Step B: Methyl (2S)-2-(tert-butoxycarbonylamino)-3-(naphthalen-2-yl)propionate (5.52 g, 15.85 mmol) and 20 mL of ethyl acetate were added to a 500 mL round-bottom flask fitted with a magnetic stirrer. 80 mL of 2.8 M hydrogen chloride in ethyl acetate solution was slowly added under stirring and the reaction was carried out under nitrogen protection for 2.5 hours. Upon completion of the reaction, the reaction mixture was concentrated to dryness under reduced pressure to give the crude product. The crude product was dissolved in an appropriate amount of ethyl acetate, stirred for 10 minutes and filtered to collect the solid. The resulting solid was dried under vacuum at 40 °C to give (2S)-2-amino-3-(naphthalen-2-yl)propanoic acid methyl ester hydrochloride 3.91 g in 93% yield as a white solid.HPLC-MS analysis: retention time (Rt) = 3.70 min, molecular ion peak (M + 1) = 230, % ELS area = 100%.
