Isolation and characterization of impurities in docetaxel

During the process development of docetaxel, two polar impurities (Impurities I and II) and two non-polar impurities (Impurities III and IV) were detected by high performance liquid chromatography (HPLC). All the impurities were isolated by Medium Pressure Liquid Chromatography (MPLC). The Impurities I, II, III and IV were identified as 13-[(4S,5R)-2-oxo-4-phenyl-oxazolidine-5-carboxy]-10-deacetyl baccatin III ester, 2'-epi docetaxel, 7-epi docetaxel and 13-[(4S,5R)-2-oxo-4-phenyl-oxazolidine-3,5-dicarboxyl-3-tert-butyl)]-10-deacetyl baccatin III ester, respectively, based on one- (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy data. The Impurity IV was crystallized and the structure was solved by single crystal X-ray diffraction (XRD). Two impurities (Impurities II and III) were found to be process related, while the remaining two impurities (Impurities I and IV) turned out to be isomers. The formation of these impurities was discussed.