Recent developments of chalcones as potential antibacterial agents in medicinal chemistry

Discovery of Loureirin analogues with colorectal cancer suppressive activity via regulating cell cycle and Fas death receptor

Chalcones and dihydrochalcones (DHCs) are important bioactive natural products (BNPs) isolated from traditional Chinese medicine. In this study, 13 chalcones were designed with the inspiration of Loureirin, a DHC extracted from Resina Draconis, and synthesized by classical Claisen-Schmidt reactions. Afterwards the reduction reactions were carried out to obtain the corresponding DHCs. Cytotoxicity assay indicated chalcones and DHCs possessed selective cytotoxicity against colorectal cancer (CRC) cells. The preliminary structure-activity relationships (SAR) of these compounds suggested the α, β-unsaturated ketone of the chalcones were crucial for the anticancer activity. Interestingly, compounds 3d and 4c exhibited selective anticancer activity against CRC cell line HCT116 with IC50s of 8.4 and 17.9 μM but not normal cell. Moreover, 4c could also inhibit the migration and invasion of CRC cells. Mechanism investigations showed 4c could induce cell cycle G2/M arrest by regulating cell cycle-associated proteins and could also up-regulate Fas cell surface death receptor. The virtual docking further pointed out that compounds 3d and 4c could nicely bind to the Fas/FADD death domain complex (ID: 3EZQ). Furthermore, silencing of Fas significantly enhanced the proliferation of CRC cells and attenuated the cytotoxicity induced by 4c. These results suggested 4c exerted its anticancer activity possibly regulating cell cycle and Fas death receptor. In summary, this study investigated the anticancer activity and mechanism of Loureirin analogues in CRC, suggesting these compounds may warrant further investigation as promising anticancer drug candidates for the treatment of CRC.

Synthesis of Novel Triazine-Based Chalcones and 8,9-dihydro-7H-pyrimido[4,5-b][1,4]diazepines as Potential Leads in the Search of Anticancer, Antibacterial and Antifungal Agents

This study presents the synthesis of four series of novel hybrid chalcones (20,21)a-g and (23,24)a-g and six series of 1,3,5-triazine-based pyrimido[4,5-b][1,4]diazepines (28-33)a-g and the evaluation of their anticancer, antibacterial, antifungal, and cytotoxic properties. Chalcones 20b,d, 21a,b,d, 23a,d-g, 24a-g and the pyrimido[4,5-b][1,4]diazepines 29e,g, 30g, 31a,b,e-g, 33a,b,e-g exhibited outstanding anticancer activity against a panel of 60 cancer cell lines with GI50 values between 0.01 and 100 μM and LC50 values in the range of 4.09 μM to >100 μM, several of such derivatives showing higher activity than the standard drug 5-fluorouracil (5-FU). On the other hand, among the synthesized compounds, the best antibacterial properties against N. gonorrhoeae, S. aureus (ATCC 43300), and M. tuberculosis were exhibited by the pyrimido[4,5-b][1,4]diazepines (MICs: 0.25-62.5 µg/mL). The antifungal activity studies showed that triazinylamino-chalcone 29e and triazinyloxy-chalcone 31g were the most active compounds against T. rubrum and T. mentagrophytes and A. fumigatus, respectively (MICs = 62.5 μg/mL). Hemolytic activity studies and in silico toxicity analysis demonstrated that most of the compounds are safe.

Recent Advancement in Bioactive Chalcone Hybrids as Potential Antimicrobial Agents in Medicinal Chemistry

Chalcones are flavonoid-related aromatic ketones and enones generated from plants. The chalcones have a wide range of biological activities, such as anti-tumor, calming, and antimicrobial activities. In the present review, we have focused on the recently published original research articles on chalcones as a unique antibacterial framework in medicinal chemistry. Chalcones are structurally diverse moieties and can be split into simple and hybrid chalcones, with both having core pharmacophore 1,3-diaryl-2-propen-1-one. Chalcones are isolated from natural sources and also synthesized by using various methods. Their structure-activity relationship, mechanisms, and list of patents are also summarized in this paper. This review article outlines the currently published antimicrobial chalcone hybrids and suggests that chalcone derivatives may be potential antimicrobial agents in the future.

Substituent and solvent effects on UV-visible absorption spectra of chalcones derivatives: Experimental and computational studies

The electronic spectra of the title compounds were measured in ethanol and cyclohexane. Three band systems are distinguished in the spectra of which the first and second band systems are attributed to local excitation of PhCH and PhCO rings. The third absorption band is assigned to a charge transfer (CT) band and is associated with the CO-CH=CH moiety. The solvent plays an important role in the absorption spectra and causes the CT band to consist of two electronic transitions. The effect of substituents on the phenyl rings on the charge transfer band of chalcone derivatives was also established in the two solvents. The converged gas-phase geometries of the studied chalcones was optimized using the DFT PBE0 functional with the basis set 6-311++G**. DFT calculations has been performed for an ethanol solution (using TD-PBE0/6-311++G**) level to understand electronic transitions on terms of energies and oscillator strengths to study the substituent effect on the electronic transitions of the chalcone derivatives. To consider the solvation effect of ethanol on the absorptions, the integral equation formalism variant of the polarizable continuum model (IEFPCM) was used. The calculated energies were in good agreement with experiment results. The molecular modelling technique was followed to monitor the effect of substitutions on the HOMO/LUMO energy and total dipole moment. Transitions between natural transition orbitals are also described as part of this study.

Synthetic non-toxic anti-biofilm agents as a strategy in combating bacterial resistance

The tremendous increase in the bacterial resistance to the available antibiotics is a serious problem for the treatment of various infections. Biofilm formation in bacteria significantly contributes to the bacterial survival in host cells, and is considered as an crucial factor, responsible for bacterial resistance. The response of the bacterial cells in the biofilm to antibiotics is completely different from that of the free floating planktonic cells of the same strain. The anti-biofilm agents that could inhibit the biofilm production without affecting the bacterial growth, apply less selective pressure over the bacterial strains than the traditional antibiotics; thus the development of bacterial resistance would be of low incidence. Many attempts have been performed to discover novel agents capable of interfering with the bacterial biofilm life cycle, and several compounds have shown promising activities in suppressing the biofilm production or in dispersing mature existing biofilms. This review describes the different chemical classes that have anti-biofilm effects against different Gram-positive and Gram-negative bacteria without affecting the bacterial growth.

