To a mixture of N-(3-(5-(4-chlorophenyl)-1H-pyrrolo[2,3-b]pyridine-3-carbonyl)-2,4-difluorophenyl)propane-1-sulfonamide (0.5 g, 1.02 mmol) and potassium hydroxide (115 mg, 2.04 mmol) in anhydrous DMF (4 mL) was added a solution of chloromethyl isobutyrate (37 mg, 0.25 mmol) in anhydrous DMF (1 mL) over 30 min at 10° C. The reaction was stirred at 10° C. for 3 h, then diluted with EtOAc (40 mL) and filtered. The filtrate was concentrated in vacuo and the residue was purified by a silica gel column chromatography (PE/EtOAc (v/v)=5/1 to 4/1) to afford the title compound as a white solid (0.39 g, 63.3%). The title compound was characterized by LC-MS and 1H NMR as shown below:
