A mixture of 6-(3-aminopiperidin-1-yl)-N-(5,6-dimethoxypyridin-2-yl)imidazo[1,2-b]pyridazin-8-amine trifluoroacetate (350 mg, 0.94 mmol), 4-(methoxycarbonyl)benzoic acid (171 mg, 0.94 mmol), EDCI (725 mg, 3.79 mmol), triethylamine (288 mg, 2.84 mmol) and 1-methyl-1H-imidazole (311 mg, 3.79 mmol) in dichloromethane (15 mL) was stirred at room temperature for 16 h. The residue was concentrated in vacuo then purified by prep-HPLC (Gemini 5u C18 150×21.2 mm; inject volume: 3 mL/inj, flow rate: 20 mL/min; wavelength: 214 nm and 254 nm; gradient conditions: 20% acetonitrile/80% water (0.1% TFA, v/v) initially, proceeding to 40% acetonitrile/60% water (0.1% TFA, v/v) in a linear fashion over 9 min) to give methyl 4-(1-(8-(5,6-dimethoxypyridin-2-ylamino)imidazo[1,2-b]pyridazin-6-yl)piperidin-3-ylcarbamoyl)benzoate (50 mg, 10%) as a white solid. LC-MS: 532 [M+1]+, tR=1.58 min.
