Antiplasmodial activities of some abietane diterpenes from the leaves of five Plectranthus species

Seven known abietane diterpenes were isolated from five Plectranthus species, namely P. hadiensis, P. lucidus, P. ecklonii, P. purpuratus subsp. purpuratus and P. purpuratus subsp. tongaensis. The seven compounds were tested for their antiplasmodial activity and for their ability to inhibit b-haematin formation. Overall, they showed good activity (IC sub(50) values ranging from 3.11 to 14.65 kM), with one compound being 62% as effective as chloroquine in inhibiting b-haematin formation. However, the cytotoxicity profile indicated a low degree of specificity towards the malaria parasite. When combined with quinine, three compounds interacted in an additive manner whereas one interacted synergistically.