The general procedure for the synthesis of 5-methylthiazole-4-carboxylic acid from methyl 5-methylthiazole-4-carboxylate was as follows: with reference to Example 56, to a solution of methyl 5-methyl-1,3-thiazole-4-carboxylate (1.17 g, 7.4 mmol) in methanol (15 mL) was added an aqueous solution of 8N sodium hydroxide (2.00 mL), and the reaction mixture was stirred for 18 hours at room temperature. Upon completion of the reaction, 6N hydrochloric acid (2.67 mL) was slowly added to the mixture for neutralization, followed by concentration of the mixture under reduced pressure. An appropriate amount of water was added to the concentrated residue and the precipitate precipitated was collected by filtration and washed with cold water. The resulting precipitate was suspended in a solvent mixture of ethyl acetate (9 mL) and ethanol (1 mL) and stirred at 80 °C for 3 minutes. After the mixture was cooled to room temperature, the precipitate was collected by filtration, washed with ethyl acetate and finally dried under reduced pressure to afford the target product 5-methylthiazole-4-carboxylic acid (531 mg, 50% yield) as a light yellow solid. The product was characterized by 1H-NMR (DMSO-d6, 300 MHz): δ 2.71 (3H, s), 8.87 (1H, s), 12.88 (1H, br s).
