Azobenzene/Tetraethyl Ammonium Photochromic Potassium Channel Blockers: Scope and Limitations for Design of Para-Substituted Derivatives with Specific Absorption Band Maxima and Thermal Isomerization Rate.

Azobenzene/tetraethyl ammonium photochromic ligands (ATPLs) are photoactive compounds with a large variety of photopharmacological applications such as nociception control or vision restoration. Absorption band maximum and lifetime of the less stable isomer are important characteristics that determine the applicability of ATPLs. Substituents allow to adjust these characteristics in a range limited by the azobenzene/tetraethyl ammonium scaffold. The aim of the current study is to find the scope and limitations for the design of ATPLs with specific spectral and kinetic properties by introducing para substituents with different electronic effects. To perform this task we synthesized ATPLs with various electron acceptor and electron donor functional groups and studied their spectral and kinetic properties using flash photolysis and conventional spectroscopy techniques as well as quantum chemical modeling. As a result, we obtained diagrams that describe correlations between spectral and kinetic properties of ATPLs (absorption maxima of E and Z isomers of ATPLs, the thermal lifetime of their Z form) and both the electronic effect of substituents described by Hammett constants and structural parameters obtained from quantum chemical calculations. The provided results can be used for the design of ATPLs with properties that are optimal for photopharmacological applications.

Isoxazole Strategy for the Synthesis of α-Aminopyrrole Derivatives.

The synthesis of methyl 5-aminopyrrole-3-carboxylates from 4-methyleneisoxazol-5-ones via "cyanide Michael addition/methylation/reductive isoxazole-pyrrole transformation" is developed. The last step occurs in a domino mode involving Mo(CO)6-mediated reductive isoxazole ring-opening, Mo(CO)6-catalyzed cis-trans-isomerization of the enamine intermediate followed by 1,5-exo-dig cyclization. 5-Amino-1H-pyrrolo-3-carboxylates react with 1,3-diketones, affording pyrrolo[1,2-a]pyrimidine-7-carboxylates, and are easily converted into 2-diazo-2H-pyrrole-4-carboxylates. These compounds demonstrate the reactivity of both diazo compounds, giving pyrrole-containing products of intra/intermolecular azo coupling, and carbenes to give pyrrole-containing insertion products into CH and OH bonds under photolysis.