Synthesis, Docking Studies and Evaluation of Chalcones as Anti-Helicobacter pylori and antitumoral Agents

Helicobacter pylori colonizes the gastric epithelium of 50 % of world population and it is the main etiological agent of human chronic gastritis, peptic ulcer, and gastric cancer. In this study, we synthesized and characterized a series of 14 chalcones and evaluated their anti-H. pylori, NO inhibition (in vitro and in silico), and AGS cells cytotoxic effects. Compounds 3b and 3h showed MIC of 8 μg/mL. We observed structure-activity relationships, mainly related to the influence of methoxy substituent at C-2 (3b) and the nitro group at C-4 (3h) in chalcone scaffold. The fourteen chalcones inhibited the NO production in LPS-stimulated macrophages and showed potential for interaction on the active site of the iNOS enzyme. Finally, 3b and 3h showed the highest selectivity to the AGS cell lines. Thus, ours results suggest 3b and 3h as potential candidates for design of new and effective agents against H. pylori and related diseases.

Synthesis, characterization and evaluation of prenylated chalcones ethers as promising antileishmanial compounds

Drug therapy for leishmaniasis remains a major challenge as currently available drugs have limited efficacy, induce serious side-effects and are not accessible to everyone. Thus, the discovery of affordable drugs is urgently needed. Chalcones present a great potential as bioactive agents due to simple structure and functionalization capacity. The antileishmanial activity of different natural and synthetic chalcones have been reported. Here we report the synthesis of twenty-five novel prenylated chalcones that displayed antiparasitic activity in Leishmania mexicana. All the chalcones were evaluated at 5 µg/mL and eleven compounds exhibited a metabolic inhibition close to or exceeding 50%. Compounds 49, 30 and 55 were the three most active with IC50 values < 10 μM. These chalcones also showed the highest selectivity index (SI) values. Interestingly 49 and 55 possessing a substituent at a meta position in the B ring suggests that the substitution pattern influences antileishmanial activity. Additionally, a tridimensional model of fumarate reductase of L. mexicana was obtained by homology modeling. Docking studies suggest that prenylated chalcones could modulate fumarate reductase activity by binding with good affinity to two binding sites that are critical for the target. In conclusion, the novel prenylated chalcones could be considered as promising antileishmanial agents.

Synthesis and antibacterial activity of 2-benzylidene-3-oxobutanamide derivatives against resistant pathogens

Antibiotic resistance evolves naturally through random mutation. Resistance to antimicrobials is an urgent public health crisis that requires coordinated global action. The ESKAPE bacteria (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are primarily responsible for the rise in resistant pathogens. There is an immediate requirement to identify a novel molecular scaffold with potent anti-microbial properties. We developed an efficient one-step synthesis of 2-benzylidene-3-oxobutanamide and its derivatives, which allowed the introduction of an α,β-unsaturated ketone moiety in the quest to identify a new molecular scaffold. Seven compounds exhibited very good antibacterial activity in vitro against WHO priority drug-resistant bacteria such as methicillin resistant Staphyloccus aureus (MRSA) and Acinetobacter baumannii-Multi drug resistant (MDR-AB). In cultured human embryonic kidney cells and hemolysis assays, the potent compounds displayed minimal toxicity. These findings suggest that these small molecules with excellent diversity have the potential to combat antibacterial resistance.

Cryopreservation of bioflavonoid-rich plant sources and bioflavonoid-microcapsules: emerging technologies for preserving bioactivity and enhancing nutraceutical applications

Bioflavonoids are natural polyphenolic secondary metabolites that are medicinal. These compounds possess antitumor, cardioprotective, anti-inflammatory, antimicrobial, antiviral, and anti-psoriasis properties to mention a few. Plant species that contain bioflavonoids should be preserved as such. Also, the bioactivity of the bioflavonoids as neutraceutical compounds is compromised following extraction due to their sensitivity to environmental factors like light, pH, and temperature. In other words, the bioflavonoids' shelf-life is affected. Scientists noticed that bioflavonoids have low solubility properties, poor absorption, and low bioavailability following consumption. Researchers came up with methods to encapsulate bioflavonoids in order to circumvent the challenges above and also to mask the unpleasant order these chemicals may have. Besides, scientists cryopreserve plant species that contain bioflavonoids. In this review, we discuss cryopreservation and bioflavonoid microencapsulation focusing mainly on vitrification, slow freezing, and freeze-drying microencapsulation techniques. In addition, we highlight bioflavonoid extraction techniques, medicinal properties, challenges, and future perspectives of cryopreservation and microencapsulation of bioflavonoids. Regardless of the uniqueness of cryopreservation and microencapsulation as methods to preserve bioflavonoid sources and bioflavonoids' bioactivity, there are challenges reported. Freeze-drying technology is costly. Cryoprotectants damage the integrity of plant cells, to say the least. Researchers are working very hard to overcome these challenges. Encapsulating bioflavonoids via coaxial electrospray and then cryopreserving the micro/nanocapsules produced can be very interesting.

Synthesis and molecular docking of new N4-piperazinyl ciprofloxacin hybrids as antimicrobial DNA gyrase inhibitors

A series of N-4 piperazinyl ciprofloxacin derivatives as urea-tethered ciprofloxacin-chalcone hybrids 2a-j and thioacetyl-linked ciprofloxacin-pyrimidine hybrids 5a-i were synthesized. The target compounds were investigated for their antibacterial activity against S. aureus, P. aeruginosa, E. coli, and C. albicans strains, respectively. Ciprofloxacin derivatives 2a-j and 5a-i revealed broad antibacterial activity against either Gram positive or Gram negative strains, with MIC range of 0.06-42.23 µg/mL compared to ciprofloxacin with an MIC range of 0.15-3.25 µg/mL. Among the tested compounds, hybrids 2b, 2c, 5a, 5b, 5h, and 5i exhibited remarkable antibacterial activity with MIC range of 0.06-1.53 µg/mL against the tested bacterial strains. On the other hand, compounds 2c, 2e, 5c, and 5e showed comparable antifungal activity to ketoconazole against candida albicans with MIC range of 2.03-3.89 µg/mL and 2.6 µg/mL, respectively. Further investigations showed that some ciprofloxacin hybrids have inhibitory activity against DNA gyrase as potential molecular target compared to ciprofloxacin with IC50 range of 0.231 ± 0.01-7.592 ± 0.40 µM and 0.323 ± 0.02 µM, respectively. Docking studies of compounds 2b, 2c, 5b, 5c, 5e, 5h, and 5i on the active site of DNA gyrase (PDB: 2XCT) confirmed their ability to form stable complex with the target enzyme like that of ciprofloxacin.

