Isolation, identification, and characterization of 17-oxo dexamethasone, an oxidative degradation impurity of dexamethasone using flash chromatography and NMR/HRMS/IR

摘要

Some formulations of dexamethasone available in the market require ?radiation sterilized dexamethasone active pharmaceutical ingredient (API). A new impurity was detected in the ?radiation sterilized dexamethasone API and determined using gradient ultra performance liquid chromatography (UPLC) method with UV detection. This impurity was identified as the major peroxide degradation impurity of dexamethasone. This impurity standard was consequently isolated via oxidative degradation followed by flash liquid chromatography (LC) method. Using high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), and infrared (IR) study the impurity was identified as 17-oxo dexamethasone (dexamethasone 17-ketone). In this method, about 600 mg of relatively pure 17-oxo dexamethasone impurity (chromatographic purity: 99.34% w/w by LC) was obtained with 1000 mg of extract loaded. This isolated 17-oxo dexamethasone impurity served as external standard for determination of percentage amounts of this impurity present in dexamethasone API and various formulation of dexamethasone. Several HPLC methods were developed and reported for the determination of dexamethasone and its related substances using UV detection. But till now there are no reports on isolation and characterization of 17-oxo dexamethasone formed during ?radiation sterilized dexamethasone API.