Selective Antiprotozoal Activity of Some Strychnos Alkaloids

The in vitro activities of 28 Strychnos alkaloids have been determined against three species of protozoa and the most active compounds were then assessed for in vitro cytotoxic activity against KB cells. 3',4'-dihydrousambarensine was the most active against Plasmodium falciparum and was relatively nontoxic to KB cells (cytotoxic/antiplasmodial ratio, 1474). Usambarensine displayed the most selectivity against Entamoeba histolytica while "',4'-dihydrousambarensine was the most selective compound against Giardia intestinalis although the cytotoxic/antiprotozoal ratios (20.4 and 6.6 respectively) were less favourable than the above.The four strychnobiline-type alkaloids were found devoid of activity against E. histolytica and G. intestinalis but to have weak antiplasmodial properties (7-13 times less active than chloroquine). None of the compounds containing only one indole ring system displayed antiprotozoal properties.