To a solution of 0.085 g of 4-{[1-[2-(5,6-dimethoxy-1-methyl-1H-pyrrolo[3,2-b]pyridin-3-yl)-1H-pyrrolo[2,3-b]pyridin-4-yl]meth-(E)-ylidene]amino}phenol in 20 cm3 of methanol, at a temperature in the region of 20° C., are added 0.013 g of zinc chloride and 0.013 g of sodium cyanoborohydride. The reaction medium is stirred at the same temperature for 4 hours. The reaction medium is concentrated under reduced pressure. The residue obtained is taken up in 10 cm3 of water and 25 cm3 of dichloromethane, and then basified with 0.1N sodium hydroxide. After separation of the phases by settling, the organic phase is dried over magnesium sulfate, filtered and then concentrated under reduced pressure to give 0.04 g of 4-{[2-(5,6-dimethoxy-1-methyl-1H-pyrrolo[3,2-b]pyridin-3-yl)-1H-pyrrolo[2,3-b]pyridin-4-ylmethyl]amino}phenol with the following characteristics:
