[NH2:1][C:2]1[C:3]([C:19]#[N:20])=[N:4][C:5]([C:9]2[CH:14]=[CH:13][C:12](=[O:15])[N:11]([CH:16]([CH3:18])[CH3:17])[N:10]=2)=[CH:6][N+:7]=1[O-:8].[O:21]1CCOCC1>Br.CC(O)=O>[NH2:1][C:2]1[C:3]([C:19]([NH2:20])=[O:21])=[N:4][C:5]([C:9]2[CH:14]=[CH:13][C:12](=[O:15])[N:11]([CH:16]([CH3:18])[CH3:17])[N:10]=2)=[CH:6][N+:7]=1[O-:8]A suspension of 3-amino-6-(1-isopropyl-6-oxo-1,6-dihydro-3-pyridazinyl)-2-pyrazinecarbonitrile 4-oxide (500 mg) in 25% hydrogen bromide in AcOH (3 ml) was stirred at 20-25° C. for 4 hours. After addition of dioxane (9 ml), a precipitate was collected by filtration. The precipitate was added in water (3 ml) and adjusted to pH 8 with 1N aq. NaOH solution. The solid was collected by filtration and dried under reduced pressure to give 3-amino-6-(1-isopropyl-6-oxo-1,6-dihydro-3-pyridazinyl)-2-pyrazinecarboxamide 4-oxide (366 mg).
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