Synthesis and Biological Evaluation of Novel FtsZ-targeted 3-arylalkoxy-2,6-difluorobenzamides as Potential Antimicrobial Agents

Recent advances in studies on FtsZ inhibitors

With the abuse of antibiotics, multidrug resistant strains continue to emerge and spread rapidly. Therefore, there is an urgent need to develop new antimicrobial drugs. As a highly conserved cell division protein in bacteria, filamenting temperature-sensitive mutant Z (FtsZ) has been identified as a potential antimicrobial target. This paper reviews the structure, function, and action mechanism of FtsZ and a variety of natural and synthetic compounds targeting FtsZ, including 3-MBA derivatives, taxane derivatives, cinnamaldehyde, curcumin, quinoline and quinazoline derivatives, aromatic compounds, purpurin, and totarol. From these studies, FtsZ has a clear supporting role in the field of antimicrobial drug discovery. The urgent need and interest of antibacterial drugs will contribute to the discovery of new clinical drugs targeting FtsZ.

A synergistic investigation of azo-thiazole derivatives incorporating thiazole moieties: a comprehensive exploration of their synthesis, characterization, computational insights, solvatochromism, and multimodal biological activity assessment

In the present study, a novel series of azo-thiazole derivatives (3a-c) containing a thiazole moiety was successfully synthesized. The structure of these derivatives was examined by spectroscopic techniques, including 1H NMR, 13C NMR, FT-IR, and HRMS. Further, the novel synthesized compounds were evaluated for their in vitro biological activities, such as antibacterial and anti-inflammatory activities, and an in silico study was performed. The antibacterial results demonstrated that compounds 3a and 3c (MIC = 10 μg mL-1) have a notable potency against Staphylococcus aureus compared to azithromycin (MIC = 40 μg mL-1). Alternatively, compound 3b displayed a four-fold higher potency (24 recovery days, 1.83 mg day-1) than Hamazine (28 recovery days, 4.14 mg day-1) in promoting burn wound healing, and it also exhibited a comparable inhibitory activity against screened bacterial pathogens compared to the reference drug. Docking on 1KZN, considering the excellent impact of compounds on the crystal structure of E. coli1KZN, a 24 kDa domain, in complex with clorobiocin, indicated the close binding of compounds 3a-c with the active site of the 1KZN protein, which is consistent with their observed biological activity. Additionally, we conducted molecular dynamics simulations on the docked complexes of compounds 3a-c with 1KZN retrieved from the PDB to assess their stability and molecular interactions. Furthermore, we assessed their electrochemical characteristics via DFT calculations. Employing PASS and pkCSM platforms, we gained insights into controlling the bioactivity and physicochemical features of these compounds, highlighting their potential as new active agents.

Design, synthesis and biological evaluation of biphenyl-benzamides as potent FtsZ inhibitors

The rapid emergence of antibiotic resistance has become a prevalent threat to public health, thereby development of new antibacterial agents having novel mechanisms of action is in an urgent need. Targeting at the cytoskeletal cell division protein filamenting temperature-sensitive mutant Z (FtsZ) has been validated as an effective and promising approach for antibacterial drug discovery. In this study, a series of novel biphenyl-benzamides as FtsZ inhibitors has been rationally designed, synthesized and evaluated for their antibacterial activities against various Gram-positive bacteria strains. In particular, the most promising compound 30 exhibited excellent antibacterial activities, especially against four different Bacillus subtilis strains, with an MIC range of 0.008 μg/mL to 0.063 μg/mL. Moreover, compound 30 also showed good pharmaceutical properties with low cytotoxicity (CC₅₀ > 20 μg/mL), excellent human metabolic stability (T_1/2 = 111.98 min), moderate pharmacokinetics (T_1/2 = 2.26 h, F = 61.2%) and in vivo efficacy, which can be identified as a promising FtsZ inhibitor worthy of further profiling.

Synthesis and antischistosomal activity of linker- and thiophene-modified biaryl alkyl carboxylic acid derivatives

Schistosomiasis is a neglected tropical disease caused by blood flukes of the genus Schistosoma and causes severe morbidity in infected patients. In 2018, 290.8 million people required treatment, and 200,000 deaths are reported per year. Treatment of this disease depends on a single drug, praziquantel (PZQ). However, in the past few years, reduced sensitivity of the parasites toward PZQ has been reported. Therefore, there is an urgent need for new drugs against this disease. In the past few years, we have focused on a new substance class called biaryl alkyl carboxylic acid derivatives, which showed promising antischistosomal activity in vitro. Structure-activity relationship (SAR) studies of the carboxylic acid moiety led to three promising carboxylic amides (morpholine, thiomorpholine, and methyl sulfonyl piperazine) with an antischistosomal activity down to 10 µM (morpholine derivative) and no cytotoxicity up to 100 µM. Here, we show our continued work on this substance class. We investigated, in extended SAR studies, whether modification of the linker and the thiophene ring could improve the antischistosomal activity. We found that the exchange of the alkyl linker by a pentadienyl or benzyl linker was tolerated and led to similar antischistosomal effects, whereas the exchange of the thiophene ring was not tolerated. Our data suggest that the thiophene ring is important for the antischistosomal activity of this compound class.

