Identification and characterization of potential impurities of quetiapine fumarate.

Seven potential impurities, including by-products, starting materials and intermediates were identified in pharmaceutical substance quetiapine fumarate and characterized by spectroscopic methods (MS, IR, NMR). Based on these methods the structures of the impurities were assigned or confirmed as: impurity I: 2-(phenylthio)aniline; impurity II: phenyl N-[2-(phenylthio)phenyl]carbamate; impurity III: N,N'-bis[2-(phenylthio) phenyl]urea; impurity IV: N-[2-(phenylthio)phenyl]-1-piperazinecarboxamide hydrochloride; impurity V: N,N'-bis[(2-phenylthio)phenyl]-1,4-piperazinedicarboxamide; impurity VI: 11-(1-piperazinyl) dibenzo[b,f][1,4]thiazepine fumarate; impurity VII: 1,4-bis(dibenzo[b,f][1,4] thiazepin-11-yl)piperazine. Structural elucidation of compounds, proposed MS fragmentation pathway and possible ways of formation of the impurities are also discussed.