昆仑雪菊结合型黄酮类化合物的分离与鉴定

Isolation and Identification of Bound Flavonoids from Coreopsis tinctoria Nutt

昆仑雪菊结合型黄酮类化合物因与细胞壁以共价键结合,难以直接用溶剂萃取出来。本研究采用碱降解法使结合型化合物释放出来并优化降解条件,在此基础上,利用不同溶剂对降解产物进行提取筛选出最佳的溶剂得到粗提物,利用常压硅胶柱层析和SepdexLH-20凝胶柱层析对粗提物中的黄酮类化合物进行分离纯化得到单体化合物,采用Fe3+还原/抗氧化能力(ferric reducing antioxidant power,FRAP)法、1,1-二苯基-2-三硝基苯肼(1,1-diphenyl-2-picrylhydrazyl radical 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl,DPPH)法及2,2’-联氮-二(3-乙基-苯并噻唑-6-磺酸)二铵盐(2,2’-Azinobis-(3-ethylbenzthiazoline-6-sulphonate),ABTS)法对单体化合物进行抗氧化活性评价。结果表明:最佳的碱降解时间2h、温度50℃、NaOH浓度2mol/L,最佳提取溶剂为正丁醇;从粗提物中分离得到2个单体化合物,采用核磁共振(nuclear magnetic resonance,NMR)和电喷雾质谱(electrospray ionization mass spectra,ESIMS)鉴定其化学结构分别为金鸡菊查尔酮-4’-O-β-D-吡喃葡萄糖(化合物1)、3’,4’,7,8-四羟基二氢黄酮(化合物2);活性测定结果表明两个化合物的总抗氧化能力均强于阳性对照VE,化合物1与化合物2对DPPH自由基的半数抑制率IC50分别为(17.29±0.17)μmol/L和(70.09±0.09)μmol/L、对ABTS+·半数抑制率IC50分别为(22.86±0.21)μmol/L和(33.4±0.18)μmol/L,远低于阳性对照VE的IC50值(分别为(78.08±1.63)μmol/L和(38.54±0.42)μmol/L),说明两个化合物均有很强的抗氧化活性。

It is difficult to extract bound flavonoids directly from Coreopsis tinctoria Nutt owing to their binding to the cell wall material by covalent bond. The bound compounds were released using an alkaline digestion method in the current study and the process parameters were optimized. A crude extract was obtained from the digestion products using the selected optimum solvent and pure flavonoid compounds were isolated from the crude extract by open silica gel column chromatography and Sephedex LH-20 gel column chromatography. The antioxidant activities of the purified compounds were evaluated by DPPH, FRAP and ABTS assays. The results revealed that the optimum alkaline degradation conditions were 50 ℃, 2 h and 2 mol/L for temperature, time and NaOH concentration, respectively, and n-butanol was selected as the optimum extraction solvent for flavonoids. Two pure compounds were isolated from the crude extract and their chemical structures were elucidated as okanin-4'-O-β-D-glucopyranoside and 3',4',7,8-tetrahydroxyflavanone by nuclear magnetic resonance(NMR) and electro-spray ionization mass spectrometry(ESI-MS). Antioxidant experiments showed that the total antioxidant capacity of these two compounds was higher than that of the positive control vitamin E. The IC50 values of compounds 1 and 2 in the DPPH assay were(17.29 ± 0.17) and(70.09 ± 0.09) μmol/L, respectively, while those in the ABTS assay were(22.86 ± 0.21) and(33.4 ± 0.18) μmol/L, respectively, which were far lower than that of vitamin E(the IC50 values were(78.08 ± 1.63) and(38.54 ± 0.42) μmol/L for DPPH and ABTS+ radicals, respectively), suggesting that both flavonoids possess powerful antioxidant activities.