Photolysis of NSAIDs. IV. Photoproducts of zomepirac determined by LC-ESI-MS

A sample of 10 mM zomepirac in methanol was photo-irradiated with a Hanovia 200 W high-pressure quartz Hg lamp for 14 days. In total, four photoproducts were observed from the HPLC chromatogram, The preparative HPLC included an YMC-Pack Pro C₁₈ column (250 × 20 mm i.d.), a mobile phase of CH₃CN-CH₃OH-1% HOAc (10:60:30, v/v/v), and UV detection at 254 mn. The most probable structures of the four photoproducts were determined by LC-MS. Two major photoproducts were separated, and their structures were further confirmed by the spectroscopic methods. A reaction scheme of zomepirac was proposed that the photochemical reaction routes occur mainly via bond fission between carbonyl-pyrrolyl groups (α-cleavage of a ketone), and decarboxylation followed by oxidation with singlet oxygen to produce an aldehyde.