Synthesis and Biological Evaluation of Quinoline‐Based Novel Aurones

Design and Synthesis of Novel Amino and Acetamidoaurones with Antimicrobial Activities

The development of new and effective antimicrobial compounds is urgent due to the emergence of resistant bacteria. Natural plant flavonoids are known to be effective molecules, but their activity and selectivity have to be increased. Based on previous aurone potency, we designed new aurone derivatives bearing acetamido and amino groups at the position 5 of the A ring and managing various monosubstitutions at the B ring. A series of 31 new aurone derivatives were first evaluated for their antimicrobial activity with five derivatives being the most active (compounds 10, 12, 15, 16, and 20). The evaluation of their cytotoxicity on human cells and of their therapeutic index (TI) showed that compounds 10 and 20 had the highest TI. Finally, screening against a large panel of pathogens confirmed that compounds 10 and 20 possess large spectrum antimicrobial activity, including on bioweapon BSL3 strains, with MIC values as low as 0.78 µM. These results demonstrate that 5-acetamidoaurones are far more active and safer compared with 5-aminoaurones, and that benzyloxy and isopropyl substitutions at the B ring are the most promising strategy in the exploration of new antimicrobial aurones.

Pyrazole-based and N,N-diethylcarbamate functionalized some novel aurone analogs: Design, synthesis, cytotoxic evaluation, docking and SAR studies, against AGS cancer cell line

The present study involves the design, synthesis, and biological evaluation of a series of thirty-three, pyrazole-based and N,N-diethylcarbamate functionalized, novel aurone analogs, against AGS cancer cell line. These novel aurone analogs are obtained from the reaction of pyrazole-based 6-hydroxyaurones with diethyl carbamoyl chloride using mild basic reagent. The cytotoxic activities of these compounds were evaluated against a human gastric adenocarcinoma cell line (AGS) and disclosed some potential outcomes as several analogs were found to have cytotoxicity better than the reference drugs Oxaliplatin and Leucovorin. The structure-activity relationship (SAR) study further unveiled the critical role of replacing the hydroxyl group in ring A with a carbamoyl group for cytotoxic activity. Among these aurone analogs, 8e and 8f, with IC50 values of 6.5 ± 0.024 μM and 6.6 ± 0.035 μM, respectively, are identified as the most active compounds. Molecular docking studies were conducted against HER2, a human epidermal growth factor involved in gastric and ovarian cancer, to investigate the binding interactions between the compounds and the protein HER2, where7e and 8e exhibited maximum interactions.

Some morpholine tethered novel aurones: Design, synthesis, biological, kinetic and molecular docking studies

Enzymes are the biological macromolecules that have emerged as an important drug target as their upregulation/imbalance leads to various pathological conditions, such as inflammation, parasitic infection, Alzheimer's, cancer, and many others. Here, we designed and synthesized some morpholine tethered novel aurones and evaluated them as potential inhibitors for CTSB, α-amylase, lipase and activator for trypsin. All the newly synthesized compounds were fully characterized by various spectroscopic techniques (1H NMR, 13C NMR, HRMS) and the Z-configuration to them was assigned based on single crystal XRD data and 1H NMR chemical shift values. Further, the hybrids were evaluated for their intracellular (cathepsin B) and extracellular (trypsin, lipase, amylase) enzyme inhibition potencies. The in-vitro inhibition screening against cathepsin B revealed that most of the synthesized compounds are good competitive inhibitors (% inhibition = 22.91-75.04), with 6q (% inhibition = 75.04) and 6r (% inhibition = 71.13) as the eminent inhibitors of the series. At the same time, they exhibited weak to moderate inhibition towards amylase (% inhibition = 7.22-22.48) and lipase (% inhibition = 16.29-54.83). A significant trypsin activation (% activation = 107.42-196.47) was observed even at the micromolar concentration of the compounds. Furthermore, the drug-modeling studies showed a good correlation between the in-vitro experimental results and the calculated binding affinity of the screened compounds with all the tested enzymes. These findings are expected to provide a new lead in drug development for different pathological disorders wherever these enzymes are involved.

