Balancing Physicochemical Properties of Phenylthiazole Compounds with Antibacterial Potency by Modifying the Lipophilic Side Chain

Structure optimizing of flavonoids against both MRSA and VRE

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) cause more than 100,000 deaths each year, which need efficient and non-resistant antibacterial agents. SAR analysis of 162 flavonoids from the plant in this paper suggested that lipophilic group at C-3 was crucial, and then 63 novel flavonoid derivatives were designed and total synthesized. Among them, the most promising K15 displayed potent bactericidal activity against clinically isolated MRSA and VRE (MICs = 0.25-1.00 μg/mL) with low toxicity and high membrane selectivity. Moreover, mechanism insights revealed that K15 avoided resistance by disrupting biofilm and targeting the membrane, while vancomycin caused 256 times resistance against MRSA, and ampicillin caused 16 times resistance against VRE by the same 20 generations inducing. K15 eliminated residual bacteria in mice skin MRSA-infected model (>99 %) and abdominal VRE-infected model (>92 %), which was superior to vancomycin and ampicillin.

N- and s-substituted Pyrazolopyrimidines: A promising new class of potent c-Src kinase inhibitors with prominent antitumor activity

In this work, readily achievable synthetic pathways were utilized for construction of a library of N/S analogues based on the pyrazolopyrimidine scaffold with terminal alkyl or aryl fragments. Subsequently, we evaluated the anticancer effects of these novel analogs against the proliferation of various cancer cell lines, including breast, colon, and liver lines. The results were striking, most of the tested molecules exhibited strong and selective cytotoxic activity against the MDA-MB-231 cancer cell line; IC50 1.13 µM. Structure-activity relationship (SAR) analysis revealed that N-substituted derivatives generally enhanced the cytotoxic effect, particularly with aliphatic side chains that facilitated favorable target interactions. We also investigated apoptosis, DNA fragmentation, invasion assay, and anti-migration effects, and discussed their underlying molecular mechanisms for the most active compound 7c. We demonstrated that 7c N-propyl analogue could inhibit MDA-MB-231 TNBC cell proliferation by inducing apoptosis through the regulation of vital proteins, namely c-Src, p53, and Bax. In addition, our results also revealed the potential of these compounds against tumor metastasis by downregulating the invasion and migration modes. Moreover, the in vitro inhibitory effect of active analogs against c-Src kinase was studied and proved that might be the main cause of their antiproliferative effect. Overall, these compelling results point towards the therapeutic potential of these derivatives, particularly those with N-substitution as promising candidates for the treatment of TNBC type of breast cancer.

Current Development of Thiazole-Containing Compounds as Potential Antibacterials against Methicillin-Resistant Staphylococcus aureus

The emergence of multi-drug-resistant bacteria is threatening to human health and life around the world. In particular, methicillin-resistant Staphylococcus aureus (MRSA) causes fatal injuries to human beings and serious economic losses to animal husbandry due to its easy transmission and difficult treatment. Currently, the development of novel, highly effective, and low-toxicity antimicrobials is important to combat MRSA infections. Thiazole-containing compounds with good biological activity are widely used in clinical practice, and appropriate structural modifications make it possible to develop new antimicrobials. Here, we review thiazole-containing compounds and their antibacterial effects against MRSA reported in the past two decades and discuss their structure-activity relationships as well as the corresponding antimicrobial mechanisms. Some thiazole-containing compounds exhibit potent antibacterial efficacy in vitro and in vivo after appropriate structural modifications and could be used as antibacterial candidates. This Review provides insights into the development of thiazole-containing compounds as antimicrobials to combat MRSA infections.

Discovery of 1,2-diaryl-3-oxopyrazolidin-4-carboxamides as a new class of MurA enzyme inhibitors and characterization of their antibacterial activity

