Antiproliferative and Antiplasmodial Dimeric Phloroglucinols from <i>Mallotus oppositifolius</i> from the Madagascar Dry Forest

Bioassay-guided fractionation of an ethanol extract of the leaves and inflorescence of <i>Mallotus oppositifolius</i> collected in Madagascar led to the isolation of the two new bioactive dimeric phloroglucinols mallotojaponins B (<b>1</b>) and C (<b>2</b>), together with the known mallotophenone (<b>3</b>). The structures of the new compounds were determined on the basis of spectroscopic evidence, including their 1D- and 2D-NMR spectra, mass spectrometry, and an X-ray crystal structure. Compounds <b>1</b> and <b>2</b> showed potent antimalarial activity against chloroquine-resistant <i>Plasmodium falciparum,</i> with IC<sub>50</sub> values of 0.75 ± 0.30 and 0.14 ± 0.04 μM, while <b>3</b> was inactive in this assay. Compounds <b>1</b>–<b>3</b> also displayed strong antiproliferative activity against the A2780 human ovarian cancer cell line (IC<sub>50</sub> 1.10 ± 0.05, 1.3 ± 0.1 and 6.3 ± 0.4 μM, respectively).