Synthesis of Ursodeoxycholic Acid Conjugate

Following general procedure B, ursodeoxycholic acid (0.045 g, 0.115 mmol) was reacted with di-tert-butyl butane-1,4-diylbis((3-aminopropyl)carbamate) (6a) (0.023 g, 0.0573 mmol), EDC·HCl (0.033 g, 0.172 mmol), HOBt (0.008 g, 0.0573 mmol) and DIPEA (0.040 mL, 0.229 mmol) to afford di-tert-butyl butane-1,4-diylbis((3-((R)-4-((3R,5S,7S,8R,9S,10S,13R,14S,17R)-3,7-dihydroxy-10,13-dimethylhexadecahydro-1H-cyclopenta[a]phenanthren-17-yl)pentanamido)propyl)carbamate) (0.061 g, 92%) as a clear colorless oil. Following general procedure C, a sub-sample of the product (0.005 g, 0.00434 mmol) was reacted with TFA in CH₂Cl₂ to afford, after chromatography, the di-TFA salt 8a (0.005 g, 98%) as a pale-yellow oil. [α ${]}_{\mathsf{D}}^{19.1}$ = +24 (c = 0.1, MeOH); R_f (RP-18, 10% aq. HCl:MeOH 1:3) 0.26; IR (ATR) ν_max 3328, 1638, 1202, 1038, 1027 cm⁻¹; ¹H NMR (DMSO-d₆, 400 MHz) δ 8.42 (4H, br s, NH₂-29), 7.99 (2H, t, J = 5.5 Hz, NH-25), 3.39–3.28 (4H, m, H-3, H-7), 3.11 (4H, q, J = 6.2 Hz, H₂-26), 2.92–2.88 (8H, m, H₂-28, H₂-30), 2.09–0.83 (72H, m, H₂-1, H₂-2, H₂-4, H-5, H₂-6, H-8, H-9, H₂-11, H₂-12, H-14, H₂-15, H₂-16, H-17, H₃-19, H-20, H₃-21, H₂-22, H₂-23, H₂-27, H₂-31), 0.61 (6H, s, H₃-18); ¹³C NMR (DMSO-d₆, 100 MHz) δ 173.3 (C-24), 69.7 (C-3), 69.5 (C-7), 55.9 (C-14), 54.7 (C-17), 46.1 (C-30), 44.6 (C-28), 43.1, 43.0 (C-8, C-13), 42.2 (C-5), 39.2 (C-12, obscured by solvent), 38.8 (C-10), 37.7 (C-4), 37.3 (C-6), 35.6 (C-26), 35.0, 34.9 (C-9, C-15, C-20), 33.8 (C-1), 32.4 (C-23), 31.7 (C-22), 30.2 (C-2), 28.2 (C-16), 26.1 (C-27), 23.3 (C-19), 22.7 (C-31), 20.9 (C-11), 18.4 (C-21), 12.0 (C-18); (+)-HRESIMS [M + H]⁺ m/z 951.7873 (calcd for C₅₈H₁₀₃N₄O₆, 951.7872).