Bioactive Seco-Lanostane-Type Triterpenoids from the Roots of <i>Leplaea mayombensis</i>

Fractionation of the ethyl acetate-soluble extract of the roots of <i>Leplaea mayombensis</i> afforded two new 3,4-seco-lanostane-type triterpenoids, leplaeric acids A and B (<b>1</b>, <b>2</b>), the new lanostane-type triterpenoid leplaeric acid C (<b>3</b>), and six known natural products (<b>5</b>–<b>10</b>). Derivatization of the main constituent, <b>1</b>, afforded the dimethyl ester <b>4</b>, the monoamide <b>11</b>, and diamide <b>12</b> for SAR studies. The structures of these compounds were established through spectroscopic methods, and a single-crystal X-ray diffraction analysis was used to confirm the relative configuration of compound <b>1</b>. These lanostane derivatives are unique since they are the first C-21-oxygenated lanostanes isolated from plant sources. Preliminary biological assays against the MDA MB 231 breast cancer cell line showed that compounds <b>1</b>, <b>2</b>, <b>4</b>, and <b>11</b> have modest cytotoxic activity. Compound <b>2</b> was the most active, with an IC₅₀ of 55 ± 7 μM. From these results, the amides (<b>11</b>, <b>12</b>) derived from triterpenoid <b>1</b> were found to be less active than the derived esters (<b>2</b>, <b>4</b>)