Acid catalyzed stereoselective rearrangement and dimerization of flavenes: synthesis of dependensin

Composition and Biological Activity of Flavonoid-containing Fractions of an Extract from Gratiola officinalis L

INTRODUCTION

Gratiola officinalis L. (hedge hyssop), a medicinal plant of the Scrophulariaceae family, has diuretic, purgative, and vermifuge properties. It is used as a herbal tea to treat chronic gastroenteritis, renal colic, jaundice, and intestinal worms. Previously, we have found that an extract from G. officinalis is nontoxic and has antitumor, antioxidant, antimicrobial, antiinflammatory, anticachexic, and other properties. Our aims in this study were to separate the G. officinalis extract into individual fractions, to identify the most biologically active fractions, and to examine the chemical composition of these fractions and their biological activity toward A498 renal carcinoma cells.

METHODS

The G. officinalis extract was fractionated by reversed-phase high-performance liquid chromatography, and each fraction was tested for antitumor activity. The active fractions were characterized by UV-visible electron spectral analysis, circular dichroism analysis, Fourier transform infrared spectroscopy, high-performance liquid chromatography, electrospray ionization tandem mass spectrometry, and nuclear magnetic resonance spectroscopy.

RESULTS

Two antitumor-active fractions of a flavonoid nature were isolated and chromatographically purified. On the basis of the nuclear magnetic resonance data, the aglycone fragment of the main component of one fraction was found to be structured as 2-(3,4-dimethoxyphenyl)-7-hydroxychroman-4-one, or 3',4'-dimethoxy-7- hydroxyflavanone.

CONCLUSION

The antitumor effect of the most active fraction containing 7-O-glucoside of apigenin, glycoside 7,3'-di-O-luteolin and trace amounts of eupatilin against renal carcinoma A498 cells was manifested in its cytotoxic, cytostatic, apoptotic and autophagosomal activities. In addition, we found 3-(1-2)-glucoside of soyaspogenol B, which is a pentacyclic triterpenoid in the structure.

Aphrodisiac Principles and other Constituents from the Roots of Panax quinguefolium and Panax ginseng

Bioassay-guided fractionation of P. quinquefolium and P. ginseng root extracts afforded six compounds. Among these, two bioactive compounds ginsenoside Re (1) and (20S)-ginsenoside Rg2 (5) exhibiting significant relaxation in rabbit corpus cavernosum with EC50 values of 95.1 and 114.7 μM, respectively. In addition, the phytochemical composition of the water extract of the roots of P. quinquefolium was investigated, and thirty-one compounds were characterized, including four undescribed compounds panajaponol B (18) and panaxjapynes D-F (21-23). Moreover, the spectral characteristics and biosynthetic pathway of Panax triterpene saponins were discussed according to our results and some previous reports.

Effects of Compounds Isolated from Lindera erythrocarpa on Anti-Inflammatory and Anti-Neuroinflammatory Action in BV2 Microglia and RAW264.7 Macrophage

Lindera erythrocarpa contains various constituents such as cyclopentenedione-, flavonoid-, and chalcone-type components. In this study, a novel bi-linderone derivative and 17 known compounds were isolated from the leaves of L. erythrocarpa by using various chromatographic methods. The structures of the components were determined from nuclear magnetic resonance and mass spectrometry data. All isolated compounds were tested for anti-inflammatory and anti-neuroinflammatory activities in lipopolysaccharide (LPS)-induced BV2 and RAW264.7 cells. Some of these compounds showed anti-inflammatory effects by inhibiting the nitric oxide (NO) produced by LPS. In particular, linderaspirone A (16), bi-linderone (17) and novel compound demethoxy-bi-linderone (18) showed significant inhibitory effects on the production of prostaglandin E2 (PGE₂), tumor necrosis factor-α, and interleukin-6. The three compounds also inhibited the expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), which are pro-inflammatory proteins, and the activation of nuclear factor κB (NF-κB). Therefore, linderaspirone A (16), bi-linderone (17), and demethoxy-bi-linderone (18) isolated from the leaves of L. erythrocarpa have therapeutic potential in neuroinflammatory diseases.

