Amlodipine EP Impurity C is a chloro-substituted dihydropyridine derivative featuring a pyridine ring fused to a partially hydrogenated 1,4-dihydropyridine core, with a methyl ester functionality and a 2-methoxyphenyl substituent. The compound retains the parent drug's aminopropyl side chain but incorporates a chlorine atom at the 4-position of the dihydropyridine ring, distinguishing it from amlodipine. This structural modification arises from a side reaction during synthetic amination steps, leading to chlorinated byproducts. The impurity serves as a critical HPLC reference standard for quantifying process-related impurities in amlodipine bulk drug substance.
