3.1.2. General Procedure for the Synthesis of 6a–n
Ac2O (0.15 mL, 1.5 mmol) was added to a solution of 23-hydroxybetulinic acid (1, 120.0 mg, 0.25 mmol) in dry pyridine (5 mL). The mixture was stirred overnight at room temperature. After adding acetic ether (10 mL), the mixture was washed with 9% HCl (20 mL × 3) and brine (20 mL × 3), dried over anhydrous Na2SO4, filtered, and evaporated to dryness. The residue was purified by crystallization from ethyl acetate to afford the desired compound 4 as yellow powder (136.0 mg, 98%). (COCl)2 (0.1 mL) was added to a solution of 4 (100.0 mg, 0.18 mmol) in dry CH2Cl2 (10 mL). The mixture was stirred for 4 h at room temperature and evaporated to dryness. Immediately, the corresponding alcohol (5 equiv.) and CH2Cl2 (10 mL) were added and the mixture allowed to stir for 8vh at room temperature, evaporated to dryness and purified by column chromatography on silica gel, eluted with an mixture of petroleum ether/ethyl acetate to give compounds 5a–d. The corresponding R2(CO)2O (4 equiv.) was added to a solution of compounds 5a–d in CH2Cl2 (10 mL) in the presence of DMAP (1.5 equiv.). The mixture was stirred for 10 h at room temperature and washed with 9% HCl (20 mL × 2), H2O (20 mL × 2), brine (20 mL × 2), dried over anhydrous Na2SO4, filtered, and concentrated to dryness. The residue was purified by column chromatography on silica gel to afford compounds 6a–n.
Butanedioic acid, 1-[2-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6a). From 1,2-ethanediol (56.0 mg, 0.9 mmol) and succinic anhydride (55.0 mg, 0.55 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 73.0 mg (76%) as a yellow solid, mp 68 °C–70 °C; IR (KBr, cm−1) ν 3429, 2985, 2947, 2872, 1738, 1731, 1649, 1453, 1370, 1246, 1151, 1039, 881; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.88, 0.91, 0.96, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.02, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.67 (4H, m, 28-COOCH2CH2O COCH2CH2), 2.99 (1H, m, 19-CH), 3.68 (1H, d, J = 11.9 Hz, 23-CH2), 3.84 (1H, d, J = 11.9 Hz, 23-CH2), 4.29 (4H, m, 17-COOCH2CH2), 4.61 (1H, s, 29=CH2), 4.72 (1H, s, 29=CH2), 4.74 (1H, m, 3-CH); HR-MS (ESI, M+H) m/z: calcd for C40H61O10 701.4108, found 701.4104.
Pentanedioic acid, 1-[2-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6b). From 1,2-ethanediol (56.0 mg, 0.9 mmol) and glutaric anhydride (63.0 mg, 0.55 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 71.0 mg (73%) as a yellow oil; IR (KBr, cm−1) ν 3457, 2948, 2873, 1738, 1711, 1642, 1451, 1375, 1245, 1153, 1039, 885, 756; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.87, 0.91, 0.96, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.43 (4H, m, 28-COOCH2CH2OCOCHCH2), 2.98 (1H, m, 19-CH), 3.68 (1H, d, J = 11.6 Hz, 23-CH2), 3.85 (1H, d, J = 11.6 Hz, 23-CH2), 4.29 (4H, m, 17-COOCH2CH2), 4.60 (1H, s, 29=CH2), 4.72 (1H, s, 29=CH2), 4.75 (1H, m, 3-CH); HR-MS (ESI, M+H) m/z: calcd for C41H63O10 715.4265, found 715.4262.
Butylenedioic acid, 1-[2-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6c). From 1,2-ethanediol (56.0 mg, 0.9 mmol) and maleic anhydride (54.0 mg, 0.55 mmol); column chromatography with petroleum ether/ethyl acetate = 1:1 (v:v). Yield: 59.0 mg (62%) as a white solid; mp 68 -70 °C; IR (KBr, cm−1) ν 3458, 3418, 2945, 2869, 1732, 1640, 1452, 1375, 1245, 1155, 1038, 758; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.87, 0.91, 0.96, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.95 (1H, m, 19-CH), 3.69(1H, d, J = 11.3 Hz, 23-CH2), 3.83 (1H, d, J = 11.3 Hz, 23-CH2), 4.36 (2H, m, 17-COOCH2CH2), 4.44 (2H, m, 17-COOCH2CH2), 4.61 (1H, s, 29=CH2), 4.72 (1H, s, 29=CH2), 4.76 (1H, m, 3-CH), 6.36(1H, d, J = 12.8 Hz, 28-COOCH2CH2OCOCH=CH), 6.50 (1H, d, J = 12.8 Hz, 28-COOCH2CH2OCOCH=CH). HR-MS (ESI, M+H) m/z: calcd for C40H59O10 699.3952, found 699.3959.