Targeting the FtsZ Allosteric Binding Site with a Novel Fluorescence Polarization Screen, Cytological and Structural Approaches for Antibacterial Discovery

Bacterial resistance to antibiotics makes previously manageable infections again disabling and lethal, highlighting the need for new antibacterial strategies. In this regard, inhibition of the bacterial division process by targeting key protein FtsZ has been recognized as an attractive approach for discovering new antibiotics. Binding of small molecules to the cleft between the N-terminal guanosine triphosphate (GTP)-binding and the C-terminal subdomains allosterically impairs the FtsZ function, eventually inhibiting bacterial division. Nonetheless, the lack of appropriate chemical tools to develop a binding screen against this site has hampered the discovery of FtsZ antibacterial inhibitors. Herein, we describe the first competitive binding assay to identify FtsZ allosteric ligands interacting with the interdomain cleft, based on the use of specific high-affinity fluorescent probes. This novel assay, together with phenotypic profiling and X-ray crystallographic insights, enables the identification and characterization of FtsZ inhibitors of bacterial division aiming at the discovery of more effective antibacterials.

Antimicrobial Action and Reversal of Resistance in MRSA by Difluorobenzamide Derivatives Targeted at FtsZ

The bacterial cell division protein, FtsZ, has been identified as a target for antimicrobial development. Derivatives of 3-methoxybenzamide have shown promising activities as FtsZ inhibitors in Gram-positive bacteria. We sought to characterise the activity of five difluorobenzamide derivatives with non-heterocyclic substituents attached through the 3-oxygen. These compounds exhibited antimicrobial activity against methicillin resistant Staphylococcus aureus (MRSA), with an isopentyloxy-substituted compound showing modest activity against vancomycin resistant Enterococcus faecium (VRE). The compounds were able to reverse resistance to oxacillin in highly resistant clinical MRSA strains at concentrations far below their MICs. Three of the compounds inhibited an Escherichia coli strain lacking the AcrAB components of a drug efflux pump, which suggests the lack of Gram-negative activity can partly be attributed to efflux. The compounds inhibited cell division by targeting S. aureus FtsZ, producing a dose-dependent increase in GTPase rate which increased the rate of FtsZ polymerization and stabilized the FtsZ polymers. These compounds did not affect the polymerization of mammalian tubulin and did not display haemolytic activity or cytotoxicity. These derivatives are therefore promising compounds for further development as antimicrobial agents or as resistance breakers to re-sensitive MRSA to beta-lactam antibiotics.

Efficient Synthesis of Amine-Linked 2,4,6-Trisubstituted Pyrimidines as a New Class of Bacterial FtsZ Inhibitors

We have recently identified a new class of filamenting temperature-sensitive mutant Z (FtsZ)-interacting compounds that possess a 2,4,6-trisubstituted pyrimidine-quinuclidine scaffold with moderate antibacterial activity. Employing this scaffold as a molecular template, a compound library of amine-linked 2,4,6-trisubstituted pyrimidines with 99 candidates was successfully established by employing an efficient convergent synthesis designed to explore their structure-activity relationship. The results of minimum inhibitory concentration (MIC) assay against Staphylococcus aureus strains and cytotoxicity assay against the mouse L929 cell line identified those compounds with potent antistaphylococcal properties (MIC ranges from 3 to 8 μg/mL) and some extent of cytotoxicity against normal cells (IC₅₀ ranges from 6 to 27 μM). Importantly, three compounds also exhibited potent antibacterial activities against nine clinically isolated methicillin-resistant S. aureus (MRSA) strains. One of the compounds, 14av_amine16, exhibited low spontaneous frequency of resistance, low toxicity against Galleria mellonella larvae, and the ability to rescue G. mellonella larvae (20% survival rate at a dosage of 100 mg/kg) infected with a lethal dose of MRSA ATCC 43300 strain. Biological characterization of compound 14av_amine16 by saturation transfer difference NMR, light scattering assay, and guanosine triphosphatase hydrolysis assay with purified S. aureus FtsZ protein verified that it interacted with the FtsZ protein. Such a property of FtsZ inhibitors was further confirmed by observing iconic filamentous cell phenotype and mislocalization of the Z-ring formation of Bacillus subtilis. Taken together, these 2,4,6-trisubstituted pyrimidine derivatives represent a novel scaffold of S. aureus FtsZ inhibitors.

A Thiazole Orange Derivative Targeting the Bacterial Protein FtsZ Shows Potent Antibacterial Activity

The prevalence of multidrug resistance among clinically significant bacteria calls for the urgent development of new antibiotics with novel mechanisms of action. In this study, a new small molecule exhibiting excellent inhibition of bacterial cell division with potent antibacterial activity was discovered through cell-based screening. The compound exhibits a broad spectrum of bactericidal activity, including the methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus and NDM-1 Escherichia coli. The in vitro and in vivo results suggested that this compound disrupts the dynamic assembly of FtsZ protein and Z-ring formation through stimulating FtsZ polymerization. Moreover, this compound exhibits no activity on mammalian tubulin polymerization and shows low cytotoxicity on mammalian cells. Taken together, these findings could provide a new chemotype for development of antibacterials with FtsZ as the target.