基于环糊精本征识别能力的手性色谱介质点击制备及应用

目前环糊精（CD）手性固定相（CSP）的研究大多集中于对CD或桥联臂进行功能衍生引入更多作用位点以提升手性拆分能力，鲜有能够反映天然CD本征识别能力的CSP的研究报道，该文通过"巯基-烯"点击化学反应合成了结构明确可控的单（6-巯基-6-去氧）-β -环糊精手性固定相（CSP1），其最大限度地保留了天然CD的本征结构，且桥联臂无识别作用位点，固体核磁共振（¹³ C SSNMR）和红外光谱（FTIR）的表征结果证明了CSP1的成功制备，元素分析结果表明，与双键功能化硅胶相比，CSP1的C、H、N的百分含量均得到了提高，计算得出CSP1的表面CD固载量为0.82 μmol/m²。采用高效液相色谱反相模式对50多种手性对映体包括异（口恶）唑啉、手性交酯、手性酮、黄烷酮以及丹磺酰氨基酸等进行了手性拆分，充分考察了天然CD的本征手性识别能力，结果表明CD的本征识别能力比较有利于异（口恶）唑啉类样品中含有两个疏水苯环基团Ph-Ph类样品的分离，对于其他几类样品仅利于部分样品的分离。同时与前期制备的功能三唑桥联CD-CSP及咪唑嗡桥联CD-CSP在同一色谱条件下进行了结果比对，结果证明样品的分离过程除了与手性介质的结构有关外，还与样品分子的结构有很大关系，对桥联臂进行功能改性可提升对部分对映体的选择性，但同时会小幅损失CD的本征手性识别能力。对于环糊精本征识别能力易于分离的样品，在设计手性介质时，其桥联臂不需要任何官能团，这为CD固定相结构的设计提供了有益参考。

Click preparation and application of chiral stationary phase based on intrinsic recognition ability of cyclodextrin

Most of the studies on cyclodextrin (CD)-based chiral stationary phase (CSP) have focused on the functional derivatization of CD or the bridging arms to introduce more interaction sites and thus improve the chiral resolution ability. At present, there are only a few reports on CSP that can reflect the intrinsic recognition ability of natural CD. In this study, a mono(6-mercapto-6-deoxy)-β -CD CSP (CSP1) with a clear and controllable structure was synthesized by the "thiol-ene" click reaction. CSP1 retained the intrinsic structure of natural CD to the maximum extent, and the bridge arm had no recognition site. The results of ¹³ C solid-state nuclear magnetic resonance (SSNMR) and Fourier transform infrared (FTIR) analyses confirmed the successful preparation of CSP1. Elemental analysis results showed that compared with double-bond functionalized silica, the percentages of C, H, and N in CSP1 increased, and the calculated CD loading of CSP1 was 0.82 μmol/m² . Reversed-phase high performance liquid chromatography was performed for the chiral resolution of more than 50 chiral enantiomers, including isoxazoline, chiral lactide, chiral ketone, flavone, and dansyl amino acid. This fully demonstrated the intrinsic chiral recognition ability of natural CD, and the results showed that the intrinsic recognition ability of cyclodextrin was more conducive to the separation of Ph-Ph samples containing two hydrophobic benzene ring groups in the isoxazoline samples. For the Ph-Py and Ph-OPr samples, the separation effect was not satisfactory. The separation results for the Ph-Py samples were not ideal because the outer hydroxyl group of cyclodextrin could form a hydrogen bond with the pyridine nitrogen, thus hindering the inclusion and the separation effect. This eventually led to poor separation of the enantiomers. While the pyrrolidone group in the Ph-OPr sample could also form a good inclusion complex with cyclodextrin, its higher polarity weakened the inclusion effect compared to that for benzene rings, thus leading to poor chirality separation results. For chiral lactides, the intrinsic recognition ability of CD was good only for the separation of some samples. In the separation of chiral ketones, large steric hindrance effect inhibited the intrinsic recognition ability of CD, and the separation effect of such samples on CSP1 was not ideal. External functional groups were required in some cases to further regulate the chiral recognition performance. The molecular structure of dansyl amino acids played an important role in the separation effect, in addition to the intrinsic recognition ability of CD. The number of side chains in the substituent also affected the quality of separation. Lengthening the side chain or increasing the hydrophobicity could effectively improve the separation efficiency. The separation effect of flavanone samples on CSP1 was ordinary. The substituent positions also affected the separation effect. In order to further explore the intrinsic recognition ability of CD, the functional triazole-bridged CD-CSP (CSP2) and imidazole-bridged CD-CSP (CSP3) (the surface CD loadings of CSP2 and CSP3 were 0.51 μmol/m² and 0.46 μmol/m² , respectively) prepared earlier were selected and compared under the same chromatographic conditions. The results showed that the separation of the sample was related not only to the structure of the chiral medium but also to the structure of the sample molecules. Functional modification of the bridge arm could improve the selectivity of some enantiomers, but would also cause partial loss of the intrinsic chiral recognition ability of CD. For samples with the intrinsic recognition ability of CD to facilitate separation, no functional group had to be added to the bridge arm when designing a chiral medium. This study provides a useful reference for the design of CD-based CSPs.