A solution of 1α,3β-bis(tert-butyldimethylsilyloxy)-20(R)-(3-hydroxy-3-methylbutyloxy)pregna-5,7,16-triene (50 mg, 0.0775 mmol) in tetrahydrofuran (1 ml) was combined with 1M tetra-n-butylammonium fluoride solution in tetrahydrofuran (0.5 ml) and stirred at room temperature for 12 hours, then with heating under reflux for 5 hours. The reaction solution was diluted with ethyl acetate and washed with saturated aqueous sodium bicarbonate solution and brine successively, and the organic layer was dried over magnesium sulfate. The solvent was distilled off under reduced pressure and the resulting residue was purified by preparative thin layer chromatography (0.5 mm×2, dichloromethane:ethanol=20:1, developed twice) to give the title compound as a colorless oil (23.8 mg, 74%) and recovered raw materials (6 mg, 12%).
