Reaction Steps
Trifluoroacetic acid in CH2Cl2 (2:25, 10 mL) was added to tert-butyl 3-[(3-{(3β)-cholest-5-en-3-yl [(2-nitrophenyl)sulfonyl]amino}propyl)amino]-3-oxopropylcarbamate (17) (50 mg, 0.062 mmol). After 1 h at 23° C., TLC analysis (MeOH /CH2Cl2, 1:50) revealed conversion to the more polar primary amine. Aqueous NaOH (1 M, 20 mL) was added, the mixture was extracted with CH2Cl2 (2×5 mL), the combined organic extracts were dried over anhydrous Na2SO4, and solvent was removed in vacuo. Boc-β-alanine N-hydroxysuccinimidyl ester (54 mg, 0.189 mmol), CH2Cl2 (9 mL) and diisopropylethylamine (50 μL, 0.277 mmol) were added. After stirring for 5 h at 23° C., CH2Cl2 (5 mL) and aqueous citric acid (10%, 25 mL) were added followed by extraction with CH2Cl2 (2×5 mL). The organic extracts were dried over anhydrous Na2SO4 and removed in vacuo. Flash column chromatography (MeOH/CH2Cl2, 3:100) afforded 18 (52 mg, 95%), mp 96-98° C.; 1H NMR (400 MHz, CDCl3) δ 8.03-7.97 (m, 1H), 7.73-7.67 (m, 2H), 7.65-7.59 (m, 1H), 6.66 (br s, 1H), 6.58 (br s, 1H), 5.30 (br s, 1H), 5.21 (d, J=4.6 Hz, 1H), 3.63-3.52 (m, 3H), 3.40-3.32 (m, 6H), 2.46-2.35 (m, 5H), 2.01-0.98 (m, 29H), 1.42 (s, 9H), 0.95 (s, 3H), 0.91 (d, J=6.5 Hz, 3H), 0.87 (d, J=1.8 Hz, 3H), 0.86 (d, J=1.8 Hz, 3H), 0.66 (s, 3H); 13C NMR (75.5 MHz, CDCl3) δ 172.2, 171.8, 156.3, 148.1, 140.1, 134.0, 133.8, 131.9, 130.8, 124.3, 122.7, 79.3, 59.3, 56.8, 56.3, 50.1, 42.4, 41.8, 39.8, 39.7, 38.4, 37.8, 37.0, 36.7, 36.4 (×2), 36.3 (×2), 35.9, 35.8, 32.0 (×2), 31.9, 28.6 (×3), 28.4, 28.2, 27.7, 24.4, 24.0, 23.0, 22.7, 21.1, 19.6, 18.9, 12.0; IR (film) νmax 3378, 3284, 2935, 2867, 1688, 1643, 1548, 1366 cm−1; CI m/z 870.5407 (MH+, C47H76N5O8S requires 870.5415).
