Reaction Steps
To a solution of 2-(dimethylamino)acetaldehyde, hydrochloride (6.75 g, 54.6 mmol) in methanol (20 mL) was added 4-(((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-((R)-2-((4-chlorobenzyl)amino)-1-hydroxyethyl)-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, Trifluoroacetic acid salt (46) (9.5 g, 10.92 mmol). The pH was adjusted to 7-8 with Et3N. The reaction mixture was stirred at rt for 2 h. Sodium cyanoborohydride (0.686 g, 10.92 mmol) was then added and the mixture was stirred at rt overnight. After the reaction was complete, water (15 mL) and EtOAc (15 mL) were added, and then the organic phase was removed and concentrated under reduced pressure. The product was extracted with EtOAc (80 mLx3), the combined organic phase was washed with brine, dried, and concentrated. The product was purified by flash chromatography (DCM:EtOAc=2:1 to 1:1, then DCM:MeOH=100:1 to 20:1) to give 4-(((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-((R)-2-((4-chlorobenzyl)(2-(dimethylamino)ethyl)amino)-1-hydroxyethyl)-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 (51) (6 g, 7.41 mmol, 67.9% yield) as white solid. Multiple batches of this material (were combined 95 g), dissolved in 600 mL of dichloromethane and washed with NaHCO3 (400 mL*3) and the organic phase was dried over Na2SO4, filtered and concentrated. The solids were washed with a mixture of EtOAc: petroleum ether (600 mL), and filtered followed by lyophilization to provide the final title compound 62 g as a white solid. 1H NMR (400 MHz, METHANOL-d4) δ=7.47-7.29 (m, 4H), 4.48 (dd, J=5.8, 10.3 Hz, 1H), 4.15-4.04 (m, 1H), 3.80 (d, J=13.8 Hz, 1H), 3.57 (d, J=14.1 Hz, 1H), 3.21-2.82 (m, 5H), 2.72-2.41 (m, 9H), 2.37-2.05 (m, 4H), 2.05-0.74 (m, 45H);
