Isolation and structural elucidation of two impurities from a diacerein bulk drug.

Two impurities were found in the crude sample of diacerein. The level of these impurities 1.14% and 1.24% were detected by isocratic reverse-phase high performance liquid chromatography (HPLC). The molecular weights of the impurities were determined by liquid chromatography-mass spectroscopy (LC-MS) analysis. These impurities were isolated from crude sample of diacerein by reverse-phase preparative liquid chromatography. These impurities were characterized as 5-acetoxy-4-hydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxylic acid (Impurity-1) and 4-acetoxy-5-hydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxylic acid (Impurity-2) respectively. Structural elucidation of both the impurities were carried out by (1)H NMR, (13)C NMR, DEPT, 1D NOESY, MS and IR spectroscopy.