To a solution of 2-(dimethylamino)acetaldehyde, hydrochloride (238 mg, 1.922 mmol) in methanol (12 mL) was added 4-(((3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-((S)-1-acetoxy-2-((4-chlorobenzyl)amino)ethyl)-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 (50) (150 mg, 0.192 mmol). The reaction mixture was stirred at rt for 2 h then sodium cyanoborohydride (121 mg, 1.922 mmol) was added and the mixture was stirred overnight. Upon completion, the mixture was purified preparative-HPLC to provide the title compound (50 mg, 24%). 1H NMR (400 MHz, CHLOROFORM-d) δ=7.35-7.12 (m, 4H), 5.65 (d, J=9.3 Hz, 1H), 4.49 (dd, J=5.8, 10.0 Hz, 1H), 3.83 (d, J=13.6 Hz, 1H), 3.55 (d, J=13.6 Hz, 1H), 3.25-2.91 (m, 7H), 2.91-2.73 (m, 7H), 2.73-2.52 (m, 3H), 2.33 (d, J=18.1 Hz, 1H), 1.99-0.72 (m, 48H); LC/MS: m/z calculated 850.5. found 851.4 (M+1)+.
