Lithocholic acid (81) (9.78 g, 26 mmol) was sissolved in anhydrous tetrahydrofuran (60 mL). Isobutylchloroformate (3.55 g, 3.55 mL, 26 mmol) was added followed by the addition of triethylamine (5.26 g, 7.25 mL, 52 mmol) and dioctadecylamine (7 g, 26 g). The reaction mixture was brought to ambient temperature and allowed to stir over night. The reaction mixture was concentrated under vacuum, and the residue was dissolved in dichloromethane (250 mL). The organic layer was washed with 5% sodium bicarbonate, 3% aqueous HCl and water. After drying over anhydrous sodium sulfate, the solvent was removed under reduced pressure to afford amide 88 (14.5 g) in 89% yield. This was used as such for the next step.
