In a photochemical chamber, a sample of 27.9 mM indomethacin (IN) in methanol was exposed to a Philips 400-W UV lamp for 5 days in normal atmosphere. Four photoproducts were separated using high-performance liquid chromatography, and their structures were elucidated by various spectroscopic methods, including liquid chromatography–electrospray ionization–mass spectrometry. A reaction scheme of IN in methanol is proposed: The photochemical reaction routes occur mainly via esterification and decarboxylation, followed by oxidation with singlet oxygen to produce an aldehyde. A β-hydroxy-γ-lactone was also formed through a photochemical [2 + 2] cycloaddition, and its structure was confirmed by single-crystal X-ray diffraction.
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