The compound obtained in Step b (53.7 mg) was dissolved in trifluoroacetic acid (2 ml), added with triethylsilane (0.4 ml, Aldrich) and stirred at room temperature for 2.5 days. The reaction mixture was diluted with ethyl acetate, washed successively with saturated aqueous sodium hydrogencarbonate and saturated brine, dried over magnesium sulfate and concentrated. The resulting residue was applied on a silica gel column and eluted with chloroform/methanol (10:1) to obtain the title compound (28.1 mg).
