O-tert-butyl-L-tyrosine (2.00 g, 8.42 mmol, 1.0 equiv.) and di-tert-butyl dicarbonate (2.20 g, 10.10 mmol, 1.2 equiv.) were dissolved in a mixture of THF (15 mL) and NaOH (1 N, 30 mL) and stirred at room temperature for 10 h. THF was removed under reduced pressure, and the pH of residual solution was adjusted to 3.0 with dilute hydrochloric acid and the crude product was extracted by ethyl acetate. The combined organic phases was washed with saturated brine (pH 3.0) and dried over anhydrous Na2SO4. The organic solvent was removed under reduced pressure and dried in a vacuum oven at room temperature overnight, affording (N-Boc-O-tert-butyl)-L-Tyr (Boc-O-tert-butyl-L-tyrosine) as a yellowish solid (2.64 g, 93%)[1].