Novel Thiazolylketenyl Quinazolinones as Potential Anti-MRSA Agents and Allosteric Modulator for PBP2a

Bacterial infections caused by methicillin-resistant Staphylococcus aureus have seriously threatened public health. There is an urgent need to propose an existing regimen to overcome multidrug resistance of MRSA. A unique class of novel anti-MRSA thiazolylketenyl quinazolinones (TQs) and their analogs were developed. Some synthesized compounds showed good bacteriostatic potency. Especially TQ 4 was found to exhibit excellent inhibition against MRSA with a low MIC of 0.5 μg/mL, which was 8-fold more effective than norfloxacin. The combination of TQ 4 with cefdinir showed stronger antibacterial potency. Further investigation revealed that TQ 4, with low hemolytic toxicity and low drug resistance, was not only able to inhibit biofilm formation but also could reduce MRSA metabolic activity and showed good drug-likeness. Mechanistic explorations revealed that TQ 4 could cause leakage of proteins by disrupting membrane integrity and block DNA replication by intercalated DNA. Furthermore, the synergistic antibacterial effect with cefdinir might be attributed to TQ 4 with the ability to induce PBP2a allosteric regulation of MRSA and further trigger the opening of the active site to promote the binding of cefdinir to the active site, thus inhibiting the expression of PBP2a, thereby overcoming MRSA resistance and significantly enhancing the anti-MRSA activity of cefdinir. A new strategy provided by these findings was that TQ 4, possessing both excellent anti-MRSA activity and allosteric effect of PBP2a, merited further development as a novel class of antibacterial agents to overcome increasingly severe MRSA infections.

Examining the Scope of Deriving β-Aryl Enones from Enol Silanes as Ketone Equivalents via Pd(II)-Mediated Sequential Dehydrosilylation and Arylation

Silyl enol ethers were examined as a masked source of saturated ketones to derive β-aryl enones and their derivatives by dehydrosilylation to generate enones in situ and subsequent oxidative arylation with arylboronic acids as transmetallation coupling partners using relayed Pd(II) catalysis in one pot under base-free conditions. Oxygen was found to be an efficient and green oxidant to enable both dehydrosilylation of enol silanes and arylation. Additionally, arylation conditions can be custom-designed to take advantage of aryl halides as an alternative source of arylating agents. The preparative scope was investigated with 35 examples (up to 95% yield), and mechanistic studies implied a cationic Pd(II)-based catalytic system.

Synthesis of chalcones and their antimicrobial and drug potentiating activities

The increased resistance of microorganisms to antimicrobial drugs makes it necessary to search for new active compounds, such as chalcones. Their simple chemical structure makes them molecules easy to synthesize. Therefore, the aim of this study was to evaluate the antimicrobial and potentiating activity of antibiotics and antifungals by synthetic chalcones against strains of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Candida tropicalis. The synthesis of chalcones was carried out by Claisen-Schimidt aldol condensation. Nuclear Magnetic Resonance (NMR) and Gas Chromatography Coupled to Mass Spectrometry (GC/MS) were also performed. Microbiological tests were performed by the broth microdilution method, using gentamicin, norfloxacin and penicillin as standard drugs for the antibacterial assay, and fluconazole for the antifungal assay. Three chalcones were obtained (1E,4E)-1,5-diphenylpenta-1,4-dien-3-one (DB-Acetone), (1E,3E,6E,8E)-1,9-diphenylnone-1,3,6,8-tetraen-5-one (DB-CNM), (1E,4E)-1,5-bis (4-methoxyphenyl) penta-1,4-dien-3-one (DB-Anisal). The compound DB-Acetone was able to inhibit P. aeruginosa ATCC 9027 at a concentration of 1.4 × 10² μM (32 μg/mL), while DB-CNM and DB-Anisal inhibited the growth of S. aureus ATCC 25923 at 17.88 × 10² μM and 2.71 × 10¹ μM (512 μg/mL and 8 μg/mL) respectively. In the combined activity, DB-Anisal was able to potentiate the effect of the three antibacterial drugs tested against E. coli 06, norfloxacin (128 for 4 μg/mL ±1) against P. aeruginosa 24 and penicillin (1,024 for 16 μg/mL ±1) against S. aureus 10. In antifungal assays, chalcones were not able to inhibit the growth of fungal strains tested. However, both showed potentiating activity with fluconazole, ranging from 8.17 x 10^-1 μM (0.4909 μg/mL) to 2.35 μM (13.96 μg/mL). It is concluded that synthetic chalcones have antimicrobial potential, demonstrating good intrinsic activity against fungi and bacteria, in addition to potentiating the antibiotics and antifungal tested. Further studies are needed addressing the mechanisms of action responsible for the results found in this work.

Thiocarbohydrazone and Chalcone-Derived 3,4-Dihydropyrimidinethione as Lipid Peroxidation and Soybean Lipoxygenase Inhibitors

The potential of the 4,6-diphenyl-3,4-dihydropyrimidine-2(1H)-thione (abbreviated as KKII5) and (E)-N'-benzylidenehydrazinecarbothiohydrazide (abbreviated as DKI5) compounds as possible drug leads is investigated. KKII5 and DKI5 are synthesized in high yield of up to 97%. Their structure, binding in the active site of the LOX-1 enzyme, and their toxicity are studied via joint experimental and computational methodologies. Specifically, the structure assignment and conformational analysis were achieved by applying homonuclear and heteronuclear 2D nuclear magnetic resonance (NMR) spectroscopy (2D-COSY, 2D-NOESY, 2D-HSQC, and 2D-HMBC) and density functional theory (DFT). The obtained DFT lowest energy conformers were in agreement with the NOE correlations observed in the 2D-NOESY spectra. Additionally, docking and molecular dynamics simulations were performed to discover their ability to bind and remain stabile in the active site of the LOX-1 enzyme. These in silico experiments and DFT calculations indicated favorable binding for the enzyme under study. The strongest binding energy, -9.60 kcal/mol, was observed for dihydropyrimidinethione KKII5 in the active site of LOX-1. ADMET calculations showed that the two molecules lack major toxicities and could serve as possible drug leads. The redox potential of the active center of LOX-1 with the binding molecules was calculated via DFT methodology. The results showed a significantly smaller energy attachment of 2.8 eV with KKII5 binding in comparison to DKI5. Thus, KKII5 enhanced the ability of the active center to receive electrons compared to DKI5. This is related to the stronger binding interaction of KKII5 relative to that of DK15 to LOX-1. The two very potent LOX-1 inhibitors exerted IC₅₀ 19 μΜ (KKII5) and 22.5 μΜ (DKI5). Furthermore, they both strongly inhibit lipid peroxidation, namely, 98% for KKII5 and 94% for DKI5.

