Design, synthesis, antioxidant properties and mechanism of action of new N,N′-disubstituted benzimidazole-2-thione hydrazone derivatives

Synthesis, characterization, PXRD studies, and theoretical calculation of the effect of gamma irradiation and antimicrobial studies on novel Pd(II), Cu(II), and Cu(I) complexes

The main objective of this study is to synthesize and characterize of a new three complexes of Pd (II), Cu (II), and Cu (I) metal ions with novel ligand ((Z)-2-(phenylamino)-N'-(thiophen-2-ylmethylene)acetohydrazide) H2LB. The structural composition of new compounds was assessed using several analytical techniques including FT-IR, 1H-NMR, electronic spectra, powder X-ray diffraction, and thermal behavior analysis. The Gaussian09 program employed the Density Functional Theory (DFT) approach to optimize the geometry of all synthesized compounds, therefore obtaining the most favorable structures and crucial parameters. An investigation was conducted to examine the impact of γ-irradiation on ligands and complexes. Before and after γ-irradiation, the antimicrobial efficiency was investigated for the activity of ligands and their chelates. The Cu(I) complex demonstrated enhanced antibacterial activity after irradiation, as well as other standard medications such as ampicillin and gentamicin. Similarly, the Cu(I) complex exhibited superior activity against antifungal species relative to the standard drug Nystatin. The docking investigation utilized the target location of the topoisomerase enzyme (2xct) chain A.

Novel N-Acyl Hydrazone Compounds as Promising Anticancer Agents: Synthesis and Molecular Docking Studies

In this study, a new series of N-acyl hydrazones 7a-e, 8a-e, and 9a-e, starting from methyl δ-oxo pentanoate with different substituted groups 1a-e, were synthesized as anticancer agents. The structures of obtained target molecules were identified by spectrometric analysis methods (FT-IR, ¹¹H NMR, ¹³C NMR, and LC-MS). The antiproliferative activity of the novel N-acyl hydrazones was evaluated on the breast (MCF-7) and prostate (PC-3) cancer cell lines by an MTT assay. Additionally, breast epithelial cells (ME-16C) were used as reference normal cells. All newly synthesized compounds 7a-e, 8a-e, and 9a-e exhibited selective antiproliferative activity with high toxicity to both cancer cells simultaneously without any toxicity to normal cells. Among these novel N-acyl hydrazones, 7a-e showed the most potent anticancer activities with IC₅₀ values at 7.52 ± 0.32-25.41 ± 0.82 and 10.19 ± 0.52-57.33 ± 0.92 μM against MCF-7 and PC-3 cells, respectively. Also, molecular docking studies were applied to comprehend potential molecular interactions between compounds and target proteins. It was seen that the docking calculations and the experimental data are in good agreement.

Acylhydrazones and Their Biological Activity: A Review

Due to the structure of acylhydrazones both by the pharmacophore -CO-NH-N= group and by the different substituents present in the molecules of compounds of this class, various pharmacological activities were reported, including antitumor, antimicrobial, antiviral, antiparasitic, anti-inflammatory, immunomodulatory, antiedematous, antiglaucomatous, antidiabetic, antioxidant, and actions on the central nervous system and on the cardiovascular system. This fragment is found in the structure of several drugs used in the therapy of some diseases that are at the top of public health problems, like microbial infections and cardiovascular diseases. Moreover, the acylhydrazone moiety is present in the structure of some compounds with possible applications in the treatment of other different pathologies, such as schizophrenia, Parkinson's disease, Alzheimer's disease, and Huntington's disease. Considering these aspects, we consider that a study of the literature data regarding the structural and biological properties of these compounds is useful.

