Antimalarial and antitrypanosomal activity of strychnogucine B, a bisindole alkaloid from Strychnos icaja

Strychnogucine B, a bisindole alkaloid isolated from Strychnos icaja (Loganiaceae), showed promising in vitro antiplasmodial properties (IC50 < 1μM) in previous studies [1, 2]. In order to obtain sufficient quantities to further investigate its antiprotozoal activity, this compound was synthesized in four steps from (-)-strychnine [3]. The in vivo antimalarial activity of this semi-synthetic strychnogucine B (30 mg/kg/d, i.p) was determined in a Plasmodium berghei murine model using the Peters’ 4-day suppressive test.
This alkaloid confirmed a promising antimalarial activity in vivo by suppressing the parasitaemia by almost 36 percent on day 5 and 60 percent on day 7 compared to vehicle treated mice.
In addition to this interesting antiplasmodial potential, it also showed a moderate in vitro anti-trypanosomal activity (IC50 = 2.7μM) but no in vivo activity in an acute Trypanosoma brucei model. It was also inactive in vitro on Leishmania mexicana promastigotes. This study highlights the selective antiplasmodial efficacy of strychnogucine B and warrants further investigations to assess the potential of this alkaloid as new antimalarial lead compound.