(R)-OP-1074 is an isomer of OP-1074 and can serve as a control compound in experiments. OP-1074 , a pure anti-estrogen drug, is a selective ER degrader ( PA-SERD ) with specific anti-estrogenic activity against ERα and ERβ , inhibiting 17β-estradiol (E2)-stimulated transcription with IC 50 values of 1.6 and 3.2 nM, respectively.