To a solution of of 2-methoxy-2,8-diazaspiro[4,5]decane-1,3-dione.hydrochloride (0.21 g) obtained in Example 9, 1,4-dihydro-2,6-dimethyl-5-methoxycarbonyl-4-(3-nitrophenyl)pyridine-3-carboxylic acid (0.3 g) and triethylamine (0.26 ml) in dimethylformamide (7 ml) was added dropwise, under ice-cooling, 0.22 ml of diethyl cyano phosphate, and the mixture was stirred for 30 minutes. To the reaction mixture was added water (20 ml), which was stirred at room temperature, followed by extraction with dichloromethane. The dichloromethane solution was dried over anhydrous sodium sulfate. The solvent was then evaporated off under reduced pressure. The residual oily product was subjected to a silica gel column chromatography (eluent, ethyl acetate), and the solvent for the solution containing the desired product was evaporated off under reduced pressure. The residual solid was recrystallized from ethanol to obtain 0.31 g of yellow crystals, m.p. 228° to 230° C.
