804 (3.1 mmol) of diethyl 2-(cyclohexylamino)-vinyl-phosphate dissolved in 6 ml of dry tetrahydrofuran are added dropwise under nitrogen to a suspension of 59 mg (2.5 mmol) of sodium hydride in 6 ml of dry tetrahydrofuran at -5° C. After 30 min, 0.65 g (2.05 mmol) of the compound from Example 9 in 15 ml of dry tetrahydrofuran is added dropwise at the same temperature and the mixture is heated to reflux for 30 min. After cooling to room temperature, the mixture is added to 200 ml of ice-cold water and extracted three times using 100 ml of ethyl acetate each time. The combined organic phases are washed with saturated sodium chloride solution and dried over sodium sulphate. After concentration in vacuo, the residue is taken up in 5 ml of toluene, treated with a solution of 0.9 g (7 mmol) of oxalic acid dihydrate in 12 ml of water and heated to reflux for 90 min. After cooling to room temperature, the phases are separated, and the organic phase is washed with saturated sodium chloride solution, dried over sodium sulphate and concentrated in vacuo. The residue is dissolved in methylene chloride and filtered through silica gel.
