Cytotoxic constituents in the holdfast of cultivated Laminaria japonica

Four steroidal ketones were isolated from the holdfast of cultivated Laminaria japonica. The structures were characterized as ergosta‐4,24(28)‐diene‐3‐one (1), ergosta‐4,24(28)‐diene‐3,6‐dione (2), stigmasta‐4,24(28)‐diene‐3‐one (3) and stigmasta‐4,24(28)‐diene‐3,6‐dione (4), by spectral data. Compounds 2 and 4 were shown to be cytotoxic against the MCF‐7 human breast cancer cell, and the growth of MCF‐7 was inhibited by 96% and 79%, respectively, at 10 µg/mL. It is the first report on the isolation of cytotoxic steroidal ketones from the kelp in the genus of Laminaria.