Variability of Surface Exudates of Dodonaea angustifolia L.f, Antioxidant and Antiplasmodial activities of the compounds

Dodonaea angustifolia L.f is a medicinal plant used in the Kenyan traditional system of medicine to cure human diseases. The secondary metabolites present in the surface exudates, showed phytochemical diversity of this plant from different geographical conditions in Kenya. There was great geographical variability in the composition of the surface exudates in D. angustifolia populations as reflected in the antiplasmodial and radical scavenging activities (RSA) of this substance from the Ngong forest, Nairobi and Taita hills, Voi populations. Most of the compounds from the exudates of D. angustifolia and Senecio roseiflorus showed moderate antiplasmodial activities against chloroquine sensitive (D6) and resistant (W2) strains of P. falciparum with IC50 values ranging between 3.2 and 23.6 μg/ml. Of the pure compounds tested flavonols ca kaempferol (1) and rhamnocitrin (2) exhibited radical scavenging activities (RSA) comparable to the standard, quercetin (3) at 50 μM. These studies showed that flavonoids exhibited both antiplasmodial and RSA although there was no direct relationship between these activities. This is elaborated in 5,4 ́-dihydroxy-7-methoxyflavanone (4), exhibiting good antiplasmodial activities but minimal % RSA. The structure-activity relationship of the active flavonoids showed that flavonols had appreciable RSA activities as compared to 3-methoxy flavones from the surface exudates.