Atenolol impurity D

Atenolol impurity D is a structurally related degradation byproduct arising from the N-deethylation of the parent β-blocker Atenolol. It retains the 4-(2-amino-1-hydroxyethyl)-1,2-benzenediol core but features an unbranched primary amine in place of the secondary ethylamine side chain, resulting in a reduced aliphatic chain. The molecule incorporates a methoxy group, a chlorinated benzene ring, and three ionizable hydroxyl functionalities. This impurity forms under acidic hydrolysis conditions during synthesis or storage, reflecting a key pathway of Atenolol’s chemical instability. It serves as an HPLC reference standard for quantifying N-deethylation-derived impurities in Atenolol formulations.