Exploration of Molecular Structure, DFT Calculations, and Antioxidant Activity of a Hydrazone Derivative

The hydrazine derivatives are known to possess several biological activities including anticancer, antibacterial and anti-fungal, anticonvulsant, and antioxidant. This communication presents the synthesis, X-ray crystal structure analysis, DFT calculations, cell cytotoxicity, and antioxidant activity of the Schiff base 4,4'-((1E,1'E)-hydrazine-1,2-diylidenebis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (compound 2). We have also isolated the side product compound 1 and characterized it using single X-ray crystallography. The crystal structure of compound 1 depicts that the ensuing C-H···N hydrogen bonding interaction is presented and discussed herein. In addition, the calculations using density functional theory (DFT) approximation supported by experimental 1H and 13C NMR studies on the key compound 2 are reported. The results of theoretical and experimental 1H and 13C NMR were concordant. The antioxidant activity of compound 2 was determined by using 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS•+) radical cation assays and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay. Compound 2 demonstrated excellent antioxidant activity in ABTS assay (IC50 = 4.30 ± 0.21 µM) and DPPH assay (IC50 = 81.06 ± 0.72 µM) with almost no cytotoxicity below 25 µM.

Synthesis and Biological Activity Characterization of Novel 5-Oxopyrrolidine Derivatives with Promising Anticancer and Antimicrobial Activity

The 1-(4-acetamidophenyl)-5-oxopyrrolidine carboxylic acid was applied for synthesizing derivatives bearing azole, diazole, and hydrazone moieties in the molecule. Modification of an acetamide fragment to the free amino group afforded compounds with two functional groups, which enabled to provide a series of 4-substituted-1-(4-substituted phenyl)pyrrolidine-2-ones. The resulted compounds 2 and 4-22 were subjected to the in vitro anticancer and antimicrobial activity determination. The compounds 18-22 exerted the most potent anticancer activity against A549 cells. Furthermore, compound 21 bearing 5-nitrothiophene substituents demonstrated promising and selective antimicrobial activity against multidrug-resistant Staphylococcus aureus strains, including linezolid and tedizolid-resistant S. aureus. These results demonstrate that 5-oxopyrolidine derivatives are attractive scaffolds for the further development of anticancer and antimicrobial compounds targeting multidrug-resistant Gram-positive pathogens.

Synthesis, Characterization, PXRD Studies, Theoretical Calculation, and Antitumor Potency Studies of a Novel N,O-Multidentate Chelating Ligand and Its Zr(IV), V(IV), Ru(III), and Cd(II) Complexes

A new series of Zr(IV), V(IV), Ru(III), and Cd(II) complexes with the ligand N-((5-hydroxy-4-oxo-4H-pyran-3-yl)methylene)-2-(p-tolylamino)acetohydrazide (H2L) have been prepared. FT-IR, 1H-NMR, electronic spectra, powder X-ray, and thermal behavior methods were applied to elucidate the structural composition of new compounds. Geometry optimization for all synthesized compounds was conducted using the Gaussian09 program via the DFT method, to obtain optimal structures and essential parameters. Moreover, the antibacterial and antitumor activity of the ligand and its complexes were studied, where the Cd(II) complex acquires probably the best antibacterial activity followed by the Ru(III) complex towards bacterial species than others when using ampicillin and gentamicin were used as standard drugs. The complexes exhibited interestingly antitumor potential against the MCF-7 breast cancer cell line. The cytotoxicity of the new complexes has been arranged to follow the order: Ru(III) complex > Cd(II) complex > Zr(IV) complex > V(IV) complex > ligand. Molecular docking was performed on the active site of ribosyltransferase and obtained good results. Structure-based molecular docking is used to identify a potential therapeutic inhibitor for NUDT5.

Study on the Neuroprotective, Radical-Scavenging and MAO-B Inhibiting Properties of New Benzimidazole Arylhydrazones as Potential Multi-Target Drugs for the Treatment of Parkinson's Disease

Oxidative stress is a key contributing factor in the complex degenerating cascade in Parkinson's disease. The inhibition of MAO-B affords higher dopamine bioavailability and stops ROS formation. The incorporation of hydroxy and methoxy groups in the arylhydrazone moiety of a new series of 1,3-disubstituted benzimidazole-2-thiones could increase the neuroprotective activity. In vitro safety evaluation on SH-SY5Y cells and rat brain synaptosomes showed a strong safety profile. Antioxidant and neuroprotective effects were evaluated in H2O2-induced oxidative stress on SH-SY5Y cells and in a model of 6-OHDA-induced neurotoxicity in rat brain synaptosomes, where the dihydroxy compounds 3h and 3i demonstrated the most robust neuroprotective and antioxidant activity, more pronounced than the reference melatonin and rasagiline. Statistically significant MAO-B inhibitory effects were exerted by some of the compounds where again the catecholic compound 3h was the most potent inhibitor similar to selegiline and rasagiline. The most potent antioxidant effect in the ferrous iron induced lipid peroxidation assay was observed for the three catechols-3h and 3j, 3q. The catecholic compound 3h showed scavenging capability against superoxide radicals and antioxidant effect in the iron/deoxyribose system. The study outlines a perspective multifunctional compound with the best safety profile, neuroprotective, antioxidant and MAO-B inhibiting properties.

