Redox reaction of artemisinin with ferrous and ferric ions in aqueous buffer

Artemisinin, a sesquiterpene with endoperoxide bond, possesses potent antim alarial activity against the ring and late stage of chloroqine-resistant Pl asmodium falciparum malaria both in vitro and in vivo. The mode of antimala rial activity of artemisinin is iron-dependent. The aim of this study was t o investigate the reactions of artemisinin with ferrous and ferric ions in aqueous buffer. Artemisinin generated a cycle of iron oxidation and reducti on. It oxidized ferrous and reduced ferric ions with similar rate of reacti on (k=10 +/-0.5 M-1.s(-1) for ferrous and k=8.5 +/-2.0 M-1.s(-1) for ferric ion). The major active product was dihydroartemisinin which exhibited anti malarial activity at least 3 times more potent than artemisinin. Dihydroart emisinin preferably binds to ferric ion, forming ferric-dihydroartemisinin complex. The re-oxidation of the complex gives artemisinin and ferric ion. This suggests that in aqueous buffer, the reaction of artemisinin with iron may give rise to the active reaction products, one of them being dihydroar temisinin, which is responsible for antimalarial activity.