4.10. 30-nor-3β-acetoxy-11-oxo-20-(3′-ethyl-1′,2′,4′-oxadiazol-5′-yl)-18βH-olean-12-en (4b)

Crude product 4b (0.45 g, 67%) was obtained according to the general procedure B from compound 3b (0.69 g, 1.17 mmol), Bu₄NF 1M solution in THF (1.2 mL, 1.17 mmol), and THF (8 mL). Crude product 4b was purified by flash column chromatography (SiO₂, CHCl₃) and recrystallized from MeOH–CH₂Cl₂ to give a pure sample of 4b (0.38 g, 57%). Mp 279.5–280.6 °C. [αD23] +163 (c 0.20 g/100 mL; CHCl₃). HRMS: Calc. for (C₃₅H₅₂O₄N₂)⁺ m/z = 564.3922; found m/z = 564.3919. ¹H NMR (CDCl₃, 400 MHz): δ = 5.66 (s, 1H, H-12), 4.47 (dd, 1H, J_3a,2a = 11.4, J_3a,2e = 4.4, H-3a), 2.75 (dm, 1H, J_1e,1a = 13.6, H-1e), 2.71 (ddd, 2H, J = J = J = 7.6, CH₂-1″), 2.32 (s, 1H, H-9), 2.20-1.96 (m, 7H; H-21, H-18, H-19, H-15, 2.01 (s, 3H, CH₃-32)), 1.84 (ddd, 1H, J = J = 14.03, H-19′), 1.78 (m, 1H, H-16), 1.73-1.49 (m, 5H; H-2, H-7, H-2′, H-21, H-6), 1.49-1.32 (m, 6H; H-6′, H-22, H-7′, 1.35 (s, 3H, CH₃-27)), 1.32-0.95 (m, 16H; 1.28 (dd, 3H, J = J = 7.5, CH₃-2′′), 1.26 (s, 3H, CH₃-29), H-22′, H-16′, 1.11 (s, 3H, CH₃-25), 1.07 (s, 3H, CH₃-26), H-1a, H-15e), 0.83 (s, 6H, CH₃-23, CH₃-24), 0.76 (dm, 1H, H-5a), 0.71 (s, 3H, CH₃-28). ¹³C NMR (CDCl₃, 100 MHz): δ = 199.79 (s, C-11), 183.28 (s, C-5′(30)), 171.37 (s, C-3′), 170.83 (s, C-31), 168.39 (s, C-13), 128.56 (d, C-12), 80.41 (d, C-3), 61.55 (d, C-9), 54.82 (d, C-5), 47.30 (d, C-18), 45.23 (s, C-14), 42.98 (s, C-8), 41.41 (t, C-19), 38.58 (t, C-1), 38.31 (s, C-20), 37.86 (s, C-4), 36.93 (s, C-10), 36.73 (t, C-22), 32.50 (t, C-7), 31.75 (t, C-21), 31.64 (s, C-17), 29.91 (q, C-29), 28.15 (q, C-28), 27.86 (q, C-23), 26.21 (t, C-16, C-15), 23.37 (t, C-2), 23.26 (q, C-27), 21.16 (q, C-32), 19.68 (t, C-1″), 18.46 (q, C-26), 17.18 (t, C-6), 16.51 (q, C-24), 16.23 (q, C-25), 11.15 (q, C-2″).