Cytotoxic bisbenzylisoquinoline alkaloids from Stephania epigaea

Six new bisbenzylisoquinoline alkaloids (1-6) and seven known compounds (8-14) were isolated from the tubers of Stephania epigaea, in addition to the major alkaloid, cepharanthine (7). The structures of 1-6 were elucidated by combined spectroscopic data analysis and chemical methods, with their configurations determined from their optical rotation values and confirmed using circular dichroism. Compounds 1-6 belong to the oxyacanthine type of bisbenzylisoquinoline alkaloids and have a rare methylenedioxy substituent. Compound 1, a dimer composed of benzylisoquinoline and seco-aristolactam units, represents a new type of bisbenzylisoquinoline alkaloid, while compounds 3-6 are bisbenzylisoquinoline N-oxides. These compounds were evaluated for their in vitro cytotoxicities against six human cancer cell lines (A-549, ECA109, HL-60, MCF-7, SMMC-7721, and SW480). Cepharanthine (7), the major component of S. epigaea, exhibited cytotoxicity against all of these cancer cell lines except ECA109, while its known analogue, 10, displayed cytotoxicity against all six cancer cell lines.