A Practical and Economical High-Yielding, Six-Step Sequence Synthesis of a Flavone: Application to the Multigram-Scale Synthesis of Ladanein

Synthetic Studies toward 5,6,7,3',4'-Monomethoxytetrahydroxyflavones: Synthesis of Pedalitin

During the synthetic studies toward 5,6,7,3',4'-monomethoxytetrahydroxyflavones, a concise pedalitin synthesis procedure was achieved. As previously reported, 6-hydroxy-2,3,4-trimethoxyacetophenone was prepared by Friedel-Crafts acylation of 1,4-dihydroxy-2,6-dimethoxybenzene with boron trifluoride diethyl etherate in acetic acid. When aldol condensation of 6-hydroxy-2,3,4-trimethoxyacetophenone 2b with vanillin was performed in basic conditions, it produced 2'-hydroxychalcone 3b, and, surprisingly, along with 3-hydroxyflavone 4 in a considerable amount. We propose that this oxidative cyclization is presumably due to the contribution of a quinone methide, likely to be subjected to aerobic oxidation. The chalcone was then subjected to oxidative cyclization with iodine in dimethyl sulfoxide to afford flavone 5 in good yield. To our delight, serial demethylation of the three methoxy groups at the 5-, 6-, and 3'-positions of 5 proceeded smoothly to produce pedalitin 1, under hydrogen bromide solution (30% in acetic acid). The crystal structures of 3-hydroxyflavone 4 and pedalitin tetraacetate 6 were unambiguously determined by X-ray crystallography.

7-Imidazolyl-substituted 4'-methoxy and 3',4'-dimethoxy-containing polyfluoroflavones as promising antiviral agents

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Synthesis of the new 2-aryl-4-oxo-4H-polyfluorochromen-3-carboxylates as analogs of natural methoxy-containing flavones.

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The alternative flavone-5-hydroxyflavone and flavone-coumarin rearrangements of polyfluoroflavones in basic aqueous acetonitrile medium.

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New 7-(1H-imidazol-1-yl)-substituted polyfluorinated flavones and coumarins.

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Imidazolyl-functionalized flavones as high prospective antiviral agents.

A simple and convenient method for the synthesis of new methyl 2-(4-methoxyphenyl)- and 2-(3,4-dimethoxyphenyl)-4-oxo-4H-polyfluorochromen-3-carboxylates as analogs of natural methoxy-containing flavones is proposed. As a result of their directed modification under basic conditions, 7-imidazolyl-substituted derivatives were obtained. In aqueous-organic medium under basic conditions, 5,6,7,8-tetrafluoro-3-(methoxycarbonyl)flavones were transformed into 6,8-difluoro-5-hydroxy-7-(1H-imidazol-1-yl)-3-(methoxycarbonyl)flavones as a result of flavone-5-hydroxyflavone rearrangement, while 6,7,8-trifluorinated analogs underwent a flavone-coumarin rearrangement to give 6,8-difluoro-3-(hydroxyarylidene)-7-(1H-imidazol-1-yl)coumarins under the same conditions. Acid hydrolysis of methyl polyfluoroflavone-3-carboxylates allowed to obtain 2-aryl-4H-polyfluorochromen-4-ones. Evaluation of the antiviral activity of the synthesized compounds against influenza A (H1N1) and Coxsackie B3 viruses showed that 2-(3,4-dimethoxyphenyl)-5,6,8-trifluoro-7-(1H-imidazol-1-yl)-4H-chromene-4-one has the most promising properties.

Polymethoxylated flavones from Orthosiphon stamineus leaves as antiadhesive compounds against uropathogenic E. coli

Aqueous and acetone extracts of O. stamineus leaves reduce the adhesion of uropathogenic E. coli (UPEC, strain UTI89) to T24 bladder cells significantly (IC₂₅ ~ 524 mg/mL, resp. 40 μg/mL). The acteonic extract had no cytotoxic effects against UPEC in concentrations that inhibited the bacterial adhesion. The extract significantly reduced the gene expression of fimH, fimC, fimD, csgA and focG, which are strongly involved in the formation of bacterial adhesins. The antiadhesive effect was due to the presence of polymethoxylated flavones, enriched in the acetonic extract. Five flavones have been isolated by fast centrifugal partition chromatography, followed by preparative HPLC. Eupatorin, ladanein, salvigenin, sinensetin, 5,6,7,4'-tetramethoxyflavone and 5-hydroxy-6,7,3',4'-tetramethoxyflavone were identified as the main polymethoxylated flavones. With the exception of eupatorin, all of these flavones reduced the bacterial adhesion in a concentration depending manner, indicating that B-ring hydroxylation and methoxylation seems to have a major impact on the antiadhesive activity. In addition, this was confirmed by investigation of the flavones chrysoeriol and diosmetin, which had only very weak antiadhesive activity. From these data, Orthosiphon extracts can be assessed to have a pronounced antiadhesive activity against UPEC, based on a variety of polymethoxylated flavones.

