[NH2:1][C:2]1[C:7]([N+:8]([O-])=O)=[C:6]([C:11]2[S:12][CH:13]=[CH:14][CH:15]=2)[CH:5]=[C:4]([NH:16][C:17]([O:19][CH2:20][CH3:21])=[O:18])[N:3]=1.[BH4-].[Na+].[Cl-].[NH4+].C(Cl)Cl>C(O)C.C(OCC)(=O)C.[C].[Pd]>[NH2:1][C:2]1[C:7]([NH2:8])=[C:6]([C:11]2[S:12][CH:13]=[CH:14][CH:15]=2)[CH:5]=[C:4]([NH:16][C:17]([O:19][CH2:20][CH3:21])=[O:18])[N:3]=12-Amino-3-nitro-4-(2-thienyl)-6-ethoxycarbonylaminopyridine (1.57 g, 5.1 mmol) and 10% palladium-carbon (255 mg) were dissolved in ethanol (77 ml)-ethyl acetate (38 ml). To this mixture, a 1 M aqueous sodium borohydride solution (15.3 ml) was added at 0° C. and stirred at 0° C. for 1 hour. This solution was mixed with a 5% aqueous ammonium chloride solution (23.4 ml) and filtered through celite. The celite was washed with water (204 ml). The filtrate and this washing solution were mixed and evaporated under reduced pressure to remove ethanol and ethyl acetate, followed by extraction three times with ethyl acetate (150 ml). This solution was dried over sodium sulfate and evaporated under reduced pressure to remove the solvent, followed by silica gel column chromatography (methylene chloride:ethyl acetate=7:3 to 1:1) to purify the desired product, 2,3-diamino-4-(2-thienyl)-6-ethoxycarbonylaminopyridine (Rf 0.39/methylene chloride:ethyl acetate=1:2) (1.28 g, yield 90%).
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