ORIGINAL ARTICLES Aurobindo Pharma Ltd. Research Centre1, Bachupally, J. N. T. University2, Kukatpally, Hyderabad, India Identification, isolation, synthesis and characterization of impurities of quetiapine fumarate Ch. Bharathi1, K. J. Prabahar1, Ch. S. Prasad1, M. Srinivasa Rao1, G. N. Trinadhachary1, V. K. Handa1, R. Dandala1, A. Naidu2 Received May 28, 2007, accepted June 18, 2007 Ramesh Dandala, Senior Vice-President, A. P. L. Research centre, 313, Bachupally, Hyderabad 500072, India [email protected] Pharmazie 63: 14–19 (2008) doi: 10.1691/ph.2008.7174 In the process for the preparation of quetiapine fumarate (1), six unknown impurities and one known impurity (intermediate) were identified ranging from 0.05–0.15% by reverse-phase HPLC. These impu- rities were isolated from crude samples using reverse-phase preparative HPLC. Based on the spectral data, the impurities were characterized as 2-[4-dibenzo[b,f ][1,4]thiazepine-11-yl-1-piperazinyl]1-2-etha- nol (impurity I, desethanol quetiapine), 11-[(N-formyl)-1-piperazinyl]-dibenzo[b,f ][1,4]thiazepine (impur- ity II, N-formyl piperazinyl thiazepine), 2-(2-hydroxy ethoxy)ethyl-2-[2-[4-dibenzo[b,f ][1,4]thiazepine-11- piperazinyl-1-carboxylate (impurity III, quetiapine carboxylate), 11-[4-ethyl-1-piperazinyl]dibenzo [b,f ][1,4] thiazepine (impurity IV, ethylpiperazinyl thiazepine), 2-[2-(4-dibenzo[b,f ][1,4]thiazepin-11-yl-1-piperazi- nyl)ethoxy]1-ethyl ethanol [impurity V, ethyl quetiapine), 1,4-bis[dibenzo[b,f ][1,4]thiazepine-11-yl] piper- azine [impurity VI, bis(dibenzo)piperazine]. The known impurity was an intermediate, 11-piperazinyl- dibenzo [b,f ][1,4]thiazepine (piperazinyl thiazepine). The structures were established unambiguously by independent synthesis and co-injection in HPLC to confirm the retention times. To the best of our knowledge, these impurities have not been reported before. Structural elucidation of all impurities by spectral data (1H NMR, 13C NMR, MS and IR), synthesis and formation of these impurities are dis- cussed in detail. 1. Introduction 2. Investigations, results and discussion Quetiapine fumarate (1) is an antipsychotic drug belonging 2.1. Detection and identification to the chemical class of dibenzothiazepine derivatives. It is Quetiapine fumarate was analysed by HPLC under the ana- used as a hemifumarate salt. Its IUPAC name is 2-[2-(4- lytical conditions described below. The chromatogram dis- dibenzo[b,f ][1,4]thiazepin-11-yl-1-piperazinyl)ethoxy etha- played seven peaks at relative retention times compared to nol, (E)-2-butenedioate (2 : 1) salt. A literature survey re- quetiapine at 0.80, 0.94, 1.08, 1.17, 1.65, 1.67 and 2.28. vealed various methods for the synthesis of quetiapine (War- The LC-MS analysis showed six peaks having m/z values awa et al. 2001). We synthesized the compound according to 339, 323, 427, 323, 411 and 504. They were isolated from the Scheme (Warawa and Migler 1989) with modifications crude samples of quetiapine by preparative HPLC. All the to make it simpler and commercially viable. Its molecular compounds were co-injected with quetiapine fumarate sam- formula is (C H N O S) ÁC H O and molecular weight 21 25 3 2 2 4 4 4 ple in HPLC to confirm the retention times. HPLC chroma- is 883 amu as fumarate salt and 383 amu as base. togram of quetiapine fumarate spiked with all impurities is HPLC methods (Saracino et al. 2006; Mandrioli et al. 2002) shown in the Fig. Synthesis and structural elucidation of and a HPLC-electrospray ionization mass spectrometric these impurities are discussed in the following sections. method (Zhou et al. 2004) were reported for the determi- Quetiapine fumarate was synthesized as shown in the nation of quetiapine in human plasma. Scheme, impurities I–VI were synthesized as described in During the preparation of 1 in the laboratory, six unknown the Experimental section and characterized. impurities were detected in HPLC along with one known impurity. A comprehensive study was undertaken to iso- late, synthesize and characterize these impurities by spec- 2.2. Characterization and origin of impurities troscopic techniques. An impurity profile study is neces- 2.2.1. Impurity I sary for any final product to identify and characterize all the unknown impurities that are present in level of >0.1%. The ESI mass spectrum of impurity I displayed the proto- (ICH guideline, 2005). The present study describes the nated molecular ion at m/z 340. Therefore the molecular isolation, synthesis and characterization of related impuri- weight of this impurity was considered as 339 which was ties of 1. less by 44 amu than quetiapine. The odd molecular weight 14 Pharmazie 63 (2008) 1 ORIGINAL ARTICLES Scheme H O Cl N N i. Piperazine / Toluene POCl3 /Et3N/Toluene ii.Ethanol/HCl S S H O N N OH N N N i. 2-(2-Chloroethoxy)ethanol N ii. Na2CO3 /NaI/NMP/Toluene .2HCl S S Piperazinyl thiazepine (2) 4 1 5 O N 3 2 OH 7 6 23 N COOH 8 22 Fumaric acid / Ethanol 20 N 9 21 . 