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Methyl 5-(4-(tert-butoxycarbonyl)piperazin-1-yl)pyrazine-2-carboxylate (2 g, crude) was used as a raw material, which was dissolved in a mixed solvent of ethanol (5 mL) and tetrahydrofuran (5 mL), followed by the addition of 2N sodium hydroxide solution (5 mL). The reaction mixture was stirred at 60°C for 2 hours. Upon completion of the reaction, the pH was adjusted to 1 with dilute hydrochloric acid and subsequently extracted with ethyl acetate. The organic phase was concentrated to give the pink solid product 5-(4-(tert-butoxycarbonyl)piperazin-1-yl)pyrazine-2-carboxylic acid (300 mg, 15% yield, two steps).

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