4-[9-(t-Butyldimethylsilyloxy)nonyl]-7-methoxy-3-(4-methoxyphenyl)-3-methylthiochroman (400 mg, 0.72 mmol) obtained in Example 29 was dissolved in tetrahydrofuran (40 ml), and 3N--HCl (2 ml) was added thereto. The reaction mixture was stirred for 3 hours at room temperature. When the reaction is completed, water was added to the reaction solution which was then extracted with ethyl acetate. The extract was dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified with column chromatography (n-hexane:ethyl acetate=7:3) to obtain 235 mg (yield: 74%, 3RS,4RS/3RS,4SR=9:1) of the title compound as a white solid.