A Panoramic Review of Benzimidazole Derivatives and Their Potential Biological Activity

The therapeutic potential of the benzimidazole nucleus dates back to 1944, being and important heterocycle system due to its presence in a wide range of bioactive compounds such as antiviral, anticancer, antibacterial, and so on, where optimization of substituents in this class of pharmacophore has resulted in many drugs. Its extensive biological activity is due to its physicochemical properties like hydrogen bond donor-acceptor capability, π → π stacking interactions, coordination bonds with metals as ligands and hydrophobic interactions; properties that allow them to easily bind with a series of biomolecules, including enzymes and nucleic acids, causing a growing interest in these types of molecules. This review aims to present an overview to leading benzimidazole derivatives, as well as to show the importance of the nature and type of substituents at the N1, C2, and C5(6) positions, when they are biologically evaluated, which can lead to obtaining potent drug candidate with significant range of biological activities.

A Comprehensive Account on Recent Progress in Pharmacological Activities of Benzimidazole Derivatives

Nowadays, nitrogenous heterocyclic molecules have attracted a great deal of interest among medicinal chemists. Among these potential heterocyclic drugs, benzimidazole scaffolds are considerably prevalent. Due to their isostructural pharmacophore of naturally occurring active biomolecules, benzimidazole derivatives have significant importance as chemotherapeutic agents in diverse clinical conditions. Researchers have synthesized plenty of benzimidazole derivatives in the last decades, amidst a large share of these compounds exerted excellent bioactivity against many ailments with outstanding bioavailability, safety, and stability profiles. In this comprehensive review, we have summarized the bioactivity of the benzimidazole derivatives reported in recent literature (2012-2021) with their available structure-activity relationship. Compounds bearing benzimidazole nucleus possess broad-spectrum pharmacological properties ranging from common antibacterial effects to the world's most virulent diseases. Several promising therapeutic candidates are undergoing human trials, and some of these are going to be approved for clinical use. However, notable challenges, such as drug resistance, costly and tedious synthetic methods, little structural information of receptors, lack of advanced software, and so on, are still viable to be overcome for further research.

Evaluation of the combined activity of benzimidazole arylhydrazones as new anti-Parkinsonian agents: monoamine oxidase-B inhibition, neuroprotection and oxidative stress modulation

