0.15 ml (1.33 mmol) of N-methylmorpholine is added to a solution of 0.5 g (1.2 mmol) of 3-{3′-[(tert-butoxycarbonylmethylamino)methyl]biphenyl-4-yl}-2-ethoxypropionic acid, 0.14 g (1.3 mmol) of butyric hydrazide and 0.33 g (2.4 mmol) of 1-hydroxybenzotriazole in 10 ml of tetrahydrofuran cooled to −5° C. After stirring for 5 minutes, 0.2 ml (1.3 mmol) of diisopropylcarbodiimide is added. The reaction medium is stirred at 0° C. for 1 hour and then at room temperature for 2 hours, diluted with ethyl acetate, washed with saturated aqueous caesium hydrogen carbonate solution, extracted with ethyl acetate, dried over magnesium sulfate, filtered and concentrated. The residue obtained is chromatographed on a column of silica eluted with a 1/1 heptane/ethyl acetate mixture. 0.6 g of tert-butyl N-{4′-[3-(N′-butyrylhydrazino)-2-ethoxy-3-oxopropyl]biphenyl-3-ylmethyl}-N-methylcarbamate is obtained in a yield of 100%.
