Synthesis, antibacterial activity and docking studies of substituted quinolone thiosemicarbazones

2-Oxoquinoline-based-thiosemicarbazones as multitargeting neurotherapeutics against Alzheimer's disease: In vitro and in silico studies of MAO and ChE inhibitors

Alzheimer's disease (AD) presents a multifactorial neurological disorder with multiple enzyme involvement in its onset. Conventional monotherapies fall short in providing long-term relief, necessitating the exploration of alternative multitargeting approaches to address the complexity of AD. Therefore, the design, synthesis, and in vitro and in silico evaluation of 2-oxoquinoline-based thiosemicarbazones 9a-r as multipotent analogs, able to simultaneously inhibit the cholinesterase (ChE) and monoamine oxidase (MAO) enzymes for the potential treatment of AD, are reported. In the in vitro experimental evaluation of MAO and ChE inhibition, all tested compounds demonstrated remarkable potency exhibiting nonselective inhibition of both MAO-A and MAO-B, and selective inhibition of acetylcholinesterase (AChE) over butyrylcholinesterase (BChE), with 9d, 9j, and 9m evolving as lead compounds for MAO-A, MAO-B, and AChE, displaying IC50 values of 0.35 ± 0.92, 0.50 ± 0.02, and 0.25 ± 0.13 μM, respectively. Moreover, the kinetic studies revealed that all tested compounds inhibited all three enzymes through a competitive mode of inhibition. Furthermore, the molecular docking studies of the most active compounds revealed several crucial interactions, particularly hydrogen bonding interactions. These interactions were observed between the nitrogen and sulfur atoms of thiosemicarbazone and the nitrogen and oxygen atoms of the quinoline ring with various amino acids, suggesting the strong interactions of these compounds with the enzymes.

Current scenario of quinolone hybrids with potential antibacterial activity against ESKAPE pathogens

The ESKAPE (Escherichia coli/E. coli, Staphylococcus aureus/S. aureus, Klebsiella pneumonia/K. pneumoniae, Acinetobacter Baumannii/A. baumannii, Pseudomonas aeroginosa/P. aeroginosa and Enterobacter spp.) pathogens, which could escape or evade common therapies through diverse antimicrobial resistance mechanisms and biofilm formation, are deemed as highly virulent bacteria responsible for life-threatening diseases, calling for novel chemotherapeutics. Quinolones including 2-quinolones and 4-quinolones have occupied a propitious place in drug design and development due to their excellent pharmacological profiles. Quinolones especially fluoroquinolones could inhibit the synthesis of nucleic acid of ESKAPE pathogens, leading to the rupture of bacterial chromosome. However, the resistance of ESKAPE pathogens to quinolones develops rapidly and spreads widely. Accordingly, it has become increasingly urgent to enhance the potency of quinolones against both drug-susceptible and drug-resistant ESKAPE pathogens. Quinolone hybrids can bind with different drug targets simultaneously and have been considered as useful prototypes to circumvent drug resistance. The purpose of this review is to summarize the current scenario (2018-present) of quinolone hybrids with potential antibacterial activity against ESKAPE pathogens, together with the structure-activity relationships and mechanisms of action to facilitate further rational design of more effective candidates.

DNA Gyrase as a Target for Quinolones

Bacterial DNA gyrase is a type II topoisomerase that can introduce negative supercoils to DNA substrates and is a clinically-relevant target for the development of new antibacterials. DNA gyrase is one of the primary targets of quinolones, broad-spectrum antibacterial agents and are used as a first-line drug for various types of infections. However, currently used quinolones are becoming less effective due to drug resistance. Common resistance comes in the form of mutation in enzyme targets, with this type being the most clinically relevant. Additional mechanisms, conducive to quinolone resistance, are arbitrated by chromosomal mutations and/or plasmid-gene uptake that can alter quinolone cellular concentration and interaction with the target, or affect drug metabolism. Significant synthetic strategies have been employed to modify the quinolone scaffold and/or develop novel quinolones to overcome the resistance problem. This review discusses the development of quinolone antibiotics targeting DNA gyrase to overcome bacterial resistance and reduce toxicity. Moreover, structural activity relationship (SAR) data included in this review could be useful for the development of future generations of quinolone antibiotics.

