ATORVASTATIN CYCLIC(FLUOROPHENYL)SODIUM SALT IMPURITY

3H-Oxireno[3,4]pyrrolo[2,1-b][1,3]oxazine-3-butanoic acid, 1b-(4-fluorophenyl)hexahydro-β,7-dihydroxy-7-(1-methylethyl)-1a-phenyl-7a-[(phenylamino)carbonyl]-