Melia is a genus of flowering trees in the mahogany family, Meliaceae. Toosendanone A (1), a new euphane (tirucallane)-type triterpene bearing a five-membered ring in the side chain and the first cyclopentanyl protolimonoid, was isolated from the bark of Melia toosendan, along with two new tirucallanes, toosendanic acids A (2) and B (3). The structure and absolute configuration of compound 1 was elucidated by spectroscopic data interpretation and X-ray diffraction analysis. Compounds 1-3 were evaluated for cytotoxicity against a small panel of cancer cell lines. Trees or shrubs, usually deciduous. Young parts usually covered with stellate trichomes. Branchlets with obvious leaf scars and lenticels. Leaves in spirals, 2- or 3-pinnate; leaflets with petiolules; leaflet blades with margin usually dentate or sometimes entire. Thyrses axillary, much branched, consisting of several dichasia.