The phosphinoboration of thiosemicarbazones

This study reports on the exploration of the phosphinoboration reaction with several thiosemicarbazones (R5R4NC(S)NR3N=CR1R2). Reactions between either Ph2PBpin (pin = 1,2-O2C2Me4) or Ph2PBcat (cat = 1,2-O2C6H4) with thiosemicarbazones containing a terminal primary or secondary amine afforded boron-containing heterocyclic 1,3,4-thiadiazoline products in excellent yield. The addition of Ph2PBpin to thiosemicarbazones containing an NMe2 group in the terminal position generated novel five-membered heterocycles in moderate yield, which included boron, sulfur, and nitrogen atoms. Heterocyclization of the thiosemicarbazones occurs preferentially in the presence of functional groups such as acetyl and pyridyl groups.

N-Arylation of 3-Formylquinolin-2(1H)-ones Using Copper(II)-Catalyzed Chan-Lam Coupling

3-formyl-2-quinolones have attracted the scientific community's attention because they are used as versatile building blocks in the synthesis of more complex compounds showing different and attractive biological activities. Using copper-catalyzed Chan-Lam coupling, we synthesized 32 new N-aryl-3-formyl-2-quinolone derivatives at 80 °C, in air and using inexpensive phenylboronic acids as arylating agents. 3-formyl-2-quinolones and substituted 3-formyl-2-quinolones can act as substrates, and among the products, the p-methyl derivative 9a was used as a substrate to obtain different derivatives such as alcohol, amine, nitrile, and chalcone.

Synthesis and Evaluation of Antiproliferative Activity, Topoisomerase IIα Inhibition, DNA Binding and Non-Clinical Toxicity of New Acridine-Thiosemicarbazone Derivatives

In this study, we report the synthesis of twenty new acridine–thiosemicarbazone derivatives and their antiproliferative activities. Mechanisms of action such as the inhibition of topoisomerase IIα and the interaction with DNA have been studied for some of the most active derivatives by means of both in silico and in vitro methods, and evaluations of the non-clinical toxicities (in vivo) in mice. In general, the compounds showed greater cytotoxicity against B16-F10 cells, with the highest potency for DL-08 (IC₅₀ = 14.79 µM). Derivatives DL-01 (77%), DL-07 (74%) and DL-08 (79%) showed interesting inhibition of topoisomerase IIα when compared to amsacrine, at 100 µM. In silico studies proposed the way of bonding of these compounds and a possible stereoelectronic reason for the absence of enzymatic activity for CL-07 and DL-06. Interactions with DNA presented different spectroscopic effects and indicate that the compound CL-07 has higher affinity for DNA (Kb = 4.75 × 10⁴ M⁻¹; Ksv = 2.6 × 10³ M⁻¹). In addition, compounds selected for non-clinical toxicity testing did not show serious signs of toxicity at the dose of 2000 mg/kg in mice; cytotoxic tests performed on leukemic cells (K-562) and its resistant form (K-562 Lucena 1) identified moderate potency for DL-01 and DL-08, with IC₅₀ between 11.45 and 17.32 µM.

New N-Alkylated Heterocyclic Compounds as Prospective NDM1 Inhibitors: Investigation of In Vitro and In Silico Properties

A new family of pyrazole-based compounds (1–15) was synthesized and characterized using different physicochemical analyses, such as FTIR, UV-Visible, ¹H, ¹³C NMR, and ESI/LC-MS. The compounds were evaluated for their in vitro antifungal and antibacterial activities against several fungal and bacterial strains. The results indicate that some compounds showed excellent antibacterial activity against E. coli, S. aureus, C. freundii, and L. monocytogenes strains. In contrast, none of the compounds had antifungal activity. Molecular electrostatic potential (MEP) map analyses and inductive and mesomeric effect studies were performed to study the relationship between the chemical structure of our compounds and the biological activity. In addition, molecular docking and virtual screening studies were carried out to rationalize the antibacterial findings to characterize the modes of binding of the most active compounds to the active pockets of NDM1 proteins.

Conformational Properties of New Thiosemicarbazone and Thiocarbohydrazone Derivatives and Their Possible Targets

The structure assignment and conformational analysis of thiosemicarbazone KKI15 and thiocarbohydrazone KKI18 were performed through homonuclear and heteronuclear 2D Nuclear Magnetic Resonance (NMR) spectroscopy (2D-COSY, 2D-NOESY, 2D-HSQC, and 2D-HMBC) and quantum mechanics (QM) calculations using Functional Density Theory (DFT). After the structure identification of the compounds, various conformations of the two compounds were calculated using DFT. The two molecules showed the most energy-favorable values when their two double bonds adopted the E configuration. These configurations were compatible with the spatial correlations observed in the 2D-NOESY spectrum. In addition, due to the various isomers that occurred, the energy of the transition states from one isomer to another was calculated. Finally, molecular binding experiments were performed to detect potential targets for KKI15 and KKI18 derived from SwissAdme. In silico molecular binding experiments showed favorable binding energy values for all four enzymes studied. The strongest binding energy was observed in the enzyme butyrylcholinesterase. ADMET calculations using the preADMET and pKCSm software showed that the two molecules appear as possible drug leads.

