Reaction Steps
To a solution of methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-3a-thioureido-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 (150 mg, 0.249 mmol) in DMF (5 mL) was added N,N-diisopropylethylamine (0.173 mL, 0.995 mmol) and 3-bromobutan-2-one (56.4 mg, 0.373 mmol). The reaction mixture was stirred at rt. After 18 h, the reaction mixture was poured into a separatory funnel containing H2O (10 mL) and extracted with EtOAc (50 mL). The organic layer was washed with brine, dried over MgSO4, filtered and concentrated to white solid. The material was redissolved in DCM (5 mL) and MeOH was added to effect precipitation. The mixture was concentrated to remove most of DCM and the resulting white precipitate was filtered, washed with cold MeOH, and dried in a vacuum oven to give methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(4,5-dimethylthiazol-2-ylamino)-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 (121 mg, 0.175 mmol, 70.5% yield) as a white solid. LCMS: m/e 655.3 (M+H)+, 2.72 min (method 2). 1H NMR (500 MHz, CHLOROFORM-d) δ 7.95 (d, J=8.2 Hz, 2H), 7.21 (d, J=8.2 Hz, 2H), 5.31 (d, J=4.6 Hz, 1H), 4.76 (br. s., 1H), 4.65 (s, 1H), 3.93 (s, 3H), 2.43 (d, J=10.4 Hz, 1H), 2.21 (s, 3H), 2.15 (s, 3H), 2.11 (d, J=6.7 Hz, 1H), 2.07-1.96 (m, 1H), 1.80-1.65 (m, 6H), 1.57-1.36 (m, 8H), 1.35-1.27 (m, 2H), 1.23 (d, J=10.1 Hz, 1H), 1.17-1.11 (m, 1H), 1.09 (s, 3H), 1.03 (s, 3H), 1.00 (s, 3H), 0.94 (s, 6H).
