To a suspension of 0.6 g (1.43 mmol) of N-[6-(acetylamino)pyrid-3-yl]-5-fluoro-1-[(3-fluorophenyl)methyl]-1H-indole-2-carboxamide, prepared according to the protocol described in step 4.1, in 9 mL of anhydrous methanol, stirred at 0° C. under an inert atmosphere, are added dropwise 2.03 mL (28.54 mmol) of acetyl chloride. The reaction mixture is stirred at 0° C. for 30 minutes and then gradually brought to 70° C. and stirred for 48 hours. The reaction mixture is concentrated to dryness. The residue obtained is taken up in a mixture of 200 mL of saturated aqueous NaHCO3 solution and 200 mL of ethyl acetate. The phases are separated by settling and the aqueous phase is extracted with 200 mL of ethyl acetate. The combined organic phases are dried over sodium sulfate and then concentrated under reduced pressure. 0.46 g of the expected product is thus obtained.
