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.

Repurposing Synthetic Congeners of a Natural Product Aurone Unveils a Lead Antitumor Agent Inhibiting Folded P-Loop Conformation of MET Receptor Tyrosine Kinase

A library of 24 congeners of the natural product sulfuretin were evaluated against nine panels representing nine cancer diseases. While sulfuretin elicited very weak activities at 10 µM concentration, congener 1t was identified as a potential compound triggering growth inhibition of diverse cell lines. Mechanistic studies in HCT116 colon cancer cells revealed that congener 1t dose-dependently increased levels of cleaved-caspases 8 and 9 and cleaved-PARP, while it concentration-dependently decreased levels of CDK4, CDK6, Cdc25A, and Cyclin D and E resulting in induction of cell cycle arrest and apoptosis in colon cancer HCT116 cells. Mechanistic study also presented MET receptor tyrosine kinase as the molecular target mediating the anticancer activity of compound 1t in HCT116 cells. In silico study predicted folded p-loop conformation as the form of MET receptor tyrosine kinase responsible for binding of compound 1t. Together, the current study presents compound 1t as an interesting anticancer lead for further development.

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.

An update of aurones: food resource, health benefit, biosynthesis and application

Aurones are a subclass of active flavonoids characterized with a scaffold of 2-benzylidene-3(2H)-benzofuranone. This type of chemicals are widely distributed in fruit, vegetable and flower, and contribute to human health. In this review, we summarize the natural aurones isolated from dietary plants. Their positive effects on immunomodulation, antioxidation, cancer prevention as well as maintaining the health status of cardiovascular, nervous system and liver organs are highlighted. The biosynthesis strategies of plant-derived aurones are elaborated to provide solutions for their limited natural abundance. The potential application of natural aurones in food coloration are also discussed. This paper combines the up-to-date information and gives a full image of dietary aurones.

Nature as a source and inspiration for human monoamine oxidase B (Hmao-B) inhibition: A review of the recent advances in chemical modification of natural compounds

INTRODUCTION

Over the past five years, we have witnessed intense research activity about the biological potential of natural products (NPs) as human monoamine oxidase B (MAO-B) inhibitors. Despite the promising inhibitory activity, natural compounds are often characterized by pharmacokinetic limitations such as poor aqueous solubility, extensive metabolism, and low bioavailability.

AREAS COVERED

This review provides an overview of the current landscape NPs as selective hMAO-B inhibitors and highlights their use as a starting scaffold to design (semi)synthetic derivatives to overcome the therapeutic (pharmacodynamic and pharmacokinetic) limitations of NPs and to obtain more robust structure-activity relationships (SARs) for each scaffold.

EXPERT OPINION

All the natural scaffolds herein presented displayed a broad chemical diversity. The knowledge of their biological activity as inhibitors of hMAO-B enzyme allows the positive correlations associated with the consumption of specific food or the possible herb-drug interactions and suggests to the Medicinal Chemists how to address chemical functionalization to obtain more potent and selective compounds.

Semi-Synthesis of Different Pyranoflavonoid Backbones and the Neurogenic Potential

Flavonoids and chalcones are known for their manifold biological activities, of which many affect the central nervous system. Pyranochalcones were recently shown to have a great neurogenic potential, which is partly due to a specific structural motif-the pyran ring. Accordingly, we questioned if other flavonoid backbones with a pyran ring as structural moiety would also show neurogenic potential. Different semi-synthetic approaches starting with the prenylated chalcone xanthohumol, isolated from hops, led to pyranoflavanoids with different backbones. We identified the chalcone backbone as the most active backbone with pyran ring using a reporter gene assay based on the promoter activity of doublecortin, an early neuronal marker. Pyranochalcones therefore appear to be promising compounds for further development as a treatment strategy for neurodegenerative diseases.

