Donepezil open ring

Donepezil open ring is a structurally modified impurity derived from the parent drug donepezil through ring-opening of the 1,4-benzodiazepine core, resulting in a linearized aminocarbonyl moiety conjugated to a substituted indan backbone. This transformation disrupts the cyclic pharmacophore while retaining key substituents, including a tertiary amine and a hydroxylated aromatic ring. The compound arises via acid-catalyzed degradation pathways, generating a distinct chromophore with altered UV spectral characteristics. It serves as an HPLC reference standard for quantifying process-related impurities in donepezil formulations.