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General procedure for the synthesis of 5-bromo-1H-pyrazolo[3,4-b]pyridine-3-carboxylic acid using methyl 5-bromo-1H-pyrazolo[3,4-b]pyridine-3-carboxylate: 5-bromo-1H-pyrazolo[3,4-b]pyridine-3-carboxylic acid methyl ester (3.4 g, 13.2 mmol) was dissolved in methanol (50 mL), and 2M sodium hydroxide solution ( 10 mL) and the reaction was refluxed for 4 hours. After completion of the reaction, the mixture was cooled to room temperature, acidified with hydrochloric acid to pH<7, precipitated as a solid, and filtered to afford 5-bromo-1H-pyrazolo[3,4-b]pyridine-3-carboxylic acid (3.22 g, 100% yield). The product was characterized by 1H NMR (300 MHz, CD3OD): δ 8.62 (s, 1H), 8.58 (s, 1H); mass spectrometry (ESI) m/z: 359 (M+H+).

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