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Antiplasmodial and cytotoxic activity of natural bisbenzylisoquinoline alkaloids.

As part of an ongoing collaborative effort to discover new antimalarial agents from natural sources, we have tested 53 bisbenzylisoquinoline alkaloids for cytotoxicity against cultured mammalian cells and for antiplasmodial activity against chloroquine-sensitive and chloroquine-resistant clones of Plasmodium falciparum. The isolates from Cyclea barbata, Stephania pierrei, Stephania erecta, Pachygone dasycarpa, Cyclea atjehensis, Hernandia peltata, Curare candicans, Albertisia papuana, and Berberis valdiviana exhibited a wide range of biological potencies in antiplasmodial assays, and the majority exhibited some degree of cytotoxicity against human KB cells. More than half of the compounds tested, however, showed selective antiplasmodial activity, with >100-fold greater toxicity toward one or both of the P. falciparum clones, relative to cultured mammalian cells. The most selective alkaloids were (-)-cycleanine (40), (+)-cycleatjehine (50), (+)-cycleatjehenine (49), (+)-malekulatine (3), (-)-repandine (13), and (+)-temuconine (2). As a result of these studies, relationships between the structures, the stereochemistry, and the substitution patterns of these alkaloids and their in vitro antiplasmodial and cytotoxic activities are beginning to emerge.