[O:1]1[CH2:6][CH2:5][CH2:4][CH2:3][CH:2]1[O:7][CH2:8][CH2:9][C:10]1[N:11]=[CH:12][C:13]([C:16]([O:18]C)=[O:17])=[N:14][CH:15]=1.[OH-].[Na+].Cl>CO.[Cl-].[Na+].O>[O:1]1[CH2:6][CH2:5][CH2:4][CH2:3][CH:2]1[O:7][CH2:8][CH2:9][C:10]1[N:11]=[CH:12][C:13]([C:16]([OH:18])=[O:17])=[N:14][CH:15]=1To a solution of methyl 5-[2-(tetrahydro-2H-pyran-2-yloxy)ethyl]pyrazine-2-carboxylate (1.36 g) in methanol (20 mL) was added 1 M aqueous sodium hydroxide solution (15 mL) under ice-cooling. It was stirred at room temperature for 2 hours. To the reaction mixture was added 1 M hydrochloric acid under ice-cooling to adjust the pH to 3. A saturated brine was added, followed by extraction with a solvent (chloroform:methanol=4:1). The organic layer was dried over anhydrous magnesium sulfate, filtered, and concentrated to obtain 5-[2-(tetrahydro-2H-pyran-2-yloxy)ethyl]pyrazine-2-carboxylic acid (1.50 g) as a brown oily substance.
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