A new procyanidin B from <i>Campylospermum zenkeri</i> (Ochnaceae) and antiplasmodial activity of two derivatives of (±)-serotobenine

<p>Phytochemical investigation of the stem bark of <i>Campylospermum zenkeri</i> led to the isolation of five known compounds: (<i>Z,Z</i>)-9,12-octadecadienoic acid (<b>1),</b> serotobenine (<b>2</b>), agathisflavone (<b>3</b>), lophirone A (<b>4</b>) and lophirone F (<b>5</b>), together with a new derivative of procyanidin B, a catechin dimer named zenkerinol (<b>6</b>). Serotobenine (<b>2</b>) is structurally related to decursivine which shows moderate activity against D6 and W2 strains of <i>Plasmodium falciparum</i>. For a better understanding of structure-activity relationships, three new semi-synthetic derivatives of serotobenine (<b>2</b>) have been prepared. These are: serotobenine monopropionate (<b>2a</b>), serotobenine monopivalate (<b>2b</b>) and serotobenine cyclohexyl ether (<b>2c</b>) respectively. Two of them (<b>2a)</b> and <b>(2b)</b>, were evaluated for their antiplasmodial activity against <i>P. falciparum</i> 3D7 strain in a parasite lactate-dehydrogenase (pLDH) assay. Compound <b>2b</b> was more active than compound <b>2a</b> based on their IC<sub>50</sub> values (36.6 and 123 μM, respectively).</p>