Determination of the impurity profile of ethyl-2-(4-[(5R)-3[4-(methoxycarboxamidoiminomethyl)-phenyl]-2- oxo-5-oxazolidinylmethyl]-1-piperazinyl) acetate, citrate, a highly active platelet aggregation inhibitor, by liquid chromatography-mass spectrometry.

Ethyl-2-(4-[(5R)-3-[4-(methoxycarboxamidoiminomethyl)-phenyl] -2-oxo-5-oxazolidinylmethyl]-1-piperazinyl) acetate, a glycoprotein IIb/IIIa antagonist, is a drug substance of the oxazolidinone type from Merck's research to be developed for the chronic oral treatment of thrombotic disorders. For the separation of the byproducts in the bulk drug substance, a reversed-phase HPLC gradient separation was developed. The eluent consisting of a nonvolatile phosphate buffer system had to be changed to a volatile acetate buffer system in order to perform on-line LC-MS coupling.With a triple quadrupole system it was possible to characterize most of the unknown byproducts occuring during synthesis and during scale-up to kg amounts of the bulk drug substance.