4-[3-(3-Bromophenyl)-1-(4-cyclohexylphenyl)ureidomethyl]benzoic acid (0.20 g, 0.39 mmol) was dissolved in DMF (2.5 mL) and EDAC (0.12 g, 0.6 mmol) and HOBt (0.089 mg, 0.6 mmol) were added and the mixture was stirred at room temperature for 10 min. (R)-Isoserine ethyl ester hydrochloride (0.10 g, 0.6 mmol) and N,N-diisopropylethylamine (130 μL) dissolved in DMF (2.5 mL) were added and the resulting mixture was stirred at room temperature for 16 hours. The mixture was added ethyl acetate (70 mL) and washed with water (2×100 mL), the organic phase was dried with sodium sulphate and concentrated in vacuo. The residue was purified by column chromatography on silica gel eluting with a mixture of ethyl acetate:n-heptane (1:2) containing 10% acetic acid. This afforded 100 mg of (R)-3-{4-[3-(3-bromophenyl)-1-(4-cyclohexylphenyl)ureidomethyl]benzoylamino}-2-hydroxypropionic acid ethyl ester. HPLC-MS (Method B): m/z=624 (M+1); Rt=5.33 min.
