Antiprotozoal activity of saponins from Anogeissus leiocarpus (Combretaceae)

In the frame work of our research on African species presenting antiparasitic activities, we reported previously the good antiprotozoal activity of Anogeissus leiocarpus (DC.) Guill. & Perr. (Combretaceae) [1]. In continuation of our work, we examined the constituents of the bark of this species. Fractionation of the ethanolic bark crude extract was carried out by combination of gel filtration on Sephadex LH-20 and preparative TLC. Two saponins of oleane type were isolated for the first time from this genus and their structures were established by spectroscopic methods, including 2D-NMR heteronuclear correlation experiments. They were identified as olean-12-en-28-oic acid 2α,3β,19α,23,24-pentahydroxy-β-D-glucopyranosyl ester (trachelosperoside E1) ( 1 ) and olean-12-en-28-oic acid 2α,3β,19α,23-tetrahydroxy-β-D-glucopyranosyl ester (arjunglucoside I) ( 2 ), both previously isolated from Rudgea viburnioides [2]. A comparison of their antiprotozoal activity shows that ( 1 ) has a good antitrypanosomal activity (IC 50 =1.24µM), without significant cytotoxicity (SI >100). Structure elucidation of three other saponins and three ellagic acid derivatives are currently under progress. Data shown are values of duplicate a Plasmodium falciparum K1 resistant strain; b Leishmania donovani amastigotes; c Trypanosoma cruzi Talahuen strain trypomastigotes; d Trypanosoma brucei rhodensiense STIB 900 strain trypomastigotes; e L6 cells, f SI: selectivity index, ratio of cytotoxic activity on L6 cells to antitrypanosomal activity against STIB 900 strain of T. brucei rhodensiense trypomastigotes. Samples In vitro antiprotozoal activity IC 50 (µM) Cytotoxicity e Antiplasmodialactivity a Leishmanicidalactivity b Antitrypanosomalactivity c Antitrypanosomalactivity d IC 50 (µM) SI f 1 >5 >5 >5 1.24 >150 >100 2 >5 >5 >5 >5 >150 >5 Chloroquine 0.19 - - - - - Artemisinin 0.007 - - - - - Miltefosin - 0.47 - - - - Benznidazole - - 1.69 - - - Melarsoprol - - - 0.005 - - Podophyllotoxin - - - - 0.048 - References : 1. Vonthron-Sénécheau, C. et al. (2003), J. Ethnopharmacol. 87: 221–225. 2. Young, M.C. et al. (1998), J. Nat. Prod. 617: 936–938.