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      竹根七化學成分的研究

      2019-01-10 14:30:00李玉澤梁小飛王西林張化為黃文麗郭東艷崔九成宋小妹
      中成藥 2019年10期
      關鍵詞:竹根分子式硅膠

      李玉澤,梁小飛,王西林,宋 蓓,張化為,黃文麗,郭東艷,崔九成,宋小妹?

      (1.陜西中醫(yī)藥大學藥學院,陜西 咸陽 712046;2.西北大學生命科學學院,陜西 西安 710069)

      竹根七為百合科開口箭屬植物開口箭Tupistra chinensisBaker.的根及根莖,屬于“太白七藥”之一,在陜西、湖北等地分布較廣泛,多作為民族民間用藥,具有清熱解毒、祛風除濕、散瘀止痛等功效,用于治療頭痛咳嗽、咽喉腫痛、跌打損傷等[1]。目前從該植物中已經(jīng)發(fā)現(xiàn)甾體皂苷類、黃酮類、強心苷類等化合物[2],甾體皂苷類是其主要成分[3],為了有效利用竹根七資源,進一步開發(fā)秦巴山區(qū)特色藥用植物資源[4-5],本課題對其化學成分進行系統(tǒng)研究,從中分離得到15 個化合物,其中甾體類14 個,化合物15 為首次從該屬植物中分離得到,化合物9~12 為首次從該植物中分離得到。

      1 材料

      AVANCE 型核磁共振波譜儀(德國Burker 公司);WFH-203 三用紫外分析儀(上海精科實業(yè)有限公司);YMC-Pack Pro C18半制備色譜柱、ODS柱層析填料(日本YMC 公司);LC-6AD 型半制備液相色譜儀(日本島津公司);D-101 大孔吸附樹脂(天津南開大學化工廠);柱色譜硅膠、薄層色譜用硅膠G(青島海洋硅膠干燥劑廠);Sephadex LH-20 柱填料(美國Pharmacia 公司)。色譜甲醇和乙腈(美國Fisher 公司);其他試劑均為分析純;水為超純水。

      竹根七購自陜西眉縣,經(jīng)陜西中醫(yī)藥大學藥學院王繼濤高級實驗師鑒定為正品。

      2 提取與分離

      取干燥竹根七粗粉2 kg,8 倍量60%乙醇回流提取3 次,1.5 h/次,提取液合并減壓回收至無醇味,蒸餾水溶解至19 L,采用D-101 大孔吸附樹脂柱色譜,依次用水、20%、60%、95% 乙醇洗脫,得到的浸膏量分別為89、97、45 g。95%乙醇部位浸膏和等量硅膠粉干法拌樣后,8 倍樣品量的硅膠裝柱,經(jīng)硅膠柱色譜,三氯甲烷-甲醇(100∶0~50∶50)梯度洗脫,得6 個餾分Fr.1~9。Fr.2 反復采用硅膠柱色譜三氯甲烷-甲醇(100∶0~80∶20)和Sephadex LH-20 柱 色 譜 三 氯 甲 烷-甲 醇(50∶50)得化合物1(16 mg)、2(21 mg)、3(18 mg)、4(35 mg);Fr.4 經(jīng)過硅膠柱色譜,用三氯甲烷-甲醇(100∶0~60∶40)梯度洗脫后,得3個餾分Fr.4-1~Fr.4-3;Fr.4-3 采用硅膠柱色譜三氯甲烷-甲醇(100∶0~60∶40)和結晶方法得化合物5(10 mg)、6(15 mg)、7(26 mg)、14(21 mg)。Fr.8 經(jīng)硅膠柱色譜三氯甲烷-甲醇(100∶0~50∶50)梯度洗脫,得4 個餾分Fr.8-1~Fr.8-4。Fr.8-2 采用ODS 柱色譜水-甲醇(100∶0~0∶100)和Sephadex LH-20 柱色譜水-甲醇(50∶50)洗脫得化合物8(15 mg)、9(23 mg),F(xiàn)r.8-3 和Fr.8-4 采用半制備液相方法水-甲醇(77∶23)等度洗脫得化合物10(11 mg)、11(16 mg)、12(22 mg)、13(16 mg)、15(11 mg)。

