4-O-tert-butyl 1-O-methyl butanedioate

Conditions: temp:20.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A mixture of tert-butyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(2-((2-hydroxyethyl)(methyl)amino)ethylcarbamoyl)-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 (40 mg, 0.056 mmol), tert-butyl methyl succinate (21.06 mg, 0.112 mmol), Hunig'sBase (0.049 mL, 0.280 mmol) and EDC (21.45 mg, 0.112 mmol) in dichloromethane (1 mL) was stirred at 20° C. for 12 hours. LCMS indicated the formation of desired product. The reaction mixture was quenched with distilled water, extracted with DCM (3×4 mL). All the extracts were combined, dried over sodium sulfate, filtered and concentrated under reduced pressure to provide the crude including the title compound as a white solid (40 mg, 82%). LCMS: m/e 871.43 (M+H)+, 3.93 min (method 1).

Conditions: temp:20.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A mixture of tert-butyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-(2-((2-hydroxyethyl)(methyl)amino)ethylcarbamoyl)-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 (40 mg, 0.056 mmol), tert-butyl methyl succinate (21.06 mg, 0.112 mmol), Hunig'sBase (0.049 mL, 0.280 mmol) and EDC (21.45 mg, 0.112 mmol) in dichloromethane (1 mL) was stirred at 20° C. for 12 hours. LCMS indicated the formation of desired product. The reaction mixture was quenched with distilled water, extracted with DCM (3×4 mL). All the extracts were combined, dried over sodium sulfate, filtered and concentrated under reduced pressure to provide the crude including the title compound as a white solid (40 mg, 82%). LCMS: m/e 871.43 (M+H)+, 3.93 min (method 1).