1-Cyclohexyl-4-oxo-4,5-dihydroimidazo[1,5-a]quinoxaline-8-carboxyic acid as synthesized in Example 103, 6.23 g, N,O-dimethylhydroxyamine hydrochloride 2.15 g, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride 5.75 g, 1-hydroxybenzotriazole monohydrate 3.97 g, acetonitrile 51 mL and N,N-diisopropylethylamine 7.3 mL were mixed and stirred for 24 hours. The reaction liquid was poured in saturated aqueous sodium hydrogencarbonate solution and extracted with tetrahydrofuran and ethyl acetate. The organic layer was washed twice with saturated brine and dried over magnesium sulfate. After distilling the solvent off, the residue was heat-suspended in 200 mL of acetone and purified, to provide 3.36 g of the title compound.
