To a stirred mixture of 2.52 g (13.32 mMol) 2-hydroxyquinoline-4-carboxylic acid, 2.7 g (15.98 mMol) HOBt (80%), 3.7 ml (26.64 mMol) triethylamine and 3.8 g (18.64 mMol) DCC in 50 ml of CH2Cl2 were added at room temperature 12.3 g (13.32 mMol) [(2R,4S)-4-Amino-2-(4-chloro-benzyl)-piperidin-1-yl]-(3,5-bis-trifluoromethyl-phenyl)-methanone (synthesis described in EP 707006A). After 18 h the reaction mixture was diluted with 500 ml THF and filtered through a fritted glass funnel with suction. The filtrate was further diluted with ethyl acetate and washed three times with brine. The organic phase was dried with Na2SO4 and concentrated in vacuo. The product was purified by chromatography on silica gel using successively EtOAc/CH2Cl2 (2:1), EtOAc and EtOAc/THF (3:1) as eluents. The product was suspended in hexane and stirred at 60° C. overnight. The mixture was filtered and dried and a yield of 6.2 g of white crystals. M.p.222-224° C.
