1,4-Di-N-oxide quinoxaline-2-carboxamide: Cyclic voltammetry and relationship between electrochemical behavior, structure and anti-tuberculosis activity

Structural Characterization and Electrochemical Studies of Selected Alkaloid N-Oxides

In this work, we synthesized and confirmed the structure of several alkaloid N-oxides using mass spectrometry and Fourier-transform infrared spectroscopy. We also investigated their reduction mechanisms using voltammetry. For the first time, we obtained alkaloid N-oxides using an oxidation reaction with potassium peroxymonosulfate as an oxidant. The structure was established based on the obtained fragmentation mass spectra recorded by LC-Q-ToF-MS. In the FT-IR spectra of the alkaloid N-oxides, characteristic signals of N-O group vibrations were recorded (bands in the range of 928 cm⁻1 to 971 cm⁻1), confirming the presence of this functional group. Electrochemical reduction studies demonstrated the reduction of alkaloid N-oxides at mercury-based electrodes back to the original form of the alkaloid. For the first time, the products of the electrochemical reduction of alkaloid N-oxides were detected by mass spectrometry. The findings provide insights into the structural characteristics and reduction behaviors of alkaloid N-oxides, offering implications for pharmacological and biochemical applications. This research contributes to a better understanding of alkaloid metabolism and degradation processes, with potential implications for drug development and environmental science.

An appraisal on synthetic and pharmaceutical perspectives of quinoxaline 1,4-di-N-oxide scaffold

Quinoxaline 1,4-di-N-oxides (QdNOs) exhibit multifaceted biological properties, wherein antimicrobial, anticancer, antitrypanosomal, and anti-inflammatory properties are included. Because of their various activities in clinical practice and research, they have a wide spectrum of uses and possibilities. QdNOs have received a significant amount of attention, and research into their medicinal chemistry is still a part of experimental investigation and analytical studies. In this review, QdNOs are classified depending on their actions, which include antibacterial and anti-mycobacterial, anticancer or antitumor, antimalarial, antifungal, and other activities. In a conclusion, it's important to base the development of novel synthetic techniques and the design of new QdNO derivatives on the most up-to-date knowledge gleaned from recent research. With the summarised structure-activity relationship of fascinating QdNOs, this review aims to provide insights into the developments in the chemistry and biological activity of QdNO derivatives.

Stimulation of Sulfonamides Antibacterial Drugs Activity as a Result of Complexation with Ru(III): Physicochemical and Biological Study

Antibiotic resistance is a global problem, and one promising solution to overcome this issue is using metallodrugs, which are drugs containing metal ions and ligands. These complexes are superior to free ligands in various characteristics including anticancer properties and mechanism of action. The pharmacological potential of metallodrugs can be modulated by the appropriate selection of ligands and metal ions. A good example of proper coordination is the combination of sulfonamides (sulfamerazine, sulfathiazole) with a ruthenium(III) ion. This work aimed to confirm that the activity of sulfonamides antibacterial drugs is initiated and/or stimulated by their coordination to an Ru(III) ion. The study determined the structure, electrochemical profile, CT-DNA affinity, and antimicrobial as well as anticancer properties of the synthesized complexes. The results proved that Ru(III) complexes exhibited better biological properties than the free ligands.

Photosensitive and pH-dependent activity of pyrazine-functionalized carbazole derivative as promising antifungal and imaging agent

Carbazole skeleton plays a significant role as a structural scaffold of many pharmacologically active compounds. Pyrazine-functionalized carbazole derivative was constructed by coupling 2-amino-5-bromo-3-methylaminepyrazine (ABMAP) into 3 and 6 positions of the carbazole ring. Multi-experimental methods were used, e.g., potentiometric, spectroscopic (ATR, UV, XRD powder,1H and13C NMR), electrochemical (cyclic voltammetry), and optical techniques, to receive the complete structural analysis, physicochemical (pKa, logP) and biological profile of a new carbazole derivative with acronym 3,6-PIRAMICAR. The interaction ability of the compound studied with potential cellular targets like Calf Thymus DNA (CT-DNA), or Bovine Serum Albumin (BSA) were also taken into account. Experiments showed the existence of strong binding, but no DNA or BSA cleavage was observed. The comparative analyzes of compounds anti-Candida action clearly show pH-dependent antifungal activity of 3,6-PIRAMICAR, which was strongly stimulated in the acidic media. Surprisingly, the titled compound turn out to be much more effective (14 times by MIC50; 8 times by MIC; c.a. 4 times by MFC) against Candida krusei than fluconazole at pH 4.

