Cl[C:2](=[CH:7][OH:8])[C:3]([O:5][CH3:6])=[O:4].CN(C=O)C.[SH:14][C:15]1[NH:16][C:17]2[CH:23]=[C:22]([C:24]([OH:26])=[O:25])[CH:21]=[CH:20][C:18]=2[N:19]=1>O>[OH:8][CH:7]1[N:19]2[C:15](=[N:16][C:17]3[CH:23]=[C:22]([C:24]([OH:26])=[O:25])[CH:21]=[CH:20][C:18]=32)[S:14][CH:2]1[C:3]([O:5][CH3:6])=[O:4]Methyl 2-chloro-3-hydroxypropenoate (114 g) was added to DMF (460 ml) solution of 2-mercaptobenzoimidazole-5-carboxylic acid (135 g), and the mixture was stirred overnight at 60° C. After cooling to room temperature, water (3 L) was gradually added to the reaction solution and stirred. The thus precipitated crystals were collected by filtration to obtain crude crystals of 2-methyl hydrogen 2,3-dihydro-3-hydroxythiazolo[3,2-a]benzoimidazole-2,7-dicarboxylate (168 g). Next, the thus obtained crude crystals were suspended in 1,4-dioxane (1.5 L), and the suspension was mixed with 4 M HCl 1,4-dioxane solution (500 ml) and stirred at room temperature for 60 hours. The resulting precipitate was collected by filtration and washed with 1,4-dioxane to obtain crude crystals of 2-methyl hydrogen 2,3-dihydro-3-hydroxythiazolo[3,2-a]benzoimidazole-2,6-dicarboxylate hydrochloride (189 g). The thus obtained crude crystals were slowly added to concentrated sulfuric acid (750 ml) which was heated at 60° C. and stirred at the same temperature for 1 hour. After cooling to room temperature, the reaction solution was poured into ice water, and the thus precipitated crystals were collected by filtration to obtain the title compound (152 g).
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