New insights into the nature of short-lived paramagnetic intermediates of ketoprofen. Photo-CIDNP study

Babenko, Simon V., Polina S. Kuznetsova, Nikolay E. Polyakov, Aleksandr I. Kruppa, and Tatyana V. Leshina. “New Insights into the Nature of Short-Lived Paramagnetic Intermediates of Ketoprofen. Photo-CIDNP Study.” Journal of Photochemistry and Photobiology A: Chemistry 392 (April 2020): 112383.

The short-lived paramagnetic particles formed during the UV irradiation of nonsteroidal antiinflammatory drug – ketoprofen (KP) have been investigated using chemically induced dynamic nuclear polarization (CIDNP). This study answers the questions about the nature of paramagnetic particles which can be responsible for KP phototoxic effects. Phototoxic side effects of NSAIDs, according modern point of view, are associated with the action of free radicals, however, there is insufficient information regarding the nature of the radical species. In contrast, most ketoprofen photodegradation schemes include carbanion as a precursor of products. CIDNP effects analysis has shown that all the major products of KP photodegradation can form via radical pairs (RPs) involving benzyl (2’), ketyl (3’) and CO2H● or CO2-● free radicals and solvated electron. Radical ways of KP photodegradation include: decarboxylation via RP with benzyl radical formation (I) in nonaqueous solution and both, (I) and photoreduction with formation of ketyl radicals in the presence of water. Moreover, it was found that the photoinduced radical decarboxylation of KP represents a reversible process.

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