DNA-Based Asymmetric Catalysis: Role of Ionic Solvents and Glymes.
DNA-Based Asymmetric Catalysis: Role of Ionic Solvents and Glymes.
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基于DNA的不对称催化：离子溶剂和甘油的作用。
DOI：
10.1039/c4ra10749g
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发表时间：
2014-01-01
期刊：
影响因子：
3.9
通讯作者：
Shen K
中科院分区：
文献类型：
--
作者：
Zhao H;Shen K
最近，DNA被评价为金属络合物的手性支架，用于构建所谓的DNA基杂化催化剂，这是一种强大而廉价的酶替代品。DNA独特的手性结构使杂化催化剂能够催化各种不对称合成反应。然而，目前的大多数研究都使用水缓冲液作为这些不对称反应的溶剂，其中底物/产物通常悬浮在溶液中。传质限制通常需要较长的反应时间。为了克服这一障碍，促进基于DNA的不对称催化，我们评估了一系列离子液体(ILS)、无机盐、深共熔溶剂(DES)、甘醇、乙二醇、乙腈和甲醇作为基于DNA的不对称Michael加成的共溶剂/添加剂。一般说来，这些添加剂会引起圆二色谱(CD)所显示的DNA B型双链构象难以区分的变化，但对DNA基杂化催化剂的催化效率有显著影响。传统的有机溶剂(如乙腈和甲醇)导致产品产率低和/或对映体选择性低。除0.2M[BMIM][CF3COO](95.4%ee和93%产率)和0.2M[BMIM]Cl(93.7%ee和89%产率)外，大多数ILS和无机盐导致杂化催化剂失活。还发现了其他几种添加剂可以提高DNA基杂化催化剂的催化效率(不加添加剂的控制反应得到99%ee和87%的产率)：0.4M甘油(5℃时99%ee，产率96%或96.2%ee，室温下83%产率)，0.2M氯化胆碱/甘油(1：2)(92.4%ee，5℃时90%产率，94.0%ee，室温下88%产率)，和0.5M二丙二醇二甲醚(>；室温下99%ee和87%产率)。使用一些共溶剂/添加剂可以在更高的温度(如室温比5℃)和更短的反应时间(如24小时比3天)下进行Michael加成反应。此外，我们还发现，在反应前将DNA在MOPS缓冲液中进行短暂的预超声处理(5min)可以提高DNA基复合催化剂的性能。我们还表明，这种基于DNA的催化方法适用于各种不同的底物和相对较大规模的反应。总之，合理选择良性助溶剂/添加剂可以提高DNA基杂化催化剂的催化效率。
Recently, DNA has been evaluated as a chiral scaffold for metal complexes to construct so called ‘DNA-based hybrid catalysts’, a robust and inexpensive alternative to enzymes. The unique chiral structure of DNA allows the hybrid catalysts to catalyze various asymmetric synthesis reactions. However, most current studies used aqueous buffers as solvents for these asymmetric reactions, where substrates/products are typically suspended in the solutions. The mass transfer limitation usually requires a long reaction time. To overcome this hurdle and to advance DNA-based asymmetric catalysis, we evaluated a series of ionic liquids (ILs), inorganic salts, deep eutectic solvents (DES), glymes, glycols, acetonitrile and methanol as co-solvents/additives for the DNA-based asymmetric Michael addition. In general, these additives induce indistinguishable changes to the DNA B-form duplex conformation as suggested by circular dichroism (CD) spectroscopy, but impose a significant influence on the catalytic efficiency of the DNA-based hybrid catalyst. Conventional organic solvents (e.g. acetonitrile and methanol) led to poor product yields and/or low enantioselectivities. Most ILs and inorganic salts cause the deactivation of the hybrid catalyst except 0.2 M [BMIM][CF3COO] (95.4% ee and 93% yield) and 0.2 M [BMIM]Cl (93.7% ee and 89% yield). Several other additives have also been found to improve the catalytic efficiency of the DNA-based hybrid catalyst (control reaction without additive gives >99% ee and 87% yield): 0.4 M glycerol (>99% ee and 96% yield at 5 °C or 96.2% ee and 83% yield at room temperature), 0.2 M choline chloride/glycerol (1:2) (92.4% ee and 90% yield at 5 °C or 94.0% ee and 88% yield at room temperature), and 0.5 M dipropylene glycol dimethyl ether (>99% ee and 87% yield at room temperature). The use of some co-solvents/additives allows the Michael addition to be performed at a higher temperature (e.g. room temperature vs 5 °C) and a shorter reaction time (24 h vs 3 days). In addition, we found that a brief pre-sonication (5 min) of DNA in MOPS buffer prior to the reaction could improve the performance of the DNA-based hybrid catalyst. We have also shown that this DNA-based catalysis method is suitable for a variety of different substrates and relatively large-scale reactions. In conclusion, a judicious selection of benign co-solvents/additives could improve the catalytic efficiency of DNA-based hybrid catalyst.