100 mg of (S)-α-[(S)-α[(t-butylsulphonyl)methyl]-hydrocinnamamido]-N-[(1S,2R,3S)-1-(cyclohexylmethyl)-2,3-dihydroxy-4-methylpentyl]imidazole-4-propionamide, 200 mg of succinic anhydride and 200 mg of sodium carbonate in 10 ml of dimethylformamide are stirred at 50° overnight. Thereafter, the reaction mixture is taken up in ethyl acetate and the organic phase is washed with saturated ammonium chloride solution and water, dried and evaporated. Chromatography of the resiude on 20 g of silica gel with a 90:10:1:0.5 mixture of methylene chloride, methanol, water and acetic acid yields (1S,2R,3S)-3-[(S)-α-[(t-butylsulphonyl)methyl]-hydrocinnamamido]imidazole-4-propionamido]-4-cyclohexyl-1-isopropylbutyl hydrogen succinate as a foam, MS: 733 (M+H)+, and (1R,2S)-1-[(S)-1-[(S)-α-[(t-butylsulphonyl)methyl]hydrocinnamamido]imidazole-4-propionamide]-2-cyclohexylethyl]-2-isopropylethylene bis(hydrogen succinate) in the form of a foam, MS: 833 (M+H)+.
