Antiproliferative agent-51 (Compound 18h) exhibits inhibitory efficacy against estrogen receptor α ( ERα ) mediated transcription, with an IC 50 of 1.6 nM. Antiproliferative agent-51 inhibits the proliferation of cancer cell ZR-75, with an IC 50 of 0.031 μM. Antiproliferative agent-51 exhibits antitumor efficacy in mouse models.