Discovery of 1,2,3-triazole based quinoxaline-1,4-di-N-oxide derivatives as potential anti-tubercular agents

A series of thirty one novel 2-(((1-(substituted phenyl)-1H-1,2,3-triazol-4-yl)methoxy)carbonyl)-3-methylquinoxaline-1,4-dioxide (7a-l), 3-(((1-(substituted phenyl)-1H-1,2,3-triazol-4-yl)methoxy)carbonyl)-6-chloro-2-methylquinoxaline-1,4-dioxide (8a-l) and 2-(((1-(substituted phenyl)-1H-1,2,3-triazol-4-yl)methoxy)carbonyl)-6,7-dichloro-3-methylquinoxaline-1,4-dioxide (9a-g) analogues were synthesized, characterized using various analytical techniques and single crystal was developed for the compounds 8 g and 9f. Synthesized compounds were evaluated for in vitro anti-tubercular activity against Mycobacterium tuberculosis H37Rv strain and two clinical isolates Spec. 210 and Spec. 192. The titled compounds exhibited minimum inhibitory concentration (MIC) ranging from 30.35 to 252.00 µM. Among the tested compounds, 8e, 8 l, 9c and 9d exhibited moderate activity (MIC = 47.6 - 52.0 µM) and 8a exhibited significant anti-tubercular activity (MIC = 30.35 µM). Furthermore, 8e, 8 l, and 9d were found to be less toxic against human embryonic kidney, HEK 293 cell lines. Finally, a docking study was also performed using MTB DNA Gyrase (PDB ID: 5BS8) for the significantly active compound 8a to know the exact binding pattern within the active site of the target enzyme.

Reduction Potential Predictions for Some 3-Aryl-Quinoxaline-2-Carbonitrile 1,4-Di-N-Oxide Derivatives with Known Anti-Tumor Properties

The ability for DFT: B3LYP calculations using the 6-31g and lanl2dz basis sets to predict the electrochemical properties of twenty (20) 3-aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives with varying degrees of cytotoxic activity in dimethylformamide (DMF) was investigated. There was a strong correlation for the first reduction and moderate-to-low correlation of the second reduction of the diazine ring between the computational and the experimental data, with the exception of the derivative containing the nitro functionality. The four (4) nitro group derivatives are clear outliers in the overall data sets and the derivative E4 is ill-behaved. The remaining three (3) derivatives containing the nitro groups had a strong correlation between the computational and experimental data; however, the computational data falls substantially outside of the expected range.

Voltammetric Study of Some 3-Aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide Derivatives with Anti-Tumor Activities

The electrochemical properties of twenty 3-aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives with varying degrees of cytotoxic activity were investigated in dimethylformamide (DMF) using cyclic voltammetry and first derivative cyclic voltammetry. With one exception, the first reduction of these compounds was found to be reversible or quasireversible and is attributed to reduction of the N-oxide moiety to form a radical anion. The second reduction of the diazine ring was found to be irreversible. Compounds containing a nitro group on the 3-phenyl ring also exhibited a reduction process that may be attributed to that group. There was good correlation between molecular structure and reduction potential, with reduction being facilitated by an enhanced net positive charge at the electroactive site created by electron withdrawing substituents. Additionally, the reduction potential was calculated using two common basis sets, 6-31g and lanl2dz, for five of the test molecules. There was a strong correlation between the computational data and the experimental data, with the exception of the derivative containing the nitro functionality. No relationship between the experimentally measured reduction potentials and reported cytotoxic activities was evident upon comparison of the data.

