Bioactive Seco-Lanostane-Type Triterpenoids from the Roots of Leplaea mayombensis

Fractionation of the ethyl acetate-soluble extract of the roots of Leplaea mayombensis afforded two new 3,4-seco-lanostane-type triterpenoids, leplaeric acids A and B (1, 2), the new lanostane-type triterpenoid leplaeric acid C (3), and six known natural products (5–10). Derivatization of the main constituent, 1, afforded the dimethyl ester 4, the monoamide 11, and diamide 12 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 1. 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 1, 2, 4, and 11 have modest cytotoxic activity. Compound 2 was the most active, with an IC50 of 55 ± 7 μM. From these results, the amides (11, 12) derived from triterpenoid 1 were found to be less active than the derived esters (2, 4).