Functionalized Photochromic Scaffolds for Biological Applications

The major part of this thesis (Chapter 1 – 3) focuses on the functionalization of different photochromic scaffolds for biological applications. Chapter 4 deals with a modified dye for purification of triplex DNA. Chapter 1 describes different synthetic routes to photochromic dithienylmaleimides functionalized either at each of the thiophene moieties or at the maleimide nitrogen. A Perkin-type condensation of two independently prepared thiophene precursors was successfully employed as the key step to assemble the maleimide core for non-symmetric diarylmaleimides. Thus, a photoswitchable amino acid was obtained and a variety of aromatic substituted dithienylmaleimides were synthesized by applying a Suzuki coupling strategy prior to the condensation. A different synthetic approach gave access to photochromic labeled natural amino acids as well as maleimide protected dithienylmaleimides by the reaction of a dithienylmaleic anhydride with amines or hydrazines. All prepared photoswitchable compounds exhibited reversible photochromism in polar organic solvents. Photoswitchable histone deacetylase (HDAC) inhibitors are presented in Chapter 2. These inhibitors were gained by equipping dithienylethenes (DTEs) and fulgimides with hydroxamic acids to enable binding to zinc dependent HDACs. The control of these enzymes is of high biomedical interest in anticancer research and epigenetics due to their crucial role in numerous biological processes. While the photochromic performance of the two prepared classes of DTEs was only moderate in polar solvents the fulgimides featured excellent reversible photochromism even in aqueous buffer with very high photostationary states. All synthesized target compounds showed the anticipated inhibitory effect on the tested hHDAC1, hHDAC6, hHDAC8 and smHDAC8 with best IC50 values in the low nanomolar range. However, the corresponding photoisomers showed only a maximum four-fold difference in inhibitory ability. The differences in activity observed in the in vitro experiments could be rationalized by molecular dockings. Chapter 3 reports the synthesis and biological evaluation of photochromic ligands for modulation of γ-aminobutyric acid (GABA) and glycine-receptors by light. Therefore, photochromic ligands were synthesized by merging structural elements of nitrazepam and nicardipine, which are well-known pharmacophores for ion channels, with photoswitchable azobenzenes. The photochromic properties of the ligands were outstanding with very good fatigue resistance and high photostationary states. Initial in vitro electrophysiological investigations identified one azo benzodiazepine as very promising ligand. This compound acted not only as a UV sensitive blocker of GABAA-receptors, but also as subtype specific photoswitchable modulator of glycine-receptors. Preliminary molecular dockings could partly explain these experimental effects. Furthermore, in vivo investigations of the photochromic ligands were performed and another azo benzodiazepine showed photoswitchable influence on the activity of zebrafish larvae. The attempt to purify triplex DNA with a biotinylated thiazole orange derivative, which was synthesized by azide-alkyne click chemistry, is described in Chapter 4. Biological investigations of the functionalized compound could prove that the prepared thiazole orange kept the ability to stabilize triplexes against competitor oligonucleotides. However, a loss of overall affinity and specificity to triplex DNA was observed, which disqualified the biotinylated thiazole orange for a utilization to purify triplexes. Overall, this thesis presents functionalized synthetic compounds for biological applications. In particular, the contributions of this work are relevant for the future development of novel molecular tools to light-control cellular processes or living organisms