      3 結構鑒定

      化合物1:白色針晶(甲醇),ESI-MSm/z:501.3 [M+Na]+,分子式C27H42O7。1H-NMR(Pyrd5,600 MHz)譜中,包括3 個甲基氫δ0.88(3H,s,H-18),1.91(3H,s,H-19),1.08(3H,d,J=6.8 Hz,H-21),1 對末端烯氫δ4.83(1H,s,H-27a),4.79(1H,s,H-27b);13C-NMR(Pyr-d5,150 MHz)δ:75.3(C-1),33.5(C-2),71.4(C-3),69.9(C-4),79.6(C-5),69.9(C-6),35.5(C-7),30.6(C-8),46.0(C-9),45.8(C-10),21.6(C-11),40.3(C-12),41.0(C-13),56.4(C-14),32.6(C-15),81.8(C-16),63.4(C-17),16.9(C-18),16.7(C-19),42.3(C-20),15.4(C-21),109.8(C-22),33.5(C-23),29.3(C-24),144.8(C-25),65.4(C-26),109.1(C-27)。以上數(shù)據(jù)與文獻[6]基本一致,故鑒定為tupichigenin B。

      化合物2:白色針晶(甲醇),ESI-MSm/z:531.2 [M+Na]+,分子式C27H40O9。1H-NMR(Pyrd5,500 MHz)譜中,包括3 個甲基氫δ0.88(3H,s,H-18),1.44(3H,s,H-19),1.06(3H,d,J=6.8 Hz,H-21),1 對末端烯氫δ4.83(1H,s,H-27a),4.75(1H,s,H-27b);13C-NMR(Pyr-d5,125 MHz)δ:76.9(C-1),68.3(C-2),75.9(C-3),71.6(C-4),86.7(C-5),211.5(C-6),75.2(C-7),41.3(C-8),38.4(C-9),50.6(C-10),22.4(C-11),39.8(C-12),41.1(C-13),49.7(C-14),31.9(C-15),81.8(C-16),63.3(C-17),16.7(C-18),13.4(C-19),42.5(C-20),15.3(C-21),109.9(C-22),33.4(C-23),29.4(C-24),144.9(C-25),65.4(C-26),109.1(C-27)。以上數(shù)據(jù)與文獻[7]基本一致,故鑒定為1β,2β,3β,4β,5β,7α-hexahydroxy-spirost-25(27)-ene-6-one。

      化合物3:白色針晶(甲醇),ESI-MSm/z:533.3 [M+Na]+,分子式C27H42O9。1H-NMR(Pyrd5,400 MHz)譜中,包括3 個甲基氫δ0.93(3H,s,H-18),1.95(3H,s,H-19),1.05(3H,d,J=6.9 Hz,H-21),1 對末端烯氫δ4.76(1H,s,H-27a),4.74(1H,s,H-27b);13C-NMR(Pyr-d5,100 MHz)δ:80.1(C-1),67.6(C-2),76.1(C-3),70.2(C-4),78.7(C-5),74.1(C-6),72.2(C-7),35.1(C-8),40.0(C-9),46.2(C-10),21.8(C-11),40.2(C-12),40.8(C-13),50.5(C-14),32.4(C-15),82.0(C-16),63.5(C-17),16.7(C-18),16.0(C-19),42.5(C-20),15.4(C-21),109.9(C-22),33.6(C-23),29.4(C-24),144.9(C-25),65.4(C-26),109.0(C-27)。以上數(shù)據(jù)與文獻[7]基本一致,故鑒定為spirost-25(27)-ene-1β,2β,3β,4β,5β,6β,7α-heptol。

      化合物4:白色無定型粉末,ESI-MSm/z:615.4 [M+Na]+,分子式C33H52O9。1H-NMR(Pyrd5,400 MHz)譜中,包括3 個甲基氫δ0.84(3H,s,CH3-18),1.25(3H,s,CH3-19),1.23(3H,d,J=6.9 Hz,CH3-21),1 對末端烯氫δ4.82(1H,brs,H-27a),4.87(1H,brs,H-27b),1 個糖端基氫δ5.29(1H,d,J=7.7 Hz,H-Glc-1);13CNMR(Pyr-d5,100 MHz)δ:25.9(C-1),28.8(C-2),67.3(C-3),35.7(C-4),81.6(C-5),29.7(C-6),31.8(C-7),34.7(C-8),43.4(C-9),41.7(C-10),21.7(C-11),40.5(C-12),41.2(C-13),56.8(C-14),32.6(C-15),82.0(C-16),63.5(C-17),17.0(C-18),18.1(C-19),42.4(C-20),15.5(C-21),110.0(C-22),33.7(C-23),29.5(C-24),144.9(C-25),65.5(C-26),109.3(C-27),97.8(C-Glc-1),75.9(C-Glc-2),79.4(C-Glc-3),72.3(C-Glc-4),79.1(CGlc-5),63.5(C-Glc-6)。以上數(shù)據(jù)與文獻 [8]基本一致,故鑒定為(20S,22R)-3β,5β-diolspirost-25(27)-en-5-O-β-D-glucopyranoside。

