Step E. Synthesis of 7-hydroxyquinoline-3-carboxylic acid. Ethyl 7-methoxyquinoline-3-carboxylate (7.03 g, 30.4 mmol) was dissolved in 48% aqueous hydrobromic acid (150 mL) and heated to reflux at 105 °C for 88.5 hours. After completion of the reaction, it was cooled to room temperature and the precipitate precipitated was collected by filtration to afford the title compound 7-hydroxyquinoline-3-carboxylic acid as a brown solid (5.2 g, 90% yield). 1H NMR (400 MHz, DMSO-d6) δ 12.05-11.67 (m, 1H), 9.49 (d, J = 2.0 Hz, 1H), 9.43 (s, 1H), 8.39 (d, J = 9.8 Hz, 1H), 7.55-7.51 (m, 2H). Mass spectrum (ESI) [M + H]+ m/z = 190.2.
