Reaction Steps
Preparation of methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(isobutylamino)-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. To a sealable vial containing 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, HCl (0.075 g, 0.129 mmol) was added potassium carbonate (0.036 g, 0.258 mmol). The mixture was diluted with DMF (1 mL) and isobutyl iodide (0.045 mL, 0.388 mmol) was added. The vial was sealed and the mixture was heated to 75° C. for 23 h, then the mixture was cooled to rt. LC/MS showed formation of the expected product, but starting material still remained. To the mixture was added additional isobutyl iodide (0.045 mL, 0.388 mmol) and the vial was sealed and heated to 75° C. for 48 h. The mixture was cooled to rt then was diluted with 5 mL of water. The solids that formed were collected by filtration then were washed with water to give the expected product, methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(isobutylamino)-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 (53 mg, 0.075 mmol, 58.1% yield) as a light-yellow solid. The crude product was used in the next step with no additional purification. LCMS: m/e 600.6 (M+H)+, 2.14 min (method 2). Step 2. To a solution of methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(isobutylamino)-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 (52 mg, 0.087 mmol) in 1,4-dioxane (1.5 mL) was added NaOH (1N) (0.3 mL, 0.300 mmol). The mixture was heated to 75° C. for 67 h then was cooled to rt. The mixture was diluted with 1,4-dioxane and methanol, was filtered through a plug of glass wool, and was purified by prep HPLC. The fractions containing the expected product were combined and concentrated under reduced pressure to give 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(isobutylamino)-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)benzoic acid (25.2 mg, 0.041 mmol, 47.1% yield) as a white solid. LCMS: m/e 586.6 (M+H)+, 1.85 min (method 2). 1H NMR (400 MHz, Acetic acid d4) δ 8.00 (d, J=8.28 Hz, 2H), 7.26 (d, J=8.28 Hz, 2H), 5.33 (d, J=4.52 Hz, 1H), 4.81 (s, 1H), 4.69 (s, 1H), 3.15 (dd, J=5.02, 12.05 Hz, 1H), 2.88-2.98 (m, 1H), 2.78 (dd, J=9.03, 11.80 Hz, 1H), 1.72 (s, 3H), 1.22 (s, 3H), 1.10 (s, 3H), 1.09 (d, J=6.78 Hz, 3H), 1.06 (s, 3H), 1.01 (d, J=6.78 Hz, 3H), 0.98 (s, 3H), 0.96 (s, 3H), 0.83-2.31 (m, 23H).
