Cabazitaxel Impurity: 3,5-Oxazolidinedicarboxylic acid, 2-(4-methoxyphenyl)-4-phenyl-, 5-[(2aR,4S,4aS,6R,9S,11S,12S,12aR,12bS)-12b-(acetyloxy)-12-(benzoyloxy)-2a,3,4,4a,5,6,9,10,11,12,12a,12b-dodecahydro-11-hydroxy-4a,8,13,13-tetramethyl-5-oxo-4,6-bi.