RAPID COMMUNICATIONS Crystallization Using Reverse Micelles and Water-in-Oil Microemulsion Systems: The Highly Selective Tool for the Purification of Organic Compounds from Complex Mixtures ALEN KLJAJIC, 1 MARIJA BESTER-ROGAC, 2 ANDREJ KLOBCAR, 1 ROK ZUPET, 3 STANE PEJOVNIK 2 1 Farma GRS, d.o.o., Novo Mesto 8000, Slovenia 2 University of Ljubljana, Faculty of Chemistry and Chemical Technology, Ljubljana 1000, Slovenia 3 Krka, d.d., Novo Mesto 8501, Slovenia Received 2 August 2012; revised 8 October 2012; accepted 24 October 2012 Published online 18 November 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jps.23376 ABSTRACT: The active pharmaceutical ingredient orlistat is usually manufactured using a semi-synthetic procedure, producing crude product and complex mixtures of highly related impurities with minimal side-chain structure variability. It is therefore crucial for the overall success of industrial/pharmaceutical application to develop an effective purification process. In this communication, we present the newly developed water-in-oil reversed micelles and microemulsion system-based crystallization process. Physiochemical properties of the presented crystallization media were varied through surfactants and water composition, and the impact on efficiency was measured through final variation of these two parameters. Using precisely defined properties of the dispersed water phase in crystallization media, a highly efficient separation process in terms of selectivity and yield was developed. Small-angle X-ray scattering, high-performance liquid chromatography, mass spectrometry, and scanning electron microscopy were used to monitor and analyze the separation processes and orlistat products obtained. Typical process characteristics, especially selectivity and yield in regard to reference examples, were compared and discussed. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:330–335, 2013 Keywords: separation science; crystallization; colloid; surfactants; micelle; w/o microemulsion-based crystallization; related impurities; orlistat; SAXS; LC–MS INTRODUCTION (S)-((S)-1-((2S,3S)-3-Hexyl-4-oxooxetan-2-yl)tridecan- 2-yl) 2-formamido-4-methylpentanoate, also known as orlistat or tetrahydrolipstatin, is an active phar- maceutical ingredient (API) used in the treatment of obesity. 1 The drug is marketed as a prescription or over-the-counter drug by the originator and generic producers. The molecular structure of orlistat is a saturated derivative of lipstatin—a potent natural inhibitor of pancreatic lipases—isolated from the bacterium Streptomyces toxytricini. 2 Because of its simplicity and stability in particular, orlistat—rather Additional Supporting Information may be found in the online version of this article. Supporting Information Correspondence to: Alen Kljajic (Telephone: +386-7-331-2949; Fax: +386-7-331-2313; E-mail: alen.kljajic@krka.si, alen.kljajic@ gmail.com) Journal of Pharmaceutical Sciences, Vol. 102, 330–335 (2013) © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association than lipstatin—was developed into an antiobesity drug. 3 In the commercial production of orlistat, synthetic or semi-synthetic technologies can be used. In the scope of development of a cost-effective production process, we analyzed the semi-synthetic route, with lipstatin acting as a reactive biosynthetic interme- diate. There are several challenges involved in the semi-synthetic production route. The main challenge, which is the focus of this communication, is the downstream process (especially purification) used to control the quality of API orlistat. Several possible technologies were used in an attempt to purify the drug substance with the downstream process. Among 330 JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 102, NO. 2, FEBRUARY 2013