      化合物5:白色無定形粉末,ESI-MSm/z:453.3 [M+Na]+,分子式C27H42O4。1H-NMR(Pyrd5,400 MHz)譜中,包括4 個甲基氫δ0.96(3H,s,H-18),1.38(3H,s,H-19),1.11(3H,d,J=6.7 Hz,H-21),0.68(3H,d,J=5.6 Hz,H-27),1 個烯氫δ5.64(1H,d,J=5.6 Hz,H-6);13CNMR(Pyr-d5,100 MHz)δ:75.2(C-1),40.7(C-2),66.3(C-3),40.8(C-4),139.9(C-5),124.4(C-6),32.2(C-7),31.6(C-8),51.1(C-9),44.4(C-10),24.2(C-11),40.4(C-12),40.0(C-13),56.8(C-14),32.2(C-15),80.8(C-16),62.9(C-17),16.4(C-18),13.1(C-19),41.8(C-20),14.8(C-21),109.0(C-22),32.7(C-23),29.0(C-24),30.4(C-25),66.6(C-26),17.1(C-27)。以上數(shù)據(jù)與文獻[9]基本一致,故鑒定為3-epiruscogenin。

      化合物6:白色針晶(甲醇),ESI-MSm/z:485.1 [M+Na]+,分子式C27H43O6。1H-NMR(Pyrd5,400 MHz)譜中,包括3 個甲基氫δ0.87(3H,s,H-18),1.63(3H,s,H-19),1.12(3H,d,J=7.3 Hz,H-21),1 對末端烯氫δ4.77(1H,s,H-27a),4.86(1H,s,H-27b);13C-NMR(Pyr-d5,100 MHz)δ:74.0(C-1),33.8(C-2),71.5(C-3),68.4(C-4),78.7(C-5),30.8(C-6),28.8(C-7),35.4(C-8),46.0(C-9),45.8(C-10),21.8(C-11),40.4(C-12),41.1(C-13),56.6(C-14),32.5(C-15),81.8(C-16),63.4(C-17),17.0(C-18),14.3(C-19),42.4(C-20),15.4(C-21),109.8(C-22),33.6(C-23),29.3(C-24),144.8(C-25),65.4(C-26),109.1(C-27)。以上數(shù)據(jù)與文獻[6]基本一致,故鑒定為ranmogenin A。

      化合物7:白色無定形粉末,ESI-MSm/z:711.3 [M+Na]+,分子式C33H52O15。1H-NMR(Pyrd5,400 MHz)譜中,包括3 個甲基氫δ0.92(3H,s,H-18),1.45(3H,s,H-19),1.33(3H,d,J=6.9 Hz,H-21),1 對末端烯氫δ4.95(1H,s,H-27a),4.93(1H,s,H-27b),1 個糖端基氫δ4.74(1H,brs,H-Glc-1);13C-NMR(Pyr-d5,100 MHz)δ:76.3(C-1),67.6(C-2),75.1(C-3),70.9(C-4),86.1(C-5),211.0(C-6),75.3(C-7),37.7(C-8),40.8(C-9),50.0(C-10),21.7(C-11),39.2(C-12),40.7(C-13),49.0(C-14),31.5(C-15),80.9(C-16),63.6(C-17),16.1(C-18),12.9(C-19),40.5(C-20),16.2(C-21),110.5(C-22),37.7(C-23),28.2(C-24),147.0(C-25),71.9(C-26),110.2(C-27),103.7(C-Glc-1),75.0(C-Glc-2),78.4(C-Glc-3),70.9(C-Glc-4),78.4(C-Glc-5),62.6(C-Glc-6)。以上數(shù)據(jù)與文獻 [10]基本一致,故鑒定為5βfurost-Δ25(27)-en-1β,2β,3β,4β,5β,7α,22ξ,26-octaol-6-one-26-O-β-D-glucopyranoside。

