27.25 g of O-benzyl-N-benzyloxycarbonyltyrosine methyl ester was dissolved in a mixed solvent of 185 ml of ethanol and 122 ml of tetrahydrofuran, and to the solution were added 5.8 g of lithium chloride and 5.2 g of sodium borohydride under ice cooling. The reaction mixture was stirred at a room temperature for 18 hours, and after the addition of 500 ml of saturated sodium chloride aqueous solution, extracted twice with 300 ml of chloroform. The extract was dried over magnesium sulfate and concentrated under a reduced pressure to obtain 25.4 g of the title compound as colorless crystals