1,2-Xylenedioic acid, 1-[2-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6d). From 1,2-ethanediol (56.0 mg, 0.9 mmol) and phthalic anhydride (81.0 mg, 0.55 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 75.0 mg (73%) as a white solid, mp 70 °C–72 °C; IR (KBr, cm−1) ν 3450, 2947, 2871, 1731, 1635, 1448, 1380, 1248, 1128, 1038, 883, 743; 1H-NMR (CDCl3, 300 MHz) δ 0.79, 0.82, 0.89, 0.92, 1.65 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.97 (1H, m, 19-CH), 3.68 (1H, d, J = 11.6 Hz, 23-CH2), 3.83 (1H, d, J = 11.6 Hz, 23-CH2), 4.58 (7H, m, 29 = CH2, 3-CH and 17-COOCH2CH2), 7.70 (4H, m, 17-COOCH2CH2OCOC6H4COOH); HR-MS (ESI, M+H) m/z: calcd for C44H61O10 749.4108, found 749.4111.
Butanedioic acid, 1-[4-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6e). From 1,4-butanediol (81.0 mg, 0.9 mmol) and succinic anhydride (44.0 mg, 0.44 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 56.0 mg (70%) as a yellow oil; IR (KBr, cm−1) ν 3488, 3422, 2923, 2854, 1738, 1641, 1461, 1377, 1245, 1157, 1037, 974, 883; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.88, 0.91, 0.96, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.65 (4H, m, 28-COOCH2(CH2)2CH2OCOCH2CH2), 2.99 (1H, m, 19-CH), 3.68 (1H, d, J = 11.7 Hz, 23-CH2), 3.84 (1H, d, J = 11.7 Hz, 23-CH2), 4.13 (4H, m, 17-COOCH2(CH2)2CH2), 4.60 (1H, s, 29=CH2), 4.72 (1H, s, 29=CH2), 4.74 (1H, m, 3-CH); HR-MS (ESI, M+H) m/z: calcd for C42H65O10 729.4421, found 729.4428.
Pentanedioic acid, 1-[4-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6f). From 1,4-butanediol (81.0 mg, 0.9 mmol) and glutaric anhydride (50.0 mg, 0.44 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 55.0 mg (67%) as a yellow oil; IR (KBr, cm−1) ν 3425, 2947, 2871, 1735, 1641, 1451, 1384, 1244, 1155, 1036, 975; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.87, 0.91, 0.96, 1.70 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.43 (4H, m, 28-COOCH2(CH2)2CH2OCOCH2CH2CH2), 2.99 (1H, m, 19-CH), 3.68 (1H, d, J = 12.3 Hz, 23-CH2), 3.85 (1H, d, J = 12.3 Hz, 23-CH2), 4.10 (4H, m, 28-COOCH2(CH2)2CH2), 4.60 (1H, s, 29=CH2), 4.73 (1H, s, 29=CH2), 4.76 (1H, m, 3-CH); HR-MS (ESI, M+H) m/z: calcd for C43H67O10 743.4578, found 743.4573.
1,2-xylenedioic acid, 1-[4-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6g). From 1,4-butanediol (81.0 mg, 0.9 mmol) and phthalic anhydride (65.0 mg, 0.44 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 53.0 mg (62%) as a white solid, mp 163 °C–165 °C; IR (KBr, cm−1) ν 3457, 2973, 2866, 1643, 1455, 1381, 1055, 1025, 1012, 771; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.88, 0.91, 0.95, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.02, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.99 (1H, m, 19-CH), 3.69 (1H, d, J = 11.6 Hz, 23-CH2), 3.84 (1H, d, J = 11.6 Hz, 23-CH2), 4.12 (4H, m, 28-COOCH2(CH2)2CH2), 4.60 (1H, s, 29=CH2), 4.72 (1H, s, 29 = CH2), 4.76 (1H, m, 3-CH), 7.52 (4H, m, 17-COO(CH2)4OCOC6H4COOH); HR-MS (ESI, M+H) m/z: calcd for C46H65O10 777.4421, found 777.4427.
