Photodegradation Products of New Dihydropyridine Derivatives

Photodegradation of two dihydropyridine compounds has been studied in accordance with the recommendations of the first version of the ICH guidelines. Photodecomposition was monitored by UV–visible spectroscopy, LC, and LC–MS. Quantum yields and kinetic data were obtained for the photochemical reactions. The new dihydropyridine derivatives were found to decompose into different numbers of photoproducts with different rate constants. The derivative with two chlorine atoms in the phenyl ring proved to be more stable than the nitro derivative.