3-(4-Acetoxy-5-oxo-3-phenyl-2,5-dihydro-2-furyl)propionic acid (58 mg) was dissolved in a mixture of tetrahydrofuran (3 ml) and triethylamine (28 μl), and a solution of ethyl chlorocarbonate (19 μl) in tetrahydrofuran (1 ml) was added dropwise slowly at -5° C. over 10 minutes. The mixture was stirred at -5° C. for 30 minutes and filtered. To the filtrate was added a solution of sodium borohydride (23 mg) in water (1 ml) at 10° C. Then, the mixture was stirred at room temperature for 1.5 hours, acidified with cooled 1N hydrochloric acid, and extracted with ethyl acetate. After drying, the solvent was distilled off, and the residue was subjected to preparative silica gel thin layer chromatography (0.5 mm×4, Merck) using 35% ethyl acetate-chloroform as the developing solvent to give 3-hydroxy-5-(3-hydroxypropyl)-4-phenyl-2(5H)-furanone (Compound I, 10 mg) and 3-acetoxy-5-(3-hydroxypropyl)-4-phenyl-2(5H)-furanone (Compound II, 12 mg).
