Flunarizine EP Impurity D

Flunarizine EP Impurity D is a di-chlorinated analog of the parent drug, featuring a piperazine ring linked to a substituted benzothiazole core with fluorine and chlorine substitutions. Its structure incorporates two chloro groups at distinct aromatic positions compared to flunarizine, altering electronic and steric properties. This impurity arises via side-chain chlorination during synthetic pathways, retaining the piperazine-bridged scaffold but with modified halogenation patterns. It serves as a critical HPLC reference standard for quantifying process-related impurities in flunarizine formulations.