Cytotoxic constituents of Brachistus stramoniifolius.

Phytochemical investigation of Brachistus stramoniifolius (Kunth) Miers (formerly Witheringia stramoniifolia Kunth) (Solanaceae) was initiated following primary biological screening and in view of the absence of prior phytochemical studies conducted on this species. Fractionation of an ethyl acetate extract from the roots of the plant, guided by in vitro cytotoxic activity using cultured KB (human nasopharyngeal carcinoma) cells, led to the isolation of three known compounds of the 13,14-seco-16,24-cyclosteroid type, physalins B (1), F (2) and H (3). Their structures were characterized by comparison of their physical and spectral data to published values, with 1D- and 2D-NMR experiments being performed to assure unambiguous resonance assignments. Biological evaluation of these three compounds against a panel of human and murine cancer cell lines demonstrated their broad cytotoxic activity.