(8E,12E,14E)-3,16,21-tris(1-ethoxyethoxy)-7-hydroxy-6,10,12,16,20-pentamethyl-18,19-epoxytricosa-8,12,14-trien-11-olide (129 mg, 182 μmol) was dissolved in methylene chloride (1 mL). Triethylamine (127 μL, 911 μmol) and 4-dimethylaminopyridine (67.0 mg, 548 μmol) were added to the reaction mixture, and the reaction mixture was stirred at room temperature for 30 minutes. A solution of 4-nitrophenyl chloroformate (112 mg, 556 μmol) in methylene chloride (1 mL) was added dropwise to this reaction mixture and the reaction mixture was stirred at room temperature for 3.5 hours. The reaction mixture was diluted with ethyl acetate (30 mL), and the organic layer was washed with a saturated aqueous solution of sodium hydrogencarbonate (10 mL) and purified water (10 mL) twice, and with brine (10 mL). The resulting organic layer was dried over anhydrous sodium sulfate, filtered and concentrated. The resulting concentrate was purified by silica gel column chromatography (Merck Silica gel 60, 63 to 200 μm; hexane:ethyl acetate=5:1->4:1) to obtain the title compound (137 mg, 156 μmol, 85.8%) as a colorless oil.
