Reaction Steps
A mixture of 4-tert-butoxy-3,3-dimethyl-4-oxobutanoic acid 10 (119 mg, 0.587 mmol), 3-(1-(5-chloropyrimidin-2-yl)cyclopropyl)-5-((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-9-hydroxy-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-3a-yl)oxazolidin-2-one (108) (130 mg, 0.196 mmol), EDC (188 mg, 0.978 mmol) and DMAP (71.7 mg, 0.587 mmol) in DCM (5 mL) was stirred at rt overnight. After the reaction finished, the mixture was diluted with DCM (25 ml), washed with water (2×15 ml) and brine (20 ml), dried over sodium sulfate, filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography using petroleum ether/EtOAc (6:1 to 3:1) as eluent to give the two diastereomeric products 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) and 1-tert-butyl 4-((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-((R)-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 (110) in the amounts of (80 mg, 45%) and (50 mg, 22%) as white solids. The stereochemical assignments for each diastereomer were not made. Compound A (tentatively designated as 109): LC/MS: m/z calculated 847.5. found 848.3 (M+1)+. Compound B (tentatively designated as 110): LC/MS: m/z calculated 847.5. found 848 (M+1)+.