Chemoenzymatic Stereoselective Synthesis of trans-Flavan-4-ols via Lipase-Catalyzed Kinetic Resolutions

Flavan-4-ols are a subclass of flavonoids that are present in complex molecules with application in the industrial sector as pigments, antioxidants, or antimitotics, among many others. The most traditional way to achieve their synthesis is from naturally abundant flavanones, asymmetric transfer hydrogenation reactions or bioreduction being well known strategies, while their preparation from racemic flavan-4-ols has been less explored. In this article, we have focused on the synthesis of a series of trans-flavan-4-ols bearing different substitution patterns in the aromatic ring to explore later the potential of lipases as biocatalysts for stereoselective acylation reactions. Therefore, a series of flavanones have been chemically prepared, starting from the corresponding benzaldehydes by aldol condensation with 2′-hydroxyacetophenone in a strongly basic medium, and later transformed into the corresponding racemic trans-flavan-4-ols following a carbonyl reduction, Mitsunobu reaction, and ester deprotection sequence. A screening of lipases and optimization of the reaction conditions for the stereoselective acylation of racemic 2-phenylchroman-4-ol were performed before expanding the best reaction conditions to the kinetic resolution of other 2-arylchroman-4-ols. Interestingly, the combination of AK lipase from Pseudomonas fluorescens as enzyme and vinyl acetate as both acyl donor and solvent allowed the performance of highly asymmetric transformations (E > 200, 50–99% eeS and >99% eeP) under mild reaction conditions (30 °C and 250 rpm).

Polygala tenuifolia-Acori tatarinowii herbal pair as an inspiration for substituted cinnamic α-asaronol esters: Design, synthesis, anticonvulsant activity, and inhibition of lactate dehydrogenase study

Inspired by the traditional Chinese herbal pair of Polygala tenuifolia-Acori Tatarinowii for treating epilepsy, 33 novel substituted cinnamic α-asaronol esters and analogues were designed by Combination of Traditional Chinese Medicine Molecular Chemistry (CTCMMC) strategy, synthesized and tested systematically not only for anticonvulsant activity in three mouse models but also for LDH inhibitory activity. Thereinto, 68-70 and 75 displayed excellent and broad spectra of anticonvulsant activities with modest ability in preventing neuropathic pain, as well as low neurotoxicity. The protective indices of these four compounds compared favorably with stiripentol, lacosamide, carbamazepine and valproic acid. 68-70 exhibited good LDH1 and LDH5 inhibitory activities with noncompetitive inhibition type, and were more potent than stiripentol. Notably, 70, as a representative agent, was also shown as a moderately positive allosteric modulator at human α1β2γ2 GABA_A receptors (EC₅₀ 46.3 ± 7.3 μM). Thus, 68-70 were promising candidates for developing into anti-epileptic drugs, especially for treatment of refractory epilepsies such as Dravet syndrome.

A facile 2H-chromene dimerization through an ortho-quinone methide intermediate catalyzed by a sulfonyl derived MIL-101 MOF

An efficient homo-dimerization of 2H-chromenes was achieved in high yield and diastereoselectivity using a MIL-101–SO₃H MOF catalyst.

Synthesis and Characterization of a Phosphate Prodrug of Isoliquiritigenin

Isoliquiritigenin (1) possesses a variety of biological activities in vitro. However, its poor aqueous solubility limits its use for subsequent in vivo experimentation. In order to enable the use of 1 for in vivo studies without the use of toxic carriers or cosolvents, a phosphate prodrug strategy was implemented relying on the availability of phenol groups in the molecule. In this study, a phosphate group was added to position C-4 of 1, leading to the more water-soluble prodrug 2 and its ammonium salt 3, which possesses increased stability compared to 2. Herein are reported the synthesis, characterization, solubility, and stability of phosphate prodrug 3 in biological medium in comparison to 1, as well as new results on its anti-inflammatory properties in vivo. As designed, the solubility of prodrug 3 was superior to that of the parent natural product 1 (9.6 mg/mL as opposed to 3.9 μg/mL). Prodrug 3 as an ammonium salt was also found to possess excellent stability as a solid and in aqueous solution, as opposed to its phosphoric acid precursor 2.

