GENERAL PROCEDURE: Compound 5a (183 mg, 0.79 mmol) was dissolved in methanol (10 mL) and cooled to 0°C. To this cooled solution was added 1N LiOH aqueous solution (1.6 mL), followed by stirring the reaction mixture for 6 hours at room temperature. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. To the remaining aqueous solution, 6N HCl was added and the pH was adjusted to about 6.8. After removing the water again by reduced pressure evaporation, the residue was purified using column chromatography (eluent: chloroform/methanol containing 3% formic acid, 9:1, v/v/v/v) to afford the target product, (1-oxo-1H-isoquinolin-2-yl)-acetic acid 6a, as a white powder (168 mg, 97% yield).
