67 μl of triethylamine, 34 mg of 4-aminobutyric acid amide hydrochloride and 38 μl of cyanophosphonic acid diethyl ester are added in succession to 128 mg of 5(S)-tert-butoxycarbonylamino-4(S)-tert-butyldimethylsilyloxy-7(S)-isopropyl-2(R)-methyl-8-[4-methoxy-3-(3-methoxy-propyloxy)-phenyl]-octanoic acid in 8 ml of dimethylformamide at 0° C. The reaction mixture is stirred for a further 18 hours at room temperature. The reaction mixture is concentrated by evaporation and 20 ml of 10% citric acid solution and ice are added to the residue. The mixture is extracted repeatedly with ethyl acetate and the organic phases are then washed with saturated sodium hydrogen carbonate solution and saturated sodium chloride solution. After concentration by evaporation, the residue is purified by means of FC (70 g of silica gel, dichloromethane/methanol=9:1). The title compound is obtained: Rf (dichloromethane/methanol=9:1)=0.38.
