Antimalarial and cytotoxic activities of pregnene-type steroidal alkaloids from <i>Holarrhena pubescens</i> roots

<p>The phytochemical investigation of an alkaloidal extract of <i>Holarrhena pubescens</i> roots led to the isolation and identification of a new pregnene-type alkaloid, mokluangin D (<b>1</b>), together with nine known steroidal alkaloids (<b>2–10</b>). The structure of the new metabolite was determined on the basis of spectroscopic analyses including 1D- and 2D-NMR spectroscopy and mass spectrometry. Compounds <b>3</b> and <b>4</b> showed potent antimalarial activity against <i>Plasmodium</i> <i>falciparum</i> K1 stain with IC<sub>50</sub> values of 1.2 and 2.0 μM, respectively, and showed weak cytotoxic activity against the NCI-H187 cell line with IC<sub>50</sub> values of 27.7 and 30.6 μM, respectively. The substituent groups at C-3 and the carbonyl group at C-18 are important for the activity against the <i>P. falciparum</i> K1 stain.</p>