General procedure for the synthesis of 2-((tert-butoxycarbonyl)amino)-3-phenylpropionic acid from DL-phenylalanine and di-tert-butyl dicarbonate: DL-phenylalanine (1 g, 6.05 mmol) was suspended in a mixture of dioxane (15 mL) and NaOH (2M aqueous solution; 3.63 mL, 7.26 mmol) at 0 °C. Subsequently, di-tert-butyl dicarbonate (1.546 mL, 6.66 mmol) was added slowly and dropwise to this suspension. The reaction mixture was stirred continuously for 5 hours at room temperature. Upon completion of the reaction, the mixture was concentrated under vacuum to remove the solvent. Water (30 mL) was added to the concentrate and the pH of the mixture was adjusted to 3 by dropwise addition of cold 1.5 N HCl solution.The aqueous layer was extracted with ethyl acetate (3 x 50 mL) and the organic layers were combined and washed with brine solution (2 x 50 mL). The organic layer was dried over anhydrous sodium sulfate and concentrated to afford the target product 2-((tert-butoxycarbonyl)amino)-3-phenylpropanoic acid (1.3 g, 4.90 mmol, 81% yield) as a gelatinous liquid. The product was confirmed by 1H NMR (400 MHz, DMSO-d6) and mass spectrometry (ESI): 1H NMR δ 12.6 (br-s, 1H), 7.32-7.26 (m, 5H), 7.10-6.95 (br-s, 1H), 4.12-4.00 (m, 1H), 3.05-2.92 (m, 1H), 2.87- 2.75 (m, 1H), 1.31 (s, 9H); MS (ESI) m/z 266.2 [M+H]+.
