4.6 g (10.8 mmol) of 7-benzyl-8-(tert.-butyl)-3-(2-methoxycarbonylethyl)-1-n-propyl-xanthine are dissolved 50 ml of tetrahydrofuran and 120 ml of water and 3.24 g of LiOH×H2O are added successively with stirring. After about 16 hours' stirring at ambient temperature, the mixture is cooled to about 5° C. and adjusted to pH 5 with 2N HCl (aq.). The organic solvent is largely distilled off in vacuo and the aqueous phase remaining is extracted twice with 150 ml of dichloromethane. The organic phase is dried over MgSO4 and the solvent is distilled off in vacuo. The crude product remaining is purified by chromatography on silica gel (dichloromethane:methanol 90:10). Yield: 3.1 g (88%), amorphous solid.