Physicochemical Properties Govern the Activity of Potent Antiviral Flavones

Ladanein (i.e., 5,6,7-trihydroxylated flavone) was demonstrated to act as a powerful virucidal agent toward a broad range of enveloped virus particles. Fe(III) coordination and pH are indeed among the key parameters that might favor both bioactivation of the flavone and consequent host cell entry inhibition. In this present work, the impact of fluorinated groups on the physicochemical and antiviral properties of the flavone was investigated, thus allowing a deeper understanding of the antiviral mode of action. The improved synthesis of ladanein allowed accessing a broad range of analogues, some of them being significantly more active than the former ladanein lead compound. We first determined the acido-basic properties of this homogenous series of compounds and then investigated their electrochemical behavior. Fe(III) coordination properties (stability, spectral behavior, and kinetics) of ladanein and its analogues were then examined (quasiphysiological conditions) and provided key information of their stability and reactivity. Using the determined physicochemical parameters, the critical impact of the iron complexation and medium acidity was confirmed on hepatitis C virus (HCV) particles (pre)treated with ladanein. Finally, a preliminary structure-HCV entry inhibition relationship study evidenced the superior antiviral activity of the ladanein analogues bearing an electron-withdrawing group in para position (FCF ₃ > FOCF ₃ > FFCF ₃ > FF > FOMe) on the B cycle in comparison with the parent ladanein itself.

Naringin-Chalcone Bioflavonoid-Protected Nanocolloids: Mode of Flavonoid Adsorption, a Determinant for Protein Extraction

In order to highlight the applications of bioflavonoids in materials chemistry, naringin and its chalcone form were used in the nanomaterial synthesis to produce flavonoid-conjugated nanomaterials in aqueous phase. Chalcone form proved to be excellent reducing as well as stabilizing agent in the synthesis of monodisperse Au, Ag, and Pd nanoparticles (NPs) of ∼5-15 nm, following in situ reaction conditions where no external reducing or stabilizing agents were used. The mechanism of NP surface adsorption of flavonoid was determined with the help of dynamic light scattering and zeta potential measurements. Surface-adsorbed flavonoids also allowed NPs to easily transfer into the organic phase by using aqueous insoluble ionic liquid. Pd NPs attracted the excessive amount of surface adsorption of both naringin as well as its chalcone form that in turn drove Pd NPs in self-assembled state in comparison to Au or Ag NPs. An amount of surface-adsorbed flavonoids selectively determined the extraction of protein fractions from complex zein corn starch protein solution. Self-assembled Pd NPs with a large amount of surface-adsorbed naringin preferentially extracted zein fraction of higher molar mass, whereas Au and Ag NPs almost equally extracted the zein fractions of lower molar masses.

Bright Side of Lignin Depolymerization: Toward New Platform Chemicals

Lignin, a major component of lignocellulose, is the largest source of aromatic building blocks on the planet and harbors great potential to serve as starting material for the production of biobased products. Despite the initial challenges associated with the robust and irregular structure of lignin, the valorization of this intriguing aromatic biopolymer has come a long way: recently, many creative strategies emerged that deliver defined products via catalytic or biocatalytic depolymerization in good yields. The purpose of this review is to provide insight into these novel approaches and the potential application of such emerging new structures for the synthesis of biobased polymers or pharmacologically active molecules. Existing strategies for functionalization or defunctionalization of lignin-based compounds are also summarized. Following the whole value chain from raw lignocellulose through depolymerization to application whenever possible, specific lignin-based compounds emerge that could be in the future considered as potential lignin-derived platform chemicals.

Iron(iii) coordination properties of ladanein, a flavone lead with a broad-spectrum antiviral activity

The Fe(iii) complexation properties of ladanein, a potent antiviral flavone, and related analogues (negletein and salvigenin), have been studied in solution under quasi-physiological conditions using physico-chemical tools and provided important insights into their stability/reactivity in solution.

Synthesis of plasmodione metabolites and13C-enriched plasmodione as chemical tools for drug metabolism investigation

A 10-step synthesis of the antimalarial lead,¹³C₁₈-enriched plasmodione, and of seven putative metabolites is described.

Copper-catalyzed generation of flavone selenide and thioether derivatives using KSeCN and KSCN via C–H functionalization

Two simple Cu-catalyzed methods using KSeCN and KSCN to construct C–Se and C–S bonds on flavone skeletal structures via C–H functionalization are developed.

A Practical Synthesis of the Flavone, Scutellarein

A practical and economical five-step synthesis of the flavone scutellarein has been achieved in 60% overall yield using the available and cheap 2,6-dimethoxy-1,4-benzoquinone as starting material. The reaction sequence involved reduction to the corresponding quinol, Friedel-Crafts acetylation, Claisen-Schmidt condensation with p-methoxybenzaldehyde, cyclisation and demethylation. The procedure is operationally simple and amenable to scale-up synthesis.