1,2,4-Trioxanes as potential antimalarial agents.

A number of 1,2,4-trioxanes were prepared and tested for antimalarial activity in search of a simplified analogue of the naturally occurring antimalarial qinghaosu. The compounds were assayed in an in vitro system for antimalarial activity against chloroquine-susceptible and chloroquine-resistant strains of Plasmodium falciparum. The most active compounds were methyl 2-(2,4a-epidioxy-4a,5,6,7,8,8a-hexahydro-5,5,8a-trimethyl-2H-1-benzop yra n-2-yl) acetate (3b), which showed IC20's of 96 and 39 ng/mL, respectively, and 2,4a-epidioxy-3,4,4a,5,6,7,8,8a-octahydro-2-[2-(benzoyloxy)propyl]-5,5,8 a- trimethyl-2H-1-benzopyran (12), which showed IC50's of 24 and 99 ng/mL, respectively. For comparison, qinghaosu exhibits an IC50 of 1 ng/mL for both strains.