Reaction Steps
To a solution of 1-tert-butyl 4-((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-((S)-3-(1-(5-chloropyrimidin-2-yl)cyclopropyl)-2-oxooxazolidin-5-yl)-1-isopropyl-5a,5b,8,8,11a-pentamethyl-2-oxo-3,3a,4,5,5a,5b,6,7,7a,8,9,10,11,11a,11b,12,13,13a-octadecahydro-2H-cyclopenta[a]chrysen-9-yl) 2,2-dimethylsuccinate (109) (80 mg, 0.094 mmol) in DCM (10 mL) was added TFA (1 mL, 0.094 mmol). The reaction mixture was stirred at rt overnight, then diluted with DCM (20 ml) and washed with water (2×15 ml), saturated sodium bicarbonate solution (20 ml) and brine (20 ml), dried over sodium sulfate, filtered and concentrated to get a residue. The residue was purified on silica gel using petroleum ether/EtOAc (4:1 to 1:1) as eluent to give the product 4-(((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-((S)-3-(1-(5-chloropyrimidin-2-yl)cyclopropyl)-2-oxooxazolidin-5-yl)-1-isopropyl-5a,5b,8,8,11a-pentamethyl-2-oxo-3,3a,4,5,5a,5b,6,7,7a,8,9,10,11,11a,11b,12,13,13a-octadecahydro-2H-cyclopenta[a]chrysen-9-yl)oxy)-2,2-dimethyl-4-oxobutanoic acid (111) (50 mg, 67%) as a white solid. This material was lyophilized to give a white powder. Stereochemistry was tentatively assigned as drawn but not fully confirmed spectroscopically. 1H NMR (400 MHz, CHLOROFORM-d) δ=8.58 (s, 2H), 5.04 (t, J=8.5 Hz, 1H), 4.51 (dd, J=4.6, 10.9 Hz, 1H), 3.41-3.04 (m, 4H), 2.75-2.44 (m, 3H), 2.36 (d, J=13.3 Hz, 1H), 2.12-0.72 (m, 49H); LC/MS: m/z calculated 791.4. found 792.3 (M+1)+.
