Pyridine → acetic acid (2-oxo-2,3-dihydro-1H-indol-5-ylcarbamoyl)-methyl ester

5-Amino-1,3-dihydro-indol-2-one 30c (500 mg, 3.38 mmol) was dissolved in 10 ml of dichloromethane under stirring at room temperature, and pyridine (470 μl, 5 mmol) was added to the solution at −40° C. in a dry ice-acetone bath. Acetic acid chlorocarbonylmethyl ester (473 mg, 3.48 mmol) was dissolved in 10 ml of dichloromethane, the resulting solution was added dropwise to the above reaction solution. Upon completion of the addition, the dry ice-acetone was removed, and the reaction mixture was allowed to warm up to room temperature and stirred overnight. After thin lay chromatography showed the disappearance of starting materials, the reaction mixture was filtered. The filter cake was washed with water (10 ml×3) and recrystallized to obtain the title compound acetic acid (2-oxo-2,3-dihydro-1H-indol-5-ylcarbamoyl)-methyl ester 44a (510 mg, yield 60.7%) as a yellow solid.