Antiprotozoal activities of new bicyclo[2.2.2]octan-2-imines and esters of bicyclo[2.2.2]octan-2-ols

Several bicyclo[2.2.2]octan-2-imines and esters of bicyclo[2.2.2]octan-2-ols were prepared. Their antitrypanosomal and antiplasmodial activities against Trypanosoma brucei rhodesiense (STIB 900) and the K1 strain of Plasmodium falciparum (resistant to chloroquine and pyrimethamine) were determined using microplate assays. Two of the synthesized bicyclo[2.2.2]octan-2-one 4′-phenylthiosemicarbazones showed the highest antitrypanosomal activity (IC50 < 0.3 μM) of the so far prepared 4-amino-6,7-diarylbicyclo[2.2.2]octane derivatives, but they are distinctly less active than suramine (IC50 = 0.0075 μM). Most of the 4′-phenylthiosemicarbazones and a single bicyclo[2.2.2]octan-2-yl benzoate exhibit attractive antimalarial activity (IC50 = 0.23-0.72 μM). Two bicyclooctanone oximes are even as active as chloroquine (IC50 = 0.08-0.15 μM, chloroquine: IC50 = 0.12 μM against sensitive strains).