The cytoplasmic steps of peptidoglycan synthesis represent an important targeted pathway for development of new antibiotics. Herein, we report the synthesis of novel 3-oxopyrazolidin-4-carboxamide derivatives with variable amide side chains as potential antibacterial agents targeting MurA enzyme, the first committed enzyme in these cytosolic steps. Compounds 15 (isoindoline-1,3-dione-5-yl), 16 (4-(1H-pyrazol-4-yl)phenyl), 20 (5-cyanothiazol-2-yl), 21 and 31 (5-nitrothiazol-2-yl derivatives) exhibited the most potent MurA inhibition, with IC50 values of 9.8-12.2 μM. Compounds 15, 16 and 21 showed equipotent inhibition of the C115D MurA mutant developed by fosfomycin-resistant Escherichia coli. NMR binding studies revealed that some of the MurA residues targeted by 15 also interacted with fosfomycin, but not all, indicating an overlapping but not identical binding site. The antibacterial activity of the compounds against E. coli ΔtolC suggests that inhibition of MurA accounts for the observed effect on bacterial growth, considering that a few potent MurA inhibitors could not penetrate the bacterial outer membrane and were therefore inactive as proven by the bacterial cell uptake assay. The most promising compounds were also evaluated against a panel of Gram-positive bacteria. Remarkably, compounds 21 and 31 (MurA IC50 = 9.8 and 10.2 μM respectively) exhibited a potent activity against Clostridioides difficile strains with MIC values ranging from 0.125 to 1 μg/mL, and were also shown to be bactericidal with MBC values between 0.25 and 1 μg/mL. Furthermore, both compounds were shown to have a limited activity against human normal intestinal flora and showed high safety towards human colon cells (Caco-2) in vitro. The thiolactone derivative (compound 5) exhibited an interesting broad spectrum antibacterial activity despite its weak MurA inhibition. Altogether, the presented series provides a promising class of antibiotics that merits further investigation.

New Phenylthiazoles: Design, Synthesis, and Biological Evaluation as Antibacterial, Antifungal, and Anti-COVID-19 Candidates

The combination of antibacterial and antiviral agents is becoming a very important aspect of dealing with resistant bacterial and viral infections. The N-phenylthiazole scaffold was found to possess significant anti-MRSA, antifungal, and anti-COVID-19 activities as previously published; hence, a slight refinement was proposed to attach various alkyne lipophilic tails to this promising scaffold, to investigate their effects on the antimicrobial activity of the newly synthesized compounds and to provide a valuable structure-activity relationship. Phenylthiazole 4 m exhibited the most potent anti-MRSA activity with 8 μg/mL MIC value. Compounds 4 k and 4 m demonstrated potent activity against Clostridium difficile with MIC values of 2 μg/mL and moderate activity against Candida albicans with MIC value of 4 μg/mL. When analyzed for their anti-COVID-19 inhibitory effect, compound 4 b emerged with IC50 =1269 nM and the highest selectivity of 138.86 and this was supported by its binding score of -5.21 kcal mol-1 when docked against SARS-CoV-2 M pro . Two H-bonds were formed, one with His164 and the other with Met49 stabilizing phenylthiazole derivative 4 b, inside the binding pocket. Additionally, it created two arene-H bonds with Asn142 and Glu166, through the phenylthiazole scaffold and one arene-H bond with Leu141 via the phenyl ring of the lipophilic tail.

Quaternary Ammonium Salts: Insights into Synthesis and New Directions in Antibacterial Applications

The overuse of antibiotics has led to the emergence of a large number of antibiotic-resistant genes in bacteria, and increasing evidence indicates that a fungicide with an antibacterial mechanism different from that of antibiotics is needed. Quaternary ammonium salts (QASs) are a biparental substance with good antibacterial properties that kills bacteria through simple electrostatic adsorption and insertion into cell membranes/altering of cell membrane permeability. Therefore, the probability of bacteria developing drug resistance is greatly reduced. In this review, we focus on the synthesis and application of single-chain QASs, double-chain QASs, heterocyclic QASs, and gemini QASs (GQASs). Some possible structure-function relationships of QASs are also summarized. As such, we hope this review will provide insight for researchers to explore more applications of QASs in the field of antimicrobials with the aim of developing systems for clinical applications.

SAR investigation and optimization of benzimidazole-based derivatives as antimicrobial agents against Gram-negative bacteria

Antibiotic-resistant bacteria represent a serious threat to modern medicine and human life. Only a minority of antibacterial agents are active against Gram-negative bacteria. Hence, the development of novel antimicrobial agents will always be a vital need. In an effort to discover new therapeutics against Gram-negative bacteria, we previously reported a structure-activity-relationship (SAR) study on 1,2-disubstituted benzimidazole derivatives. Compound III showed a potent activity against tolC-mutant Escherichia coli with an MIC value of 2 μg/mL, representing a promising lead for further optimization. Building upon this study, herein, 49 novel benzimidazole compounds were synthesized to investigate their antibacterial activity against Gram-negative bacteria. Our design focused on three main goals, to address the low permeability of our compounds and improve their cellular accumulation, to expand the SAR study to the unexplored ring C, and to optimize the lead compound (III) by modification of the methanesulfonamide moiety. Compounds (25a-d, 25f-h, 25k, 25l, 25p, 25r, 25s, and 26b) exhibited potent activity against tolC-mutant E. coli with MIC values ranging from 0.125 to 4 μg/mL, with compound 25d displaying the highest potency among the tested compounds with an MIC value of 0.125 μg/mL. As its predecessor, III, compound 25d exhibited an excellent safety profile without any significant cytotoxicity to mammalian cells. Time-kill kinetics assay indicated that 25d exhibited a bacteriostatic activity and significantly reduced E. coli JW55031 burden as compared to DMSO. Additionally, combination of 25d with colistin partially restored its antibacterial activity against Gram-negative bacterial strains (MIC values ranging from 4 to 16 μg/mL against E. coli BW25113, K. pneumoniae, A. baumannii, and P. aeruginosa). Furthermore, formulation of III and 25d as lipidic nanoparticles (nanocapsules) resulted in moderate enhancement of their antibacterial activity against Gram-negative bacterial strains (A. Baumannii, N. gonorrhoeae) and compound 25d demonstrated superior activity to the lead compound III. These findings establish compound 25d as a promising candidate for treatment of Gram-negative bacterial infections and emphasize the potential of nano-formulations in overcoming poor cellular accumulation in Gram-negative bacteria where further optimization and investigation are warranted to improve the potency and broaden the spectrum of our compounds.

