[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][C:11]2[N:14]=[CH:15][S:16][C:10]=2[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[C:17](=[O:19])=[O:18].[OH-].[Na+].C(OCC)C>O1CCCC1.C([Li])CCC>[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][C:11]2[N:14]=[C:15]([C:17]([OH:19])=[O:18])[S:16][C:10]=2[CH2:9]1)=[O:7])([CH3:4])([CH3:2])[CH3:3]To a solution of 5-tert-butoxycarbonyl-4,5,6,7-tetrahydrothiazolo[5,4-c]pyridine (845 mg) in absolute tetrahydrofuran (20 ml), n-butyllithium (1.65N hexane solution, 2.13 ml) was added dropwise at −78° C., and the mixture was stirred for 30 minutes with ice cooling. After passing carbon dioxide gas into the reaction mixture at −78° C. for 1 hour, the reaction mixture was warmed to room temperature. A 5N aqueous solution of sodium hydroxide and diethyl ether were added to the reaction mixture to separate a water layer. 6N Hydrochloric acid was added to the water layer to adjust the pH thereof to 1 to 2. After addition of dichloromethane, an organic layer separated was washed with saturated saline and dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure to obtain the title compound (562 mg) as a pale yellow foamy substance.
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