      化合物8:白色無定形粉末,ESI-MSm/z:673.3 [M+Na]+,分子式C33H54O14。1H-NMR(Pyrd5,400 MHz)譜中,包括3 個甲基氫δ0.74(3H,s,H-18),1.96(3H,s,H-19),1.55(3H,s,H-21),1 對末端烯氫δ5.24(1H,s,H-27a),5.36(1H,s,H-27b),1 個糖端基氫δ4.86(1H,brs,H-Glc-1);13C-NMR(Pyr-d5,100 MHz)δ:79.6(C-1),67.2(C-2),75.2(C-3),69.8(C-4),78.2(C-5),73.6(C-6),72.0(C-7),34.4(C-8),37.5(C-9),45.9(C-10),21.5(C-11),39.6(C-12),43.3(C-13),48.5(C-14),31.1(C-15),84.7(C-16),64.7(C-17),15.5(C-18),14.2(C-19),104.0(C-20),11.8(C-21),151.7(C-22),34.3(C-23),24.6(C-24),146.2(C-25),71.7(C-26),111.7(C-27),103.8(C-Glc-1),75.6(C-Glc-2),78.6(C-Glc-3),71.7(CGlc-4),78.5(C-Glc-5),62.9(C-Glc-6)。以上數(shù)據(jù)與文獻 [11]基本一致,故鑒定為tupisteroide B。

      化合物9:白色無定形粉末,ESI-MSm/z:615.4 [M+Na]+,分子式C33H52O9。1H-NMR(Pyrd5,600 MHz)譜中,包括4 個甲基氫δ0.93(3H,s,H-18),1.27(3H,s,H-19),1.17(3H,d,J=6.7 Hz,H-21),0.67(3H,d,J=5.5 Hz,H-27),1 個烯氫δ5.65(1H,d,J=5.4 Hz,H-6),1 個糖端基氫δ4.97(1H,d,J=7.9 Hz,H-Glc-1);13CNMR(Pyr-d5,150 MHz)δ:75.3(C-1),37.1(C-2),74.3(C-3),41.0(C-4),140.1(C-5),124.6(C-6),32.2(C-7),32.7(C-8),51.0(C-9),44.6(C-10),24.6(C-11),39.7(C-12),40.5(C-13),57.3(C-14),32.6(C-15),81.4(C-16),63.5(C-17),17.0(C-18),13.6(C-19),42.0(C-20),15.4(C-21),109.6(C-22),32.9(C-23),29.5(C-24),30.9(C-25),66.8(C-26),17.7(C-27),103.3(C-Glc-1),75.1(C-Glc-2),79.1(C-Glc-3),72.0(C-Glc-4),78.8(CGlc-5),63.2(C-Glc-6)。以上數(shù)據(jù)與文獻[12]基本一致,故鑒定為25(R)-1β-hydroxy-spirost-5-en-3α-ylO-β-D-glucopyranoside。

      化合物10:白色無定形粉末,ESI-MSm/z:663.3 [M+Na]+,分子式C33H52O12。1H-NMR(Pyrd5,400 MHz)譜中,包括3 個甲基氫δ0.87(3H,s,CH3-18),1.06(3H,d,J=6.8 Hz,CH3-21),1.75(3H,s,CH3-19),1 對末端烯氫δ4.79(1H,s,H-27a),4.83(1H,s,H-27b),1 個糖端基氫δ5.25(1H,d,J=7.7 Hz,H-Glc-1);13C-NMR(Pyr-d5,100 MHz)δ:77.6(C-1),67.4(C-2),76.0(C-3),67.8(C-4),87.2(C-5),24.7(C-6),28.7(C-7),34.4(C-8),46.5(C-9),46.0(C-10),21.5(C-11),39.7(C-12),40.3(C-13),55.7(C-14),31.9(C-15),81.2(C-16),62.8(C-17),16.2(C-18),13.5(C-19),41.7(C-20),14.7(C-21),109.2(C-22),33.0(C-23),28.2(C-24),144.2(C-25),64.8(C-26),108.5(C-27),97.3(C-Glc-1),75.6(C-Glc-2),78.6(C-Glc-3),71.7(C-Glc-4),78.4(C-Glc-5),62.6(C-Glc-6)。以上數(shù)據(jù)與文獻[13]基本一致,故鑒定為aspidoside A。

