artificial surrogate stems treated with a water or chloroform surface extract of each plant were then compared with surrogate stems treated with, respectively, water or chloroform as controls, under similar conditions. Surrogate stems treated with plant water extracts did not show an increase in oviposition when compared to controls, indicating that the major compounds in these extracts, i.e., simple sugars and free amino acids, are not significantly responsible for the oviposition preference. By contrast, a chloroform extract of sorghum enhanced oviposition on the surrogate stems compared to the control, while those of maize and Napier grass showed no significant effects. Analysis of the chloroform extract of sorghum showed higher amounts of α- amyrin, ß-amyrin, and n-nonacosane compared to those of maize and Napier grass. A blend of the three chemicals significantly increased oviposition compared to the chloroformtreated control, indicating that these compounds are part of the surface chemical signature of the plant responsible for host recognition and oviposition by B. fusca.
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    Synergistic antiplasmodial activity of artemisia annua fractions against in vitro cultures of plasmodium falciparum
    (2016) Kangethe, Lucy N.; Ahmed, Hassanali; Omar, Sabah; Gathirwa, Jeremiah; Kirira, Peter; Kaniaru, Stephen; Kamau, Timothy; Kimani, Francis; Nganga, Joseph K.; Irungu, Lucy
    Background: Artemisia annua has a very rich phytochemistry comprising several classes of compounds, mainly monoterpenes, sesquiterpenes, and flavonoids. It has been used in China for about 2000 years in the treatment of fever. Objective: The aim was to determine if there is any synergistic effect on the Artemisia annua phytochemicals. Materials and methods: Artemisia annua used in this study was obtained from a hybrid of the plant grown in the Tanzania highlands (2000-2200 m altitude) in Arusha by Natural Uwemba System for Health (N.U.S.Ag). The dried leaves were ground, and sequentially extracted with hexane, dichloromethane (DCM), methanol and water and the extracts were then combined. The extract was then fractionated using high performance liquid chromatography (HPLC). The effect of the combined crude extract was tested at different doses on in-vitro cultures (a CQ sensitive isolate D6 and CQ resistant isolate W2) of Plasmodium falciparum. The fractions and different blends of these were tested at different doses to determine their role, if any, on the activity of the full blend of the plant. Results: Of nine fractions thus tested against D6 and W2, four had activities of less than 3.9μg /ml, three fractions had activities of between 4.77-14.76 μg/ml and the remaining two had activities above 250g/μml. The seven more active fractions were re-evaluated in a subtractive bioassay procedure, in which one of each fraction was excluded at a time from the full 7-component blend. The activity of the combined seven active compounds was 10.40+0.50 μg/ml against W2. Of these, one showed IC50 of less than 3.9 μg/ml and all blends showed IC50 at below 27μg/ml. Conclusion: The results show that different components of A. annua contribute to the synergistic anti-Plasmodium activity. The results constitute a useful basis for identifying the components of the plant other than artemisinin that contribute to the activity of herb.