Four new neo-clerodane diterpenes from the stem bark of Croton oligandrus.

Four new neo-clerodanes, crotonolins C-F (3-6), were isolated from the stem bark of Croton oligandrus together with the known clerodane crotonzambefuran A, the abietanes 7-ß-hydroxydehydroabietic acid and 7-oxodehydroabietic acid, and ferulic acid. Their structures were elucidated by spectroscopic analyses including 1D and 2D NMR and HRESIMS and by comparison with previously reported data. The cytotoxicity of the isolated compounds against A549, MCF7, PC3 and PNT2 cells was evaluated using the MTT assay. Only 7-ß-hydroxydehydroabietic acid showed a moderate level of activity against PC3 cells with an IC50 value of 68.9 ± 6.6 µM.