darifenacin R-Isomer

Darifenacin R-Isomer is the non-pharmacologically active enantiomer of the muscarinic antagonist darifenacin, characterized by the R-configuration at the chiral piperidin-4-ol center. Its structure incorporates a 3,5-dibromo-4-hydroxyphenyl moiety linked via a methylene bridge to a piperidine ring bearing an N-benzyl substitution. The compound retains the core brominated aromatic and ester functionalities of the parent drug but exhibits inverted stereochemistry at the key stereocenter, rendering it inert to muscarinic receptor interactions. This impurity arises during asymmetric synthesis or resolution processes of darifenacin. It serves as a critical HPLC reference standard for enantiomeric purity assessment in API manufacturing.