Butanedioic acid, 1-[6-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6h). From 1,6-hexanediol (106.0 mg, 0.9 mmol) and succinic anhydride (42.0 mg, 0.42 mmol); column chromatography with petroleum ether/ethyl acetate = 2:1 (v:v). Yield: 58.0 mg (73%) as a yellow oil; IR (KBr, cm−1) ν 3480, 3417, 2945, 2867, 1738, 1641, 1454, 1372, 1244, 1160, 1038, 885, 756; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.88, 0.91, 0.96, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.65 (4H, m, 17-COOCH2(CH2)4CH2OCOCH2CH2), 2.99 (1H, m, 19-CH), 3.68 (1H, d, J = 11.5 Hz, 23-CH2), 3.86 (1H, d, J = 11.5 Hz, 23-CH2), 4.05 (4H, m, 17-COOCH2(CH2)4CH2), 4.60 (1H, s, 29=CH2), 4.72 (1H, s, 29=CH2), 4.74 (1H, m, 3-CH); HR-MS (ESI, M+H) m/z: calcd for C44H69O10 757.4734, found 757.4738.
Pentanedioic acid, 1-[6-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6i). From 1,6-hexanediol (106 mg, 0.9 mmol) and glutaric anhydride (48.0 mg, 0.42 mmol); column chromatography with petroleum ether/ethyl acetate = 1:2 (v:v). Yield: 55.0 mg (68%) as a yellow oil; IR (KBr, cm−1) ν 3454, 2943, 2866, 1731, 1642, 1454, 1378, 1247, 1157, 1054, 771; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.87, 0.91, 0.96, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 1.98, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.41 (4H, m, 28-COOCH2(CH2)4CH2OCOCH2CH2CH2), 2.99 (1H, m, 19-CH), 3.69 (1H, d, J = 10.2 Hz, 23-CH2), 3.83 (1H, d, J = 10.2 Hz, 23-CH2), 4.06 (4H, m, 28-COOCH2(CH2)4 CH2), 4.60 (1H, s, 29=CH2), 4.72 (1H, s, 29=CH2), 4.74 (1H, m, 3-CH); HR-MS (ESI, M+H) m/z: calcd for C45H71O10 771.4891, found 771.4896.
1,2-Xylenedioic acid, 1-[6-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]ethyl] ester (6j). From 1,6-hexanediol (106.0 mg, 0.9 mmol) and phthalic anhydride (62.0 mg, 0.42 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 50.0 mg (59%) as a yellow oil; IR (KBr, cm−1) ν 3479, 2946, 2866, 1735, 1704, 1591, 1384, 1369, 1246, 1130, 1040, 652; 1H-NMR (CDCl3, 300 MHz) δ 0.79, 0.87, 0.91, 0.95, 1.68 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.05 (3H each, s, 3 and 23-OCOCH3), 2.99 (1H, m, 19-CH), 3.68(1H, d, J = 11.6 Hz, 23-CH2), 3.84 (1H, d, J = 11.6 Hz, 23-CH2), 4.07 (4H, m, 28-COOCH2(CH2)4CH2), 4.60 (1H, s, 29=CH2), 4.73 (1H, s, 29=CH2), 4.76 (1H, m, 3-CH), 7.48 (4H, m, 17-COO(CH2)6OCOC6H4COOH); HR-MS (ESI, M+H) m/z: calcd for C48H69O10 805.4734, found 805.4739.
Butanedioic acid, 1-[4-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]butynyl] ester (6k). Butyne-1,4-diol (77.0 mg, 0.9 mmol) and succinic anhydride (37.0 mg, 0.37 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 50.0 mg (64%) as a yellow solid, mp 99 °C–101 °C; IR (KBr, cm−1) ν 3450, 2929, 2870, 1736, 1649, 1427, 1370, 1246, 1148, 1041, 971, 803, 641; 1H-NMR (CDCl3, 300 MHz) δ 0.80, 0.87, 0.90, 0.96, 1.68(3H each, s, 24, 25, 26, 27, 30-CH3), 2.01, 2.06 (3H each, s, 3 and 23-OCOCH3), 2.69 (4H, t, 17- 17-COOCH2C≡CCH2O COCH2CH2COOH), 2.99 (1H, m, 19-CH), 3.68 (1H, d, J = 11.7 Hz, 23-CH2), 3.85 (1H, d, J = 11.7 Hz, 23-CH2), 4.69 (7H, m, 29=CH2, 3-CH and 17-COOCH2C≡CCH2); HR-MS (ESI, M+H) m/z: calcd for C42H61O10 725.4108, found 725.4102.
