To a solution of Tyr(3-tBu)-OMe (1.1 g) in H2O (10 ml), 0.7 g (6.57 mmol) of NaHCO3 and 0.92 ml (6.57 mmol) of Z-Cl were added under cooling with ice and the mixture was stirred at room temperature for 1 hour. The reaction mixture was diluted with ethyl acetate and washed with water and saturated brine. The organic layer was dried with anhydrous sodium sulfate and concentrated under reduced pressure. The resulting residue was subjected to silica gel column chromatography (eluting solvent; ethyl acetate:n-hexane=1:2) to give Z-Tyr(3-t-Bu)-OMe in the amount of 1.44 g (85%).
