Tolterodine lactone Impurity

Tolterodine lactone impurity is a cyclic ester derivative arising from the intramolecular esterification of a hydroxycarboxylic acid intermediate in the synthesis of tolterodine. It features a γ-lactone ring fused to a substituted piperidine and a 1,2-benzodioxole moiety, retaining the core aromatic framework of the parent drug. The compound lacks the quaternary ammonium salt characteristic of tolterodine, instead forming a five-membered lactone cycle via ester linkage between a γ-hydroxy and α-carboxy group. This impurity serves as an HPLC reference standard for quantifying lactone-related degradation byproducts in tolterodine APIs.