0.01 g of sodium hydride (60%) is added to a solution of 0.1 g of 2-[5,6-dimethoxy-1H-indol-3-yl]-1-(toluene-4-sulfonyl)-1H-pyrrolo[2,3-b]pyridine in 2.5 ml of anhydrous dimethylformamide, under an inert argon atmosphere at a temperature in the region of 20° C. Agitation is maintained at this temperature for 30 minutes. 0.023 ml of bromoethyl methyl ether is added. The reaction medium is agitated at the same temperature for 16 hours. 3 ml of water and 3 ml of ethyl acetate are added. After separation by settling out, the organic phase is dried over sodium sulfate, filtered, and then concentrated under reduced pressure. The residue obtained is purified on a flash-pack chromatography cartridge (silica, dichloromethane as eluent). The fractions containing the product are concentrated under reduced pressure. 0.082 g of 2-[5,6-dimethoxy-1-(2-methoxyethyl)-1H-indol-3-yl]-1-(toluene-4-sulfonyl)-1H-pyrrolo[2,3-b]pyridine is thus obtained, the characteristics of which are as follows:
