Nisoldipine Impurity-III

Nisoldipine Impurity-III is a dihydropyridine derivative featuring a 1,4-dihydropyridine core substituted with 2-methyl-5-(2-nitrophenyl) groups, lacking the methoxy moiety at the 4-position characteristic of parent nisoldipine. Its structure incorporates a nitro-substituted aromatic ring conjugated to the pyridine framework, with a saturated cyclic linkage between positions 1 and 6. This impurity arises via oxidative degradation of the methoxy ether under acidic conditions, resulting in a stable aromatic nitro compound. The absence of the 4-methoxy group alters lipophilicity and metabolic stability compared to the parent API. Functions as a critical HPLC reference standard for quantifying degradation pathways in nisoldipine formulations.