Newly Discovered Photodegradation Products of Nifedipine in Hospital Prescriptions

New photodegradation products of nifedipine (1) have been isolated. They were found in tablets dispensed in the pulverized form by hospitals.1decomposed concurrently into six components after storage of 30 days under exposure to normal room light. The main photoproduct was a nitroso derivative (2) and others were minor. Preparative thin-layer chromatography has been used to isolate the six photodegradation products. The chemical structures of these isolated compounds were identified or estimated by comparison with authentic samples and/or using UV, IR,1H NMR, mass spectroscopy, melting point determination, and elementary analysis. From these analyses, it was found that1was converted into acis-azoxy derivative (4), atrans-azoxy derivative (5), aN,N′-dioxide derivative (6) and a lactam derivative (7) in addition to2and a nitro derivative (3). Furthermore, it is proposed that2is mainly responsible for the formation of these new products (4–7) by photochemical condensation.