Selective formation of a phenathridine derivative by photodegradation of azilsartan

Abstract Photodegradation of azilsartan produces a phenanthridine derivative, with its molecular structure determined by 1H and 13C NMR spectroscopy. This is confirmed single-crystal X-ray diffraction alternative synthesis. The ring formation explained through the closure an imidoylnitrene intermediate produced decarboxylation 5-oxo-1,2,4-oxadiazole (oxadiazolone).