2 g of (8S,9R)-2,3-dimethyl-8-hydroxy-9-phenyl-7,8,9,10-tetrahydroimidazo[1,2-h][1,7]naphthyridin-7-one, 1 g of Adogen 464, 7 ml of 50% strength aqueous sodium hydroxide solution and 0.8 ml of benzyl bromide are intensively stirred at room temperature for 16 h in 10 ml of dichloromethane. The mixture is then adjusted to pH 7 using ½ conc. aqueous hydrochloric acid with cooling and extracted three times with 100 ml of dichloromethane each time, and the organic phases are combined and washed twice with a little water. After stripping off the volatile components in vacuo, the residue obtained is chromatographed on silica gel (eluent: dichloromethane/methanol 100/3). 1.2 g of the title compound are obtained as yellowish crystals of melting point 248-51° C.
