Under a nitrogen atmosphere, (E)-10-hexylsulfamoyl-dec-3-enoic acid (100 mg, 0.30 mmol) obtained in Step C-3 and (S)-4-isopropyl-5,5-diphenyl-oxazolidine-2-thione (89.2 mg, 0.30 mmol) were dissolved in dichloromethane (3.5 mL), and the mixture was cooled to 0° C. While maintaining the temperature at 0° C., N,N-dimethyl-4-aminopyridine (3.7 mg, 0.03 mmol) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (74.7 mg, 0.39 mmol) were added in order, and the mixture was stirred at 0° C. for 2 minutes and at room temperature for 13 hours. To the reaction solution was added an aqueous solution (4.2 mL) of 10% sodium dihydrogen phosphate and ethyl acetate and the mixture was extracted. The organic layer was washed with water and a saturated brine in order, dried over anhydrous sodium sulfate, and filtered. The solvent was distilled off. The resulting residue was then purified with SP1 (SiO2 cartridge, 20% ethyl acetate/n-hexane, Rf=0.25) to obtain the target compound, (E)-104(S)-4-isopropyl-5,5-diphenyl-2-thioxo-oxazolidin-3-yl)-10-oxo-dec-7-ene-1-sulfonic acid hexylamide (ESI (LC/MS positive mode) m/z 613 (M+H); Rt 2.60 min.; 65% purity, 96.8 mg, 53% yield).