22 19 10 11 23 HOOC 18 16 12 17 S 15 14 13 2 Quetiapine fumarate (1) indicated the presence of odd number of nitrogens which azinyl thiazepine with the impurity, 2-chloro ethanol leads in turn indicated the intactness of dibenzo[b,f ][1,4]thia- to the formation of impurity I (desethanol quetiapine). zepine piperazinyl ring in this impurity structure. Pre- sence of broad signals at 3.70 ppm (4 H) and 4.34 ppm 2.2.2. Impurity II (4 H) in 1H NMR spectrum was attributed to piperazinyl ring. Two triplets were observed in impurity spectrum at ESI mass spectrum of impurity II exhibited a protonated 3.39 ppm and 3.89 ppm corresponding to 2 Â CH2 sig- molecular ion peak at m/z 324, indicating the molecular nals instead of 4 Â CH2 groups present in the side chain weight as 323. The molecular weight of impurity II was 28 13 of quetiapine. In C NMR two CH2 signals were ob- amu more than that of the intermediate, 4-piperazinyl di- served at 61.1 ppm and 73.1 ppm instead of four CH2 benzo[b,f ][1,4]thiazepine (2), m/z 295. MS fragmentation signals. Based on the above spectral data observations, peaks were observed at m/z 296 and 251. 1H NMR spec- the structure of impurity I was characterized as 2-[4-di- trum of this impurity showed signals similar to those of 2 benzo[b,f ][1,4]thiazepine-11-yl-1-piperazinyl] l-2-ethanol and in addition one new signal was observed at 8.13 ppm (desethanol quetiapine). integrated to one proton which was not exchangeable. This 2-[2-Chloroethoxy]ethanol is a raw material for the pre- data suggested the attachment of a ––CHO group on piper- paration of quetiapine. 2-Chloroethanol may be present as azine NH. Based on the spectral data, the structure of im- an impurity in this raw material. During the alkylation purity II was characterized as 11-[(N-formyl)-1-piperazi- step in the preparation of quetiapine, alkylation of piper- nyl]-dibenzo[b,f ][1,4]thiazepine (N-formyl piperazinyl O 22 5 4 O 1 4 CHO NO22 OH 5 OH 7 3 2 N 5 N 6 3 N 7 6 7 6 N 9 8 N N 20 21 8 8 10 N 9 11 N 9 11 19 11 12 20 21 10 20 21 10 12 12 18 16 S 15 13 19 19 17 13 13 14 16 S 15 16 S 15 18 14 17 18 17 14 Impurity I (Desethanol quetiapine) Impurity II (N-Formyl piperazinyl thiazepine) Impurity III (Quetiapine carboxylate) 17 18 14 16 S 15 13 19 12 20 21 4 1 10 11 4 3 5 O 22 23 N 9 5 CH3 N OCH2CH3 N N 7 3 2 6 5 6 7 6 N 7 8 N N 9 8 N 8 20 21 N 9 11 10 11 N 9' 11' 20 21 10 19 12 20' 21' 10' 12 12' 19 18 16 S 15 13 19' 13 16 S 15 17 14 16' S 15' 13' 18 14 17 18' 17' 14' Impurity IV (N-Ethylpiperazinyl thiazepine) Impurity V ( Ethyl quetiapine) Impurity VI (Bis (dibenzo) piperazine) Pharmazie 63 (2008) 1 15 ORIGINAL ARTICLES Fig.: LC-Chromatogram of Quetiapine fumarate sample spiked with impurities thiazepine). This impurity arises when the alkylation of pi- ture of impurity III was characterized as 2-(2-hydroxy perazinyl thiazepine with 2-chloroethoxyethanol is carried ethoxy)ethyl-2-[2-[4-dibenzo[b,f ][1,4]thiazepine-11-piper- out in N,N-dimethyl formamide. azinyl-1-carboxylate (quetiapine carboxylate). This impurity arises when the alkylation of piperazinyl thiazepine is car- ried out in the presence of sodium carbonate (quetiapine 2.2.3. Impurity III carboxylate). ESI mass spectrum of impurity III displayed a protonated molecular ion peak at m/z 428, indicating the molecular 2.2.4. Impurity IV weight of the compound as 427 which is 44 amu more than quetiapine. MS fragmentation peaks were observed at ESI mass spectrum of this impurity exhibited a protonated m/z, 384, 340 and 324. After thorough study of 1H NMR molecular ion peak at m/z 324 indicated the molecular and 13C NMR spectra of this impurity, it was found to be weight of this impurity as 323. Molecular weight of this as carboxy group attachment. It was observed from the 1H impurity is 28 amu more than that of 11-piperazinyl thi- NMR spectrum that there was no change in the number of azepine (intermediate).