Trifluoroacetic acid → 4-(1-(8-(5,6-Dimethoxypyridin-2-ylamino)imidazo[1,2-b]pyridazin-6-yl)pyrrolidine-3-carboxamido)benzoic acid

A mixture of tert-butyl 4-(1-(8-(5,6-dimethoxypyridin-2-ylamino)imidazo[1,2-b]pyridazin-6-yl)pyrrolidine-3-carboxamido)benzoate (200 mg, 0.36 mmol) and TFA (2 mL) in dichloromethane (2 mL) was stirred at room temperature for 2 h. The residue was concentrated in vacuo. The crude product was 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: 25% acetonitrile/75% water (0.1% TFA, v/v) initially, proceeding to 50% acetonitrile/50% water (0.1% TFA, v/v) in a linear fashion over 9 min) to give 4-(1-(8-(5,6-dimethoxypyridin-2-ylamino)imidazo[1,2-b]pyridazin-6-yl)pyrrolidine-3-carboxamido)benzoic acid (6 mg, 4%) as a yellow solid. 1H NMR (300 MHz, DMSO): δ 10.54 (s, 1H), 8.88 (brs, 2H), 7.95-7.82 (m, 4 h), 7.49-6.69 (m, 3H), 4.06-3.57 (m, 6H), 3.19-3.02 (m, 5H), 2.05 (brs, 2H). LC-MS: [M+H]+, 504, tR=1.269 min, HPLC: 96.47% at 214 nm, 97.69% at 254 nm, tR=4.72 min.