GENERAL STEPS: (S)-2-Amino-3-(4-fluorophenyl)propanoic acid (1.97 g, 10 mmol) was dissolved in a mixture of dioxane (20 mL), water (20 mL) and 1M NaOH (10 mL), stirred and cooled in an ice water bath. Di-tert-butyl dicarbonate (2.4 g, 11 mmol) was added to the reaction system, followed by continued stirring for 6 hours at room temperature. Upon completion of the reaction, the solution was concentrated under vacuum to about 15-20 mL and again cooled in an ice water bath. The concentrate was covered with ethyl acetate (~30 mL) and acidified to pH 2-3 by adding dilute KHSO4 solution. the aqueous phase was separated and extracted three times with ethyl acetate. The ethyl acetate extracts were combined and dried over anhydrous Na2SO4 followed by vacuum evaporation of the solvent. The resulting product was a waxy solid with a yield of 2.115 g (7.25 mmol, 72.5% yield). The product was characterized by 1H NMR (DMSO-d6, 400 MHz) and MALDI-TOF mass spectrometry.1H NMR data: δ 12.60 (s, 1H, COOH), 7.29-7.25 and 7.11-7.07 (m, 4H, aromatic protons), 4.10-3.00 (m, 1H, CH-4F-Phe), 3.03- 2.77 (m, 2H, CH2-4F-Phe), 1.33 (s, 9H, Boc).MALDI-TOF mass spectrometry data (matrix: α-cyano-4-hydroxycinnamic acid (CHCA)): m/z [M + H]+ 284.12 (calculated), 284.29 (observed); [M + Na]+ 306.11 (calculated), 306.25 (calculated). 306.25 (observed value).
