Reaction Steps
To a solution of methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(2-(tert-butyldimethylsilyloxy)ethylamino)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1H-cyclopenta[a]chrysen-9-yl)benzoate (0.211 g, 0.301 mmol) in THF (2 mL) was added TBAF (1M in THF) (0.601 mL, 0.601 mmol). The mixture was stirred at rt for 2.75 h then was diluted with water (10 mL) and was extracted with dichloromethane (3×10 mL). The combined organic layers were dried with Na2SO4, the drying agent was removed by filtration and the filtrate was concentrated under reduced pressure. The residue was adsorbed to silica gel and was purified by flash chromatography using a 0-25% EtOAc in hexanes gradient. The title compound (93.4 mg, 0.159 mmol, 52.9% yield), was isolated as a colorless film. LCMS: m/e 588.6 (M+H)+, 1.98 min (method 2). 1H NMR (500 MHz, CHLOROFORM-d) d ppm 7.91 (d, J=8.24 Hz, 2H), 7.18 (d, J=8.24 Hz, 2H), 5.27 (d, J=4.58 Hz, 1H), 4.70 (d, J=1.83 Hz, 1H), 4.59 (s, 1H), 3.89 (s, 3H), 3.54-3.64 (m, 2H), 2.52-2.69 (m, 3H), 2.09 (dd, J=17.09, 6.41 Hz, 1H), 1.68 (s, 3H), 1.07 (s, 3H), 0.98 (s, 3H), 0.97 (s, 3H), 0.93-2.05 (m, 21H), 0.91 (s, 3H), 0.91 (s, 3H).