Potential thiosemicarbazone-based enzyme inhibitors: Assessment of antiproliferative activity, metabolic enzyme inhibition properties, and molecular docking calculations

A new series of thiosemicarbazone derivatives (1-11) were prepared from various aldehydes and isocyanates with high yields and practical methods. The structures of these compounds were elucidated by Fourier transform infrared, ¹ H-nuclear magnetic resonance (NMR), ¹³ C-NMR spectroscopic methods and elemental analysis. Cytotoxic effects of target compounds were determined by 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide assay and compound 1 showed significant cytotoxic activity against both MCF-7 and MDA-MB-231 cells, with half-maximal inhibitory concentration values of 2.97 μM and 6.57 μM, respectively. Moreover, in this study, the anticholinergic and antidiabetic potentials of these compounds were investigated. To this aim, the effect of the newly synthesized thiosemicarbazone derivatives on the activities of acetylcholinesterase (AChE) and αglycosidase (α-Gly) was evaluated spectrophotometrically. The title compounds demonstrated high inhibitory activities compared to standard inhibitors with K_i values in the range of 122.15-333.61 nM for α-Gly (K_i value for standard inhibitor = 75.48 nM), 1.93-12.36 nM for AChE (K_i value for standard inhibitor = 17.45 nM). Antiproliferative activity and enzyme inhibition at the molecular level were performed molecular docking studies for thiosemicarbazone derivatives. 1M17, 5FI2, and 4EY6, 4J5T target proteins with protein data bank identification with (1-11) compounds were docked for anticancer and enzyme inhibition, respectively.

Design, synthesis, in vitro and in silico characterization of new 2-quinolone- L -alaninate-1,2,3-triazoles as novel antimicrobial agents

Due to the ever‐increasing antimicrobial resistance there is an urgent need to continuously design and develop novel antimicrobial agents. Inspired by the broad antibacterial activities of various heterocyclic compounds such as 2‐quinolone derivatives, we designed and synthesized new methyl‐(2‐oxo‐1,2‐dihydroquinolin‐4‐yl)‐L‐alaninate‐1,2,3‐triazole derivatives via 1,3‐dipolar cycloaddition reaction of 1‐propargyl‐2‐quinolone‐L‐alaninate with appropriate azide groups. The synthesized compounds were obtained in good yield ranging from 75 to 80 %. The chemical structures of these novel hybrid molecules were determined by spectroscopic methods and the antimicrobial activity of the compounds was investigated against both bacterial and fungal strains. The tested compounds showed significant antimicrobial activity and weak to moderate antifungal activity. Despite the evident similarity of the quinolone moiety of our compounds with fluoroquinolones, our compounds do not function by inhibiting DNA gyrase. Computational characterization of the compounds shows that they have attractive physicochemical and pharmacokinetic properties and could serve as templates for developing potential antimicrobial agents for clinical use.

Recent advancements in the medicinal chemistry of bacterial type II topoisomerase inhibitors

Replication proteins are sought as a potential targets for antimicrobial agents. Despite their promising target characteristics, only topoisomerase II inhibitors targeting DNA gyrase and/or topoisomerase IV have reached clinical use. Topoisomerases are the enzymes that are essential for cellular functions and various biological activities. A wide range of natural and synthetic compounds have been identified as potential topoisomerase inhibitors but the resistance is most commonly found in these drugs. The emergence of FQ resistance has increased the need for the development of novel topoisomerase inhibitors with efficacy and high potency against FQ-resistant strains. Besides structural modifications of existing FQ scaffolds, novel non-quinolone topoisomerase II inhibitors, known as novel bacterial topoisomerase inhibitors, have been developed which showed remarkable inhibitory activity against DNA gyrase/topoisomerase IV or both with an improved spectrum of antibacterial potency including drug-resistant strains. This review aims to summarize various recent advancements in the medicinal chemistry of topoisomerase inhibitors with the following objectives: (1) To represent inclusive data on types of topoisomerases and various marketed topoisomerase inhibitors as drugs; (2) To discuss the recent advances in the medicinal chemistry of various topoisomerase inhibitors (DNA gyrase and topo IV) belonging to different structural classes as potential antibacterial agents; (3) To summarizes the structure activity relationship (SAR) including in silico and mechanistic studies to afford ideas and to provide focused direction for the development of new chemical entities which are effective against drug-resistant bacterial pathogens and biofilms.