Prenylated Flavonoids with Selective Toxicity against Human Cancers

The antiproliferative activity of xanthohumol (1), a major prenylated chalcone naturally occurring in hops, and its aurone type derivative (Z)-6,4'-dihydroxy-4-methoxy-7-prenylaurone (2) were investigated. Both flavonoids, as well as cisplatin as a reference anticancer drug, were tested in vivo against ten human cancer cell lines (breast cancer (MCF-7, SK-BR-3, T47D), colon cancer (HT-29, LoVo, LoVo/Dx), prostate cancer (PC-3, Du145), lung cancer (A549) and leukemia (MV-4-11) and two normal cell lines (human lung microvascular endothelial (HLMEC)) and murine embryonic fibroblasts (BALB/3T3). Chalcone 1 and aurone 2 demonstrated potent to moderate anticancer activity against nine tested cancer cell lines (including drug-resistant ones). The antiproliferative activity of all the tested compounds against cancer and the normal cell lines was compared to determine their selectivity of action. Prenylated flavonoids, especially the semisynthetic derivative of xanthohumol (1), aurone 2, were found as selective antiproliferative agents in most of the used cancer cell lines, whereas the reference drug, cisplatin, acted non-selectively. Our findings suggest that the tested flavonoids can be considered strong potential candidates for further studies in the search for effective anticancer drugs.

A New Method of Preparing Aurone by Marine Actinomycetes and Its Potential Application in Agricultural Fungicides

A strain of marine actinomycetes was isolated from an intertidal zone and identified as Streptomyces cinereoruber. Through the fermentation of this strain, a compound with fungicidal activity was extracted and purified. Using mass spectrometry (MS) and nuclear magnetic resonance (NMR) data, the metabolite was determined to be an aurone. The toxicity of the aurone toward four kinds of tumor cells-SH-SY5Y, HepG2, A549, and HeLa cells-was verified by the MTT method, delivering IC₅₀ values of 41.81, 47.19, 63.95, and 51.92 μg/mL, respectively. Greenhouse bioassay showed that the aurone exhibited a high fungicidal activity against powder mildew (Botrytis cinerea), cucurbits powder mildew (Sphaerotheca fuliginea (Schlecht ex Ff.) Poll), and rice blast (Pyricularia oryzae).

Biochemistry and regulation of aurone biosynthesis

Aurones are a group of flavonoids that confer a bright yellow coloration to certain ornamental flowers and are a promising structural target for the development of new therapeutic drugs. Since the first identification of the snapdragon aurone synthase as a polyphenol oxidase (PPO) in 2000, several important advances in the biochemistry and regulation of aurone biosynthesis have been achieved. For example, several other aurone synthases have been identified in distantly related plants, which not only include PPOs but also peroxidases. Elucidation of the subcellular localization of aurone biosynthesis in snapdragon led to the establishment of a method to genetically engineer novel yellow flowers. The crystal structure of an aurone-producing PPO was clarified and provided important insights into the structure-function relationship of aurone-producing PPOs. A locus (SULFUREA) that negatively regulates aurone biosynthesis in snapdragon was identified, illustrating the evolution of flower color pattern through selection on regulatory small RNAs.

Chemical constituents from the stems of Acanthopanax senticosus with their inhibitory activity on α-glucosidase

A new aurone named (2Z)-2-[(4'-hydroxy-3'-methoxyphenyl) methylene]-6-methoxy-7-prenyl-3(2H)-benzofurane (1), together with five known compounds (2-6), were isolated from EtOAc-soluble extract of the stems of Acanthopanax senticosus. The chemical structures were elucidated on the basis of spectroscopic analyses. All isolates were evaluated for in vitro inhibitory activity on α-glucosidase. Among them, compounds 1 and 4 were found to exhibit moderate inhibitory activity on α-glucosidase with IC₅₀ value of 64.1 ± 1.2 and 48.9 ± 1.1 μM, respectively.[Formula: see text].

