Phytochemical and Antiplasmodial Evaluation of the Root Bark of Kenyan Warburgia Stuhlmannii Engl

Abstract

Malaria is a huge social, economic and health problem, particularly in tropical countries. Approximately 350-500 million malaria cases are reported annually, out of which 1-3 million die, majority of who are young children from sub-Saharan Africa. Malaria parasites have become resistant to almost every antimalarial drug currently available and most of the drugs in use have serious side effects. The genus Warburgia is valued for curing several ailments, including malaria. Phytochemical investigation of Warburgia species revealed presence of sesquiterpenes. Sesquiterpenes such as artemisinin are reported to be effective in treating malaria. Warburgia stuhlmannii, a species of Warburgia is used by communities in Kwale District Kenya, for malaria treatment and remedy for toothache and rheumatism. This work aimed at isolation and characterization of compounds from W stuhlmannii root bark and evaluation of its extracts and isolates for antiplasmodial activity. The dried and ground root bark was extracted sequentially with ethyl acetate and methanol by cold percolation at room temperature. The extracts showed antiplasmodial activity against the chloroquine sensitive (DI0) and chloroquine resistant (W2) strains of Plasmodium falciparum, with ICso values of 32.511g/mI and 38.4Ilg/ml respectively for the ethyl acetate extract but 80.51lg/ml and 95.351lg/ml respectively for methanol extract. Fractionation of W stuhlmannii root bark ethyl acetate and methanol extracts led to the isolation of 10 compounds of famesane-type sesquiterpenes. 6a,9a-dihydroxy-4( 13),7,coloratadiene-ll, 12-dial (52) is being reported for the first time from this species. Fractionation of the ethyl acetate extract afforded the sesquiterpenes; mukaadial (11), ugandensidial (12), muzigadial (14), warburganal (29), polygodial (30), ugandensolide (35), deacetylugandensolide (36) cinnamolide (37), bemadienolide (45), and 6a,9a-dihydroxy-4(13),7,coloratadiene-ll,12-dial (52) The methanol extract gave mukaadial (11), ugandensolide (35) and deacetylugandensolide (36). The isolated compounds were active against chloroquine sensitive (DIO) and chloroquine resistant (W2) strains' of P. Jalciparum. The antiplasmodial activities for warburganal (29), polygodial (30), deacetylugandensolide (36) and bemadienolide (45) are being reported for the first time. Mukaadial (11) had the highest antiplasmodial activity against both DI0 and W2 strains of P. falciparum, with ICso values of 4.311Mand 5.8IlM, respectively, while muzigadial (13) though very effective on DIO strain (ICso 5.6IlM) was less effective against W2 strain (ICso 16.4IlM). The antiplasmodial activity of W root bark extracts and compounds authenticates its ethno pharmacological use in treatment of malaria.