Neuroprotective drugs and selective monoamine oxidase inhibitors can slow down the progression and improve symptoms of Parkinson’s disease (PD). Since there is an implication of oxidative stress in the pathophysiological mechanisms of the disease, the compounds possessing an ability to reduce the oxidative stress are prime candidates for neuroprotection. Thereby our current study is focused on the development of new multi-target PD drugs capable of inhibiting the activity of monoamine oxidase-B while exerting neuroprotective and antioxidant properties. A small series of benzimidazole derivatives containing hydroxy and methoxy arylhydrazone fragments has been synthesized and the neurotoxicity of the compounds has been evaluated in vitro on neuroblastoma SH-SY5Y cells and on isolated rat brain synaptosomes by measuring the cell viability and the levels of reduced glutathione and a good safety profile has been shown. The 2-hydroxy-4-methoxy substituted arylhydrazone 7 was the least toxic on neuronal SH-SY5Y cells and showed the lowest neurotoxicity in rat brain synaptosomes. The neuroprotective properties of the test compounds were further assessed using two models: H₂O₂ -induced oxidative stress on SH-SY5Y cells and 6-hydroxydopamine-induced neurotoxicity in rat brain synaptosomes. Compound 7 showed more pronounced neuroprotective activity on SH-SY5Y cells, compared to the referent melatonin and rasagiline. It also preserved the synaptosomal viability and the reduced glutathione levels; the effects were stronger than those of rasagiline and comparable to melatonin. All the tested compounds were capable to inhibit human monoamine oxidase-B enzyme to a significant extent, however, compound 7 exerted the most prominent inhibitory activity, similar to selegiline and rasagiline. The carried out molecular docking studies revealed that the activity is related to the appropriate molecular structure enabling the ligand to enter deeper in the narrow and highly lipophylic active site pocket of the human monoamine oxidase-B and has a favoring interaction with the key amino acid residues Tyr326 and Cys172. Since much scientific evidence points out the implication of iron dyshomeostasis in PD, the compounds were tested to reduce the ferrous iron induced oxidative molecular damage on biologically important molecules in an in vitro lecithin containing model system. All the investigated compounds denoted protection effect, stronger than the one of the referent melatonin. In order to support the assignments of the significant neuroprotective and antioxidant pharmacological activities, the radical-scavenging mechanisms of the most promising compound 7 were evaluated using DFT methods. It was found that the most probable free radicals scavenging mechanism in nonpolar phase is the hydrogen atom transfer from the amide group of compound 7, while in polar medium the process is expected to occur by a proton transfer. The current study outlines a perspective leading structure, bearing the potential for a new anti-PD drug. All performed procedures were approved by the Institutional Animal Care Committee of the Medical University of Sofia (Bulgarian Agency for Food Safety with Permission № 190, approved on February 6, 2020).

New 1H-benzimidazole-2-yl hydrazones with combined antiparasitic and antioxidant activity

Parasitic infections, caused mainly by the species Trichinella spiralis (T. spiralis), are widespread around the world and lead to morbidity and mortality in the population. Meanwhile, some studies have showed that these parasites induce oxidative stress in the infected host. With the aim of developing a class of compounds combining anthelmintic with antioxidant properties, a series of new benzimidazolyl-2-hydrazones 5a-l, bearing hydroxyl- and methoxy-groups, were synthesized. The anthelmintic activity on encapsulated T. spiralis was studied in vitro thus indicating that all hydrazones were more active than the clinically used anthelmintic drugs albendazole and ivermectin. 5b and 5d killed the total parasitic larvae (100% effectiveness) after 24 hours incubation period at 37 °C in both concentrations (50 and 100 μg ml⁻¹). The antioxidant activity of the target compounds was elucidated in vitro against stable free radicals DPPH and ABTS as well as iron induced oxidative damage in model systems containing biologically relevant molecules lecithin and deoxyribose. The two 2,3- and 3,4-dihydroxy hydrazones 5b and 5d were the most effective radical scavengers in all studied systems. DFT calculations were applied to calculate the reaction enthalpies in polar and nonpolar medium and estimate the preferred mechanism of antioxidant activity. The relative radical scavenging ability of compounds 5a-l showed a good correlation to the experimentally observed trends. It was found that the studied compounds are capable to react with various free radicals – ˙OCH₃, ˙OOH and ˙OOCH₃, through several possible reaction pathways – HAT in nonpolar medium, SPLET in polar medium and RAF in both media.

The design of new drug candidates that combine anthelmintic and antioxidant actions in one molecule offers a beneficial approach in the treatment of the tissue damages, immune system dysfunction and oxidative stress caused by trichinellosis.

Spectroscopic and in silico study on the conversion of N,N'-disubstituted hydrazone derivatives of 5-nitrobenzimidazole-2-thione into anion and radical anion products: Implications in hepatotoxicity

