ESR2 and breast carcinoma: The conjugate 28 in the series was the most promising compound in the study, with potent antiproliferative activity in MCF-7 human breast cancer cell line (IC50: 5 nM), low cytotoxicity and impressive ER competitive binding IC50 values (ERα: IC50 0.9 nM; ERβ: IC50 4.7 nM).