Design and synthesis of novel quinoxaline derivatives as potential candidates for treatment of multidrug-resistant and latent tuberculosis

Twenty-four quinoxaline derivatives were evaluated for their antimycobacterial activity using BacTiter-Glo microbial cell viability assay. Five compounds showed MIC values <3.1 μM and IC50 values<1.5 μM in primary screening and therefore, they were moved on for further evaluation. Compounds 21 and 18 stand out, showing MIC values of 1.6 μM and IC50 values of 0.5 and 1.0 μM, respectively. Both compounds were the most potent against three evaluated drug-resistant strains. Moreover, they exhibited intracellular activity in infected macrophages, considering log-reduction and cellular viability. In addition, compounds 16 and 21 were potent against non-replicating Mycobacterium tuberculosis and compound 21 was bactericidal. Therefore, quinoxaline derivatives could be considered for making further advances in the future development of antimycobacterial agents.

Electrochemistry and bioactivity relationship of 6-substituted-4H-pyrido[4,3,2-kl]acridin-4-one antitumor drug candidates

We report here the electrochemical characterization of eight synthetic DNA intercalators based on the 4H-pyrido[4,3,2-kl]acridin-4-one structure. We found that the electrochemical behavior of these redox active drugs is strongly influenced by the nature of the solvent. A single two-electron reduction is observed in an aqueous phosphate buffer (PB) whereas two successive one-electron reductions are observed in aprotic solution (acetonitrile). The influence of the molecular structure on the potential values is addressed along with a comparison between the DNA binding constant (K(DNA)) and the cytotoxic activity against HT29 cells (IC(50)). For typical DNA intercalators, one could expect that toxicity will be roughly proportional to the DNA binding constant. Yet, a structure/activity comparison solely based on the DNA affinity was not conclusive. In contrast, a direct relationship was evidenced for the first time between the decimal logarithm of the in vitro bioactivity and the reduction potential of pyridoacridones recorded in PB at pH 7.0. Moreover, most of the bio/electrochemical relationships previously described for quinone-based drugs were reported with electrochemical characterization in aprotic solvents (typically acetonitrile, dimethylformamide or dimethylsulfoxide). But aqueous solution electrochemistry is definitely the most bio-relevant because the redox mechanism of quinone or iminoquinone reduction directly depends on the protic nature of the solvent.

Novel multifunctional organic semiconductor materials based on 4,8-substituted 1,5-naphthyridine: synthesis, single crystal structures, opto-electrical properties and quantum chemistry calculation

A series of 4,8-substituted 1,5-naphthyridines (1a-1h) have been successfully synthesised by a Suzuki cross-coupling between 4,8-dibromo-1,5-naphthyridine (4) and the corresponding boronic acids (2a-2h) in the presence of catalytic palladium acetate in yields of 41.4-75.8% and have ben well characterized. They are thermally robust with high phase transition temperatures (above 186 °C). Compounds 1b, 1e and 1f crystallized in the monoclinic crystal system with the space groups P2(1)/c, P2(1)/c and P2(1)/n, respectively. All of them show the lowest energy absorption bands (λ(max)(Abs): 294-320 nm), revealing low optical band gaps (2.77-3.79 eV). These materials emit blue fluorescence with λ(max)(Em) ranging from 434-521 nm in dilute solution in dichloromethane and 400-501 nm in the solid state. 4,8-Substituted 1,5-naphthyridines 1a-1h have estimated electron affinities (EA) of (2.38-2.72 eV) suitable for electron-transport materials and ionization potentials (IP) of 4.85-5.04 eV facilitate excellent hole-injecting/hole-transport materials properties. Quantum chemical calculations using DFT B3LYP/6-31G* showed nearly identical the lowest unoccupied molecular orbitals (LUMO) of -2.39 to -2.19 eV and the highest occupied molecular orbitals (HOMO) of -5.33 to -6.84 eV. These results demonstrate the 4,8-substituted 1,5-naphthyridines 1a-1h with a simple architecture might be promising blue-emitting (or blue-green-emitting) materials, electron-transport materials and hole-injecting/hole-transport materials for applications for developing high-efficiency OLEDs.