Synthesis and biological activities of some new dibenzopyranones and dibenzopyrans: search for potential oestrogen receptor agonists and antagonists

Relevant Developments in the Use of Three-Component Reactions for the Total Synthesis of Natural Products. The last 15 Years

Multicomponent reactions (MCRs) offer a highly useful and valuable strategy that can fulfill an important role in synthesizing complex polysubstituted compounds, by simplifying otherwise long sequences and increasing their efficiency. The total synthesis of selected natural products employing three-component reactions as their common strategic MCR approach, is reviewed on a case-by-case basis with selected targets conquered during the last 15 years. The revision includes detailed descriptions of the selected successful sequences; relevant information on the isolation, and bioactivity of the different natural targets is also briefly provided.

Anti-proliferative, Morphological and Molecular Docking Studies of New Thiophene Derivatives and their Strategy in Ionic Liquids Immobilized Reactions

BACKGROUND

A number of research were conducted on the pyran and thiophene derivatives, which were attributed to have a wide range of biological activities, including anti-plasmodial, as well as acting as caspase, hepatitis C and cancer inhibitors.

OBJECTIVE

The multicomponent reactions of the 5-acetyl-2-amino-4-(phenylamino)-thiophene-3-carbonitrile produced biologically active target molecules like pyran and their fused derivatives. Comparison between regular catalytic multi-component reactions and solvent-free ionic liquids immobilized multicomponent was studied.

METHODS

The multicomponent reactions in this work were carried out not only under the reflux conditions using triethylamine as a catalyst but also in solvent-free ionic liquids immobilized magnetic nanoparticles (MNPs) catalysts.

RESULTS

Through this work, thirty-one new compounds were synthesized and characterized and were evaluated toward the six cancer cell lines, namely A549, HT-29, MKN-45, U87MG, and SMMC-7721 and H460. The most active compounds were further screened toward seventeen cancer cell lines classified according to the disease. In addition, the effect of compound 11e on the A549 cell line was selected to make further morphological changes in the cell line. The Molecular docking studies of 11e and 11f were carried and promising results were obtained.

CONCLUSION

The synthesis of heterocyclic compounds derived from thiophene derivatives has been receiving significant attention. After a detailed optimizing study, it has been found that the solvent-free ionic liquids immobilized multi-component syntheses afforded a high yield of compounds, opening a greener procedure for this synthetically relevant transformation. Many of the synthesized compounds can be considered anticancer agents, enhancing further studies.

Efficient Protocol for Novel Hybrid Pyrimidines Synthesis: Antiproliferative Activity, DFT Analyses, and Molecular Docking Studies

An efficient, microwave/ultrasound-irradiated synthesis of novel chromenopyrimidines has been established. 2-Amino-5-oxo-4-(thiophen-2-yl)-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (1) underwent cyclization reactions with various assorted reagents under sustainable conditions to afford a family of fused pyrimidine derivatives. The proposed structures of the designed fused pyrimidines were confirmed by several spectral techniques. Moreover, the targeted pyrimidines were estimated for their in vitro cytotoxic activities toward three carcinoma cell lines: breast (MCF7), hepatocyte (HepG2), and lung (A549) cancer cell lines, as well as one noncancerous cell line (MCF-10A). Structure-activity relationship (SAR) analyses revealed that derivatives 3 and 7 exhibited the highest potency in inhibiting the growth of cancer cells tested in vitro. Particularly, 3-amino-4-imino-5-(thiophen-2-yl)-3,4,5,7,8,9-hexahydro-6H-chromeno[2,3-d]pyrimidin-6-one (3) displayed a robust impact with IC50 values ranging from 2.02 to 1.61 μM. Interestingly, compound 3 was observed to have low cytotoxicity toward noncancerous cell (MCF-10A) compared to the standard drug (Doxorubicin). Further, quantum chemical computations of the designed molecules utilizing density functional theory (DFT) were conducted and shown to be compatible with the observed antiproliferative properties. Thorough docking investigations revealed that the assembled compounds possess exceptionally low binding energies toward our three selected proteins: 4b3z-Lung, HepG2-2JW2, and 6ENV-MCV-7. Based on these intriguing results, compound 3 could be further evaluated for preclinical screening, potentially paving the way for its utilization as a promising cancer treatment.

