Reaction Steps
To a solution mixture of methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-amino-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1H-cyclopenta[a]chrysen-9-yl)benzoate (0.302 g, 0.555 mmol) and N,N-diisopropylethylamine (0.580 mL, 3.33 mmol) in DCM (5 mL) was added 2-(3H-[1,2,3]triazolo[4,5-b]pyridin-3-yl)-1,1,3,3-tetramethylisouronium hexafluorophosphate(V) (0.465 g, 1.222 mmol) and 1-(tert-butoxycarbonylamino)cyclopropanecarboxylic acid (0.223 g, 1.111 mmol). The reaction mixture was stirred at rt. After 18 h, the reaction was diluted with DCM (20 mL) and silica gel (4 g) was added. The mixture was concentrated to dryness and dried in vacuo to a free flowing powder. The material was loaded onto a silica gel column (25 g cartridge) gradient 100% hexanes to 25% EtOAc in hexanes over 240 mL, hold 25% EtOAc in hexanes to give methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(1-(tert-butoxycarbonylamino)cyclopropanecarboxamido)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1H-cyclopenta[a]chrysen-9-yl)benzoate (234 mg, 0.309 mmol, 55.6% yield) as a white solid. LCMS: m/e 727.4 (M+H)+, 5.17 min (method 2). 1H NMR (500 MHz, CHLOROFORM-d) δ 7.97-7.89 (m, 2H), 7.20 (d, J=8.5 Hz, 2H), 6.47 (br. s., 1H), 5.30 (dd, J=6.3, 1.7 Hz, 1H), 5.16-5.06 (m, 1H), 4.72 (d, J=1.8 Hz, 1H), 4.62 (s, 1H), 4.19-4.09 (m, 1H), 3.92 (s, 3H), 2.66-2.60 (m, 1H), 2.49 (d, J=4.6 Hz, 2H), 2.11 (dd, J=17.1, 6.4 Hz, 1H), 2.07-1.96 (m, 1H), 1.53 (s, 9H), 1.46 (s, 3H), 1.43 (d, J=2.7 Hz, 1H), 1.37 (d, J=3.4 Hz, 1H), 1.34 (d, J=3.7 Hz, 1H), 1.26 (dd, J=7.0, 3.1 Hz, 1H), 1.19-1.16 (m, 1H), 1.12 (br. s., 3H), 1.10-1.07 (m, 1H), 1.01 (s, 3H), 1.01-0.99 (m, 3H), 0.94 (s, 3H), 0.94 (s, 3H).
