1.3 g of 1,3-dimethyl-6-[4-(2-ethoxycarbonyl-2-phenylethyl)piperazin-1-yl]-2,4(1H,3H)-pyrimidinedione obtained in Example 4 was dissolved in 50 ml of tetrahydrofuran, and while the resulting solution was cooled to -20° C., 1.1 g of aluminum lithium hydride was divided into several portions and then added thereto separately. After stirring at -10° C. for 1 hour, 0.7 ml of water was added to the solution at the same temperature. The reaction solution was stirred for 2 or 3 hours, and 3 g of anhydrous sodium sulfate was added thereto, followed by allowing the solution to stand overnight. Afterward, insolubles were removed from the solution by filtration, and the filtrate was concentrated and the resulting residue was then dissolved in ethyl acetate. The obtained solution was washed with water and then dried over anhydrous sodium sulfate, and the solvent was distilled off under reduced pressure. The resulting residue was purified through a silica gel column chromatograph (chloroform/methanol=100/1 to 30/1 in volume ratio), thereby obtaining 0.5 g of oily 1,3-dimethyl-6-[4-(3-hydroxy-2-phenylpropyl)piperazin-1-yl]-2,4(1H,3H)-pyrimidinedione.