Exploring Aurone Derivatives as Potential Human Pancreatic Lipase Inhibitors through Molecular Docking and Molecular Dynamics Simulations

Inhibition of human pancreatic lipase, a crucial enzyme in dietary fat digestion and absorption, is a potent therapeutic approach for obesity treatment. In this study, human pancreatic lipase inhibitory activity of aurone derivatives was explored by molecular modeling approaches. The target protein was human pancreatic lipase (PDB ID: 1LPB). The 3D structures of 82 published bioactive aurone derivatives were docked successfully into the protein catalytic active site, using AutoDock Vina 1.5.7.rc1. Of them, 62 compounds interacted with the key residues of catalytic trial Ser152-Asp176-His263. The top hit compound (A14), with a docking score of −10.6 kcal⋅mol⁻¹, was subsequently submitted to molecular dynamics simulations, using GROMACS 2018.01. Molecular dynamics simulation results showed that A14 formed a stable complex with 1LPB protein via hydrogen bonds with important residues in regulating enzyme activity (Ser152 and Phe77). Compound A14 showed high potency for further studies, such as the synthesis, in vitro and in vivo tests for pancreatic lipase inhibitory activity.

Synthesis and Anticancer Cytotoxicity of Azaaurones Overcoming Multidrug Resistance

The resistance of tumors against anticancer drugs is a major impediment for chemotherapy. Tumors often develop multidrug resistance as a result of the cellular efflux of chemotherapeutic agents by ABC transporters such as P-glycoprotein (ABCB1/P-gp), Multidrug Resistance Protein 1 (ABCC1/MRP1), or Breast Cancer Resistance Protein (ABCG2/BCRP). By screening a chemolibrary comprising 140 compounds, we identified a set of naturally occurring aurones inducing higher cytotoxicity against P-gp-overexpressing multidrug-resistant (MDR) cells versus sensitive (parental, non-P-gp-overexpressing) cells. Follow-up studies conducted with the P-gp inhibitor tariquidar indicated that the MDR-selective toxicity of azaaurones is not mediated by P-gp. Azaaurone analogs possessing pronounced effects were then designed and synthesized. The knowledge gained from structure–activity relationships will pave the way for the design of a new class of anticancer drugs selectively targeting multidrug-resistant cancer cells.

Isolation, characterization, and xanthine oxidase inhibitory activities of flavonoids from the leaves of Perilla frutescens

Phytochemical investigation of the water extract from the leaves of Perilla frutescens (Lamiaceae) led to the isolation of a new flavanone, a new chalcone, and a new aurone, namely, (2S)-5,7-dimethoxy-8,4'-dihydroxyflavanone (1), 2',4'-dimethoxy-4,5',6'-trihydroxychalcone (2), and (Z)-4,6-dimethoxy-7,4'-dihydroxyaurone (3), respectively. The structures were unambiguously elucidated on the basis of spectroscopic data. And the absolute configuration of 1 was determined by analysis of electronic circular dichroism spectrum. The isolated compounds were evaluated for their inhibitory effects on xanthine oxidase in vitro. Among them, 2 showed more potent activity than the positive control allopurinol, a well-known XO inhibitor clinically used for treatment of gout. Lineweaver-Burk transformation of the inhibition kinetics data demonstrated that it was a mixed-type inhibitor.[Formula: see text].

Convenient Synthesis and Physiological Activities of Flavonoids in Coreopsis lanceolata L. Petals and Their Related Compounds

Chalcones, flavanones, and flavonols, including 8-methoxybutin isolated from Coreopsis lanceolata L. petals, were successfully synthesized with total yields of 2⁻59% from O-methylpyrogallols using the Horner⁻Wadsworth⁻Emmons reaction as a key reaction. Aurones, including leptosidin, were also successfully synthesized with 5⁻36% total yields using the Aldol condensation reaction as a key reaction. Each chalcone, flavanone, flavonol, and aurone with the 3,4-dihydroxy groups in the B-ring showed high antioxidant activity. Additionally, each of the chalcones, flavanones, flavonols, and aurones with the 2,4-dihydroxy groups in the B-ring showed an excellent whitening ability.

