Styrylquinoline – A Versatile Scaffold in Medicinal Chemistry

Background: :

Styrylquinolines are characteristic fully aromatic compounds with flat, rather lipophilic structures. The first reports on their synthesis and biological activity were published roughly a century ago. However, their low selectivity, unfavorable toxicity and problems with their mechanism of action significantly hampered their development. As a result, they have been abandoned for most of the time since they were discovered.

Objective: :

Their renaissance was observed by the antiretroviral activity of several styrylquinoline derivatives that have been reported to be HIV integrase inhibitors. Subsequently, other activities such as their antifungal and anticancer abilities have also been revisited.

Methods:

In the present review, the spectrum of the activity of styrylquinolines and their use in drug design is presented and analyzed.

Results:

New properties and applications that were reported recently have re-established styrylquinolines within medicinal and material chemistry. The considerable increase in the number of published papers regarding their activity spectrum will ensure further discoveries in the field.

Conclusions:

Styrylquinolines have earned a much stronger position in medicinal chemistry due to the discovery of their new activities, profound mechanisms of action and as drug candidates in clinical trials.

Visible-light-driven two-way photoisomerization of 1-(1-pyrenyl)-2-(2-quinolyl)ethylene in neutral and protonated forms

Diarylethylenes with large π-systems often lose their photochemical activity (the size effect). 1-(1-Pyrenyl)-2-(2-quinolyl)ethylene (1P2QE), despite having a large conjugated π-system of 28 electrons, undergoes two-way reversible trans-cis photoisomerization both in the neutral and protonated forms with quantum yields as high as 0.13-0.83. For the neutral 1P2QE, experimental data and quantum-chemical calculations indicate a diabatic (nonadiabatic) reaction mechanism. Due to high photoisomerization quantum yields and the long-wavelength absorption band at 340-460 nm and 390-560 nm for the neutral and protonated compounds, respectively, 1P2QE can be used as a molecular photoswitch that is sensitive to visible light.

Molecular logic gates based on benzo-18-crown-6 ether of styrylquinoline: a theoretical study

In the present work, we examine the possibility of a benzo-18-crown-6 ether of styrylquinoline molecule (1) in acetonitrile solvent to act as a sensor for the Ca⁺⁺ cation and as a molecular logical gate. DFT and TDDFT calculations are carried out using the M06-2X and the PBE0 functionals. The quinoline moiety is an electron donor and an H⁺ receptor, while the crown ether is a Ca⁺⁺ receptor forming host-guest complexes with Ca⁺⁺. The calculations show that there are 8 thermally stable forms, i.e., trans and cis isomers of neutral (1), protonated (1H+), complexed with Ca⁺⁺ (1Ca++), and both protonated and Ca⁺⁺ complexed (1H+Ca++), with different absorption and emission spectra, and which can be interconverted from one form to another. The addition of H⁺ and/or Ca⁺⁺ to 1 results in variation of the oscillator strength of the major absorption and emission peaks as well as in significant shifts of the major absorption and emission peaks including shifting from the vis spectral area to UV and vice versa. Consequently, 1 is a candidate for a sensor for the Ca⁺⁺ cation. Furthermore it is shown that 1 can act as a molecular optical switch owing to its ability to be reversibly protonated and/or Ca⁺⁺ complexed with substantial accompanying differences in the spectral properties. Similarly, 1 can be used as a sensor molecular logic gate, in which using H⁺ and Ca⁺⁺ and irradiation as input, the emission output at 500, 470, 430, and 407 nm can be utilized as output to build AND, NOR, XOR, XNOR, INHIBIT, and IMPLICATION logic gates.