The conversion of N,N'-disubstituted hydrazone derivatives of 5-nitrobenzimidazole-2-thione into radical anion and dianion products was studied through infrared (IR) spectroscopy and computational methods. The electrochemical reduction of 3,3'-(5-nitro-2-thioxo-1H-benzo[d]imidazole-1,3(2H)-diyl)bis(N'-(2-methoxybenzylidene))propane-hydrazide was performed directly in the IR cell and the spectral changes were monitored over time in order to identify the spectral bands originating from the reduction product. In order to clarify whether the reduction leads to the generation of radical anion or deprotonated radical dianion, a second spectroscopic experiment was carried out where deprotonation was achieved by treatment with sodium methoxide. Both experiments resulted in distinctly different spectral features, giving evidence that the reduction to radical anion is not accompanied by deprotonation. In order to explain the experimentally observed differences in the hepatotoxicity within the series of N,N'-disubstituted derivatives of 5-nitrobenzimidazole-2-thione, several molecular electronic parameters such as frontier molecular orbitals, spin and charge distribution over fragments, and electron affinities of the studied hydrazone derivatives were compared to those of a previously studied ester derivative. Based on the estimated electronic parameters, it was shown that the type of the side chains (ester, hydrazone etc.) attached to the N-atoms in the nitrobenzimidazole derivatives do not change significantly the propensity of the compounds towards nitro reduction, but however the generated radical anions are characterized by different reactivity accounting for the different hepatotoxicity.

New benzimidazole-aldehyde hybrids as neuroprotectors with hypochlorite and superoxide radical-scavenging activity

BACKGROUND

Many neurodegenerative disorders include oxidative stress-mediated pathology. Melatonin and its metabolites act as endogenous reactive oxygen species (ROS) scavengers and antioxidants. N,N'-Disubstituted benzimidazole-2-thiones with extended side chains could exert antioxidant and neuroprotective properties due to structural similarities to melatonin.

METHODS

The toxicological potential of the compounds was evaluated by monitoring the synaptosomal viability and the levels of reduced glutathione (GSH) in isolated rat brain synaptosomes. The neuroprotective effects were assessed in vitro in a model of 6-hydroxydopamine (6-OHDA)-induced neurotoxicity. The capability to decrease superoxide anion radical and hypochlorite was evaluated by luminol-dependent chemiluminescent assays.

RESULTS

Compounds 5-7 containing residues of veratraldehyde, vanillin, and syringaldehyde at concentration 250 μM, preserved at the highest degree the synaptosomal viability and GSH levels. Further screening of compounds 5-7 at lower concentrations of 100 μM, 10 μM, and 1 μM, respectively, demonstrated that 6 and 7 do not show any toxicity within this concentration range. In the model of 6-OHDA-induced oxidative stress, 6 revealed concentration-dependent, neuroprotective, and antioxidant activities similar to melatonin. All the three compounds demonstrated ability to decrease the chemiluminescent scavenging index (CL-SI) in the hypochlorite containing system. In the superoxide system, the hydrazones exhibited different effects on the signal.

CONCLUSIONS

Our studies suggest that the benzimidazole-aldehyde hybrids act as direct ROS scavengers and membranes' stabilizers against free radicals. Thus, they play a role in the antioxidative defense system and have a promising potential as therapeutic neuroprotective agents for the treatment of neurodegenerative disorders.

In silico design of hydrazone antioxidants and analysis of their free radical-scavenging mechanism by thermodynamic studies

Background

Antioxidants are very crucial in maintaining the normal function of body cells, as they scavenge excess free radical in the body. A set of hydrazone antioxidants was designed by in silico screening. The density functional theory (DFT) method was employed to explore the reaction energetics of their free radical-scavenging mechanism. With the aid of the developed quantitative structure-activity relationship (QSAR) model for hydrazone antioxidants, the structure and antioxidant activity of these compounds were predicted. Three potential reaction mechanisms were investigated, namely, hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). Bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA), electron transfer enthalpy (ETE) and Gibbs free energy that characterize the various steps in these mechanisms were calculated in the gas phase.

Results

A total of 25 hydrazone antioxidants were designed, in which the molecule MHD 017 gave the best antioxidant activity. Among the tested molecules, MHD 017 at the 10-OH site gave the best results for the various thermodynamic parameters calculated. The reaction Gibbs free energy results also indicate that this is the most favoured site for free radical scavenge.

Conclusion

The obtained results show that HAT and SPLET mechanisms are the thermodynamically plausible reaction pathways of free radical scavenge by hydrazone antioxidants. The reactivity of these compounds towards the hydroperoxyl radical (HOO·) was greater than that towards the methyl peroxyl radical (CH3OO·) based on the exergonicity of the calculated reaction Gibbs free energy.

Graphical abstract