Bioactive Phytochemicals: Efficient Synthesis of Optically Active Substituted Flav-3-enes and Flav-3-en-3-o-R Derivatives

The structural core of flavene (2-phenyl-2H-chromene) is commonly found in plant flavonoids, which exhibit a wide range of biological activities and diverse pharmacological profiles (e.g., antioxidant and anticancer activities). Flavonoids have attracted significant interest in medicinal and synthetic chemistry. Substituted flav-3-ene 13 was exclusively synthesized by the stereoselective elimination of the O-mesyl moiety on C-3 of 5,7,3′,4′-tetramethoxyflavan-3-mesylate 12 with 1,8-diazabicyclo[5.4.0]undec-7-ene. The reaction of 5,7,3′,4′-tetramethoxyflavan-3-one 15 with ytterbium trifluoromethanesulfonate in methanol afforded a novel 3-O-substituted flav-3-ene derivative (3,5,7,3′,4′-pentamethoxyflav-3-ene) 17. The reduction of 4-(1,3,5-trihydroxybenzene)-5,7,3′,4′-tetra-O-benzylflavan-3-one 19b with hydrogen afforded a new compound: 3-hydroxy-4-(1,3,5-trihydroxybenzene)-5,7,3′,4′-tetrahydroxyflavan-3-en-3-ol 21 in good yield (95%), while the acetylation of 19a and 21 afforded the expected novel flav-3-en-3-acetoxy derivatives 20 (92%) and 22 (90%), respectively.

The comparison of neuroprotective effects of isoliquiritigenin and its Phase I metabolites against glutamate-induced HT22 cell death

It is becoming increasingly important to investigate drug metabolites to evaluate their toxic or preventive effects after administration of the parent compound. In our previous study, isoliquiritigenin isolated from Glycyrrhizae Radix effectively protected mouse-derived hippocampal neuronal cells (HT22) against 5mM glutamate-induced oxidative stress. However, there is little information on the protective effects of the metabolites of isoliquiritigenin on HT22 cells. In this study, isoliquiritigenin and its Phase I metabolites were prepared and their neuroprotective activities on glutamate-treated HT22 cells were compared. The prepared metabolites were liquiritigenin (1), 2',4,4',5'-tetrahydroxychalcone (2), sulfuretin (3), butein (4), davidigenin (5), and cis-6,4'-dihydroxyaurone (6). Among the six metabolites, 4 showed better neuroprotective effects than the parent compound, isoliquiritigenin. Our study suggests that the neuroprotective effect of isoliquiritigenin could be elevated by its active metabolite 4, which is a chalcone containing a catechol group in the B ring.

p-TsOH-promoted synthesis of (E)-6-phenyl-7-styryl-5,6-dihydrodibenzo[b,h][1,6]naphthyridines via cascade intramolecular aza-Michael addition/Friedlander condensation of 2′-aminochalcones in a SDS/H2O system

p-TsOH-promoted one-pot cascade synthesis of novel (E)-6-phenyl-7-styryl-5,6-dihydrodibenzo[b,h][1,6]naphthyridines via homodimerization of 2′-aminochalcones has been developed in a SDS/H₂O system.

Preferentially Cytotoxic Constituents of Andrographis paniculata and their Preferential Cytotoxicity against Human Pancreatic Cancer Cell Lines

