The identification of related substances in 9α-fluoroprednisolone-21 acetate by means of high-performance liquid chromatography with diode array detector and mass spectrometry

Abstract

A method for the analysis and identification of the principal related substances in 9α-fluoroprednisolone acetate is described. This compound has been chosen as a model for the investigation of related substances which can be originated in the general procedure for introducing a fluorine substituent at position 9 of a corticosteroid molecule. HPLC procedures, both in reversed and in normal phase were used; a rapid scanning UV detector which allows direct spectrophotometric data to be obtained on chromatographic peaks, proved to be a tool of great importance. Thus, after reversed-phase chromatographic separation and observation of the UV spectra and their respective second derivatives, it was possible to characterize some of the principal effective and potential related substances such as 9α-fluorohydrocortisone acetate, 9α-bromoprednisolone acetate, 9β, 11β-epoxyprednisolone acetate and 9(11)-dehydroprednisolone acetate, emerging as chromatographic peaks. Identification of 9α-bromoprednisolone acetate and of 9α-fluorohydrocortisone acetate which proved to be the most significant impurities, was confirmed by means of an exhaustive study of the mass spectra of these substances conveniently isolated by normal-phase HPLC. The chromatographic, spectrophotometric and mass-spectrometric characteristics of the studied compounds are reported.