Atenlol Imp E

Atenlol Imp E is a structurally related impurity of the beta-blocker Atenolol, characterized by a substituted 4-hydroxycinnamic acid moiety linked via a methylene bridge to a diaminobutyric acid scaffold. The compound retains the core aromatic ring and hydroxyl functionality of Atenolol but features an additional methoxy group at the para-position of the benzene ring and a truncated side chain lacking the terminal hydroxyl. This impurity arises from an incomplete alkylation step during Atenolol synthesis, resulting in a stable, non-degradative byproduct. It serves as a critical HPLC reference standard for quantifying process-related impurities in Atenolol drug substance batches.