Reaction Steps
To a solution of (3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-(2-aminoethyl)-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 acetate (34) (5.3 g, 10.36 mmol), TEA (2.165 mL, 15.53 mmol) and TEA (2.165 mL, 15.53 mmol) in dichloromethane (DCM) (100 mL) stirred at room temp was added BOC2O (2.404 mL, 10.36 mmol). The reaction mixture was stirred at 20° C. for 2 h. The reaction mixture was poured into ice water (300 ml) and the solids were collected and dried to give (3aR,5aR,5bR,7aR,9S,11aR,11bR,13aS)-3a-(2-((tert-butoxycarbonyl)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 acetate (35) (5.8 g, 8.34 mmol, 81% yield) as a white foam. This was ssed crude in next reaction without further purification. 1H NMR (400 MHz, CHLOROFORM-d) b=4.58-4.37 (m, 2H), 3.26-2.96 (m, 4H), 2.93-2.72 (m, 2H), 2.28 (d, J=18.8 Hz, 1H), 2.11-0.71 (m, 53H); LC/MS: m/z calculated 611.5. found 634.3 (M+Na)+.