Pentanedioic acid, 1-[4-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]butynyl] ester (6l). From butyne-1,4-diol (77.0 mg, 0.9 mmol) and glutaric anhydride (42.0 mg, 0.37 mmo); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:1 (v:v:v). Yield: 50.0 mg (67%) as a yellow solid, mp 90 °C–92 °C; IR (KBr, cm−1) ν 3438, 2946, 2871, 1737, 1643, 1582, 1451, 1369, 1245, 1146, 1123, 1041, 973; 1H-NMR (DMSO, 300 MHz) δ 0.76, 0.83, 0.87, 0.94, 1.65 (3H each, s, 24, 25, 26, 27, 30-CH3), 1.96, 1.99 (3H each, s, 3 and 23-OCOCH3), 2.19 (4H, m, 17-COOCH2 C≡CCH2OCOCH2CH2CH2COOH), 2.91 (1H, m, 19-CH), 3.63 (1H, d, J = 11.9 Hz, 23-CH2), 3.78 (1H, d, J = 11.9 Hz, 23-CH2), 4.70 (7H, m, 29=CH2, 3-CH and 17-COOCH2≡CCH2); HR-MS (ESI, M+H) m/z: calcd for C43H63O10 739.4265, found 739.4261.
Butylenedioic acid, 1-[4-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]butynyl] ester (6m). From butyne-1,4-diol (77.0 mg, 0.9 mmol) and maleic anhydride (36.0 mg, 0.37 mmol); column chromatography with petroleum ether/ethyl acetate = 1:2 (v:v). Yield: 36.0 mg (53%) as a yellow oil; IR (KBr, cm−1) ν 3405, 2967, 2922, 2872, 1731, 1650, 1584, 1437, 1407, 1334, 1126, 1044, 953; 1H-NMR (DMSO, 300 MHz) δ 0.76, 0.82, 0.87, 0.94, 1.65 (3H each, s, 24, 25, 26, 27, 30-CH3), 1.96, 1.99 (3H each, s, 3 and 23-OCOCH3), 3.39 (1H, m, 19-CH), 3.63 (1H, d, J = 11.4 Hz, 23-CH2), 3.78 (1H, d, J = 11.4 Hz, 23-CH2), 4.69 (7H, m, 29=CH2, 3-CH and 17-COOCH2C≡CCH2), 6.22 (1H, d, J = 15.8 Hz, 17-COOCH2C≡CCH2OCOCH=CHCOOH), 6.77 (1H, d, J = 15.8 Hz, 17-COOCH2C≡CCH2OCO CH=CHCOOH); HR-MS (ESI, M+H) m/z: calcd for C42H59O10 723.3952, found 723.3948.
1,2-Xylenedioic acid, 1-[4-[(3β,23-diacetoxylup-20(29)-en-28-oyl)oxy]butynyl] ester (6n). From butyne-1,4-diol (77.0 mg, 0.9 mmol) and phthalic anhydride (55.0 mg, 0.37 mmol); column chromatography with petroleum ether/ethyl acetate/acetic acid = 50:50:0.4 (v:v:v). Yield: 44.0 mg (61%) as a yellow oil; IR (KBr, cm−1) ν 3435, 3070, 2948, 2871, 1728, 1591, 1450, 1385, 1247, 1131, 1040, 747; 1H-NMR (CDCl3, 300 MHz) δ 0.82, 0.88, 0.91, 0.98, 1.71 (3H each, s, 24, 25, 26, 27, 30-CH3), 2.03, 2.08 (3H each, s, 3 and 23-OCOCH3), 3.06 (1H, m, 19-CH), 3.71 (1H, d, J = 11.7 Hz, 23-CH2), 3.86 (1H, d, J = 11.7 Hz, 23-CH2), 4.83 (7H, m, 29=CH2, 3-CH and 17-COOCH2C≡CCH2), 7.78 (4H, m, 17-COOCH2C≡CCH2OCOC6H4COOH); HR-MS (ESI, M+H) m/z: calcd for C46H61O10 773.4108, found 773.4101.