Design,Synthesis Of Secondary-Face Modified β-CDs And Their Application On Catalysis And Molecular Recognition

As the second-generation supramolecular host,cyclodextrins（CDs）are widely used in the fields of supramolecular catalysis and molecular recognition because of its easy modification,ready availability and environmentally benign and non-toxic properties.However,due to the homo-functional property of native CDs,their application is relatively limited.Structural modification of CDs is the best way to solve this problem.Among the cyclodextrin derivatives that have been reported so far,most are modified on the primary face of the CDs,by contrast,CDs modified on the secondary face are almost elusive.Secondary-face modified CDs have some significant advantages in view of their unique features as followed:firstly,the modifying group on the secondary face points to the deep cavity of CD,which could better cooperates with the cavity;secondly,the hydroxyl groups on the secondary face are directly connected to the chiral carbon centers,which could better exert chiral induction;furthermore,the secondary face is larger,which could accommodate a wider range of substrates.Therefore,the design,synthesis and application of the secondary-face modified CDs are of high value.This thesis consists of the following three parts:（1）Amino groups were installed at the C-3 position ofβ-CD,resulting in eight amino-modified CDs（CD1-CD8）which were characterized by NMR and HRMS.The self-inclusion of these amino-modified CDs in water was identified by2D-ROESY.（2）These amino-modified CDs were allowed to catalyze the asymmetric aldol reaction in water.Among them,the catalyst CD8 containing a（1S,2S）-（+）-1,2-cyclohexanediamine groups showed the best catalytic activity.The reaction was performed at 0°C with a citric acid buffer solution（p H=3）can obtain better yield（86%）and stereoselectivity（94%ee）.The catalytic mechanism of CD8 was involves enamine catalysis from NMR,Job plot and HRMS analysis.（3）Molecular recognition of carboxylic acids and their analogues（p-toluic acid,p-toluenesulfonic acid,p-cresol and p-methylbenzyl alcohol）by four cyclodextrin amino derivatives（CD5-CD8）was investigated Behavior.Their inclusion stoichiometry and binding stability constants（Ks）were determined using Job plot and¹H NMR titration,respectively.The inclusion stoichiometry is 1:1,and the binding constants are between 10～10⁴ M^-1.Among them,the binding constants of CD7 to p-toluic acid and its analogues are 37842,1474,921,and 19 M^-1,respectively,showing a very high selective recognition ability for carboxylic acids.The inclusion behavior of CD7 and the above four guests were further studied by ¹H NMR and2D-ROESY.In summary,secondary-face modification of CDs could bring new opportunities for aqueous supramolecular catalysis and highly selective molecular recognition.It will also inspire future development on the emerging platform of catalysis and molecular recognition based on the secondary face of CDs.