A. Synthesis of ethyl 2-amino-5-fluorobenzoate
2-Amino-5-fluorobenzoic acid (1.0 g, 6.4 mmol) was dissolved in a mixed solvent of ethanol (15 mL) and toluene (10 mL). Several drops of concentrated sulfuric acid (H2SO4) were added as a catalyst. A Dean-Stark splitter was installed and the reaction mixture was refluxed overnight. After completion of the reaction, it was cooled to room temperature and the solvent was removed by distillation under reduced pressure. The product was purified by silica gel column chromatography (4×15 cm), and the target product was obtained in 50% yield by sequential gradient elution with chloroform/methanol (98:2, v/v, 500 mL) and (95:5, v/v, 500 mL) as eluents. Mass spectrum (ES+): m/z 184.0 ([M+H]+); 1H NMR (CDCl3) δ 7.55 (d, 1H, ArH), 7.03 (m, 1H, ArH), 6.61 (dd, 1H, ArH), 5.6 (bs, 2H, NH2), 4.33 (q, 2H, CH2), 1.40 (t, 3H, CH3).
