[O:1]=[C:2]1[C:11]([C:12]([O:14]C)=[O:13])=[CH:10][C:9]2[C:4](=[CH:5][N:6]=[CH:7][CH:8]=2)[NH:3]1.[OH-].[Li+]>C1COCC1.O>[O:1]=[C:2]1[C:11]([C:12]([OH:14])=[O:13])=[CH:10][C:9]2[C:4](=[CH:5][N:6]=[CH:7][CH:8]=2)[NH:3]1A mixture of methyl 2-oxo-1,2-dihydro-1,7-naphthyridine-3-carboxylate (prepared as described in WO 2010/016846)(4.22 g, 20.67 mmol) and lithium hydroxide (2.475 g, 103 mmol) in THF (50 mL) and water (50 mL) was heated at 65° C. for 1 hour. The white precipitate was filtered, washed with water, and dried to afford a white solid. The filtrate was concentrated, dissolved in water and neutralized to pH=7 with concentrated HCl to afford a white solid. The white precipitate was filtered, washed with water, and dried. The solids were combined to afford 2-oxo-1,2-dihydro-1,7-naphthyridine-3-carboxylic acid (3.482 g, 18.31 mmol, 89% yield) as an off-white solid. m/z (ESI) 191.2 (M+H)+.
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