Chalcone: A potential scaffold for NLRP3 inflammasome inhibitors

Overactivated NLRP3 inflammasome has been shown to associate with an increasing number of disease conditions. Activation of the NLRP3 inflammasome results in caspase-1-catalyzed formation of active pro-inflammatory cytokines (IL-1β and IL-18) resulting in pyroptosis. The multi-protein composition of the NLRP3 inflammasome and its sensitivity to several damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) make this extensively studied inflammasome an attractive target to treat chronic conditions. However, none of the known NLRP3 inhibitors has been approved for clinical use. Sulfonylurea and covalent inhibitors with electrophilic warhead (Michael acceptor) are among the prominent classes of compounds explored for their NLRP3 inhibitory effects. Chalcone, a small molecule with α, β unsaturated carbonyl group (Michael acceptor), has also been studied as a promising scaffold for the development of NLRP3 inhibitors. Low molecular weight, easy to manipulate lipophilicity and cost-effectiveness have attracted many to use chalcone scaffold for drug development. In this review, we highlight chalcone derivatives with NLRP3 inflammasome inhibitory activities. Recent developments and potential new directions summarized here will, hopefully, serve as valuable perspectives for investigators including medicinal chemists and drug discovery researchers to utilize chalcone as a scaffold for developing novel NLRP3 inflammasome inhibitors.

Exploring biogenic chalcones as DprE1 inhibitors for antitubercular activity via in silico approach

Cases of drug-resistant tuberculosis (TB) have increased worldwide in the last few years, and it is a major threat to global TB control strategies and the human population. Mycobacterium tuberculosis is a common causative agent responsible for increasing cases of TB and as reported by WHO, approximately, 1.5 million death occurred from TB in 2020. Identification of new therapies against drug-resistant TB is an urgent need to be considered primarily. The current investigation aims to find the potential biogenic chalcone against the potential targets of drug-resistant TB via in silico approach. The ligand library of biogenic chalcones was screened against DprE1. Results of molecular docking and in silico ADMET prediction revealed that ZINC000005158606 has lead-like properties against the targeted protein. Pharmacophore modeling was done to identify the pharmacophoric features and their geometric distance present in ZINC000005158606. The binding stability study performed using molecular dynamics (MD) simulation of the DprE1-ZINC000005158606 complex revealed the conformational stability of the complex system over 100 ns with minimum deviation. Further, the in silico anti-TB sensitivity of ZINC000005158606 was found to be higher as compared to the standards against Mycobacterium tuberculosis. The overall in silico investigation indicated the potential of identified hit to act as a lead molecule against Mycobacterium tuberculosis.

Geranylation of Chalcones by a Fungal Aromatic Prenyltransferase

Geranylated chalcones mainly exist in plants, and many of them have attracted attention because of their diverse pharmacological and biological activities. Herein, we report geranylation of eight chalcones by the Aspergillus terreus aromatic prenyltransferase AtaPT. Ten new mono-geranylated enzyme products (1G-5G, 6G1, 6G2, 7G, 8G1, and 8G2) were obtained. Most of the products are C-geranylated products with prenyl moieties at ring B. In comparison, plant aromatic prenyltransferases usually catalyze the geranylation at ring A. Therefore, AtaPT can be used complementarily for chalcone geranylation to increase the structural diversity of small molecules. In addition, seven compounds (1G, 3G, 4G, 6G1, 7G, 8G1, and 8G2) exhibited a potential inhibitory effect on α-glucosidase with the IC₅₀ values ranging from 45.59 ± 3.48 to 82.85 ± 2.15 μg/mL. Among them, compound 7G (45.59 ± 3.48 μg/mL) was the most potential α-glucosidase inhibitor, which is about seven times stronger than the positive control acarbose (IC₅₀ = 346.63 ± 15.65 μg/mL).

Antifungal evaluation of quinoline-chalcone derivatives combined with FLC against drug-resistant Candida albicans

With the widespread clinical use of FLC, the FLC-resistant C. albicans greatly increases the difficulty of treatment, and drug combination becomes an important method to treat C. albicans infection. In this work, we have prepared a series of quinoline-chalcone derivatives in good yields, and in vitro antifungal activity against C. albicans were evaluated. The results indicated that most title compounds combined with FLC showed good antifungal activity against drug-resistant C. albicans. Further mechanism researches demonstrated that 6a and 6c combined with FLC could significantly inhibited growth and biofilm formation of C. albicans, induce ROS accumulation, impair the mitochondrial membrane, and decrease intracellular ATP concentrations.

Discovery of N-Phenylpropiolamide as a Novel Succinate Dehydrogenase Inhibitor Scaffold with Broad-Spectrum Antifungal Activity on Phytopathogenic Fungi

Based on the structural features of both succinate dehydrogenase inhibitors (SDHIs) and targeted covalent inhibitors, a series of N-phenylpropiolamides containing a Michael acceptor moiety were designed to find new antifungal compounds. Nineteen compounds showed potent inhibition activity in vitro on nine species of plant pathogenic fungi. Compounds 9 and 13 showed higher activity on most of the fungi than the standard drug azoxystrobin. Compound 13 could completely inhibit Physalospora piricola infection on apples at 200 μg/mL concentration over 7 days and showed high safety to seed germination and seedling growth of plants at ≤100 μg/mL concentration. The action mechanism showed that 13 is an SDH inhibitor with a median inhibitory concentration, IC₅₀, value of 0.55 μg/mL, comparable with that of the positive drug boscalid. Molecular docking studies revealed that 13 can bind well to the ubiquinone-binding region of SDH by hydrogen bonds and undergoes π-alkyl interaction and π-cation interaction. At the cellular level, 1 as the parent compound could destruct the mycelial structure of P. piricola and partly dissolve the cell wall and/or membrane. Structure-activity relationship analysis showed that the acetenyl group should be a structure determinant for the activity, and the substitution pattern of the phenyl ring can significantly impact the activity. Thus, N-phenylpropiolamide emerged as a novel and promising lead scaffold for the development of new SDHIs for plant protection.

