YC-1 binds to estrogen receptor α. (A) Chemical structures of WAY-169916, WAY6 and YC-1. (B) Predicted binding mode of YC-1 (purple) in the partially constrained conformation of estrogen receptor α (ERα) (chain A, Protein Data Bank code 3OS8 [Swiss-Prot:P03372]). The binding mode of WAY6 (white sticks) is shown as a reference. (C) The results of the ERα agonist fluoligand assay using YC-1 are shown, along with the concentration–inhibition curve with duplicates. *YC-1 was not completely soluble at concentrations >100 μM.