Antimalarial activity of cassane- and norcassane-type diterpenes from Caesalpinia crista and their structure-activity relationship

Malaria is one of the most life-threatening infectious diseases worldwide and claims the millions of peoples life each year. The appearance of drug-resistance Plasmodium falciparum has made the treatment of malaria increasingly problematic, and thus, it is a dire need to search the new alternatives of current drugs. In the present study, 44 cassane- and norcassane-type diterpenes isolated from Caesalpinia crista of Myanmar and Indonesia were evaluated for their antimalarial activity against the malaria parasite Plasmodium falciparum FCR-3/A2 clone in vitro. Most of the tested diterpenes displayed antimalarial activity, and norcaesalpinin E (28) showed the most potent activity with an IC₅₀ value of 0.090 μM, more potent than the clinically used drug chloroquine (IC₅₀, 0.29 μM). Based on the observed results, a structure-activity relationship has been established.