Lactam Triterpenoids from the Bark of Toona sinensis

Three new limonoid-type triterpenoids, namely toonasins A–C (1–3) with a rare lactam E ring, along with six known compounds (4–9) were isolated from the barks of Toona sinensis. The structures of new compounds were elucidated by interpretation of spectroscopic data, and the relative configuration of compound 1 was further characterized by X-ray crystallographic analyses. The isolated compounds were evaluated for their cytotoxic activities against five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7 and SW480), and compounds 3 and 5 showed weak cytotoxicities.