Benzenesulfonyl thiazoloimines as unique multitargeting antibacterial agents towards Enterococcus faecalis

New efficient antimicrobial agents are urgently needed to combat invasive multidrug-resistant pathogens infections. Structurally unique benzenesulfonyl thiazoloimines (BSTIs) were exploited as novel potential antibacterial victors to confront terrific drug resistance. Some developed BSTIs exerted effectively antimicrobial efficacy against the tested strains. Notably, 2-pyridyl BSTI 14d exhibited good antibacterial activity against E. faecalis with MIC value of 1 μg/mL, which was superior to sulfathiazole and norfloxacin. The most active compound 14d not only showed rapid bactericidal properties and impeded E. faecalis biofilm formation to effectually relieve the development of drug resistance, but also performed low toxicity toward human red blood cells, human normal squamous epithelial cells and human non-neoplastic colon epithelial cells. Mechanistic investigation demonstrated that molecule 14d could exert efficient membrane destruction leading to the leakage of intracellular materials and metabolism inhibition, cause oxidative damage of E. faecalis through accumulation of excess reactive oxygen species and reduction of glutathione activity, and intercalate into DNA to hinder replication of DNA. Molecular docking indicated that the formation of 14d-dihydrofolate synthetase supramolecular complex could hinder the function of this enzyme. ADME analysis displayed that compound 14d possessed promising pharmacokinetic properties. These findings suggested that the newly developed benzenesulfonyl thiazoloimines with multitargeting antibacterial potential provided a new possibility for evading resistance.

In silico studies, X-ray diffraction analysis and biological investigation of fluorinated pyrrolylated-chalcones in zebrafish epilepsy models

Epilepsy is the third most common known brain disease worldwide. Several antiepileptic drugs (AEDs) are available to improve seizure control. However, the associated side effects limit their practical use and highlight the ongoing search for safer and effective AEDs. Eighteen newly designed fluorine-containing pyrrolylated chalcones were extensively studied in silico, synthesized, structurally analyzed by X-ray diffraction (XRD), and biologically and toxicologically tested as potential new AEDs in zebrafish epilepsy in vivo models. The results predicted that 3-(3,5-difluorophenyl)-1-(1H-pyrrol-2-yl)prop-2-en-1-one (compound 8) had a good drug-like profile with binding affinity to γ-aminobutyric acid receptor type-A (GABA_A, -8.0 kcal/mol). This predicted active compound 8 was effective in reducing convulsive behaviour in pentylenetetrazol (PTZ)-induced larvae and hyperactive movements in zc4h2 knockout (KO) zebrafish, experimentally. Moreover, no cardiotoxic effect of compound 8 was observed in zebrafish. Overall, pyrrolylated chalcones could serve as alternative AEDs and warrant further in-depth pharmacological studies to uncover their mechanism of action.

Flavonoid Production: Current Trends in Plant Metabolic Engineering and De Novo Microbial Production

Flavonoids are secondary metabolites that represent a heterogeneous family of plant polyphenolic compounds. Recent research has determined that the health benefits of fruits and vegetables, as well as the therapeutic potential of medicinal plants, are based on the presence of various bioactive natural products, including a high proportion of flavonoids. With current trends in plant metabolite research, flavonoids have become the center of attention due to their significant bioactivity associated with anti-cancer, antioxidant, anti-inflammatory, and anti-microbial activities. However, the use of traditional approaches, widely associated with the production of flavonoids, including plant extraction and chemical synthesis, has not been able to establish a scalable route for large-scale production on an industrial level. The renovation of biosynthetic pathways in plants and industrially significant microbes using advanced genetic engineering tools offers substantial promise for the exploration and scalable production of flavonoids. Recently, the co-culture engineering approach has emerged to prevail over the constraints and limitations of the conventional monoculture approach by harnessing the power of two or more strains of engineered microbes to reconstruct the target biosynthetic pathway. In this review, current perspectives on the biosynthesis and metabolic engineering of flavonoids in plants have been summarized. Special emphasis is placed on the most recent developments in the microbial production of major classes of flavonoids. Finally, we describe the recent achievements in genetic engineering for the combinatorial biosynthesis of flavonoids by reconstructing synthesis pathways in microorganisms via a co-culture strategy to obtain high amounts of specific bioactive compounds.

Antibacterial potential of chalcones and its derivatives against Staphylococcus aureus

Chalcones are natural substances found in the metabolism of several botanical families. Their structure consists of 1,3-diphenyl-2-propen-1-one and they are characterized by having in their chains an α, β-unsaturated carbonyl system, two phenol rings and a three-carbon chain that unites them. In plants, Chalcones are mainly involved in the biosynthesis of flavonoids and isoflavonoids through the phenylalanine derivation. This group of substances has been shown to be a viable alternative for the investigation of its antibacterial potential, considering the numerous biological activities reported and the increase of the microbial resistance that concern global health agencies. Staphylococcus aureus is a bacterium that has stood out for its ability to adapt and develop resistance to a wide variety of drugs. This literature review aimed to highlight recent advances in the use of Chalcones and derivatives as antibacterial agents against S. aureus, focusing on research articles available on the Science Direct, Pub Med and Scopus data platforms in the period 2015-2021. It was constructed informative tables that provided an overview of which types of Chalcones are being studied more (Natural or Synthetic); its chemical name and main Synthesis Methodology. From the analysis of the data, it was observed that the compounds based on Chalcones have great potential in medicinal chemistry as antibacterial agents and that the molecular skeletons of these compounds as well as their derivatives can be easily obtained through substitutions in the A and B rings of Chalcones, in order to obtain the desired bioactivity. It was verified that Chalcones and derivatives are promising agents for combating the multidrug resistance of S. aureus to drugs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03398-7.

Discovery of new cyanopyridine/chalcone hybrids as dual inhibitors of EGFR/BRAF V600E with promising antiproliferative properties

As dual EGFR and BRAF^V600E inhibitors, 2-(3-cyano-4,6-bis(aryl)-2-oxo-1,2-dihydropyridine-1-yl)-N-(4-cinnamoylphenyl) acetamide derivatives 8-20 were developed. Compounds 8, 12, and 13 showed strong antiproliferative activity when the target compounds were synthesized and tested in vitro against four cancer cell lines. These hybrids have a dual inhibition activity on EGFR and BRAF^V600E , according to in vitro studies. The EGFR was inhibited by compounds 8, 12, and 13 with IC₅₀ values between 89 and 110 nM, which were equivalent to those of erlotinib (IC₅₀  = 80 nm). Compound 13 was found to be an effective inhibitor of the proliferation of cancer cells (GI₅₀  = 0.72 µM) and demonstrated hopeful inhibitory activity of BRAF^V600E (IC₅₀  = 58 nm), which is superior to erlotinib (IC₅₀  = 65 nm). Compound 13 caused apoptosis and showed cell cycle arrest in the G0/G1phase in a study on the MCF-7 cell line. The new compounds can fit tightly into the active sites of EGFR and BRAF^V600E kinases, according to molecular docking analyses.

