Synthesis And Catalysis Of Diels-Alder Reactions Of Poly Amide-Based DNA Hybrid Catalyst

Enzymes encoded by DNA have highly efficient catalytic performance and specific stereoselectivity. Recently to imitate enantioselectivity of enzymes, scientists combine the stereostructure of biomolecule such as proteins, DNA, RNA and transition metals of catalytic properties to form artificial metal enzyme which can catalysis asymmetric reactions. DNA because of unique double helix stereostructure has achieved greate attentions from scientists. The chiral transfering directly from DNA to asymmetric reactions has got ahead.We synthesised hairpin polyamide of eight units and single stranded polyamide of four units which can specially recognize and bind AT enrichment region of DNA minor groove and they can form new ligands for recognizing DNA after covalent bind with dipyridine. New ligands can bring the reaction center of Cu2+ into the two-dimension structure of DNA. Ligands and DNA can form new artificial metal enzyme by self-assembly that can catalysis different Diels-Alder reactions of azachalcone with cyclopentadiene. Using normal phase HPLC to test the enantiomer excess ee value, and evaluate the stereoselectivity of the new catalysts.Compared to the ligand have reported, the conclusion can be get:through the reasonable design of ligands, the microenvironment of the chiral catalyst can be controlled, and then the stereoselectivity can be controlled. In order to further explore the action mode of ligands with DNA, we also carried out circular dichroism spectrum experiments to test the impact on the structure of DNA after ligands binding to DNA.From CD experiments, we can conclude that ligands can change the second dimensional structure of DNA when ligands were titrated to DNA, and ligands can make the characteristic absoption of DNA become weaker. The new induced absorption peak in CD indicated that ligands insert into the structure of DNA, but the new induced absorption peak was weak which show that ligands cannot good embed into the micro environment of the DNA.Through the experimental data we can concluded that stereoselectivity of Pys-dmbipy ligand is better than Py₄-dmbipy ligand, probably because higher identification ability and higher combining ability of DNA of the eight polyamide than four polyamide. The findings suggest that for the study of hybrid catalyst based on DNA, by controling chiral of reaction micro-environment, different chiral product can be got.