To a solution of 6-[4-(2-trifluoromethylbenzoyl)piperazin-1-yl]pyridazine-3-carboxylic acid (2-hydroxy-2-phenylethyl)amide (50 mg, 0.1 mmol) in chloroform (2 mL), acetic anhydride (0.25 mL), triethylamine (0.25 mL) and 4-dimethylaminopyridine (18 mg) were added. After stirred at ambient temperature for 6 hours, the reaction mixture was diluted with ethyl acetate (100 mL), washed with water (3×10 mL) and dried over Na2SO4. The crude product obtained after removal of the solvent was purified by column chromatography eluted sequentially with hexane:ethyl acetate=1:1 and 1:2 to give a white powder (49.6 mg, 91.5% yield). 1H NMR (500 MHz, CDCl3) δ 8.10, 8.04, 7.75, 7.65, 7.57, 7.40-7.28, 7.00, 5.92, 4.07, 3.98, 3.90, 3.82-3.68, 3.36, 2.10. MS (ES+) m/z 508 (M+1).