Exploration of Novel Urolithin C Derivatives as Non-Competitive Inhibitors of Liver Pyruvate Kinase

The inhibition of liver pyruvate kinase could be beneficial to halt or reverse non-alcoholic fatty liver disease (NAFLD), a progressive accumulation of fat in the liver that can lead eventually to cirrhosis. Recently, urolithin C has been reported as a new scaffold for the development of allosteric inhibitors of liver pyruvate kinase (PKL). In this work, a comprehensive structure-activity analysis of urolithin C was carried out. More than 50 analogues were synthesized and tested regarding the chemical features responsible for the desired activity. These data could pave the way to the development of more potent and selective PKL allosteric inhibitors.

A Novel Streptococcus thermophilus FUA329 Isolated from Human Breast Milk Capable of Producing Urolithin A from Ellagic Acid

Urolithin A, a metabolite of ellagic acid, has many beneficial biological activities for people. Strains capable of producing urolithin A from ellagic acid have the hope of becoming the next-generation probiotics. However, only a few species of these strains have been reported. In this study, FUA329, a strain capable of converting ellagic acid to urolithin A in vitro, was isolated from the breast milk of healthy Chinese women. The results of morphological observation, physiological and biochemical tests, and 16S rRNA gene sequence analysis confirmed that the strain FUA329 was Streptococcus thermophilus. In addition, the S. thermophilus FUA329 growth phase is consistent with the degradation of ellagic acid, and urolithin A was produced in the stationary phase, with a maximum concentration of 7.38 μM at 50 h. The corresponding conversion efficiency of urolithin A from ellagic acid was 82%. In summary, S. thermophilus FUA329, a novel urolithin A-producing bacterium, would be useful for the industrial production of urolithin A and may be developed as a next-generation probiotic.

Novel Regioselective Synthesis of Urolithin Glucuronides─Human Gut Microbiota Cometabolites of Ellagitannins and Ellagic Acid

Urolithins (dibenzo-pyran-[b,d]-6 one derivatives) are human gut microbiota metabolites produced from the natural food antioxidant ellagic acid. Urolithins are better absorbed than ellagic acid and demonstrate biological activities that suggest that they are responsible for the health effects observed after consuming ellagitannin- and ellagic acid-containing foods. Urolithins occur in the systemic circulation as glucuronide conjugates following phase II metabolism. These phase II conjugates are essential for testing the urolithin mechanisms of action in human cell line bioassays. Urolithin glucuronides are not commercially available, and their biosynthesis leads to mixtures of regional isomers. This study describes a novel and regioselective synthesis of urolithin A (3,8-dihydroxy urolithin) 3- and 8-glucuronides and isourolithin A (3,9-dihydroxy urolithin) 3- and 9-glucuronides. The metabolites were characterized using ¹H and ¹³C NMR spectroscopy and UV spectrophotometry. The presence of these metabolites in human subjects belonging to different urolithin metabotypes was also investigated.

Ellagic acid and intestinal microflora metabolite urolithin A: A review on its sources, metabolic distribution, health benefits, and biotransformation

Foods rich in ellagic tannins are first hydrolyzed into ellagic acid in the stomach and small intestine, and then converted into urolithins with high bioavailability by the intestinal flora. Urolithin has beneficially biological effects, it can induce adipocyte browning, improve cholesterol metabolism, inhibit graft tumor growth, relieve inflammation, and downregulate neuronal amyloid protein formation via the β3-AR/PKA/p38MAPK, ERK/AMPKα/SREBP1, PI3K/AKT/mTOR signaling pathways, and TLR4, AHR receptors. But differences have been reported in urolithin production capacity among different individuals. Thus, it is of great significance to explore the biological functions of urolithin, screen the strains responsible for biotransformation of urolithin, and explore the corresponding functional genes. Tannin acyl hydrolase can hydrolyze tannins into ellagic acid, and the genera Gordonibacter and Ellagibacter can metabolize ellagic acid into urolithins. Therefore, application of "single bacterium", "single bacterium + enzyme", and "microflora" can achieve biotransformation of urolithin A. In this review, the source and metabolic pathway of ellagic tannins, and the mechanisms of the biological function of a metabolite, urolithin A, are discussed. The current strategies of biotransformation to obtain urolithin A are expounded to provide ideas for further studies on the relationship between urolithin and human health.

A straightforward synthesis of functionalized 6H-benzo[c]chromenes from 3-alkenyl chromenes by intermolecular Diels-Alder/aromatization sequence

A new and metal-free approach to the synthesis of substituted 6H-benzo[c]chromenes has been developed. This three-step synthetic sequence starts from variously substituted salicylaldehydes and α,β-unsaturated carbonyl compounds to form the chromene core. The de novo ring-forming key step is based on a highly regioselective intermolecular Diels-Alder cycloaddition between 3-vinyl-2H-chromenes and methyl propiolate, followed by oxidative aromatization of the cyclohexadiene cycloadduct intermediate to obtain the final products in good yields (up to 94% over two steps). A modular and divergent design was followed, including a multicomponent reaction, to maximize the scaffold diversity obtained from our approach. The mechanism, investigated by DFT calculations, was confirmed to be concerted through a slightly asynchronous transition state. Energetic analysis of the transition states which have been found confirmed the experimental results in terms of regioselectivity and reactivity tendencies.

