Toward a Novel Metal-Based Chemotherapy against Tropical Diseases. 2. Synthesis and Antimalarial Activity in Vitro and in Vivo of New Ruthenium− and Rhodium−Chloroquine Complexes

Chloroquine free base (CQ) reacts with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) and RuCl3·3H2O/Zn to yield Rh(COD)(CQ)Cl (1) and [RuCl2(CQ)]2 (2), respectively. The two novel metal−CQ complexes, which were characterized mainly by 1D and 2D NMR spectroscopy, were tested against Plasmodium berghei. The in vitro activity of 1 was comparable to that of chloroquine diphosphate (CQDP), whereas 2 was about 5 times more active. In in vivo tests at equivalent concentrations of free CQ, CQDP reduced the parasitemia by 55%, while for complexes 1 and 2 the reduction reached 73% and 94%, respectively, without any sign of acute toxicity being observed up to 30 days after treatment. The Ru derivative 2 was further evaluated against two chloroquine-resistant strains of Plasmodium falciparum, and it was found to be 2−5 times more active than CQDP.