(2S)-2-amino-2-phenylpropanoic acid → (S)-2-(Boc-amino)-2-phenylpropanoic acid

To a suspension of 500 mg of 2-phenyl-D-alanine (3.02 mmol) and trimethylammonium hydroxide (aqueous solution 10%, 2.8 mL, 3.02 mmol) in 15 mL of acetonitrile, diterbutylcarbonate (1.047 g, 4.8 mmol) was added and the mixture was stirred at room temperature for 2 days. The solvent was then removed under vacuo, the residue was dissolved in water and washed with diethylether. The aqueous layer was acidified to pH=3-4 with citric acid and the product was extracted with ethyl acetate (3×20 mL). The combined organic phase was washed with water, dried over Na2SO4 and evaporated. The title product was recovered as white solid (630 mg, yield 78%).