Synthesis of an organo-ruthenium aminoquinoline-trioxane hybrid and evaluation of its activity against Plasmodium falciparum and its toxicity toward normal mammalian cells

A new hybrid compound 5 containing a ruthenocene, a 4-aminoquinoline, and a 1,2,4-trioxane within a single molecular structure has been synthesized and evaluated for antimalarial potential. In order to ascertain the role of each component of hybrid 5 , its antimalarial activity has been measured against chloroquine-resistant and chloroquine-sensitive strains of Plasmodium falciparum in comparison with those of chloroquine, artemisinin, a ruthenocene-trioxane compound 9 not containing an aminoquinoline, the precursor trioxane ketone 4 , and a trioxane dimer 10 . Hybrid 5 displays high antimalarial activity, in the mid to low nanomolar IC 50 range, and low cytotoxicity toward healthy mammalian cells, which translates into good selectivity indexes. The potency of 5 is consistently higher than those of chloroquine, the parent metal-free trioxane, and compound 9 , the structural intermediate featuring a ruthenocene moiety bound to the trioxane but lacking the aminoquinoline. These results validate our hypothesis that it is the combination of the aminoquinoline, the ruthenocenyl moiety, and the trioxane in a single molecule that provides the enhanced antiplasmodial activity, and highlight the concept of hybrid compounds as a strategy that deserves further attention. Graphical Abstract