Chapter 1 describes the synthesis of symmetric and unsymmetric diarylcyclobutenes in a cobalt-catalyzed [2+2] cycloaddition reaction. Therefore, the appropriate diarylalkyne precursors were reacted with cyclopentene or a norbornene derivative. The reaction proceeds under mild reaction conditions at room temperature and the target compounds could be obtained in 20-70 % yield. The synthesized diarylcyclobutenes are reversibly photoswitchable and show different thermal stability towards reisomerization with half-lives ranging from 9 – 300 h.
Chapter 2 deals with the synthesis of photoswitchable diarylcyclohexenes in a cobalt catalyzed Diels-Alder cycloadditon reaction. Therefore different diarylacetylenes were reacted with boroprene and a dihydroaromatic intermediate with an allylboronic ester subunit was generated and then reacted in sito with different aldehydes and photochromic diarycyclohexenes were obtained. The synthesis allows the simple introduction of functional
groups at the backbone of the photoswitch without affecting the chromophore. An application of the functionalized diarylethenes is the immobilization of the chromophore on cellulose and silica gel.
Chapter 3 describes the synthesis and purification of new and literature reported GABAamides and the determination of their effect with patch-clamp recording on GABAA-receptors which were expressed in CHO-cells. In order to exclude contaminations of GABA which could falsify test results, an improved purification method and sensitive HPLC-MS analysis was developed. We could not confirm the literature reported results, but the new GABA-amides showed moderate activation of the GABAA-receptor and we were able to predict a clear structure activity relationship.
Chapter 4 describes the synthesis of photoswitchable ligands with potential effect on the activation of the GABAA-receptor. Therefore, in a first approach, a series of benzodiazepine derivatives substituted with a diarylethene photoswitch were synthesized and their effect on GABAA- receptor activation was determined by two independent research groups with patch clamp recording. Two of the compounds out of the first series showed moderate amplification of GABA induced current, but the exact activity could not be determined because of the insufficient solubility of the compounds in aqueous solution. UV-irradiation experiments gave no clear results and were not reproducible. Therefore, a better water soluble benzodiazepine derivative was synthesized and the effect of GABAA-receptor activation was determined. The test results were inconsistent and until now, no definite scientific conclusion can be drawn
