Identification of flurbiprofen and its photoproducts in methanol by gas chromatography–mass spectrometry

Abstract

A sample of 10 mM flurbiprofen in methanol (or ethanol) was photoirradiated with sixteen 8 W low-pressure quartz mercury lamps irradiated at 306 nm in a Panchum PR-2000 photochemical reactor. In total, four major photoproducts derived from each sample were observed from the HPLC chromatogram. The photoproducts were separated and their structures elucidated by various spectroscopic methods. Alternatively, using GC-MS, 11 major photoproducts were observed. A reaction scheme of flurbiprofen in methanol is proposed: the photochemical reaction routes occur mainly via esterification and decarboxylation, followed by oxidation with singlet oxygen to produce a ketone, alcohols and other derivatives.

Time-Resolved Spectroscopic Characterization of a Novel Photodecarboxylation Reaction Mediated by Homolysis of a Carbon α-Bond in Flurbiprofen

“…40 Wu and co-workers also performed characterization experiments for Fp irradiated in methanol and identified four major photoproducts, which they presumed to be derived by esterification and decarboxylation and thus proposed a simple degradation mechanism. 41 To simplify analysis of the reactive intermediates and reaction mechanisms involved in the photochemistry of Fp, we have focused here on the photoreaction mechanism in MeCN solution which mainly produces 97% photoproduct 1 that is also the major product (87%) observed after photoexcitation in CH 3 OH and also a significant product (23%) in the PBS solution. 40 The work here will serve as an initial step to better understand the photochemistry of Fp in solution-phase environments and can be used later to help elucidate the more complex competing reactions that take place in a PBS solution where three significant photoproducts (1 (23%), 3 (50%), and 4 (27%)) are observed compared to mainly 97% photoproduct 1 in the MeCN solution.…”

“…Furthermore, in biological systems, Bp has been extensively used as photophysical probes to identify and map peptide–protein interactions . In early studies, the research groups of Wan and Scaiano independently proposed Kp decarboxylation mechanisms in which a radical versus a carbanion can be prone to act as the intermediate that is from decarboxylation based on multiple lines of experimental evidence. − Later, Phillips and co-workers directly observed these carbanion and biradical intermediates by femtosecond transient absorption spectra (fs-TA) and TR 3 , which elucidated the decarboxylation mechanism of Kp by heterolytic cleavage of a carbon–carbon bond (see Scheme ). , With regard to TPA and Sp, decarboxylation mechanisms similar to that of Kp have been put forward by Miranda and co-workers. , In contrast, limited investigations ,− were directed toward illuminating the detailed photodegradation mechanisms of Fp, due to the highly complex deactivation routes of the lowest lying excited singlet S 1 involving fluorescence emission back to the ground state, transformation to the lowest lying excited triplet T 1 via intersystem crossing (ISC) with high quantum yields, and a plausible photodecarboxylation reaction. In addition, a unique feature for Fp degradation compared with those of other NSAIDs (Kp, Sp, TPA, etc.)…”

“…This and the observation of a new product 3 in the PBS solution indicate that the solvent has an important effect on the photoreaction . Wu and co-workers also performed characterization experiments for Fp irradiated in methanol and identified four major photoproducts, which they presumed to be derived by esterification and decarboxylation and thus proposed a simple degradation mechanism . To simplify analysis of the reactive intermediates and reaction mechanisms involved in the photochemistry of Fp, we have focused here on the photoreaction mechanism in MeCN solution which mainly produces 97% photoproduct 1 that is also the major product (87%) observed after photoexcitation in CH 3 OH and also a significant product (23%) in the PBS solution .…”