Atorvastatin calcium oxidative degradation products

4- [6- (4-Fluoro-phenyl) -6-hydroxy-1b-isopropyl-6a-phenyl-1a-phenylcarbamoyl-hexahydro-1,2-dioxa-5a-azacyclopropa [a] inden-3-yl] acid -3- (R) -hydroxy-butyric.