Specifically, they showed that the orientation of 3-R-methylpyrrolidine 13a was responsible for the compound being a pure ERα (estrogen receptor α) antagonist and a selective ER degrader (PA-SERD) for the treatment of breast cancer, opposite to the 3-S-methylpyrrolidine 13b and the unsubstituted derivative 14. This evidence concerns the gene ESR1 and breast carcinoma.