Atorvastatin related compound A is a calcium salt derived from the hydrolytic cleavage of the lactone ring in the parent drug's core structure, featuring a substituted pyrrole fused to an indole moiety. Its structure retains the characteristic 2-(4-fluorophenyl)ethyl group but incorporates a carboxylate functionality in place of the cyclic ester, alongside hydroxyl and ketone groups. This impurity arises via non-enzymatic degradation under alkaline conditions during API synthesis. It serves as a critical HPLC reference standard for quantifying process-related impurities in atorvastatin calcium formulations.
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