0.36 g of (aminomethyl)[(RS)-4-methyl-2-[[(S)-3-methyl-1-(methylcarbamoyl)butyl]carbamoyl]pentyl]phosphinic acid methyl ester acetate, prepared as described in Example 2(A)(i), was dissolved in 10 ml of dichloromethane and 0.17 g of succinic anhydride and 0.17 g of triethylamine were added. After stirring at room temperature for 2 hours, 0.2 g of hydroxybenzotriazole and 0.2 g of N,N'-dicyclohexylcarbodiimide were added. The mixture was stirred at room temperature for 18 hours and then filtered in order to remove dicyclohexylurea. The filtrate was washed twice with 15 ml of saturated sodium hydrogen carbonate solution each time. After drying over anhydrous sodium sulfate the solvent was removed by evaporation to give a colorless gum. This gum was purified by flash chromatography on silica gel using ethyl acetate/methanol (8:1) for the elution. There was obtained 0.23 g of [(RS)-4-methyl-2-[[(S)-3-methyl-1-(methylcarbamoyl)butyl]carbamoyl]pentyl](succinimidomethyl)phosphinic acid methyl ester in the form of a white foam.
