N-{[6-cyano-2-oxo-4-(trifluoromethyl)-1,4-dihydro-2H-3,1-benzoxazin-4-yl]methyl}-4-fluorobenzamide (30 mg, 0.076 mmol) synthesized in Example 159, sodium azide (24.8 mg, 0.38 mmol) and ammonium chloride (20.4 mg, 0.38 mmol) were dissolved in DMF (0.5 mL), and the solution was stirred for 12 hours under heating at 110° C. Water was added to the solution and the solution was extracted twice with ethyl acetate-ethanol, and the resulting organic layer was dried over magnesium sulfate. After the drying agent was removed by filtration, the solvent was evaporated under reduced pressure. The residue was purified by reverse-phase HPLC, whereby the objective compound (3.4 mg, 10%) was obtained as a white solid.
