[C:1]([C:3]1[C:4]([C:19]2[CH:24]=[CH:23][C:22]([N+:25]([O-:27])=[O:26])=[CH:21][CH:20]=2)=[N:5][S:6][C:7]=1[NH:8][C:9]([NH:11][CH2:12][CH2:13][CH2:14][C:15](OC)=[O:16])=[O:10])#[N:2].S(=O)(=O)(O)[OH:29]>>[N+:25]([C:22]1[CH:21]=[CH:20][C:19]([C:4]2[C:3]([C:1]([NH2:2])=[O:29])=[C:7]([NH:8][C:9]([N:11]3[CH2:12][CH2:13][CH2:14][C:15]3=[O:16])=[O:10])[S:6][N:5]=2)=[CH:24][CH:23]=1)([O-:27])=[O:26]Methyl 4-[({[4-cyano-3-(4-nitrophenyl)isothiazol-5-yl]amino}carbonyl)amino]butanoate (10.0 g) was added portion wise to concentrated sulfuric acid (50.0 mL) at ambient temperature over 20 min. The resulting suspension was heated to 45° C. over 90 min. The reaction mixture was cooled to ambient temperature. The reaction mixture was poured into ice water (600 ml), stirred for 30 min. The solid which formed was collected and washed with water then dried in vacuo to give the titlee compound as off white solid (10.2 g, 99%).
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