To a solution of 0.120 g (0.36 mmol) of 9-amino-4-oxo-2-pyrimidin-4-yl-5,6,8,9-tetrahydro-4H-1,4a,7-triaza-benzocycloheptene-7-carboxylic acid ethyl ester in 3.6 ml of dichloromethane was added 0.041 g (0.38 mmol) of benzaldehyde, 0.192 g (0.91 mmol) of sodium triacetoxyborohydride and few drops of glacial acetic acid. The reaction mixture was stirred at room temperature for 15 hours. The residue was dissolved in dichloromethane and a saturated aqueous solution of sodium carbonate, extracted with dichloromethane and washed with saturated aqueous solution of sodium chloride, dried over sodium sulfate and evaporated. The crude product was purified by chromatography on silica gel eluting with a mixture of dichloromethane/methanol/aqueous ammonia solution (29%) in the proportions 97/3/0.3 to give 0.145 g (95%) of pure product. The free base was transformed into its hydrochloride salt.