Insights into chalcone analogues with potential as antioxidant additives in diesel-biodiesel blends

Biodiesel production is one of the promising strategies to reduce diesel consumption and an important contribution to climate change. However, biodiesel stability remains a challenging problem in biofuel use in the global energy matrix. In this context, organic additives have been investigated to minimize these problems and reduce harmful emissions to comply with fuel requirement standards. In this study, we discuss a comprehensive structural description, a behavior of B15 [85% volume of diesel and 15% volume of biodiesel (B100)] stability in the presence of antioxidants (chalcone analogues), and a theoretical calculation to pave the way for clarifying and expanding the potential of title compounds as an antioxidant additive for diesel-biodiesel blends. Finally, a systematic description of the oxidation stability was undertaken using a specialized machine learning computational pySIRC platform.

Pharmacotherapeutics Applications and Chemistry of Chalcone Derivatives

Chalcones have been well examined in the extant literature and demonstrated antibacterial, antifungal, anti-inflammatory, and anticancer properties. A detailed evaluation of the purported health benefits of chalcone and its derivatives, including molecular mechanisms of pharmacological activities, can be further explored. Therefore, this review aimed to describe the main characteristics of chalcone and its derivatives, including their method synthesis and pharmacotherapeutics applications with molecular mechanisms. The presence of the reactive α,β-unsaturated system in the chalcone’s rings showed different potential pharmacological properties, including inhibitory activity on enzymes, anticancer, anti-inflammatory, antibacterial, antifungal, antimalarial, antiprotozoal, and anti-filarial activity. Changing the structure by adding substituent groups to the aromatic ring can increase potency, reduce toxicity, and broaden pharmacological action. This report also summarized the potential health benefits of chalcone derivatives, particularly antimicrobial activity. We found that several chalcone compounds can inhibit diverse targets of antibiotic-resistance development pathways; therefore, they overcome resistance, and bacteria become susceptible to antibacterial compounds. A few chalcone compounds were more active than conventional antibiotics, like vancomycin and tetracycline. On another note, a series of pyran-fused chalcones and trichalcones can block the NF-B signaling complement system implicated in inflammation, and several compounds demonstrated more potent lipoxygenase inhibition than NSAIDs, such as indomethacin. This report integrated discussion from the domains of medicinal chemistry, organic synthesis, and diverse pharmacological applications, particularly for the development of new anti-infective agents that could be a useful reference for pharmaceutical scientists.

Antibacterial quaternary ammonium agents: Chemical diversity and biological mechanism

Bacterial infections have seriously threatened public health especially with the increasing resistance and the cliff-like decline of the number of newly approved antibacterial agents. Quaternary ammonium compounds (QACs) possess potent medicinal properties with 95 successfully marketed drugs, which also have a long history as antibacterial agents. In this review, we summarize the chemical diversity of antibacterial QACs, divided into chain-like and aromatic ring, reported over the past decade (2012 to mid-2022). Additionally, the structure-activity relationships, mainly covering hydrophobicity, charges and skeleton features, are discussed. In the cases where sufficient information is available, antibacterial mechanisms including biofilm, cell membrane, and intracellular targets are presented. It is hoped that this review will provide sufficient information for medicinal chemists to discover the new generation of antibacterial agents based on QACs.

Comprehensive insight into anti-staphylococcal and anti-enterococcal action of brominated and chlorinated pyrazine-based chalcones

The greatest threat and medicinal impact within gram-positive pathogens are posed by two bacterial genera, Staphylococcus and Enterococcus. Chalcones have a wide range of biological activities and are recognized as effective templates in medicinal chemistry. This study provides comprehensive insight into the anti-staphylococcal and anti-enterococcal activities of two recently published brominated and chlorinated pyrazine-based chalcones, CH-0y and CH-0w. Their effects against 4 reference and 12 staphylococcal and enterococcal clinical isolates were evaluated. Bactericidal action, the activity in combination with selected conventional antibiotics, the study of post-antimicrobial effect (PAE, PAE/SME), and in vitro and in vivo toxicity, were included. In CH-0y, anti-staphylococcal activity ranging from MIC = 15.625 to 62.5 μM, and activity against E. faecium from 31.25 to 62.5 μM was determined. In CH-0w, anti-staphylococcal activity ranging from 31.25 to 125 μM, and activity against E. faecium and E. faecalis (62.5 μM) was revealed. Both CH-0y and CH-0w showed bactericidal action, beneficial impact on bacterial growth delay within PAE and PAE/SME studies, and non/low toxicity in vivo. Compared to CH-0w, CH-0y seems to have higher anti-staphylococcal and less toxic potential. In conclusion, chalcones CH-0y and CH-0w could be considered as structural pattern for future adjuvants to selected antibiotic drugs.

<p class="CB-Manuscripttitle"><span lang="EN-US">Synthesis, Biological Activity and Molecular Docking Studies of Heterocyclic Chalcones<o:p></o:p></span></p>

Nineteen heterocyclic chalcones were synthesized from 4-acetyl-5-methylquinolylpyrazole and heteroaryl (imidazole, pyrazole, thiophene, indole and triazole) aldehydes and screened in vitro using four tumor cell lines for their anticancer capability and for antimicrobial activity. The chalcone 5b exhibited the highest activity with IC 50 values 2.14 μM against colon (HCT-116) and 5.0 μM, against prostate (PC-3) cancer cell lines and also displayed good activity against fungal strain ( A. Niger) with MIC value 9.1 μM . The chalcones 5q and 5p displayed good activity against Gram-positive bacterial strains ( S. aureus ) with MIC value 2.6 µM and fungal strain ( C. Albicans ) with MIC value 5.4 µM, respectively. Molecular docking studies revealed that the synthesized heterocyclic chalcones exhibited hydrogen bond, electrostatic and hydrophobic interactions with their respective biochemical targets.

