Cabazitaxel Impurity 45

(2aR,4S,4aS,6R,9S,11S,12S,12aR,12bS) -12b-acetoxy-9- (((2S,3S) -3- ((tert-butoxycarbonyl) amino) -2-hydroxy-3-phenylpropanoyl) oxy) -11-hydroxy-4,6-dimethoxy-4a,8,13,13-tetramethyl-5-oxo-2a,3,4,4a,5,6,9,10,11,12,12a,12b-dodecahydro-1H-7,11-methanocyclodeca[3,4]benzo[1,2-b]oxet-12-yl benzoate