Reaction Steps
To a vial containing a suspension of 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((2-(1,1-dioxidothiomorpholino)ethyl)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)cyclohex-3-enecarboxylic acid (0.025 g, 0.036 mmol) in THF (1 mL) was added (Z)-2-(trimethylsilyl)ethyl N,N′-diisopropylcarbamimidate (0.017 g, 0.070 mmol). The vial was sealed and heated to 70° C. and upon heating the solids completely dissolved. After 4.5 h of heating, the mixture was cooled to rt. LC/MS showed a mixture of starting material and product present. Since the seal on the vial started to fail, 1 mL of 1,4-dioxane was added and the mixture was again heated to 70° C. After heating the mixture for 21 h (total), the mixture was cooled to rt. LC/MS still showed starting material present, so an additional 30 mg of (Z)-2-(trimethylsilyl)ethyl N,N′-diisopropylcarbamimidate was added and the mixture was further heated to 70° C. After 7 h of heating, the mixture was cooled to rt. The mixture was purified by flash chromatography using a 0-50% ethyl acetate in hexanes gradient and a 12 g silica gel column. The fractions containing the expected product were combined and concentrated under reduced pressure to give 2-(trimethylsilyl)ethyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-((2-(1,1-dioxidothiomorpholino)ethyl)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)cyclohex-3-enecarboxylate (0.02 g, 0.025 mmol, 69.9% yield) as a white foam. The mixture of diastereomers was separated by SFC (Chiral SFC Method 1) and the fractions containing each isolate was concentrated under reduced pressure to give 4.7 mg of isomer 1 and 6.1 mg of isomer 2. Isomer 1: 1H NMR (400 MHz, chloroform-d) δ=5.35 (br. s., 1H), 5.18 (d, J=4.5 Hz, 1H), 4.71 (br. s., 1H), 4.59 (br. s., 1H), 4.21-4.14 (m, 2H), 3.16-2.95 (m, 8H), 2.75-2.39 (m, 6H), 2.30 (br. s., 2H), 2.17 (br. s., 2H), 1.69 (s, 3H), 1.06 (s, 3H), 0.98 (br. s., 3H), 0.96 (br. s., 3H), 0.90 (s, 3H), 0.86 (s, 3H), 2.04-0.83 (m, 27H), 0.065-0.04 (m, 9H). Isomer 2: 1H NMR (400 MHz, chloroform-d) δ=5.35 (br. s., 1H), 5.21-5.16 (m, 1H), 4.71 (br. s., 1H), 4.60 (br. s., 1H), 4.21-4.14 (m, 2H), 3.14-2.97 (m, 8H), 2.74-2.42 (m, 6H), 2.30 (br. s., 2H), 2.25-2.08 (m, 2H), 1.69 (s, 3H), 1.06 (s, 3H), 0.96 (br. s., 3H), 0.95 (s, 3H), 0.94 (s, 3H), 0.86 (s, 3H), 2.03-0.83 (m, 27H), 0.065-0.04 (m, 9H).