Chalcone 9X Contributed to Repressing Glioma Cell Growth and Migration and Inducing Cell Apoptosis by Reducing FOXM1 Expression In Vitro and Repressing Tumor Growth In Vivo

Objective. Natural and synthetic chalcones played roles in inflammation and cancers. Chalcone 9X was an aromatic ketone that was found to inhibit cell growth of hepatic cancer and lung cancer cells. In this study, we wanted to investigate the functions of Chalcone 9X in glioma. Materials and Methods. Chemical Chalcone 9X was added in human glioma cell lines (U87 and T98G cells) and normal astrocyte cell lines (HA1800) with various concentrations (0 μmol/L, 20 μmol/L, 50 μmol/L, and 100 μmol/L). CCK-8 assay was used to measure cell viability. Flow cytometric assay was used to measure cell apoptotic rates. Wound healing assay and transwell assay were used to measure cell invasion. RT-PCR was used to detect relative mRNA expressions, and the protein expressions were detected by western blot (WB) and immunohistochemical staining (IHC). Finally, nude mouse xenograft assay was performed to prove the effects of Chalcone 9X in vivo. Results. Results revealed that Chalcone 9X treatment suppressed cell viability and cell migration capacity; it could also induce cell apoptosis in U87 and T98G cells with dose dependence. However, it had little cytotoxicity to normal astrocyte HA1800 cells. Moreover, Chalcone 9X treatment could repress the mRNA and protein expressions of FOXM1 in human glioma cell lines, which was an oncogene that could promote the progression and malignancy of glioma. In addition, FOXM1 overexpression dismissed the Chalcone 9X effects on cell proliferation, apoptosis, and migration in human glioma cell lines. Finally, in vivo assay showed that Chalcone 9X treatment repressed the expression of FOXM1, which inhibited the tumor growth of a xenograft model injected with U87 in nude mice. Conclusions. In all, we found that Chalcone 9X could suppress cell proliferation and migration and induce cell apoptosis in human glioma cells, while it has little cytotoxicity to normal astrocyte cells. Therefore, we uncovered a novel way that Chalcone 9X could inhibit FOXM1 expression and repress the progression and biofunctions of glioma cells, which might be a potential therapeutic drug for treating human glioma.

New diarylpentanoids and chalcones as potential antimicrobial adjuvants

Antimicrobial resistance arises due to several adaptation mechanisms, being the overexpression of efflux pumps (EPs) one of the most worrisome. In bacteria, EPs can also play important roles in virulence, quorum-sensing (QS) and biofilm formation. To identify new potential antimicrobial adjuvants, a library of diarylpentanoids and chalcones was synthesized and tested. These compounds presented encouraging results in potentiating the activity of antimicrobials, being diarylpentanoid 13 the most promising. Compounds 9, 13, 16, 19, 22, and 23 displayed EP inhibitory effect, mainly in Staphylococcus aureus 272123. Compounds 13, 19, 22, and 23 exhibited inhibitory effect on biofilm formation in S. aureus 272,123 while 13 and 22 inhibited QS in the pair Sphingomonas paucimobilis Ezf 10-17 and Chromobacterium violaceum CV026. The overall results, demonstrated that diarylpentanoid 13 and chalcone 22 were active against all the resistance mechanisms tested, suggesting their potential as antimicrobial adjuvants.

Photosensitized [2 + 2]-Cycloaddition of Complex Acceptor-Donor Combinations: A Regio/Diastereoselectivity Study

The photosensitized [2 + 2]-cycloaddition of chalcones, conjugated cyclopentenones, and cyclohexenones with electron-rich alkenes such as cyclic enolethers and polymethylated alkenes was investigated. While cyclic enones showed high regio- and stereoselectivity, acyclic enones resulted in a more complex product mixture containing dimers as well as four dominant regio- and diastereoisomers. This complex product mixture can be controlled by adjusting the reaction conditions such as sensitizer, solvents, or additives.

Chalcones with potential antibacterial and antibiofilm activities against periodontopathogenic bacteria

OBJECTIVES

Periodontitis is a pathology resulting from complex interaction of microorganisms in the dental biofilm with the host's immune system. Increased use of antibiotics associated with their inappropriate use has increased resistance levels in anaerobic bacteria. Therefore, identifying new antimicrobial compounds, such as chalcones, is urgent. This study evaluates the antibacterial activity and the antibiofilm activity of 15 chalcones against the periodontopathogenic bacteria Prevotella nigrescens (ATCC 33563), P. oralis (ATCC 33269), Peptostreptococcus anaerobius (ATCC 27337), Actinomyces viscosus (ATCC 43146), Porphyromonas asaccharolytica (ATCC 25260), and Fusobacterium nucleatum (ATCC 25586).

METHODS

The compounds were evaluated by minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC) tests.

RESULTS

Compounds 1-6 showed good antibacterial and antibiofilm activities against most of the evaluated bacteria: MIC was lower than or equal to 6.25 μg/mL, biofilm biomass was reduced by 95%, and the compounds at concentrations between 0.78 and 100 μg/mL totally inhibited cell viability. Among the tested chalcones, 3 stood out: it was effective against all the bacteria, as revealed by the MIC and MBIC results.

CONCLUSIONS

Our results have consolidated a base for the development of new studies on the effects of the tested chalcones as agents to combat and to prevent periodontitis.

Chalcone Scaffolds Exhibiting Acetylcholinesterase Enzyme Inhibition: Mechanistic and Computational Investigations

This study was aimed to perform the mechanistic investigations of chalcone scaffold as inhibitors of acetylcholinesterase (AChE) enzyme using molecular docking and molecular dynamics simulation tools. Basic chalcones (C1–C5) were synthesized and their in vitro AChE inhibition was tested. Binding interactions were studied using AutoDock and Surflex-Dock programs, whereas the molecular dynamics simulation studies were performed to check the stability of the ligand–protein complex. Good AChE inhibition (IC₅₀ = 22 ± 2.8 to 37.6 ± 0.75 μM) in correlation with the in silico results (binding energies = −8.55 to −8.14 Kcal/mol) were obtained. The mechanistic studies showed that all of the functionalities present in the chalcone scaffold were involved in binding with the amino acid residues at the binding site through hydrogen bonding, π–π, π–cation, π–sigma, and hydrophobic interactions. Molecular dynamics simulation studies showed the formation of stable complex between the AChE enzyme and C4 ligand.

