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 (3 mL) was added N,N-diisopropylethylamine (0.217 mL, 1.244 mmol) and 1-bromopinacolone (0.056 mL, 0.373 mmol). The reaction mixture was stirred at rt overnight. After 18 h, the reaction mixture was poured into a separatory funnel containing H2O (5 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 (3 mL), MeOH wash added and concentrated to remove most of the DCM. 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-tert-butylthiazol-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 (154.0 mg, 0.225 mmol, 91% yield) as a white solid. LC/MS: m/e 683.4 (M+H)+, 2.88 min (method 11). 1H NMR (500 MHz, CHLOROFORM-d) δ 7.95 (d, J=8.2 Hz, 2H), 7.22 (d, J=8.2 Hz, 2H), 6.06 (s, 1H), 5.31 (d, J=4.6 Hz, 1H), 4.88 (s, 1H), 4.77 (s, 1H), 4.66 (s, 1H), 3.93 (s, 3H), 2.72 (d, J=13.7 Hz, 1H), 2.68-2.62 (m, 1H), 2.55 (dd, J=8.1, 12.7 Hz, 1H), 2.13 (dd, J=6.4, 17.1 Hz, 1H), 2.07-1.98 (m, 1H), 1.92-1.83 (m, 1H), 1.82-1.76 (m, 1H), 1.74 (s, 3H), 1.73-1.66 (m, 2H), 1.61 (s, 1H), 1.57-1.49 (m, 3H), 1.49-1.40 (m, 4H), 1.40-1.31 (m, 3H), 1.29 (s, 9H), 1.27-1.21 (m, 1H), 1.18-1.12 (m, 1H), 1.10 (s, 3H), 1.04 (s, 3H), 1.01 (s, 3H), 0.95 (s, 6H).
