Antitumor Agents. 239. Isolation, Structure Elucidation, Total Synthesis, and Anti-Breast Cancer Activity of Neo-tanshinlactone from <i>Salvia </i><i>m</i><i>iltiorrhiza</i>

Neo-tanshinlactone (1) was isolated and synthesized for the first time and evaluated in vitro against several human cancer cell lines. Compound 1 showed significant inhibition against two ER+ human breast cancer cell lines and was 10-fold more potent and 20-fold more selective as compared to tamoxifen citrate. Compound 1 also potently inhibited an ER-, HER-2 overexpressing breast cancer cell line. Therefore, this novel compound merits further development as an anti-breast cancer drug candidate.