      化合物11:白色粉末,ESI-MSm/z:457.4[M+H]+,分子式C30H48O3。1H-NMR(400 MHz,CDCl3)譜中,包括7 個甲基氫δ0.75(3H,s,H-23),0.77(3H,s,H-24),0.86(3H,s,H-25),0.88(3H,s,H-26),0.92(3H,s,H-29),0.95(3H,s,H-30),1.13(3H,s,H-27);3.25(1H,dd,J=10.9,4.3 Hz,H-3),5.26(1H,t,J=3.3,3.8 Hz,H-12);13C-NMR(100 MHz,CDCl3)δ:38.6(C-1),27.4(C-2),79.3(C-3),39.0(C-4),55.4(C-5),18.5(C-6),32.7(C-7),39.5(C-8),47.9(C-9),37.3(C-10),23.1(C-11),122.8(C-12),143.8(C-13),41.8(C-14),27.9(C-15),23.6(C-16),46.1(C-17),41.2(C-18),46.8(C-19),30.9(C-20),34.0(C-21),32.8(C-22),28.3(C-23),15.5(C-24),15.8(C-25),17.3(C-26),26.2(C-27),183.6(C-28),23.8(C-29),33.3(C-30)。以上數(shù)據(jù)與文獻[14-15]基本一致,故鑒定為齊墩果酸。

      化合物12:白色粉末,ESI-MSm/z:373.2[M+H]+,分子式C23H32O4。1H-NMR(400 MHz,CDCl3)譜中,包括3 個甲基氫δ0.83(3H,s,18-CH3),1.87(3H,s,19-CH3),0.95(3H,d,J=6.8 Hz,21-CH3);3.84(1H,d,J=12.2 Hz,H-26a),4.26(1H,d,J=12.4 Hz,H-26b),4.47(1H,m,16-H),4.75(1H,brs,H-27a),4.78(1H,brs,H-27a),6.19(1H,s,烯醇羥基);13CNMR(100 MHz,CDCl3)δ:144.7(C-5),193.5(C-6),45.3(C-7),41.5(C-8),39.9(C-9),134.3(C-10),25.8(C-11),38.8(C-12),42.0(C-13),55.3(C-14),32.3(C-15),81.4(C-16),62.8(C-17),16.9(C-18),13.6(C-19),42.7(C-20),15.7(C-21),109.8(C-22),33.3(C-23),28.9(C-24),144.6(C-25),65.8(C-26),109.1(C-27)。以上數(shù)據(jù)與文獻[16]基本一致,故鑒定為1β,2β,3β,4β,5β,7α-hexahydroxy-spirost-25(27)-ene-6-one 衍生物Ⅱ。

      化合物13:無色油狀物,ESI-MSm/z:493.3[M+H]+,分子式C27H40O8。1H-NMR(Pyr-d5,400 MHz)譜中,包括3 個甲基氫δ1.04(3H,s,H-18),1.33(3H,s,H-19),2.25(3H,s,H-21),2個烯氫δ5.66(1H,d,J=5.2 Hz,H-6),5.96(1H,d,J=5.9 Hz,H-16),1 個糖端基氫δ4.22(1H,d,J=7.2 Hz,H-Glc-1);13C-NMR(Pyr-d5,100 MHz)δ:75.8(C-1),37.5(C-2),75.6(C-3),39.8(C-4),140.4(C-5),124.3(C-6),32.8(C-7),31.3(C-8),51.9(C-9),46.1(C-10),24.1(C-11),36.2(C-12),44.7(C-13),57.1(C-14),33.3(C-15),145.7(C-16),156.9(C-17),16.8(C-18),13.6(C-19),196.5(C-20),27.9(C-21),和1 個葡萄糖(δ103.8,74.9,79.6,72.5,78.6,63.7)。以上數(shù)據(jù)與文獻[17]基本一致,故鑒定為tupichinin A。

