Leishmanicidal, antiplasmodial and cytotoxic activity of indole alkaloids from Corynanthe pachyceras.

Five indole alkaloids, corynantheidine, corynantheine, dihydrocorynantheine, α-yohimbine and corynanthine were isolated from bark of Corynanthe pachyceras K. Schum. (Rubiaceae). The structures were established by spectroscopic methods, inlcuding previously unreported assignment of all 1 H-NMR resonances by COSY and NOESY experiments. These and related alkaloids showed pronounced activity against Leishmania major promastigotes (IC 50 at the micromolar level) but no significant in vitro antiplasmodial activity (against chloroquine-sensitive Plasmodium falciparum). Cytotoxicity assessed with drug sensitive KB-3-1 and multidrug-resistant KB-V1 cell lines was low; the alkaloids are apparently not substrates for the P-glycoprotein (P-170) efflux pump.