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 μM, 3D7, respectively; 4.0, and 8.2 μM, 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).