To a solution of Z-Phg-OSu (640 mg) in DMF (10 ml), 463 mg (1.84 mmol) of Tyr(3-tBu)-OMe and 408 mg (3.34 mmol) of DMAP were added and the mixture was stirred at room temperature for 1 hour. The reaction mixture was diluted with ethyl acetate and washed first with saturated aqueous NaHCO3, then with water and finally with saturated brine. The organic layer was dried with anhydrous magnesium sulfate and concentrated under reduced pressure; the resulting residue was subjected to silica gel column chromatography (eluting solvent; ethyl acetate:n-hexane=1:1) to give Z-Phg-Tyr(3-tBu)-OMe in the amount of 905 mg (quantitative).
