The general procedure for the synthesis of 4-methylsulfonylaminophenylacetic acid from 4-aminophenylacetic acid (1 g, 6.66 mmol) and methanesulfonyl chloride (0.77 g, 9.99 mmol) was as follows: first, 4-aminophenylacetic acid was dissolved in THF (10 mL), and pH was adjusted with a 1N sodium hydroxide solution to 9. Subsequently, a THF of methanesulfonyl chloride was added slowly and dropwise under stirring solution (10 mL), and the reaction mixture continued to stir the reaction. After completion of the reaction, the pH was adjusted to 3 with 1N hydrochloric acid, the reaction mixture was diluted with distilled water and extracted several times with ethyl acetate. The organic layers were combined, washed with water, dried with anhydrous magnesium sulfate and subsequently concentrated under reduced pressure. The residue was purified by silica gel fast column chromatography using EtOAc/hexane (2:3) as eluent to give 0.855 g of yellow solid 4-(methylsulfonylamino)benzeneacetic acid in 56% yield. The product was characterized by 1H-NMR (DMSO-d6): δ 9.67 (s, 1H, COOH), 7.20 (d, 2H, J = 8.5 Hz, Ar-H), 7.13 (d, 2H, J = 8.5 Hz, Ar-H), 3.50 (s, 2H, CH2), 3.95 (s, 3H, SO2CH3).
