– ER degrader 10 (Compound 51) is an orally active estrogen receptor (ER) selective degrader and antagonist, with a DC50 of 0.43 nM and an IC50 of 0.56 nM. It inhibits the proliferation of ER-positive cells, with an IC50 ranging from 0 to 15 nM. ER degrader 10 exhibits weak inhibitory activity on the hERG channel, with an IC50 greater than 40 μM. It has blood-brain barrier permeability, with a brain/plasma ratio (Kp) of 3.05. In mouse models, ER degrader 10 demonstrates antitumor activity.