Flavones and Related Compounds: Synthesis and Biological Activity

This review focuses on the synthesis and biological activity of flavones and their related flavonoidic compounds, namely flavonols and aurones. Among the biological activities of natural and synthetic flavones and aurones, their anticancer, antioxidant, and antimicrobial properties are highlighted and detailed in this review. Starting from the structures of natural flavones acting on multiple anticancer targets (myricetin, genkwanin, and other structurally related compounds), new flavone analogs were recently designed and evaluated for their anticancer activity. The most representative compounds and their anticancer activity are summarized in this review. Natural flavones recognized for their antimicrobial properties (baicalein, luteolin, quercetol, apigenin, kaempferol, tricin) have been recently derivatized or structurally modulated by chemical synthetic methods in order to obtain new effective antimicrobial flavonoidic derivatives with improved biological properties. The most promising antimicrobial agents are systematically highlighted in this review. The most applied method for the synthesis of flavones and aurones is based on the oxidative cyclization of o-hydroxychalcones. Depending on the reaction conditions and the structure of the precursor, in some cases, several cyclization products result simultaneously: flavones, flavanones, flavonols, and aurones. Based on the literature data and the results obtained by our research group, our aim is to highlight the most promising methods for the synthesis of flavones, as well as the synthetic routes for the other structurally related cyclization products, such as hydroxyflavones and aurones, while considering that, in practice, it is difficult to predict which is the main or exclusive cyclization product of o-hydroxychalcones under certain reaction conditions.

Application of Quinoline Ring in Structural Modification of Natural Products

Natural compounds are rich in pharmacological properties that are a hot topic in pharmaceutical research. The quinoline ring plays important roles in many biological processes in heterocycles. Many pharmacological compounds, including saquinavir and chloroquine, have been marketed as quinoline molecules with good anti-viral and anti-parasitic properties. Therefore, in this review, we summarize the medicinal chemistry of quinoline-modified natural product quinoline derivatives that were developed by several research teams in the past 10 years and find that these compounds have inhibitory effects on bacteria, viruses, parasites, inflammation, cancer, Alzheimer's disease, and others.

Evaluation of the Antibacterial Effect of Aurone-Derived Triazoles on Staphylococcus aureus

Infections caused by antibiotic-resistant bacteria continue to pose a significant public health threat despite their overall decreasing numbers in the last two decades. One group of compounds fundamental to the search for new agents is low-cost natural products. In this study, we explored a group of newly synthesized novel aurone-derived triazole compounds to identify those with pharmaceutical potential as inhibitors of antibiotic-resistant Staphylococcus aureus. Using the broth microdilution method, antibacterial activities against methicillin-resistant S. aureus ATCC 43300 (MRSA) and methicillin-sensitive S. aureus ATCC 29213 (MSSA) were identified for four aurone-derived triazole compounds, AT106, AT116, AT125, and AT137, using the half-maximal inhibitory concentrations for the bacteria (IC50) and mammalian cell lines (CC50). Compounds AT125 and AT137 were identified to have pharmaceutical potential as the IC50 values against MRSA were 5.412 µM and 3.870 µM, whereas the CC50 values measured on HepG2 cells were 50.57 µM and 39.81 µM, respectively, resulting in selectivity indexes (SI) > 10. Compounds AT106 and AT116 were also selected for further study. IC50 values for these compounds were 5.439 µM and 3.178 µM, and the CC50 values were 60.33 µM and 50.87 µM, respectively; however, SI values > 10 were for MSSA only. Furthermore, none of the selected compounds showed significant hemolytic activity for human erythrocytes. We also tested the four compounds against S. aureus biofilms. Although AT116 and AT125 successfully disrupted MSSA biofilms, there was no measurable potency against MRSA biofilms. Checkerboard antibiotic assays to identify inhibitory mechanisms for these compounds indicated activity against bacterial cell membranes and cell walls, supporting the pharmaceutical potential for aurone-derived triazoles against antibiotic-resistant bacteria. Examining structure-activity relationships between the four compounds in this study and other aurone-derived triazoles in our library suggest that substitution with a halogen on either the salicyl ring or triazole aryl group along with triazoles having nitrile groups improves anti-Staphylococcal activity with the location of the functionality being very important.