BDDE-Inspired Chalcone Derivatives to Fight Bacterial and Fungal Infections

The growing number of infectious diseases around the world threatens the effective response of antibiotics, contributing to the increase in antibiotic resistance seen as a global health problem. Currently, one of the main challenges in antimicrobial drug discovery is the search for new compounds that not only exhibit antimicrobial activity, but can also potentiate the antimicrobial activity and revert antibiotics’ resistance, through the interference with several mechanisms, including the inhibition of efflux pumps (EPs) and biofilm formation. Inspired by macroalgae brominated bromophenol BDDE with antimicrobial activity, a series of 18 chalcone derivatives, including seven chalcones (9–15), six dihydrochalcones (16–18, and 22–24) and five diarylpropanes (19–21, and 25 and 26), was prepared and evaluated for its antimicrobial activity and potential to fight antibiotic resistance. Among them, chalcones 13 and 14 showed promising antifungal activity against the dermatophyte clinical strain of Trichophyton rubrum, and all compounds reversed the resistance to vancomycin in Enterococcus faecalis B3/101, with 9, 14, and 24 able to cause a four-fold decrease in the MIC of vancomycin against this strain. Compounds 17–24 displayed inhibition of EPs and the formation of biofilm by S. aureus 272123, suggesting that these compounds are inhibiting the EPs responsible for the extrusion of molecules involved in biofilm-related mechanisms. Interestingly, compounds 17–24 did not show cytotoxicity in mouse embryonic fibroblast cell lines (NIH/3T3). Overall, the results obtained suggest the potential of dihydrochalcones 16–18 and 22–24, and diarylpropanes 19–21, 25 and 26, as hits for bacterial EPs inhibition, as they are effective in the inhibition of EPs, but present other features that are important in this matter, such as the lack of antibacterial activity and cytotoxicity.

Orchestrating a β-Hydride Elimination Pathway in Palladium(II)-Catalyzed Arylation/Alkenylation of Cyclopropanols Using Organoboron Reagents

The scope of chemoselective β-hydride elimination in the context of arylation/alkenylation of homoenolates from cyclopropanol precursors using organoboronic reagents as transmetalation coupling partners was examined. The reaction optimization paradigm revealed a simple ligand-free Pd(II) catalytic system to be most efficient under open air conditions. The preparative scope, which was investigated with 48 examples, supported the applicability of this reaction to a wide range of substrates tolerating a variety of functional groups while delivering β-substituted enone and dienone derivatives in 62-95% yields.

The Medicinal Chemistry of Chalcones as Anti-Mycobacterium tuberculosis Agents

Abstract:

Tuberculosis (TB), a highly fatal infectious disease, is caused by Mycobacterium tuberculosis (Mtb) that has inflicted mankind for several centuries. In 2019, the staggering number of new cases reached 10 million resulting in 1.2 million deaths. The emergence of multidrug-resistance-Mycobacterium tuberculosis (MDR-TB) and extensively drug-resistant-Mycobacterium tuberculosis (XDR-TB) is a global concern that requires the search for novel, effective, and safer short-term therapies. Nowadays, among the few alternatives available to treat resistant-Mtb strains, the majority have limitations, which include drug-drug interactions, long-term treatment, and chronic induced toxicities. Therefore, it is mandatory to develop new anti-Mtb agents to achieve health policy goals to mitigate the disease by 2035. Among the several bioactive anti-Mtb compounds, chalcones have been described as the privileged scaffold useful for drug design. Overall, this review explores and analyzes 37 chalcones that exhibited anti-Mtb activity described in the literature up to April 2021 with minimum inhibitory concentration (MIC90) values inferior to 20 µM and selective index superior to 10. In addition, the correlation of some properties for most active compounds was evaluated, and the main targets for these compounds were discussed.

Synthesis, odor characteristics and biological evaluation of N-substituted pyrrolyl chalcones

Base-mediated transition-metal free α-functionalization of N-substituted acetylpyrroles with commercial alcohols to generate various pyrrolyl chalcones is reported, and several prominent bioactive and flavor molecules were obtained.

Optimized protocols for assessing libraries of poorly soluble sortase A inhibitors for antibacterial activity against medically-relevant bacteria, toxicity and enzyme inhibition

Increasing antimicrobial resistance is a major global health concern. Conventional antibiotics apply selection pressures, which promote the accumulation of resistant microbes. Anti-virulence strategies, in contrast, are less potent antimicrobials, but are less likely to select for resistance, can be combined with existing antibiotics to improve their activity, and in some cases can overcome antimicrobial resistance towards other antimicrobials. Sortase A inhibitors (SrtAIs) represent an exciting example of this class; however, many reported examples demonstrate poor water solubility, which complicates their biological assessment and activity. This includes reports that use antimicrobial concentrations of organic solvents or conditions that fail to solubilise these compounds for minimal inhibitory concentration (MIC) assessments. Herein, we report the first study to optimise screening processes for a library of prospective SrtAIs (trans-chalcone (TC), berberine (BR), curcumin (CUR), and quercetin (QC)), including comparative assessment of the effects of various co-solvent concentrations, along with comparative assessment of their antimicrobial activities against multiple disease relevant bacterial strains (methicillin-sensitive and resistant S. aureus, E. coli, and P. aeruginosa), inhibition of the sortase A enzyme, and toxicity towards mammalian cells (HEK-293), using these optimised conditions. Optimal solubility with minimal effect on bacterial viability was observed in the presence of 5% (v/v) dimethyl sulfoxide (DMSO)-Mueller-Hinton Broth. Three antimicrobial susceptibility tests (broth microdilution, agar dilution, and disk diffusion) were assessed for their ability to accurately determine minimal inhibitory concentration (MIC) data for each SrtAI. Broth microdilution and agar dilution were both effective; however, the broth microdilution assay required the addition of a colorimetric metabolic indicator (resazurin) to enable simple and reliable MIC determination due to the development of precipitants over time. In contrast, disk diffusion did not provide reliable zone of inhibition data. Identical MIC data was observed with methicillin-sensitive and -resistant S. aureus (MRSA; ATCC43300), with lower potency activity against E. coli and P. aeruginosa. Under these conditions, TC and CUR demonstrated significant toxicity towards human embryonic kidney (HEK-293) cells, with QC showing less toxicity and BR limited-to-no toxicity at its MIC. Overall, the findings of this work provide optimised processes, which will prove useful for the study of other poorly soluble antimicrobial agents and SrtAIs. The obtained data suggests that BR should be considered in preference to the other SrtAIs for the development of new antimicrobial formulations, based on its superior antimicrobial and SrtA inhibition potency, and greatly reduced toxicity.