Investigation of phytochemical and antimalarial activity of caesalpinia volkensii harms seeds
The purpose of the study was to do phytochemical investigation and antimalarial activity tests on the seeds of Caesalpinia volkensii Harms. Isolation of compounds, structure elucidation and brine shrimp toxicity assay studies were also done. The seeds were collected at Gatundu in Kiambu County Central province on June 2003. The seeds were extracted using water and sequentially using petroleum ether, chloroform and finally methanol. Phytochemical tests were done on the seeds for the presence of cardiac glycosides, alkaloids, saponins and anthraquinones. Isolation of compounds was carried out on the extracts using chromatographic methods. Structure elucidation of the isolated compounds was carried out using ultraviolet, infrared, mass spectrometry and nuclear magnetic resonance. In vitro antimalarial activity test was carried out on the petroleum extract, chloroform extract, methanol extract, water extracts and one of the isolated compounds. The activities were compared to that of the standard drug chloroquine. Brine shrimp toxicity testing was done on the petroleum extract, chloroform extract, methanol extract, water extract and the isolated compound. Phytochemical testing of the seeds of Caesalpinia volkensii Harms showed the presence of both alkaloids and saponins. The phytochemical tests showed absence of cardiac glycosides, tropane alkaloids and anthraquinones. From the isolation of compounds, three compounds were isolated and designated as compound 1, 2 and 3. Spectroscopic data strongly suggested that compounds 1, 2 and 3 had some structural similarities to glycerol trilinoleate [1¹,2¹,3¹-propanetriyl tris [cis,cis-9,12-octadecanedienoate], xvi beta-sitosterol [5-stigmasten-3-beta-ol] and glycerol tridocosanoate [1¹,2¹,3¹-propnetriyl tridocosanoate] a long chain carboxylic acid ester respectively. From the antimalarial activity tests, a plot of inhibition against concentrations for each extract and isolated compound gave 50 % inhibition [IC50] at 250.0 μg/mL, 290.0 μg/mL, 435.0 μg/mL, 625 μg/mL, 757.5 μg/mL and 62.5 ng/mL concentrations for methanol extract, chloroform extract, petroleum ether extract, water extract, isolated compound and standard drug chloroquine respectively. All the tested extracts and isolated compound were shown to have antiplasmodial activity at concentrations much higher than that of standard drug chloroquine. Methanol extract gave the highest activity. From the brine shrimp toxicity study, a plot of toxicity against concerntrations for each extract and isolated compound gave LD50 values at 562.5 μg/mL, 375.0 μg/mL, 375.0 μg/mL, 625.0 μg/mL and 750.0 μg/mL concentrations for methanol extract, chloroform extract, petroleum ether extract, water extract and isolated compound respectively. The water extract used by the traditional folklore was still safe at high concentrations. The present work gave a scientific basis for the use of Caesalpinia volkensii Harms as treatment for malaria and hence recommendations for further studies on qualitative and quantitative analysis and also to ascertain the structures of the isolated compounds.