[CH2:1]([NH:5][C:6]1[CH:10]=[C:9]([C:11]2[CH:16]=[CH:15][N:14]=[CH:13][CH:12]=2)[S:8][C:7]=1[C:17]([NH2:19])=[O:18])[CH2:2][CH2:3][CH3:4].[CH3:20][C:21]([CH3:23])=O.O.C1(C)C=CC(S(O)(=O)=O)=CC=1.C(=O)([O-])O.[Na+]>C(O)(=O)C>[CH2:1]([N:5]1[C:6]2[CH:10]=[C:9]([C:11]3[CH:16]=[CH:15][N:14]=[CH:13][CH:12]=3)[S:8][C:7]=2[C:17](=[O:18])[NH:19][C:21]1([CH3:23])[CH3:20])[CH2:2][CH2:3][CH3:4]A mixture of 3-(butylamino)-5-(pyridin-4-yl)thiophene-2-carboxamide (0.100 g, 0.400 mmol), acetone (3.0 mL), p-toluenesulfonic acid monohydrate (0.0095 g, 0.050 mmol) and acetic acid (2.0 mL) was stirred for 3 days at 70° C. in a sealed tube. The mixture was poured into sat. aqueous sodium hydrogen carbonate (100 mL). Extraction with ethyl acetate-tetrahydrofuran (2:1, 100 mL), drying over magnesium sulfate, filtration and concentration at reduced pressure gave an oil. The oil was purified by column chromatography (Combiflash, 12 g silica gel, hexane to ethyl acetate) to afford the title compound (0.0879 g, 70%) as a yellow solid:
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