LC-Q/TOF-HRMS and NMR Based Structural Characterization of the Major Photodegradation Impurity of Difluprednate

Difluprednate (DFL) is a corticosteroid used topically, especially in the form of emulsion for the treatment of inflammation and pain associated with ocular surgery. Till date, photodegradation of DFL has not been reported in any literature. In this study, a major unknown degradation product was observed after exposure of DFL solution to UV light. Isolation and quantification of this degradation product were performed using RP-HPLC. This major photodegradation product was isolated by using semi-preparative RP-HPLC and its structure was elucidated using mass spectrometry (LC-Q/TOF-HRMS), one and two-dimensional NMR experiments and FT–IR spectroscopy. Based on spectral data, the unknown species was identified as a rearrangement product of the steroid ring, followed by photo-induced elimination of hydrogen fluoride to its final degradant product. The findings of this study can be employed in order to achieve mass balance during photodegradation and to finalize packaging material for storage.