Reaction Steps
To DMF (10 mL) was added 3β-amino-5-cholestene (2, 386 mg, 1.0 mmol),1 ethyl 5-bromovalerate (174 μL, 1.1 mmol) and K2CO3 (276 mg, 2.0 mmol). The solution was heated to 60° C. and stirred for 24 h. The reaction was cooled to 23° C. and DMF was removed in vacuo. To the resulting solid residue was added CH2Cl2 (10 mL), insoluble salts were removed by filtration, and solids were washed with additional CH2Cl2 (5 mL). To this solution containing the crude secondary amine product was added (Boc)2O (327 mg, 1.5 mmol) and DIEA (0.5 mL, 3.0 mmol). The reaction was stirred for 3 h at 23° C. and concentrated in vacuo. Flash column chromatography (hexanes/ethyl acetate, 10:1) afforded 3 (417 mg, 68%) as a white solid, mp 78-79° C.; 1H NMR (400 MHz, CDCl3) δ 5.30 (d, 1H), 4.10 (q, J=7.1 Hz, 2H), 3.73 (br s, 1H), 3.09 (br s, 2H), 2.30 (t, J=7.1 Hz, 2H), 2.01-0.83 (m, 56H), 0.66 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 173.6, 155.5, 141.3, 121.4, 79.3, 60.4, 56.9, 56.3 (×2), 50.3, 42.6 (×2), 39.9, 39.7, 38.6, 37.1, 36.8, 36.3, 35.9, 34.2, 32.0 (×2), 28.7 (Boc Me3), 28.4, 28.1 (×2), 26.9, 24.4, 24.0, 23.0, 22.7, 22.6, 21.2, 19.6, 18.9, 14.4, 12.0; IR (film) ν max 2935, 2867, 1737, 1692, 1466, 1409, 1365, 1247, 1173 cm−1; CI m/z 614.5146 (MH+, C39H68NO4 requires 614.5148).