Hydrogel-Encapsulated Biofilm Inhibitors Abrogate the Cariogenic Activity of Streptococcus mutans

We designed and synthesized analogues of a previously identified biofilm inhibitor IIIC5 to improve solubility, retain inhibitory activities, and to facilitate encapsulation into pH-responsive hydrogel microparticles. The optimized lead compound HA5 showed improved solubility of 120.09 μg/mL, inhibited Streptococcus mutans biofilm with an IC50 value of 6.42 μM, and did not affect the growth of oral commensal species up to a 15-fold higher concentration. The cocrystal structure of HA5 with GtfB catalytic domain determined at 2.35 Å resolution revealed its active site interactions. The ability of HA5 to inhibit S. mutans Gtfs and to reduce glucan production has been demonstrated. The hydrogel-encapsulated biofilm inhibitor (HEBI), generated by encapsulating HA5 in hydrogel, selectively inhibited S. mutans biofilms like HA5. Treatment of S. mutans-infected rats with HA5 or HEBI resulted in a significant reduction in buccal, sulcal, and proximal dental caries compared to untreated, infected rats.

Design, synthesis and evaluation of 5-chloro-6-methylaurone derivatives as potential anti-cancer agents

A series of novel 5-chloro-6-methylaurone derivatives (6a-p) were synthesized and characterized by various spectroscopic techniques. The synthesized compounds were tested for anticancer activity against 60-human cancer cell line panel derived from nine cancer types at NCI, Bethesda, USA. Among the synthesized compounds, six compounds (6e, 6f, 6h, 6i, 6k and 6 m) exhibited growth inhibition and cytotoxic activity against various human cancer cell lines in one-dose data. The most potent compound among the series, 6i was active against 55 out of 60 human cancer cell lines. Compound 6i showed remarkable % growth inhibition and cytotoxicity against various cancer cell lines exhibiting % GI in the range 36.05-199.03. The compound 6i was further evaluated for five dose assay and exhibited GI50 1.90 µM and 2.70 µM against melanoma and breast cancer cell lines respectively. Further evaluation of 6i for five-dose assay exhibited a diverse spectrum of anti-cancer activity towards all the 60 human cancer cell line panel with the selectivity index ratio ranging 0.854-1.42  and 0.66-1.35  for GI50 and TGI respectively. Based on one-dose and five-dose data compound 6i was further evaluated for cell apoptosis against MDA-MB-468 breast cancer cell line and was found to induce early apoptosis in cells explaining its mode of action. The in-silico studies for the synthesized compounds as LSD1 inhibitors (2H94) have shown better docking score and binding energy comparable to vafidemstat. All the compounds followed Lipinski rule of five. These findings concluded that the compound 6i could lead to the development of a promising therapeutic anticancer agent.

Bioactive Aurones, Indanones, and Other Hemiindigoid Scaffolds: Medicinal Chemistry and Photopharmacology Perspectives

Hemiindigoids comprise a range of natural and synthetic scaffolds that share the same aromatic hydrocarbon backbone as well as promising biological and optical properties. The encouraging therapeutic potential of these scaffolds has been unraveled by many studies over the past years and uncovered representants with inspiring pharmacophoric features such as the acetylcholinesterase inhibitor donezepil and the tubulin polymerization inhibitor indanocine. In this review, we summarize the last advances in the medicinal potential of hemiindigoids, with a special attention to molecular design, structure-activity relationship, ligand-target interactions, and mechanistic explanations covering their effects. As their strong fluorogenic potential and photoswitch behavior recently started to be highlighted and explored in biology, giving rise to the development of novel fluorescent probes and photopharmacological agents, we also discuss these properties in a medicinal chemistry perspective.

