New antimalarials with a triterpenic scaffold from Momordica balsamina

Bioassay-guided fractionation of the methanol extract of Momordica balsamina led to the isolation of three new cucurbitane-type triterpenoids, balsaminols C-E (1-3). Their structures were elucidated on the basis of spectroscopic methods including 2D NMR experiments (COSY, HMQC, HMBC and NOESY). Balsaminols C-E, together with ten cucurbitacins isolated from the same plant (4-13), were evaluated for their antimalarial activity against the Plasmodium falciparum chloroquine-sensitive strain 3D7 and the chloroquine-resistant clone Dd2. Most of the compounds displayed antimalarial activity. Compounds 9 and 12 revealed the highest antiplasmodial effects against both strains (IC50 values: 4.6, and 7.4 microM, 3D7, respectively; 4.0, and 8.2 microM, Dd2, respectively). Structure-activity relationships are discussed. Furthermore, the preliminary toxicity toward human cells of compounds 1-5 and 9 was investigated in breast cancer cell line (MCF-7). Compounds were inactive or showed weak toxicity (IC50 values>19.0).