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 …