Aurones: A Golden Resource for Active Compounds

Deemed as poorly represented in nature, aurones have been often overlooked by researchers compared to other members of the flavonoid superfamily. However, over the past two decades, they have been reassessed by the scientific community, who are increasingly appreciating their ability to modulate several biological pathways. This review summarizes the recent literature on this class of compounds, which has been analyzed from both a chemical and a functional point of view. Original articles, reviews and editorials featured in Pubmed and Scifinder over the last twenty years have been taken into account to provide the readers with a view of the chemical strategies to obtain them, their functional properties, and their potential of technological use. The resulting comprehensive picture aims at raising the awareness of these natural derivatives as effective drug candidates, fostering the development of novel synthetic analogues.

2-Benzylidenebenzofuran-3(2H)-ones as a new class of alkaline phosphatase inhibitors: synthesis, SAR analysis, enzyme inhibitory kinetics and computational studies

The excelling role of organic chemistry in the medicinal field continues to be one of the main leads in the drug development process. Particularly, this industry requires organic chemists to discover small molecular structures with powerful pharmacological potential. Herein, a diverse range of chalcone (1–11) and aurone (12–22) derivatives was designed and synthesized and for the first time, and both motifs were evaluated as potent inhibitors of alkaline phosphatases (APs). Structural identification of the target compounds (1–22) was accomplished using common spectroscopic techniques. The effect of the nature and position of the substituent was interestingly observed and justified based on the detailed structure–activity relationship (SAR) of the target compounds against AP. It was concluded from the obtained results that all the newly synthesized compounds exhibit high inhibitory potential against the AP enzyme. Among them, compounds 12 (IC₅₀ = 2.163 ± 0.048 μM), 15 (IC₅₀ = 2.146 ± 0.056 μM), 16 (IC₅₀ = 2.132 ± 0.034 μM), 18 (IC₅₀ = 1.154 ± 0.043 μM), 20 (IC₅₀ = 1.055 ± 0.029 μM) and 21 (IC₅₀ = 2.326 ± 0.059 μM) exhibited excellent inhibitory activity against AP, and even better/more active than KH₂PO₄ (standard) (IC₅₀ = 2.80 ± 0.065 μM). Remarkably, compound 20 (IC₅₀ = 1.055 ± 0.029 μM) may serve as a lead structure to design more potent inhibitors of alkaline phosphatase. To the best of our knowledge, these synthetic compounds are the most potent AP inhibitors with minimum IC₅₀ values reported to date. Furthermore, a molecular modeling study was performed against the AP enzyme (1EW2) to check the binding interaction of the synthesized compounds 1–22 against the target protein. The Lineweaver–Burk plots demonstrated that most potential derivative 20 inhibited h-IAP via a non-competitive pathway. Finally, molecular dynamic (MD) simulations were performed to evaluate the dynamic behavior, stability of the protein–ligand complex, and binding affinity of the compounds, resulting in the identification of compound 20 as a potential inhibitor of AP. Accordingly, excellent correlation was observed between the experimental and theoretical results. The pharmacological studies revealed that the synthesized analogs 1–22 obey Lipinski's rule. The assessment of the ADMET parameters showed that these compounds possess considerable lead-like characteristics with low toxicity and can serve as templates in drug design.

Aurones are the plant secondary metabolites belonging to the flavonoid’s family. The bioactivities of aurones are very promising, thus these heterocyclic compounds can be considered as an alluring scaffold for drug design and development.

Recent advances on synthesis and biological activities of aurones

Aurones are naturally occurring structural isomerides of flavones that have diverse bioactivities including antiviral, antibacterial, antifungal, anti-inflammatory, antitumor, antimalarial, antioxidant, neuropharmacological activities and so on. They constitute an important class of pharmacologically active scaffolds that exhibit multiple biological activities via diverse mechanisms. This review article provides an update on the recent advances (2013-2020.4) in the synthesis and biological activities of these derivatives. In the cases where sufficient information is available, some important structure-activity relationships (SAR) of their biological activities were presented, and on the strength of our expertise in medicinal chemistry and careful analysis of the recent literature, for the potential of aurones as medicinal drugs is proposed.