944 mg of 3-(3-bromo-5-[(t-butoxycarbonyl)amino]methyl-4-hydroxyphenyl)-2-isopropoxypropionic acid ethyl ester was dissolved in 5 ml of N,N-dimethylformamide, and 0.15 ml of iodomethane and 500 mg of potassium carbonate were successively added, followed by stirring for 2 hours at room temperature. Then, the reaction mixture was diluted with ethyl acetate, and the organic layer was washed with water and brine, and dried over anhydrous magnesium sulfate, and the solvent was evaporated. The residue was purified by silica gel column chromatography, to give 876 mg of 3-(3-bromo-5-[(t-butoxycarbonyl)amino]methyl-4-methoxyphenyl)-2-isopropoxypropionic acid ethyl ester from fractions eluted with hexane-ethyl acetate (4:1).
