Newly Discovered Photodegradation Products of Nifedipine in Hospital Prescriptions

Abstract New photodegradation products of nifedipine ( 1 ) have been isolated. They were found in tablets dispensed in the pulverized form by hospitals.  1  decomposed 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,  1 H NMR, mass spectroscopy, melting point determination, and elementary analysis. From these analyses, it was found that  1  was converted into a  cis -azoxy derivative ( 4 ), a  trans -azoxy derivative ( 5 ), a  N ,  N ′-dioxide derivative ( 6 ) and a lactam derivative ( 7 ) in addition to  2  and a nitro derivative ( 3 ). Furthermore, it is proposed that  2  is mainly responsible for the formation of these new products ( 4 – 7 ) by photochemical condensation.