<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "DNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes"^^ . "The fascinating way nature relies on biomolecules, mostly proteins and sometimes RNA, to carry out sophisticated chemical processes led to more and more efforts to use the concepts of biology for preparing efficient chiral catalysts. The “hybrid catalyst” approach that combines the steric information derived from a protein scaffold with the catalytic activity of transition metal complexes offers a resourceful means of developing semisynthetic metalloenzymes for enantioselective applications. Since the discovery of nucleic acids with enzyme-like functions, the catalytic potential of nucleic acids is being revealed by in vitro selection and evolution of novel ribozymes and DNAzymes. Nucleic acids, especially RNA, appear to be versatile catalysts capable of accelerating a broad range of reactions and exquisitely discriminating between chiral targets. However, while proteins dominated the construction of hybrid catalysts, the application of DNA and RNA in asymmetric catalysis has hardly been explored. This work aimed at exploring the chirality of nucleic acids and generating hybrid catalysts based on DNA and RNA. Towards the development of metallo-(deoxy)ribozymes assisted by combinatorial strategies (e.g., SELEX), a straightforward synthetic way of embedding transition metal complexes in nucleic acids folds was established. DNA sequences carrying mono- and bidentate phosphine ligands as well as P,N-ligands were successfully prepared starting from amino-modified oligonucleotide precursors. The optimized “convertible nucleoside” approach allowed the parallel, high-yielding synthesis of various alkylamino-DNA conjugates differing in length and structure of the spacer. Coupling of amino-oligonucleotides with PYRPHOS, BINAP and PHOX ligands equipped with a carboxyl group led to the incorporation of phosphine moieties at predetermined internal sites. Moreover, the stability of the DNA-tethered BINAP and PHOX was reasonably high, which makes them attractive candidates for the development of transition metal-containing oligonucleotides. To this end, systematic studies on the behavior of phosphine- and PHOX-metal complexes in aqueous medium - a prerequisite of nucleic acid catalysts - were carried out. Two model organometallic transformations were selected that were compatible with the structure and chemistry of nucleic acids. The rhodium(I)-catalyzed 1,4-addition of phenyl boronic acid to 2-cyclohexen-1-one and iridium(I)-catalyzed allylic amination of the branched phenyl allyl acetate, respectively, proceeded efficiently in the presence of phosphorus-based ligands, in aqueous medium, at room temperature and low catalyst concentration. For the first model reaction, the best conversion (80%) was achieved with the isolated [Rh(nbd)BINAP]BF4 complex, in 6:1 dioxane/water, and TEA additive. On the basis of these data, a suitable system for assessing the catalytic potential of the DNA-BINAP ligand was implemented. In the second chosen reaction the in situ formed Ir(I)-PHOX complexes (0.05-0.1 mM) gave rise to racemic, branched allylic amination products in good yields (33-75%), in 3:7 dioxane/water. Kinetic resolution of the racemic substrate was then attempted by employing catalysts generated from the [Ir(cod)Cl]2 precursor and single- and double-stranded DNA-PHOX conjugates. Good conversions were obtained in the presence of G-poor DNA/DNA and RNA/DNA hybrids bearing the PHOX moiety, indicating a potential role of the G-N7 site in the first coordination sphere. With all tested DNA-PHOX conjugates, the levels of enantioselectivity remained modest. The results described in this work provide useful information for understanding the influence of nucleic acid sequence and covalent tethering on the reaction outcome. These are the first reported applications of DNA-based ligands in organometallic catalysis and they build the fundamentals for further development of selective nucleic acid catalysts, by means of rational design and in vitro selection approaches."^^ . "2007" . . . . . . . . "Mihaela"^^ . "Caprioara"^^ . "Mihaela Caprioara"^^ . . . . . . "DNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes (PDF)"^^ . . . "Mihaela_Caprioara_Doktorarbeit_2007.pdf"^^ . . . "DNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes (Other)"^^ . . . . . . "indexcodes.txt"^^ . . . "DNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "DNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes (Other)"^^ . . . . . . "preview.jpg"^^ . . . "DNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes (Other)"^^ . . . . . . "medium.jpg"^^ . . . "DNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes (Other)"^^ . . . . . . "small.jpg"^^ . . "HTML Summary of #7896 \n\nDNA-Based Ligands for Use in Asymmetric Catalysis and Development of Metallo-(deoxy)Ribozymes\n\n" . "text/html" . . . "570 Biowissenschaften, Biologie"@de . "570 Life sciences"@en . .