4-(3-Chloro-4-methoxybenzyl)amino-6-cyano-1(2H)-phthalazinone (0.20 g) prepared in Example 21 was dissolved in 5 ml of N-methyl-2-pyrrolidinone, followed by the addition of 0.24 g of 3-bromopropyl 2-tetrahydropyranyl ether and 0.24 g of potassium carbonate. The obtained mixture was stirred at 50° C. for 4 hours and poured into water, followed by extraction with ethyl acetate. The organic phase was washed with water twice and with a saturated aqueous solution of common salt, dried over anhydrous magnesium sulfate and freed from the solvent by vacuum distillation. The residue was purified by silica gel column chromatography [solvent: n-hexane/ethyl acetate (1:1)] to give 0.20 g of the title compound as a yellow crystal.
