Antiamoebic and Antiplasmodial Activities of Alkaloids Isolated from Strychnos usambarensis

Seven alkaloids isolated from Strychnos usambarensis have been assessed for in vitro activities against Entamoeba histolytica and Plasmodium falciparum and for in vivo activity against Plasmodium berghei in mice. Strychnopentamine and 3'-4'-dihydrousambarensine were highly active against P. falciparum in vitro, but were inactve and non-toxic against P.berghei in vivo.Usambarensine, usambarine and 18,19-dihydrousambarine were highly active against E. histolytica in vitro, but were less active against P. falciparum in vitro. Nb-methylusambarensine was less active against both protozoa than was usambarensine, and akagerine possessed little antiprotozoal activity.Structure-activity relationships are discussed in the context of the reported cytotoxic and pharmacological properties of those alkaloids.