Thiazole, Oxadiazole, and Carboxamide Derivatives of Artemisinin are Highly Selective and Potent Inhibitors of Toxoplasma gondii

We have prepared 23 new dehydroartemisinin (DART) trioxane derivatives (11 thiazoles, 2 oxadiazoles, and 10 carboxamides) and have screened them for in vitro activity in the Toxoplasma lytic cycle. Fifteen (65%) of the derivatives were noncytotoxic to host cells (TD50 >= 320 mu M). Eight thiazole derivatives and two carboxamide derivatives displayed effective inhibition of Toxoplasma growth (IC50 = 0.25-0.42 mu M), comparable in potency to artemether (IC50 = 0.31 mu M) and > 100 times more inhibitory than the currently employed front-line drug trimethoprim (IC50 = 46 mu M). The thiazoles as a group were more effective than the other derivatives at inhibiting growth of extracellular as well as intracellular parasites. Unexpectedly, two thiazole trioxanes (5 and 6) were parasiticidal; both inhibited parasite replication irreversibly after parasite exposure to 10 mu M of drug for 24 h, whereas the standard trioxane drugs artemisinin and artemether were not parasiticidal. Some of the new derivatives of artemisinin described here represent effective anti-Toxoplasma trioxanes as well as molecular probes for elucidating the mechanism of action of the DART class of artemisinin derivatives.