Thionyl chloride (21 mL, 0.29 mol) was slowly added dropwise to 500 mL of anhydrous ethanol at 0 °C and under nitrogen protection for a controlled time of 5 min. After the dropwise addition, the clarified reaction solution was continued to be stirred at 0 °C for 10 min, and then brought to room temperature and stirred for 30 min. A one-time addition of 4-nitro-L-phenylalanine (50.2 g, 0.24 mol) was added to the reaction system and the mixture was heated to reflux overnight. Upon completion of the reaction, the mixture was concentrated under reduced pressure to afford ethyl (S)-2-amino-3-(4-nitrophenyl)propionate hydrochloride (60 g, 92% yield) as a white solid. The product was characterized by 1H NMR (400 MHz, CD3OD): δ 8.21 (d, 2H), 7.54 (d, 2H), 4.39 (dd, 1H), 4.22 (q, 2H), 3.24-3.40 (m, 2H), 1.22 (t, 3H).
