[OH-].[K+].C[O:4][C:5]([C:7]1[S:8][C:9]([CH3:23])=[C:10]([NH:12][C:13]([NH:15][CH2:16][C:17]2[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=2)=[O:14])[CH:11]=1)=[O:6].Cl>CO.O>[CH3:23][C:9]1[S:8][C:7]([C:5]([OH:6])=[O:4])=[CH:11][C:10]=1[NH:12][C:13]([NH:15][CH2:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)=[O:14]A 2N aqueous potassium hydroxide solution (16 mL) was added to a stirred solution of 5-methyl-4-(3-benzyl-ureido)-thiophene-2-carboxylic acid methyl ester from Step 2 of Example 16 below (0.4 g, 1.3 mmol) in warm methanol (4 mL), and the mixture was heated under reflux. After 1 hour the mixture was cooled, diluted with water (100 mL), and acidified with aqueous HCl. The precipitate was filtered off, rinsed with water, then ethanol, then ether, and dried to afford 0.29 g of 5-methyl-4-(3-benzyl-ureido)-thiophene-2-carboxylic acid; mp 259-260° C.
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