      化合物14:白色粉末,ESI-MSm/z:575.4[M+H]+,分子式C35H58O6。1H-NMR(Pyr-d5,400 MHz)δ:5.43(1H,m,H-6),2.51(1H,m,H-17),0.68(3H,s,H-18),0.95(3H,s,H-19),0.96(3H,d,J=6.5 Hz,H-21),0.89(3H,d,J=6.9 Hz,H-27),0.92(3H,t,J=7.4 Hz,H-29),4.88(1H,d,J=7.8 Hz,Glc-1);13C-NMR(Pyr-d5,100 MHz)δ:37.6(C-1),30.4(C-2),78.3(C-3),39.5(C-4),141.1(C-5),122.1(C-6),32.2(C-7),32.3(C-8),50.5(C-9),37.1(C-10),21.4(C-11),40.0(C-12),42.6(C-13),57.0(C-14),24.7(C-15),29.4(C-16),56.2(C-17),12.7(C-18),19.2(C-19),40.9(C-20),21.6(C-21),139.0(C-22),129.6(C-23),51.6(C-24),32.2(C-25),21.4(C-26),20.1(C-27),25.8(C-28),12.7(C-29),102.7(C-Glc-1),75.5(C-Glc-2),78.8(CGlc-3),71.9(C-Glc-4),78.6(C-Glc-5),63.0(C-Glc-6)。以上數(shù)據(jù)與文獻[18-20]基本一致,故鑒定為β-豆甾醇-3-O-β-D-吡喃葡萄糖苷。

      化合物15:白色粉末,ESI-MSm/z:577.4[M+H]+,分子式C35H52O8。1H-NMR(Pyr-d5,400 MHz)譜中,包括4 個甲基氫δ0.85(3H,s,CH3-18),1.03(3H,s,CH3-19),1.17(3H,d,J=7.2 Hz,CH3-21),0.73(3H,d,J=5.8 Hz,CH3-27),1 個糖端基氫δ4.95(1H,d,J=7.9 Hz,H-Glc-1),1 個烯氫δ5.43(1H,dd,J=2.8,4.8 Hz,H-6);13C-NMR(Pyr-d5,100 MHz)δ:33.4(C-1),27.0(C-2),74.3(C-3),39.2(C-4),140.5(C-5),121.9(C-6),32.5(C-7),31.6(C-8),50.2(C-9),37.9(C-10),21.3(C-11),40.6(C-12),41.2(C-13),57.5(C-14),32.4(C-15),81.7(C-16),63.4(C-17),16.6(C-18),19.4(C-19),42.6(C-20),15.7(C-21),109.6(C-22),33.5(C-23),29.6(C-24),32.1(C-25),67.5(C-26),17.9(C-27)和1 個葡萄糖(δ103.3,75.7,79.2,72.5,79.3,63.6)。以上數(shù)據(jù)與文獻[21]基本一致,故鑒定為3-epi-diosgenin-3-β-Dglucopyranoside。

      4 討論與結論

      從竹根七中分離鑒定了15 個化合物,其中甾體類化合物14 個,化合物15 為首次從開口箭屬中分離得到,化合物9~12 為首次從該植物中分離得到。本實驗進一步豐富了竹根七的化學成分,為后續(xù)的質(zhì)量標準和藥理研究提供了基礎。

      竹根七中甾體類化合物在A 環(huán)一般具有多個羥基,導致其與糖苷類化合物極性相近,在分離上有一定難度。采用反相柱層析分離時,乙腈-水作為流動相時分離度較高,峰型好,然而化合物對其極性變化極為敏感,在操作中要精確兩者比例。對于糖鏈相同呋甾皂苷元上羥基數(shù)目有差別的化合物,在正相色譜中不能分離開,而在HPLC 上的保留時間卻有明顯差別,表明多羥基甾體皂苷采用反相填料分離效果較好。

      竹根七中的甾體皂苷類化合物在結構上有明顯特征,一般在A 環(huán)和B 環(huán)上連有多個羥基,并且大多數(shù)含有Δ25(27)雙鍵。對于螺甾皂苷,若有Δ25(27)雙鍵,27 位碳上的烯氫化學位移一般為4.81±0.5(H-27a,s)和4.84±0.5(H-27b,s);對于呋甾皂苷,若有Δ25(27)雙鍵,27 位碳上的烯氫化學位移一般為5.3±0.5(H-27a,s)和5.1±0.5(H-27b,s)。

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