Secondary metabolites of the leaves of Tricalysia atherura N. Hallé (Rubiaceae) and their potential antiplasmodial activity.

One monoterpene indole alkaloid, atheruramine ( 1 ) bearing an ether bridge linking, one hydrobenzoin derivative, tricalydioloside ( 2 ) and two ursane-type triterpenes, atherurosides (A and B) ( 3 and 4 ) were isolated from the leaves of Tricalysia atherura , together with eight known compounds. The structures of these new compounds were elucidated on the basis of the results of spectroscopic analysis, and the relative configurations of compounds 1-3 were established by NOE difference. Four of the metabolites were screened in vitro against both chloroquine (CQ)-sensitive (3D7) and -resistant (Dd2) strains of Plasmodium falciparum ; they were found to exhibit moderate activity against chloroquine-resistant (Dd2) (IC 50 64.99-92.29 μg/mL). Meanwhile, crude extract possesses high antiplasmodial activity against both 3D7 and Dd2 strains of P. falciparum (IC 50 4.39-7.54 μg/mL) and high selectivity indices values (SI > 10) and was found to be safe.