Light-switchable diazocines as potential inhibitors of testosterone-synthesizing 17β-hydroxysteroid dehydrogenase 3

In patients with prostate carcinoma as well as in some other cancer types, the reduction of testosterone levels is desired because the hormone stimulates cancer cell growth. One molecular target for this goal is the inhibition of 17β-hydroxysteroid dehydrogenase type 3 (17βHSD3), which produces testosterone from its direct precursor androstenedione. Recent research in this field is trying to harness photopharmacological properties of certain compounds so that the inhibitory effect could be turned on and off by irradiation. Seven new light-switchable diazocines were investigated with regard to their inhibition of 17βHSD3. For this purpose, transfected HEK-293 cells and isolated microsomes were treated with the substrate and the potential inhibitors with and without irradiation for an incubation period of 3 or 5 h. The amount of generated testosterone was measured by UHPLC and compared between samples and control as well as between irradiated and non-irradiated samples. There was no significant difference between samples with and without irradiation. However, four of the seven diazocines led to a significantly lower testosterone production both in cell and in microsome assays. In some of the irradiated samples, a partial destruction of the diazocines was observed, indicated by an additional UHPLC peak. However, the influence on the inhibition is negligible, because the majority of the substance remained intact. In conclusion, new inhibitors of 17βHSD3 have been found, but so far without the feature of a light switch, since the configurational alteration of the diazocines by irradiation did not lead to a change in bioactivity. Further modification might help to find a light-switching molecule that inhibits only in one configuration.

UV/Vis Spectroscopy Studies of the Photoisomerization Kinetics in Self-Assembled Azobenzene-Containing Adlayers

Direct comparative studies of the photoisomerization of azobenzene derivatives in self-assembled adlayers on Au and as free molecules in dichloromethane solution were performed using UV/vis spectroscopy. For all studied systems a highly reversible trans-cis isomerization in the adlayer is observed. Quantitative studies of the absorbance changes and photoisomerization kinetics reveal that in azobenzenes mounted as freestanding vertical groups on the surface via triazatriangulene-based molecular platforms photoswitching is nearly uninhibited by the local environment in the adlayer. The blue-shift of the π-π* transition in adlayers of these molecules is in good agreement with theoretical studies of the effect of excitonic coupling between the molecules. In contrast, in azobenzene-containing thiol self-assembled monolayers the fraction of photoswitching molecules and the photoisomerization kinetics are significantly reduced compared to free molecules in solution.

Rational design of a room temperature molecular spin switch. The light-driven coordination induced spin state switch (LD-CISSS) approach

A record player type molecule changes spin state reversibly upon irradiation with green and blue light in solution at room temperature without measureable fatigue.

The growth and electronic structure of azobenzene-based functional molecules on layered crystals

In situ ultraviolet photoelectron spectroscopy is used to study the growth of ultrathin films of azobenzene-based functional molecules (azobenzene, Disperse Orange 3 and a triazatriangulenium platform with an attached functional azo-group) on the layered metal TiTe(2) and on the layered semiconductor HfS(2) at liquid nitrogen temperatures. Effects of intermolecular interactions, of the substrate electronic structure, and of the thermal energy of the sublimated molecules on the growth process and on the adsorbate electronic structure are identified and discussed. A weak adsorbate-substrate interaction is particularly observed for the layered semiconducting substrate, holding the promise of efficient molecular photoswitching.

Magnetic bistability of molecules in homogeneous solution at room temperature

Magnetic bistability, as manifested in the magnetization of ferromagnetic materials or spin crossover in transition metal complexes, has essentially been restricted to either bulk materials or to very low temperatures. We now present a molecular spin switch that is bistable at room temperature in homogeneous solution. Irradiation of a carefully designed nickel complex with blue-green light (500 nanometers) induces coordination of a tethered pyridine ligand and concomitant electronic rearrangement from a diamagnetic to a paramagnetic state in up to 75% of the ensemble. The process is fully reversible on irradiation with violet-blue light (435 nanometers). No fatigue or degradation is observed after several thousand cycles at room temperature under air. Preliminary data show promise for applications in magnetic resonance imaging.

Synthesis of a Möbius aromatic hydrocarbon

The defining feature of aromatic hydrocarbon compounds is a cyclic molecular structure stabilized by the delocalization of pi electrons that, according to the Hückel rule, need to total 4n + 2 (n = 1,2, em leader ); cyclic compounds with 4n pi electrons are antiaromatic and unstable. But in 1964, Heilbronner predicted on purely theoretical grounds that cyclic molecules with the topology of a Möbius band--a ring constructed by joining the ends of a rectangular strip after having given one end half a twist--should be aromatic if they contain 4n, rather than 4n + 2, pi electrons. The prediction stimulated attempts to synthesize Möbius aromatic hydrocarbons, but twisted cyclic molecules are destabilized by large ring strains, with the twist also suppressing overlap of the p orbitals involved in electron delocalization and stabilization. In larger cyclic molecules, ring strain is less pronounced but the structures are very flexible and flip back to the less-strained Hückel topology. Although transition-state species, an unstable intermediate and a non-conjugated cyclic molecule, all with a Möbius topology, have been documented, a stable aromatic Möbius system has not yet been realized. Here we report that combining a 'normal' aromatic structure (with p orbitals orthogonal to the ring plane) and a 'belt-like' aromatic structure (with p orbitals within the ring plane) yields a Möbius compound stabilized by its extended pi system.

Ethynylogization of a coarctate fragmentation

Coarctate reactions form a separate class of elementary closed-shell processes in addition to polar and pericyclic reactions. Hence, they also follow a different homology principle. Whereas vinylogous polar and pericyclic reactions differ in the length of the reacting system by a double bond, coarctate reactions can be homologized (ethynylogized) by extending a known system by a triple bond. The prediction, which is based on theoretical considerations, is confirmed experimentally by the fragmentation of cyclopropylethynyl nitrene to cyano acetylene and ethylene, a reaction that is "ethynyloguous" to the known fragmentation of cyclopropyl nitrene to ethylene and HCN.

Reaction Planning: Computer-Aided Discovery of a Novel Elimination Reaction

Algorithms based on graph theory and implemented in a computer program have been used to search for unprecedented reactions. This approach is illustrated by a systematic and exhaustive screening of pericyclic reactions in order to find new reactions useful in the synthesis of conjugated dienes. Two reactions were found. They were optimized by structural variation with the aid of quantum-chemical calculations and were then experimentally verified.