Exploring the dual effect of novel 1,4-diarylpyranopyrazoles as antiviral and anti-inflammatory for the management of SARS-CoV-2 and associated inflammatory symptoms

COVID-19 and associated substantial inflammations continue to threaten humankind triggering death worldwide. So, the development of new effective antiviral and anti-inflammatory medications is a major scientific goal. Pyranopyrazoles have occupied a crucial position in medicinal chemistry because of their biological importance. Here, we report the design and synthesis of a series of sixteen pyranopyrazole derivatives substituted with two aryl groups at N-1 and C-4. The designed compounds are suggested to show dual activity to combat the emerging Coronaviruses and associated substantial inflammations. All compounds were evaluated for their in vitro antiviral activity and cytotoxicity against SARS-CoV infected Vero cells. As well, the in vitro assay of all derivatives against the SARS-CoV M^pro target was performed. Results revealed the potential of three pyranopyrazoles (22, 27, and 31) to potently inhibit the viral main protease with IC₅₀ values of 2.01, 1.83, and 4.60 μM respectively compared with 12.85 and 82.17 μM for GC-376 and lopinavir. Additionally, in vivo anti-inflammatory testing for the most active compound 27 proved its ability to reduce levels of two cytokines (TNF-α and IL-6). Molecular docking and dynamics simulation revealed consistent results with the in vitro enzymatic assay and indicated the stability of the putative complex of 27 with SARS-CoV-2 M^pro. The assessment of metabolic stability and physicochemical properties of 27 have also been conducted. This investigation identified a set of metabolically stable pyranopyrazoles as effective anti-SARS-CoV-2 M^pro and suppressors of host cell cytokine release. We believe that the new compounds deserve further chemical optimization and evaluation for COVID-19 treatment.

A New Discovery of Unique 13-(Benzimidazolylmethyl)berberines as Promising Broad-Spectrum Antibacterial Agents

A new hybridization of berberine and benzimidazoles was performed to produce 13-(benzimidazolylmethyl)berberines (BMB) as potentially broad-spectrum antibacterial agents with the hope of confronting multidrug-resistant bacterial infections in the livestock industry. Some of the newly prepared hybrids showed obvious antibacterial effects against tested strains. Particularly, 13-((1-octyl-benzimidazolyl)methyl)berberine 6f (OBMB-6f) was found to be the most promising compound that not only exerted a strong activity (MIC = 0.25-2 μg/mL) and low cytotoxicity but also possessed a fast bactericidal capacity and low propensity to develop resistance toward Staphylococcus aureus and Escherichia coli even after 26 serial passages. Moreover, OBMB-6f displayed the ability to prevent bacterial biofilm formation at low and high temperatures. The mechanistic exploration revealed that OBMB-6f could significantly disintegrate bacterial membranes, markedly facilitate intracellular ROS generation, and efficiently intercalate into DNA. These results provided a profound insight into BMB against multidrug-resistant bacterial infections in the livestock industry.

Isoquinoline Antimicrobial Agent: Activity against Intracellular Bacteria and Effect on Global Bacterial Proteome

A new class of alkynyl isoquinoline antibacterial compounds, synthesized via Sonogashira coupling, with strong bactericidal activity against a plethora of Gram-positive bacteria including methicillin- and vancomycin-resistant Staphylococcus aureus (S. aureus) strains is presented. HSN584 and HSN739, representative compounds in this class, reduce methicillin-resistant S. aureus (MRSA) load in macrophages, whilst vancomycin, a drug of choice for MRSA infections, was unable to clear intracellular MRSA. Additionally, both HSN584 and HSN739 exhibited a low propensity to develop resistance. We utilized comparative global proteomics and macromolecule biosynthesis assays to gain insight into the alkynyl isoquinoline mechanism of action. Our preliminary data show that HSN584 perturb S. aureus cell wall and nucleic acid biosynthesis. The alkynyl isoquinoline moiety is a new scaffold for the development of potent antibacterial agents against fatal multidrug-resistant Gram-positive bacteria.

