Antiplasmodial constituents in the leaves and stem barks of carapa procera dc (Meliaceae) and alstonia boonei de willd. (Apocynaceae).

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Malaria remains the most devastating infectious parasitic disease, inflicting both death and economic losses on at least half the world’s population. Presently, the most effective way of dealing with malaria is the administration of chemotherapeutic agents. There is an urgent need for the development of effective anti-malarial drugs due to emergence of resistant strains of P. falciparum. The stem and leaf extracts of Alstonia boonei are used in various traditional medicines for the treatment of malaria. A decoction of the bark of Carapa procera is taken orally for fevers whereas oil obtained from the seeds is applied topically as a mosquito repellent and also for other skin infections. Petroleum ether and hydro-alcoholic extracts of these two plants were tested in vitro on choloroquine sensitive (3D7) strains of Plasmodium falciparum for their anti-malarial activity. Growth inhibition was determined in vitro by counting GIEMSA-stained parasites by light microscopy. The petroleum ether extract of the leaves (PSL) and stem bark (PS1) of A. boonei were both inactive (IC50˃100 µg/ml). Also their hot ethanolic extracts were inactive with IC50 ˃100 µg/ml. However, the cold ethanolic extract of the leaves showed weak activity (IC50 = 71.24 µg/ml) whereas that of the stem was 88.15 µg/ml. The petroleum ether extract of the stem bark of C. procera (PC1) inhibited the growth of the chloroquine sensitive (3D7) Plasmodium falciparum parasite with IC50 value of 19.52 µg/ml. The cold ethanolic extract of C. procera had moderate activity (IC50 = 33.35 µg/ml) whereas the hot ethanolic extract (H2) showed the highest antimalaria activity (IC50 = 11.41 µg/ml). Column chromatography of H2 on silica gel (70-230 mesh) yielded four bulked fraction designated as H2A, H2B, H2C and H2D which were tested in vitro for antiplasmodial activity. Fractions H2A, H2C and H2D showed the highest antimalaria activities (IC50˂10µg/ml) whereas H2B showed moderate antimalaria activity with (IC50˂50µg/ml). The activities of fractions H2A and H2C (IC50˂1µg/ml) were comparable to the standard antimalaria drug artesunate (IC50˂0.01µg/ml). TLC analysis of the fractions described in the present work revealed the presence of steroids and terpenoids (fraction H2A), flavonoids, catechins and proanthocyanidins (H2B, H2C and H2D). Thus cold ethanolic extract of the leaves and stem bark of A. boonei have weak antiplasmodial activity whereas the hot ethanolic extract of C. procera has very good antiplasmodial activity. Antiplasmodial activity of the stem bark of C. procera may be attributed to the presence of terpenoids, flavonoids and proanthocyanidins present in the stem bark of C. procera.
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Organic Chemistry)