To a solution of methyl (S)-2-((tert-butoxycarbonyl)amino)-3-(4-methoxyphenyl)propionate (498 mg, 1.61 mmol) in THF/MeOH/H2O (3:1:1, 5 mL) was added LiOH-H2O (142 mg, 3.22 mmol) at 0 °C. The reaction mixture was stirred at 0 °C for 1 h and then evaporated to remove the organic solvent. The residue was treated with 15% aqueous citric acid solution, adjusting the pH to 3, and subsequently extracted with ethyl acetate (35 mL). The combined organic layers were washed with brine (5 mL), dried over anhydrous Na2SO4 and concentrated in vacuum. The crude product was purified by silica gel column chromatography (eluent: ethyl acetate/petroleum ether=2:1) to afford (S)-2-((tert-butoxycarbonyl)amino)-3-(4-methoxyphenyl)propanoic acid (466 mg, 98%) as a colorless oil.1H NMR (300 MHz, CD3OD): δ 7.13 (2H, d, J=8.4 Hz), 6.82 (2H d, J=8.4 Hz), 4.31-4.29 (1H, m), 3.73 (3H, s), 3.08 (1H, dd, J=13.8, 4.5 Hz), 2.85 (1H, dd, J=13.5, 8.7 Hz), 1.38 (9H, s).13C NMR (75 MHz, CD3OD): δ 175.42, 159.95, 157.00, 159.95, 157.00 (9H, s). 159.95, 157.67, 131.27, 130.37, 114.81, 80.50, 56.37, 55.64, 37.86, 28.67.
