500 mg of 4-[(3-chloro-4-methoxybenzyl)amino]-1-(2-hydroxy-7-azaspiro[3.5]non-7-yl)-6-phthalazine carbonitrile was suspended in 20 ml dichloromethane and 10 ml tetrahydrofuran, then 690 mg of 1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxsol-3(1H)-one was added thereto, and the mixture was stirred at room temperature for 15 min. Ethyl acetate, 30 ml saturated aqueous sodium bicarbonate and 2 ml saturated aqueous sodium thiosulfate 5H2O were added thereto. The organic layer was recovered and the aqueous layer was extracted with ethyl acetate. The extracted solutions were combined, washed with brine, dried over anhydrous magnesium sulfate, and then filtered. The filtrate was evaporated and the resulting residue was purified by silica gel column chromatography, crystallized from ethanol, and the resulting crystals were collected filtration by adding hexane thereto to give 420 mg of 4-[(3-chloro-4-methoxybenzyl)amino]-1-(2-oxo-7-azaspiro[3.5]non-7-yl)-6-phthalazine carbonitrile.
