A mixture of hydroxylammonium chloride (1.1 g), sodium hydrogencarbonate (1.6 g) and dimethyl sulfoxide (10 mL) was stirred at 40° C. for 30 min, 4′-{[6-ethyl-3-(4-isopropoxyphenyl)-2,4-dioxo-3,4-dihydrothieno[2,3-d]pyrimidin-1(2H)-yl]methyl}-3′-fluorobiphenyl-2-carbonitrile (0.5 g) was added, and the mixture was stirred at 90° C. for 16 hr. To the reaction mixture was added water, and the precipitated solid was collected by filtration, washed with water, and dried under reduced pressure. The solid was dissolved in tetrahydrofuran (10 mL), N,N′-carbonyldiimidazole (0.23 g) and then 1,8-diazabicyclo[5.4.0]undec-7-ene (0.21 mL) were added, and the mixture was stirred at room temperature for 2 hr. The reaction mixture was diluted with chloroform, washed successively with saturated aqueous potassium hydrogensulfate solution and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography to give the title compound as a pale-yellow solid (0.37 g, 68%).
