Antimalarial screening and chemical studies of some antimalarial plants used in traditional medicine in Kenya
Wanyoike, George Ng'ang'a
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Malaria constitutes one of the major health threats in the world especially in the third world countries. At least two million people die of it each year. The emergence and spread of parasites resistant to standard drug therapies have necessitated the search for malaria drugs especially from plants with antimalarial properties. In the aim of finding antimalarial compounds, the methanolic extracts of five plants Pentas longiflora, Pittosporum lanatum, Albizia gummifera, Cyathula polycephala, Cyathula cylindrica were screened for in vitro antimalarial activity against chloroquine sensitive M24, and chloroquine resistant K39 and V1/S Plasmodium falciparum malaria parasites. And for brine shrimp lethality bioassay using Artemia salina Leach as the test organism. The results obtained showed that all the plant extracts had good in vitro antimalarial activities with inhibitory concentration fifties (IC50) ranging between 10 and 100gml-1. The most active extracts were from Pentas longiflora IC50 = 11.4gml-1. The root extract of Pentas longiflora also showed the lowest lethality concentration fifty (LC50=6.4) against Artemia salina Leach larvae and was, therefore, sampled for further bioassays and chemical investigation. Bioassay guided fractionation of the methanolic extract of the root and leaves of Pentas longiflora by column chromatography led to the isolation of seven compounds. Further in vitro antimalarial studies of the impure fractions and pure compounds showed that the impure fraction F30 from which the pure flavonoid coded CPD-30 was isolated had the best activity IC50 0.12gml-1. This activity was comparable to that of chloroquine IC50 = 0.085gml-1. The activity of the pure compound CPD - 30 was also good IC50 = 0.33gml-1 whereas the other pure compounds were less active for example, the activity of ursolic acid a triterpenoid (CPD-E) was IC50 = 15.3gml-1. Drug interaction studies of the root and leaf extract of Pentas longiflora with chloroquine showed chloroquine potentiating properties. That is, they acted synergistically against both chloroquine-sensitive and chloroquine-resistant strains. Partial structural elucidation of the 3-hydoxyurs-12-en-17-oic acid and -glucopyranosyl--D-fructofuranoside was done by use of spectroscopic techniques 1H-NMR, 13C-NMR, DEPT, MS and IR.