Urolithin and Reduced Urolithin Derivatives as Potent Inhibitors of Tyrosinase and Melanogenesis: Importance of the 4-Substituted Resorcinol Moiety

We previously reported (E)-β-phenyl-α,β-unsaturated carbonyl scaffold ((E)-PUSC) played an important role in showing high tyrosinase inhibitory activity and that derivatives with a 4-substituted resorcinol moiety as the β-phenyl group of the scaffold resulted in the greatest tyrosinase inhibitory activity. To examine whether the 4-substituted resorcinol moiety could impart tyrosinase inhibitory activity in the absence of the α,β-unsaturated carbonyl moiety of the (E)-PUSC scaffold, 10 urolithin derivatives were synthesized. To obtain more candidate samples, the lactone ring in synthesized urolithins was reduced to produce nine reduced urolithins. Compounds 1c (IC₅₀ = 18.09 ± 0.25 μM), 1h (IC₅₀ = 4.14 ± 0.10 μM), and 2a (IC₅₀ = 15.69 ± 0.40 μM) had greater mushroom tyrosinase-inhibitory activities than kojic acid (KA) (IC₅₀ = 48.62 ± 3.38 μM). The SAR results suggest that the 4-substituted resorcinol motif makes an important contribution to tyrosinase inhibition. To investigate whether these compounds bind to human tyrosinase, a human tyrosinase homology model was developed. Docking simulations with mushroom and human tyrosinases showed that 1c, 1h, and 2a bind to the active site of both tyrosinases with higher binding affinities than KA. Pharmacophore analyses showed that two hydroxyl groups of the 4-substituted resorcinol entity act as hydrogen bond donors in both mushroom and human tyrosinases. Kinetic analyses indicated that these compounds were all competitive inhibitors. Compound 2a inhibited cellular tyrosinase activity and melanogenesis in α-MSH plus IBMX-stimulated B16F10 melanoma cells more strongly than KA. These results suggest that 2a is a promising candidate for the treatment of skin pigment disorders, and show the 4-substituted resorcinol entity importantly contributes to tyrosinase inhibition.

4-Chloro-3-formylcoumarin as a multifaceted building block for the development of various bio-active substituted and fused coumarin heterocycles: a brief review

This review presents the diverse synthesis of 3,4-substituted coumarins and 5-, 6- and 7-membered ring fused coumarins using 4-chloro-3-formylcoumarin as the precursor via classical reactions including metal-catalyzed and green reaction protocols.

A carboxylate-assisted amination/unactivated C(sp2)–H arylation reaction via a palladium/norbornene cooperative catalysis

A carboxylate-assisted palladium-catalysed Catellani reaction, which is compatible with ortho-amination and unactivated C(sp²)–H arylation, synthesized a series of 1-amino substituted dihydrophenanthridines, phenanthridines and 6H-benzo[c]chromenes.

BPO-promoted direct oxidative C-H functionalization of unactivated alkanes into 6-alkyl-6H-benzo[c]chromenes under transition-metal-free conditions

A simple and efficient BPO-promoted free radical-based cascade reaction of biaryl vinyl ethers with easily available unactivated alkanes has been developed. A series of 6-alkyl-6H-benzo[c]chromenes have been successfully obtained in moderate to high yields under transition-metal-free conditions. This method can also be utilized to synthesize 6-alkyl-6H-benzo[c]thiochromenes from the corresponding biaryl vinyl thioethers.

Crystal structure of 3,3-dimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-dione, C15H14O3

C15H14O3, monoclinic, P21/c (no. 14), a = 9.0972(11) Å, b = 11.1576(14) Å, c = 12.5933(16) Å, β = 105.368(1)°, V = 1232.6(3) Å3, Z = 4, R gt(F) = 0.0393, wR ref(F 2) = 0.1190, T = 296 K.

Urolithin C, a gut metabolite of ellagic acid, induces apoptosis in PC12 cells through a mitochondria-mediated pathway

Urolithin C includes apoptosis in PC12 cells through a mitochondria-mediated pathway.