Lipophilic Ga Complex with Broad-Spectrum Antimicrobial Activity and the Ability to Overcome Gallium Resistance in both Pseudomonas aeruginosa and Staphylococcus aureus

Antibiotic resistance (AR) necessitates the discovery of new antimicrobials with alternative mechanisms of action to those employed by conventional antibiotics. One such strategy utilizes Ga³⁺ to target iron metabolism, a critical process for survival. Still, Ga-based therapies are generally ineffective against Gram-positive bacteria and promote Ga resistance. In response to these drawbacks, we report a lipophilic Ga complex, [Ga₂L₃(bpy)₂] (L = 2,2'-bis(3-hydroxy-1,4-naphthoquinone; bpy = 2,2'-bipyridine)), effective against drug-resistant Pseudomonas aeruginosa (DRPA; minimum inhibitory concentration, MIC = 10 μM = 14.8 μg/mL) and methicillin-resistant Staphylococcus aureus (MRSA, MIC = 100 μM = 148 μg/mL) without iron-limited conditions. Importantly, [Ga₂L₃(bpy)₂] shows noticeably delayed and decreased resistance in both MRSA and DRPA, with only 8× MIC in DRPA and none in MRSA after 30 passages. This is likely due to the dual mode of action afforded by Ga (disruption of iron metabolism) and the ligand (reactive oxygen species production). Overall, [Ga₂L₃(bpy)₂] demonstrates the utility of lipophilic metal complexes with multiple modes of action in combatting AR in Gram-positive and Gram-negative bacteria.

Development of Biphenylthiazoles Exhibiting Improved Pharmacokinetics and Potent Activity Against Intracellular Staphylococcus aureus

Exploring the structure-activity relationship (SAR) at the cationic part of arylthiazole antibiotics revealed hydrazine as an active moiety. The main objective of the study is to overcome the inherited toxicity associated with the free hydrazine. A series of hydrocarbon bridges was inserted in between the groups, to separate the two amino groups. Hence, the aminomethylpiperidine-containing analog 16 was identified as a new promising antibacterial agent with efficient antibacterial and pharmacokinetic profiles. Briefly, compound 16 outperformed vancomycin in terms of the antibacterial spectrum against vancomycin-resistant staphylococcal and enterococcal strains with minimum inhibitory concentrations (MICs) ranging from 2 to 4 μg/mL, which is a faster bactericidal mode of action, completely eradicating the high staphylococcal burden within 6-8 h, and it has a unique ability to completely clear intracellular staphylococci. In addition, the initial pharmacokinetic assessment confirmed the high metabolic stability of compound 16 (biological half-life >4 h); it had a good extravascular distribution and maintained a plasma concentration higher than the average MIC value for over 12 h. Moreover, compound 16 significantly reduced MRSA burden in an in vivo MRSA skin infection mouse experiment. These attributes collectively suggest that compound 16 is a good therapeutic candidate for invasive staphylococcal and enterococcal infections. From a mechanistic point of view, compound 16 inhibited undecaprenyl diphosphate phosphatase (UppP) with an IC₅₀ value of 29 μM.

Evaluation of N-phenyl-2-aminothiazoles for treatment of multi-drug resistant and intracellular Staphylococcus aureus infections

The increasing emergence of antibiotic-resistant bacterial pathogens calls for additional urgency in the development of new antibacterial candidates. N-Phenyl-2-aminothiazoles are promising candidates that possess potent anti-MRSA activity and could potentially replenish the MRSA antibiotic pipeline. The initial screen of a series of compounds in this novel class against several bacterial strains revealed that the aminoguanidine analogues possessed promising activities and superior safety profiles. The determined MICs of these compounds were comparable to, if not better than, those of the control drugs (linezolid and vancomycin). Remarkably, compounds 3a, 3b, and 3e possessed potent activities against multidrug resistant staphylococcal isolates and several clinically important pathogens, such as vancomycin-resistant enterococci (VRE) and Streptococcus pneumoniae. In addition, the compounds were superior to vancomycin in the rapid killing of MRSA and the longer post-antibiotic effects. Furthermore, low concentrations of compounds 3a, 3b, and 3e reduced the intracellular burden of MRSA by greater than 90%. Initial in vitro PK/toxicity assessments revealed that compound 3e was highly tolerable and possessed a low metabolic clearance rate and a highly acceptable half-life.