To 350 mg of 2-methylthio-5-(1-hydroxy-6-methoxycarbonylhexyl)-4-(3-t-butyldimethylsilyloxy-1-octenyl)-2-cyclopentenone obtained in Example 6 was added a solvent mixture of 10 ml of acetic acid, 5 ml of tetrahydrofuran, and 5 ml of water, and the mixture was stirred for 24 hours. Toluene was then added, and after concentration, the concentrate was diluted with saturated aqueous sodium hydrogencarbonate and extracted with ethyl acetate. Subsequently, the extract was washed with saturated aqueous sodium chloride, dried over anhydrous magnesium sulfate, filtered and concentrated, followed by silica gel chromatography to give 178 mg (yield 65%) of 2-methylthio-5-(1-methoxycarbonylhexyl)-4-(3-hydroxy-1-octenyl)-2-cyclopentenone.
