4.8. 30-nor-3β-hydroxy-11-oxo-20-(3′-methyl-1′,2′,4′-oxadiazol-5′-yl)-18βH-olean-12-en (5a)

Crude product 5a (0.481 g, quantitative yield) was obtained according to the general procedure C from compound 4a (0.5 g, 0.91 mmol), KOH (0.30 g, 5.45 mmol), and MeOH (25 mL). Crude product 3a was purified by flash column chromatography (SiO₂, 0–1% MeOH in CHCl₃) and recrystallized from MeOH–CHCl₃ to give a pure sample of 5a (0.38 g, 82%). Mp 300.2–300.4 °C. [αD20] +181 (c 0.20 g/100 mL; CHCl₃). HRMS: m/z calc. for (C₃₂H₄₈O₃N₂)⁺ 508.3660; found 508.3651. ¹H NMR (CDCl₃, 400 MHz): δ = 5.68 (s, 1H, H-12), 3.20 (dd, 1H, J_3a,2a = 10.2, J_3a,2e = 5.7, H-3a), 2.76 (dm, 1H, J_1e,1a = 13.4, H-1e), 2.36 (s, 3H, CH₃-1″), 2.32 (s, 1H, H-9), 2.21-1.97 (m, 4H; H-21, H-18, H-19, H-15), 1.92-1.74 (m, 2H; H-19′, H-16), 1.74-1.50 (m, 5H; H-7, H-2, H-2′, H-6, H-21′), 1.50-1.32 (m, 6H; H-22, H-6′, H-7′, 1.37 (s, 3H, CH₃-27)), 1.30-1.14 (m, 5H; 1.26 (s, 3H, CH₃-29), H-22′, H-16′), 1.10 (s, 3H, CH₃-25), 1.08 (s, 3H, CH₃-26), 1.05-0.90 (m, 5H; H-15′, 0.97 (s, 3H, CH₃-23), H-1′), 0.77 (s, 3H, CH₃-24), 0.73 (s, 3H, CH₃-28), 0.67 (dm, 1H, H-5). ¹³C NMR (CDCl₃, 100 MHz): δ = 199.96 (s, C-11), 183.49 (s, C-5′(30)), 168.31 (s, C-13), 166.97 (s, C-3′), 128.65 (d, C-12), 78.61 (d, C-3), 61.68 (d, C-9), 54.77 (d, C-5), 47.33 (d, C-18), 45.27 (s, C-14), 43.01 (s, C-8), 41.42 (t, C-19), 38.99 (t, C-1*), 38.96 (s, C-4*), 38.35 (s, C-20), 36.95 (t, C-22^#), 36.91 (s, C-10^#), 32.58 (t, C-7), 31.74 (s, C-17^§), 31.69 (t, C-21^§), 30.02 (q, C-29), 28.14 (q, C-28), 27.95 (q, C-23), 27.13 (t, C-2), 26.25 (t, C-16), 26.25 (t, C-15), 23.38 (q, C-27), 18.49 (q, C-26), 17.32 (t, C-6), 16.23(q, C-25), 15.45 (q, C-24), 11.57 (q, C-1″).