COC[N:4]1[C:12]2[C:7](=[C:8]([CH3:23])[CH:9]=[CH:10][C:11]=2[N:13]([CH3:22])[S:14]([C:17]2[S:18][CH:19]=[CH:20][CH:21]=2)(=[O:16])=[O:15])[CH:6]=[C:5]1[C:24]([O:26]CC)=[O:25].Cl.O1CCCC1>C(O)C>[CH3:23][C:8]1[CH:9]=[CH:10][C:11]([N:13]([CH3:22])[S:14]([C:17]2[S:18][CH:19]=[CH:20][CH:21]=2)(=[O:15])=[O:16])=[C:12]2[C:7]=1[CH:6]=[C:5]([C:24]([OH:26])=[O:25])[NH:4]2A mixed solution of ethyl 1-(methoxymethyl)-4-methyl-7-[methyl(2-thienylsulfonyl)amino]-1H-indole-2-carboxylate (4.0 g), 6N hydrochloric acid (20 mL), tetrahydrofuran (20 mL) and ethanol (60 mL) was stirred at 80° C. for 4 hr. The reaction solution was concentrated under reduced pressure. The obtained residue was diluted with ethyl acetate, washed with saturated brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The obtained solid was dissolved in a mixed solution of tetrahydrofuran (40 mL) and methanol (40 mL), aqueous solution (20 mL) of 85% potassium hydroxide (2.2 g) was added, and the mixture was stirred at room temperature for 18 hr. The reaction solution was concentrated under reduced pressure, and the obtained residue was acidified with aqueous citric acid solution. The precipitated crystals were collected by filtration, thoroughly washed with water, and dried to give the title compound (3.3 g, yield 99%) as colorless crystals. MS:351 (MH+). melting point 223-225° C.
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