A laser flash photolysis study on fenofibric acid

Article abstract of DOI:10.1111/j.1751-1097.1999.tb08293.x

Fenofibric acid (FA) is a photosensitizing drug used in the treatment of hyperlipidemia. This compound follows two different photodegradation pathways: the free acid exhibits the typical benzophenone photoreactivity, while its sodium salt undergoes photodecarboxylation via a triplet biradical, that undergoes intramolecular electron transfer to form a carbanion, or cyclization to give an intramolecular light-absorbing transient (LAT). The obtained photoproducts are explained as the result of protonation of the carbanion, ring opening of the LAT with rearrangement or oxygen trapping of any of the triplet intermediates. The above mechanism is supported by direct detection of the triplet state of FA and two long-lived intermediates in laser flash photolysis experiments. The triplet lifetime of the carboxylate form in methanol is 0.06 μs; by contrast, in the case of the free acid, it is 10 times longer. The benzophenone moiety is clearly the key chromophore involved in the photobehavior of FA.