(S)—N′-Hydroxy-3-(9-methylthio-6-oxo-2,3,3a,4-tetrahydro-1H,6H-5,8,10,10b-tetraazabenzo[e]azulen-5-yl)benzamidine (200 mg, 0.52 mmol) obtained in Step 1 of Example 75 was suspended in THF (3.0 mL), and the mixture was stirred at room temperature for 2 hours after adding 1,1′-thiocarbonyldiimidazole (155 mg, 0.78 mmol). After diluting the mixture with ethyl acetate, the organic layer was washed with water and saturated brine, and dried over anhydrous magnesium sulfate. The residue obtained upon concentration under reduced pressure was then purified by silica gel column chromatography to give (S)-3-[3-(9-methylthio-6-oxo-2,3,3a,4-tetrahydro-1H,6H-5,8,10,10b-tetraazabenzo[e]azulen-5-yl)phenyl]-1,2,4-thiadiazol-5(4H)-one (205 mg, 92%).