Differences in Metabolism of Ellagitannins by Human Gut Microbiota ex Vivo Cultures

Ellagitannin-rich plant materials are used as popular remedies in the treatment of various inflammatory diseases. Urolithins are gut microbiota metabolites of ellagitannins and are considered responsible for in vivo health effects. Various natural products have been studied that are known sources of urolithins. However, few studies have focused on the metabolism of ellagitannin molecules. The aim of the study was to examine the metabolic fate of select ellagitannins using ex vivo cultures of human gut microbiota. Fifteen monomeric and dimeric ellagitannins, 1-O-galloyl-4,6-(S)-HHDP-β-d-glucose (2), pedunculagin (3), potentillin (4), casuarictin (5), coriariin B (6), vescalagin (7), castalagin (8), stachyurin (9), casuarinin (10), stenophyllinin A (11), stenophyllanin A (12), salicarinin A (13), gemin A (14), agrimoniin (15), and oenothein B (16), and ellagic acid (1) were studied. The formation of the metabolites in ex vivo human microbiota cultures was monitored using UHPLC-DAD-MS/MS. Ellagitannins possessing hexahydroxydiphenoyl moieties were metabolized to 6H-dibenzo[b,d]pyran-6-one derivatives, i.e., urolithins. The observed differences in amounts of produced urolithins indicated that the individual microbiota composition and type of ingested ellagitannins could determine the rate of urolithin production. When the oral ingestion of natural products containing ellagitannins with hexahydroxydiphenoyl groups is considered, the formation of urolithins and their bioactivity should be addressed.

One-pot synthesis of functionalized benzo[c]coumarins and their precursors via the reaction of 2-(polyfluoroalkyl)chromones with 4-alkyl-3-cyanocoumarins

2-(Polyfluoroalkyl)chromones react with 4-alkyl-3-cyanocoumarins in dichloromethane in the presence of triethylamine to give a wide variety of functionalized benzo[c]coumarin derivatives in good yields.

An advanced and novel one-pot synthetic method for diverse benzo[c]chromen-6-ones by transition-metal free mild base-promoted domino reactions of substituted 2-hydroxychalcones with β-ketoesters and its application to polysubstituted terphenyls

Novel one-pot syntheses of a variety of benzo[c]chromen-6-one derivatives were accomplished by Cs₂CO₃-promoted reactions of 2-hydroxychalcones.

3,4-Di-hydro-1H-benzo[c]chromene-1,6(2H)-dione

In the title compound, C₁₃H₁₀O₃, the pyran­one and benzene rings are almost coplanar, making a dihedral angle of 1.9 (1)°. The cyclo­hexenone ring adopts an envelope conformation, with a methyl­ene C atom located at the flap and displaced by 0.639 (3) Å from the mean plane of the other five atoms. In the crystal, pairs of weak C—H⋯π inter­actions occur between inversion-related mol­ecules.

Synthesis of 6H-dibenzo[b,d]pyran-6-ones using the inverse electron demand Diels-Alder reaction

A set of coumarin-fused electron-deficient 1,3-dienes was synthesized, which differ in the nature of the electron-withdrawing group (EWG) at the terminus of the diene unit and (when EWG = CO(2)Me) the nature and position of substituents. These dienes reacted with the enamine derived from cyclopentanone and pyrrolidine to afford the corresponding cyclopenteno-fused 6H-dibenzo[b,d]pyran-6-ones, most likely via a domino inverse electron demand Diels-Alder (IEDDA)/elimination/transfer hydrogenation sequence. The parent diene (EWG = CO(2)Me, no substituents) was reacted with a range of electron-rich dienophiles (mostly enamines) to afford the corresponding 6H-dibenzo[b,d]pyran-6-ones or their nondehydrogenated precursors, which were aromatized upon treatment with a suitable oxidant. The enamines could either be synthesized prior to the reaction or generated in situ. The syntheses of 30 dibenzopyranones are reported.

Urolithin as a converging scaffold linking ellagic acid and coumarin analogues: design of potent protein kinase CK2 inhibitors

Casein kinase 2 (CK2) is a ubiquitous, essential, and highly pleiotropic protein kinase; its abnormally high constitutive activity is suspected to underlie its pathogenic potential in neoplasia and other relevant diseases. Previously, using different in silico screening approaches, two potent and selective CK2 inhibitors were identified by our group: ellagic acid, a naturally occurring tannic acid derivative (K(i)=20 nM) and 3,8-dibromo-7-hydroxy-4-methylchromen-2-one (DBC, K(i)=60 nM). Comparing the crystallographic binding modes of both ellagic acid and DBC, an X-ray structure-driven merging approach was taken to design novel CK2 inhibitors with improved target affinity. A urolithin moiety is proposed as a possible bridging scaffold between the two known CK2 inhibitors, ellagic acid and DBC. Optimization of urolithin A as the bridging moiety led to the identification of 4-bromo-3,8-dihydroxy-benzo[c]chromen-6-one as a novel, potent and selective CK2 inhibitor, which shows a K(i) value of 7 nM against the protein kinase, representing a significant improvement in affinity for the target compared with the two parent fragments.

