Antiprotozoal aminosteroid alkaloids from Holarrhena pubescens Wall. ex G. Don

Human African Trypanosomiasis (HAT) and Malaria are prevalent protozoan infections in tropical regions, necessitating development of new antiprotozoal drugs. In our ongoing search for new antiprotozoal aminosteroid alkaloids from the Apocynaceae family [ 1 ], we investigated the methanolic stem bark extract of Holarrhena pubescens . It is a tropical tree that some Kenyan coastal communities have historically used to treat various diseases including fever and stomach discomfort [ 2 ]. The crude extract, alkaloid-enriched fraction, and 15 subfractions acquired through centrifugal partition chromatography (CPC) were assessed for in vitro activity against Trypanosoma brucei rhodesiense (Tbr; causing HAT ) and Plasmodium falciparum (Pf; causing Malaria ) using standard assays [ 3 ]. Compared to the crude extract (IC 50 =0.89 μg/mL, SI=68), the alkaloid-enriched fraction displayed higher activity against Tbr (IC 50 =0.24 μg/mL, SI=62). Similarly, the alkaloid fraction exhibited almost 6-fold antiplasmodial activity (IC 50 =0. 70 μg/mL, SI=21) compared to the crude extract (IC 50 =4.04 μg/mL, SI=15). Most of the CPC subfractions demonstrated strong activity (IC 50