Natural Products Laboratory, Institute of Biology, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands.
College of Pharmacy, Kyung Hee University, Seoul 02447, Korea.
Molecules. 2020 Jan 31;25(3):617. doi: 10.3390/molecules25030617.
Natural deep eutectic solvents (NADES) are a type of ionic liquid (IL) or deep eutectic solvent (DES), the ingredients of which are exclusively natural products (non-toxic and environmentally friendly). Here, we explore the potential of NADES as an alternative to conventional organic solvents (e.g., aqueous methanol or ethanol) for the extraction of flavonoids from stem bark to investigate their extractability depending on structural variation. Four NADES, each containing citric acid in combination with β-alanine, glucose, xylitol, or proline (at a molar ratio of 1:1), and a variable amount of water, were used to extract the flavonoid aglycones: baicalein (), scutellarein (), wogonin (), and oroxylin A (), and their glycosides, baicalin (), scutellarin (), wogonoside () and oroxyloside () from the powdered bark of . The chemical profile and yield of the extracts were determined using HPTLC and HPLC. The extractability of individual flavonoids was found to be influenced by the concentration of water (20-60%, w/w) in the NADES. Among the tested flavonoids, the extraction yield of baicalein (), scutellarein (), wogonin (), oroxylin A () with NADES was 2 to 6 times that of aqueous methanol. However, the amount of their corresponding glycosides (baicalin (), wogonoside () and oroxyloside ()) extracted with NADES was only 1.5-1.8 times higher than with aqueous methanol. Interestingly, the more hydrophilic glycosides were less extracted than their corresponding aglycones despite the high hydrophilicity of the NADES. These results prove that NADES may be used for extraction of compounds with a wide range of hydrophilicity.
天然深共晶溶剂 (NADES) 是离子液体 (IL) 或深共晶溶剂 (DES) 的一种，其成分均为天然产物（无毒且环保）。在这里，我们探索了 NADES 作为替代传统有机溶剂（例如水甲醇或乙醇）从树皮中提取类黄酮的潜力，以研究其根据结构变化的可提取性。我们使用了四种 NADES，每种 NADES 均含有柠檬酸与 β-丙氨酸、葡萄糖、木糖醇或脯氨酸（摩尔比为 1:1）组合，并含有不同量的水，以提取类黄酮苷元：白杨素（）、黄芩素（）、汉黄芩素（）和 7-甲氧基-4-羟基异黄酮（），以及它们的糖苷：黄芩苷（）、黄芩苷（）、汉黄芩苷（）和 7-甲氧基-4-羟基异黄酮-7-O-β-D-葡萄糖苷（），从 的粉末树皮中提取。使用 HPTLC 和 HPLC 确定提取物的化学特征和产率。发现各黄酮类化合物的提取率受 NADES 中水的浓度（20-60%，w/w）的影响。在所测试的黄酮类化合物中，NADES 提取白杨素（）、黄芩素（）、汉黄芩素（）和 7-甲氧基-4-羟基异黄酮（）的产率是水甲醇的 2 到 6 倍。然而，用 NADES 提取其相应糖苷（黄芩苷（）、汉黄芩苷（）和 7-甲氧基-4-羟基异黄酮-7-O-β-D-葡萄糖苷（））的量仅比水甲醇高 1.5-1.8 倍。有趣的是，尽管 NADES 的亲水性很高，但亲水性更强的糖苷的提取量却低于其相应的苷元。这些结果证明 NADES 可用于提取具有广泛亲水性的化合物。