Anti-implantation effect of 2-[piperidinoethoxyphenyl]-3-[4-hydroxyphenyl]-2H-benzo(b)pyran, a potent antiestrogenic agent in rats

OBJECTIVE

To investigate the anti-implantation effect and hormonal profile of 2-[piperidinoethoxyphenyl]-3-[4-hydroxyphenyl]-2H-benzo(b)pyran (K-1) in rats.

DESIGN

In vivo assays for anti-implantation activity were performed in pregnant rats. Assays for estrogenicity/antiesrogenicity were performed in immature ovariectomized female rats. In vitro competitive binding of K-1 to human recombinant ERα, transient transfection assay using ERE-luciferase reporter, and alkaline phosphatase (ALP) activity as a measure of estrogenicity and/antiestrogenicity in human endometrial carcinoma cells were performed.

SETTING

Research laboratory.

ANIMAL(S)

Adult female rats for anti-implantation activity, immature ovariectomized female rats, and immature castrated/intact male rats.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Number of implantations, uterine growth, luciferase reporter activity, ER binding affinity, and ALP activity.

RESULT(S)

Compound K-1 given orally for 1-7 days post coitum at the dose of 100 μg/kg body weight prevented pregnancy in 100% of rats. K-1 was a potent antiestrogenic, and at 50 μg/kg, it could inhibit the effect of 1 μg E(2) in immature rats. Compound was devoid of uterotrophic, androgenic, or antigonadotropic activity. A high affinity binding to ERα was displayed by K-1, with a relative binding affinity of 5% of E(2). In human endometrial carcinoma cells, K-1 did not induce ERα-mediated transcriptional activation that is measured as luciferase reporter activity. K-1 antagonized the E-induced transcriptional activation significantly. K-1 also antagonized E-induced ALP activity in human endometrial cells.

CONCLUSION(S)

K-1 appeared to exert its antifertility action by virtue of its strong antiestrogenic activity.

Identification of urinary and intestinal bacterial metabolites of ellagitannin geraniin in rats

Hydrolyzable tannins, including ellagitannins, occur in foods such as berries and nuts. Various biological activities, including antioxidant, antiviral, and antitumor activities, have been noted and reported for ellagitannins, but the absorption and metabolism of purified ellagitannins are poorly understood. We describe herein the characterization of urinary and intestinal microbial metabolites in rats after the ingestion of ellagitannins. Urine samples were collected after oral administration of ellagitannins such as geraniin ( 1), corilagin ( 2), and their related polyphenols. The suspension of rat intestinal microflora was anaerobically incubated with ellagitannins. Each sample was separated by column chromatography and/or preparative HPLC to give seven metabolites, M1- M7. The structures of these metabolites were determined on the basis of spectroscopic data and chemical evidence. These compounds, except for M1, were characterized as ellagitannin metabolites for the first time. Furthermore, among four major metabolites ( M1- M4) in urine, M2 showed an antioxidant activity comparable to intact geraniin and related polyphenols.

Domino Reactions of 1,3-Bis-Silyl Enol Ethers with Benzopyrylium Triflates: Efficient Synthesis of Fluorescent 6H-Benzo[c]chromen-6-ones, Dibenzo[c,d]chromen-6-ones, and 2,3-Dihydro-1H-4,6-dioxachrysen-5-ones

The condensation of 1,3-bis-silyl enol ethers with benzopyrylium triflates, generated in situ by the reaction of chromones with Me3SiOTf, afforded functionalized 2,3-dihydrobenzopyrans; treatment of the latter with NEt3 or BBr3 resulted in a domino retro-Michael-aldol-lactonization reaction and the formation of a variety of 7-hydroxy-6H-benzo[c]chromen-6-ones. The hydroxy group was functionalized by using Suzuki cross-coupling reactions. The methodology reported was applied to the synthesis of the natural product autumnariol and a new fluorescence dye, which exhibits promising optical properties. 2,3-Dihydro-1H-4,6-dioxachrysen-5-ones were prepared by condensation of chromones with 1,3-bis-silyl enol ethers containing a remote chloride group, domino retro-Michael-aldol-lactonization, and an intramolecular Williamson reaction.