C[O:2][C:3]([C:5]1[S:6][CH:7]=[CH:8][C:9]=1[N:10](S(C1C(C)=CC=CC=1)(=O)=O)[S:11]([C:14]1[C:15]([CH3:20])=[CH:16][CH:17]=[CH:18][CH:19]=1)(=[O:13])=[O:12])=[O:4].[OH-].[Na+].Cl>O1CCOCC1.CO.O>[C:15]1([CH3:20])[C:14]([S:11]([NH:10][C:9]2[CH:8]=[CH:7][S:6][C:5]=2[C:3]([OH:4])=[O:2])(=[O:13])=[O:12])=[CH:19][CH:18]=[CH:17][CH:16]=1To a stirred mixture of 3-(bis-(Toluene-2-sulfonyl)-amino)-thiophene-2-carboxylic acid methyl ester (2.5 g, 5.35 mmol) in 1,4-dioxane/MeOH/water (3:1:1; 62.5 mL) was added aq. 1 N NaOH solution (16.05 mL, 16.05 mmol, 3.0 eq) and heated at 85° C. for 3.5 h and it was then cooled to rt. To the reaction mixture was added 1.2 N HCl (16.0 mL), extracted with CHCl3 (3×30 mL), washed with brine and dried. Evaporation of the solvent gave 3-(Toluene-2-sulfonylamino)-thiophene-2-carboxylic acid (1.5 g, 99%) as a white solid. 1H NMR (DMSO-d6, 300 MHz) 7.94 (dd, J=7.9 Hz, 1.3 Hz, 1H), 7.76 (d, J=5.5 Hz, 1H), 7.55 (dt, J=7.5 Hz, 1.3 Hz, 1H), 7.42-7.37 (m, 2H), 7.1 (d, J=5.5 Hz, 1H), 2.57 (s, 3H).
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