4-Hydroxy Atorvastatin Lactone

4-Hydroxy Atorvastatin Lactone is a degradation byproduct of Atorvastatin, characterized by a hydroxyl substitution at the 4-position of the lactone ring, which disrupts the parent drug's core HMG-CoA reductase inhibitory scaffold. The molecule retains the fluorinated phenyl group and pyrrole-fused indane moiety of Atorvastatin but features an oxidized lactone ring and a 4-hydroxyl group, introducing steric and electronic asymmetry. This impurity arises via hydrolytic cleavage and subsequent oxidation of the Atorvastatin lactone, forming a stable cyclic ester with altered pharmacokinetic properties. It serves as a critical HPLC reference standard for quantifying oxidative degradation pathways in Atorvastatin formulations.