4-Hydroxy Ospemifene(M1)(E and Z mixture)

4-Hydroxy Ospemifene(M1)(E and Z mixture) is a geometric isomeric impurity derived from ospemifene via hydroxylation at the 4-position of the aromatic ring. The compound retains the core 4-[(5-phenoxy-1H-pyrazol-3-yl)oxy]benzene-1,2-diol scaffold, with the hydroxyl substitution introducing steric and electronic asymmetry. The E/Z configuration refers to the double bond in the pyrazole side chain, generating diastereomeric forms that coexist in equilibrium. This impurity arises during oxidative degradation pathways of the parent drug. It serves as an HPLC reference standard for quantifying process-related impurities in ospemifene formulations.