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978-3-8439-0484-1, Reihe Organische Chemie
Synthesis and Self Association of Branched DNA Hybrids
159 Seiten, Dissertation Universität Stuttgart (2011), Softcover, A5
In this dissertation, branched oligodeoxynucleotides, consisting of an organic core and short DNA chains, were studied. The hybrids were based on hexakis(hydroxyphenyl)xylene (HPX), tetrakis(hydroxybiphenyl)adamantane (TBA), or tetrakis(hydroxyphenyl)methane (TPM) as core, resulting in pseudo-octahedral or tetrahedral geometry with six or four oligonucleotide chains.
The first part of this thesis focuses on the synthesis of the DNA hybrids. First, a solid-phase synthesis on controlled pore glass was performed, by building a first DNA chain via ‘reverse’ DNA synthesis with a 5'-phosphoramidite, followed by an on-support phosphitylation, coupling of the phenolic core, and DNA synthesis with 3'-phosphoramidites.
The solid phase synthesis proved difficult to scale up and produced crudes that required extensive purification. The second synthetic approach tested involved a solution-phase synthesis, based on dimer phosphoramidites that were block-coupled to the cores. Finally, a solution phase synthesis based on H-phosphonate intermediates was developed that starts from inexpensive cyanoethyl phosphoramidites. Using this methodology, 10 mg pure DNA hybrid (CG)4TBA were obtained in a single synthetic run.
The assembly of hybrids into higher ordered structures was then monitored by UV melting analysis. Hybrids with self-complementary DNA arms, i.e. (CG)4TPM, (CG)6HPX and (CG)4TBA, showed precipitation from micromolar aqueous solution in the presence of Mg2+ salts. Exploratory electron microscopy studies on (CG)6HPX showed formation of microcrystalline material. The material obtained in the presence of magnesium chloride takes up intercalators, suggesting that it forms a porous network. The new materials obtained may become useful as storage media or catalysts, accessing a pore size beyond that typically found for small molecule assemblies or crystals.