反応手順
Preparation of tert-butyl 3-(((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-9-(4-(methoxycarbonyl)phenyl)-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-3a-ylamino)methyl)piperidine-1-carboxylate. To a solution 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 (30 mg, 0.055 mmol) in dichloroethane (0.5 mL) was added 3-formyl-piperidine-1-carboxylic acid tert-butyl ester (14.71 mg, 0.069 mmol) and titanium (IV) isopropoxide (0.020 mL, 0.069 mmol). The mixture was stirred at rt for 1 h and sodium triacetoxyborohydride (23.38 mg, 0.110 mmol) was added. The mixture was stirred at rt for 16.5 h, then was diluted with 3 mL of sat. NaHCO3 and was extracted with dichloromethane (3×5 mL). The combined organic layers were dried with Na2SO4, were filtered and were concentrated under reduced pressure. The residue was adsorbed to silica gel and was purified by flash chromatography using a 0-10% ethyl acetate in hexanes gradient and a Thomson 12 g silica gel column. The fractions containing the expected product were combined and concentrated under reduced pressure to give the title compound as an off-white foam. LCMS: m/e 741.7 (M+H)+, 3.76 min (method 2). Step 2. To a solution of tert-butyl 3-(((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-9-(4-(methoxycarbonyl)phenyl)-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-3a-ylamino)methyl)piperidine-1-carboxylate (0.029 g, 0.039 mmol) in 1,4-dioxane (2 mL) was added NaOH (1N) (0.196 mL, 0.196 mmol). The mixture was heated to 85° C. for 22 h, then was cooled to rt, was diluted with MeOH, 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-((1-(tert-butoxycarbonyl)piperidin-3-yl)methylamino)-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 (24 mg, 0.031 mmol, 56% yield over 2 steps) as a clear, colorless film. LCMS: m/e 727.7 (M+H)+, 2.00 min (method 2). 1H NMR (500 MHz, Chloroform-d) δppm 7.98 (d, J=7.93 Hz, 2H), 7.21 (d, J=7.93 Hz, 2H), 5.29 (d, J=5.49 Hz, 1H), 4.70 (br. s., 1H), 4.58 (br. s., 1H), 3.82-4.51 (m, 5H), 1.68 (s, 3H), 1.47 (d, J=4.58 Hz, 9H), 1.10 (d, J=7.93 Hz, 3H), 0.98 (br. s., 6H), 0.93 (s, 3H), 0.92 (s, 3H), 0.90-2.85 (m, 30H).
