A mixture of hydroxylammonium chloride (1.8 g), sodium hydrogencarbonate (2.8 g) and dimethyl sulfoxide (15 mL) was stirred at 40° C. for 30 min, 4′-{[6-ethyl-3-[2-(4-methoxyphenyl)-2-oxoethyl]-2,4-dioxo-3,4-dihydrothieno[2,3-d]pyrimidin-1(2H)-yl]methyl}biphenyl-2-carbonitrile (1.38 g) was added, and the mixture was stirred at 90° C. for 16 hr. The reaction mixture was diluted with chloroform, washed successively with water and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The residue was dissolved in methylene chloride (15 mL), N,N′-carbonyldiimidazole (0.28 g) and then 1,8-diazabicyclo[5.4.0]undec-7-ene (0.23 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 preparative HPLC to give the title compound as colorless crystals (0.27 g, 17%).