Physical interactions among flavonoid enzymes in snapdragon and torenia reveal the diversity in the flavonoid metabolon organization of different plant species

Flavonoid metabolons (weakly-bound multi-enzyme complexes of flavonoid enzymes) are believed to occur in diverse plant species. However, how flavonoid enzymes are organized to form a metabolon is unknown for most plant species. We analyzed the physical interaction partnerships of the flavonoid enzymes from two lamiales plants (snapdragon and torenia) that produce flavones and anthocyanins. In snapdragon, protein-protein interaction assays using yeast and plant systems revealed the following binary interactions: flavone synthase II (FNSII)/chalcone synthase (CHS); FNSII/chalcone isomerase (CHI); FNSII/dihydroflavonol 4-reductase (DFR); CHS/CHI; CHI/DFR; and flavonoid 3'-hydroxylase/CHI. These results along with the subcellular localizations and membrane associations of snapdragon flavonoid enzymes suggested that FNSII serves as a component of the flavonoid metabolon tethered to the endoplasmic reticulum (ER). The observed interaction partnerships and temporal gene expression patterns of flavonoid enzymes in red snapdragon petal cells suggested the flower stage-dependent formation of the flavonoid metabolon, which accounted for the sequential flavone and anthocyanin accumulation patterns therein. We also identified interactions between FNSII and other flavonoid enzymes in torenia, in which the co-suppression of FNSII expression was previously reported to diminish petal anthocyanin contents. The observed physical interactions among flavonoid enzymes of these plant species provided further evidence supporting the long-suspected organization of flavonoid metabolons as enzyme complexes tethered to the ER via cytochrome P450, and illustrated how flavonoid metabolons mediate flower coloration. Moreover, the observed interaction partnerships were distinct from those previously identified in other plant species (Arabidopsis thaliana and soybean), suggesting that the organization of flavonoid metabolons may differ among plant species.

Repeated gains in yellow and anthocyanin pigmentation in flower colour transitions in the Antirrhineae

BACKGROUND AND AIMS

Angiosperms display remarkable diversity in flower colour, implying that transitions between pigmentation phenotypes must have been common. Despite progress in understanding transitions between anthocyanin (blue, purple, pink or red) and unpigmented (white) flowers, little is known about the evolutionary patterns of flower-colour transitions in lineages with both yellow and anthocyanin-pigmented flowers. This study investigates the relative rates of evolutionary transitions between different combinations of yellow- and anthocyanin-pigmentation phenotypes in the tribe Antirrhineae.

METHODS

We surveyed taxonomic literature for data on anthocyanin and yellow floral pigmentation for 369 species across the tribe. We then reconstructed the phylogeny of 169 taxa and used phylogenetic comparative methods to estimate transition rates among pigmentation phenotypes across the phylogeny.

KEY RESULTS

In contrast to previous studies we found a bias towards transitions involving a gain in pigmentation, although transitions to phenotypes with both anthocyanin and yellow taxa are nevertheless extremely rare. Despite the dominance of yellow and anthocyanin-pigmented taxa, transitions between these phenotypes are constrained to move through a white intermediate stage, whereas transitions to double-pigmentation are very rare. The most abundant transitions are between anthocyanin-pigmented and unpigmented flowers, and similarly the most abundant polymorphic taxa were those with anthocyanin-pigmented and unpigmented flowers.

CONCLUSIONS

Our findings show that pigment evolution is limited by the presence of other floral pigments. This interaction between anthocyanin and yellow pigments constrains the breadth of potential floral diversity observed in nature. In particular, they suggest that selection has repeatedly acted to promote the spread of single-pigmented phenotypes across the Antirrhineae phylogeny. Furthermore, the correlation between transition rates and polymorphism suggests that the forces causing and maintaining variance in the short term reflect evolutionary processes on longer time scales.

Synthesis and anti-cancer activity evaluation of new aurone derivatives

In this study, we have synthesized 2-[3- or 4-(2-aryl-2-oxoethoxy)arylidene]benzofuran-3-one derivatives (D1-D38) and evaluated their anti-cancer activities. The final compounds were obtained in multistep synthesis reactions using benzofuranon-3-one derivatives (A1-A4, B) as starting materials which were gained in various synthetic ways. Aurone derivatives (C1-C10) were acquired with the condensation reaction of these starting materials and 3-/4-hydroxybenzaldehyde which were then reacted with α-bromoacetophenones to get final compounds. The anti-cancer activity of the selected compounds was performed by National Cancer Institute (NCI), USA against 60 human tumor cell lines derived from nine neoplastic diseases. Compounds exhibited anti-cancer activity in varying ratios.