Investigation into the Formation of the Genotoxic Impurity Ethyl Besylate in the Final Step Manufacturing Process of UK-369,003-26, a Novel PDE5 Inhibitor

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• 作者：Yousef Hajikarimian ; Steve Yeo ; Robert W. Ryan ; Philip Levett ; Christopher Stoneley ; Paul Singh
• 刊名：Organic Process Research & Development
• 出版年：2010
• 出版时间：July 16, 2010
• 年：2010
• 卷：14
• 期：4
• 页码：1027-1031
• 全文大小：179K
• 年卷期：v.14,no.4(July 16, 2010)
• ISSN：1520-586X

文摘

Sulfonate esters have a demonstrated potential for genotoxicity, and therefore their potential presence at trace levels in active pharmaceutical ingredients (APIs) has recently raised concerns [ Mesylate Ester Type Impurities Contained in Medicinal Products; Swissmedic Department for Control of the Medicinal Products Market, 23rd October 2007 and Hoog, T. J.-d. Request to Assess the Risk of Occurrence of Contamination With Mesilate Esters and Other Related Compounds in Pharmaceuticals; Coordination Group for Mutual Recognition-Human Committee (CMDh), EMEA/CMDh/98694/2008: London, 27 February, 2008, ]. Sulfonate salts however, offer useful modification of physicochemical properties of active pharmaceutical ingredients (APIs) containing basic groups such that their use can at times offer significant advantages over other counterions [Elder, D. P.; Delaney, E.; Teasdale, A.; Eyley, S.; Reif, V. D.; Jacq, K.; Facchine, K. L.; Oestrich, R. S.; Sandra, P.; David, F.The Utility of Sulfonate Salts in Drug Development. J. Pharm. Sci. 2010, 99, 2948−2961; DOI: 10.1002/jps.22058]. Indeed, the choice of benzenesulfonic acid as the counterion for the UK-369,003 API afforded many advantages over other salts such as citrate, hydrochloride, tartrate, and phosphate as well as other sulfonate salts such as tosylate, camsylate, and mesylate. The manufacturing route to the API consists of two C−C bond-forming steps (steps 1 and 2/Scheme 1) and a final salt-formation step (step 3/Scheme 1). The step 2 cyclisation process involves the use of ethanol as the reaction solvent. Residual levels of ethanol in the isolated product of the step 2 process was initially thought to be responsible for the formation of low levels of the genotoxic impurity ethyl besylate (ppm levels) during the final step salt-formation process [Glowienke, S.; Frieauff, W.; Allmendinger, T.; Martus, H. J.; Suter, W.; Mueller, L. Mutat Res. 2005, 581, 23−34]. This was thought to result from subsequent reaction of residual ethanol with benzenesulfonic acid used in the final step (step 3). On the basis of this mechanistic hypothesis, the levels of residual ethanol in the isolated product from step 2 were controlled so that formation of ethyl besylate would be minimised or avoided in the final step. Spiking experiments coupled with deuterium labelling studies have shed doubt on this mechanism of formation. Our experimental results indicate that levels of ethyl besylate in the API are independent of the level of residual ethanol in the step 2 product (UK-369,003 free base) and are detected when higher than stoichiometric amounts of benzenesulfonic acid are used in the salt-formation process (step 3). This is thought to be due to a reaction between the excess benzenesulfonic acid and the ethoxy side chain of the API. Sensitive and selective analytical methods were also developed to detect and quantify subppm and higher levels of ethyl besylate and deuterated analogues.