Step 3: 3-amino-4-(methylamino)benzoic acid (280,678 mg, 4.1 mmol) was dissolved in 50% formic acid aqueous solution (anhydrous solvent was used if the protoate was used), and the reaction was stirred at 85°C for 13 hours. After completion of the reaction, the reaction solution was concentrated, the residue was redissolved in water and freeze-dried to obtain 1-methyl-1H-benzo[d]imidazole-5-carboxylic acid (281,712 mg, 99% yield). The product was characterized as follows: 1H NMR (400.2 MHz, DMSO) δ (ppm): 12.9 (br s, 1H), 8.80 (s, 1H), 8.26 (d, J = 1.6 Hz, 1H), 7.96 (dd, J = 1.6, 8.6 Hz, 1H), 7.79 (d, J = 8.6 Hz, 1H), 3.95 (s, 3H). 3H). MS: calculated value 176.2; measured value 177.1 (M + H).
