Novel tirucallane triterpenoids from the stem bark of Toona sinensis.

Phytochemical investigation on the stem bark of Toona sinensis was carried out by various chromatographic techniques resulting in the isolation and elucidation of two novel tirucallane triterpenoids, named (20S)-3-oxo-tirucalla-25-nor-7-en-24-oic acid (1) and (20S)-5α,8α-epidioxy-3-oxo-24-nor-6.9(11)-dien-23-oic acid (2), along with fifteen known triterpenoids (3-17), their structures were determined by extensive spectroscopic methods, including 1D-, 2D-NMR and HR-ESI-MS experiments. Compound 2 is uncommon in nature, which possesses a peroxide bridge cross C-5 and C-8 in the triterpenoid skeleton. All isolated compounds were evaluated for cytotoxicity against five human tumor cell lines (A-549, Hela, HepG2, SGC-7901 and SW-480), among them, compound 17 displayed strongest cytotoxic activity against A-549 cells and the results indicated that its cytotoxicity against A-549 cells was mediated by the intrinsic mitochondrial apoptotic pathway. In addition, ROS production-inhibitory activities were also evaluated, but none of them was active.