To a suspension of N-[(2,6-dichlorophenyl)carbonyl]-4-(1,4-dimethyl-2-oxo-3-pyridinyl)-L-phenylalanine methyl ester (20 mg, 0.04 mmol) in ethanol (1 mL) was added 1N aqueous sodium hydroxide solution (0.5 mL) at room temperature. The mixture was heated to 40-45° C. and stirred for 3 h. Then, the ethanol was removed under vacuum and the residue was diluted with water (10 mL). The aqueous solution was washed with diethyl ether (25 mL) to remove any neutral impurities. The aqueous layer was acidified with 1.0 N HCl and the product was extracted into ethyl acetate (2×25 mL). The combined organic extracts were washed with brine solution (50 mL) and were dried over anhydrous magnesium sulfate. Filtration of the drying agent and concentration afforded 17 mg (89% yield) of N-[(2,6-dichlorophenyl)carbonyl]-4-(1,4-dimethyl-2-oxo-3-pyridinyl)-L-phenylalanine as an amorphous white solid. ES-HRMS m/e calcd for C23H20Cl2N2O4 (M+Na) 481.0691, found 481.0699.