In the course of our search for anticancer agents based on a novel anti-austerity strategy, we found that the 70% EtOH extract of the crude drug Andrographis Herba (aerial parts of Andrographis paniculata), used in Japanese Kampo medicines, killed PANC-1 human pancreatic cancer cells preferentially in nutrient-deprived medium (NDM). Phytochemical investigation of the 70% EtOH extract led to the isolation of 21 known compounds consisting of six labdane-type diterpenes (11, 15, 17-19, 21), six flavones (5, 7, 10, 12, 14, 20), three flavanones (2, 6, 16), two sterols (3, 8), a fatty acid (1), a phthalate (4), a triterpene (9), and a monoterpene (13). Among them, 14-deoxy-11,12-didehydroandrographolide (17) displayed the most potent preferential cytotoxicity against PANC-1 and PSN-1 cells with PC50 values of 10.0 μM and 9.27 μM, respectively. Microscopical observation, double staining with ethidium bromide (EB) and acridine orange (AO), and flow cytometry with propidium iodide/annexin V double staining indicated that 14-deoxy-11,12-didehydroandrographolide (17) triggered apoptosis-like cell death in NDM with an amino acids and/or serum-sensitive mode.

In vitro and in vivo synergistic interaction of substituted chalcone derivatives with norfloxacin against methicillin resistant Staphylococcus aureus

The present investigation shows that certain substituted chalcone derivatives diminish the escalation of bacterial cellsviainhibiting bacterial efflux pump and exhibit a synergistic interaction with norfloxacin.

Synthesis and anti-tumor activity of novel aminomethylated derivatives of isoliquiritigenin

A series of new aminomethylated derivatives of isoliquiritigenin was synthesized. The structures of the compounds were confirmed by IR, MS, NMR, 13C-NMR and elemental analyses. Cytotoxic activities of these derivatives towards the human prostatic cell line PC-3, human mammary cancer cell line MCF-7 and human oophoroma cell line HO-8910 in vitro were tested. The IC50 values showed cytotoxic activities of some of these new derivatives were relatively strong. Furthermore, tumor growth inhibition in vivo of aminomethylated derivatives of isoliquiritigenin 15 was superior to that of isoliquritigenin and reached inhibition rates of 71.68%. The detailed synthesis, spectroscopic data, biological and pharmacologicalactivities of the synthesized compounds were provided.

Antioxidant and anti-acetylcholinesterase activities of extracts and secondary metabolites from Acacia cyanophylla

OBJECTIVE

To investigate the antioxidant potential and anti-acetycholinesterase activity of compounds and extracts from Acacia cyanophylla (A. cyanophylla).

METHODS

Three polyphenolic compounds were isolated from ethyl acetate extract of A. cyanophylla flowers. They have been identified as isosalipurposide 1, quercetin 2 and naringenin 3. Their structures were elucidated by extensive spectroscopic methods including 1D and 2D NMR experiments as well as ES-MS. The prepared extracts and the isolated compounds 1-3 were tested for their antioxidant activity using 1'-1'-diphenylpicrylhydrazyl (DPPH) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) scavenging assays and reducing power. They have been also investigated for inhibitory effect against acetylcholinesterase using the microplate assay.

RESULTS

In the DPPH test, the EtOAc extract of flowers exhibited the highest antioxidant effect (67.26 µg/mL). Isosalipurposide 1 showed a significant antiradical power against DPPH (81.9 µg/mL). All extracts showed a dose-dependent acetylcholinesterase inhibition. In terms of the IC50 value, the butanolic extract (16.03 µg/mL) was the most potent sample. Isosalipurposide 1 was found to be active against AChE with an IC50 value of 52.04 µg/mL.

CONCLUSIONS

The results demonstrated the important antioxidant and anti-acetylcholinesterase activity of pure compounds and extracts from A. cyanophylla.

A practical access to highly enantiomerically pure flavanones by catalytic asymmetric transfer hydrogenation

A surprisingly selective, non-enzymatic kinetic resolution of readily available, racemic β-chiral ketones enabled the title process, which was applied to a rapid synthesis of several bioactive flavanones in virtually enantiopure form (see scheme; MOM=methoxymethyl, Ts=p-toluenesulfonyl).

Antiviral phenolic compounds from Arundina gramnifolia

Five new phenolic compounds, gramniphenols C-G (1-5), and eight known compounds (6-13) were isolated from the whole plant of Arundina gramnifolia. Compounds 1, 4, and 5 showed anti-tobacco mosaic virus activity, with IC(50) values of 20.8, 40.8, and 57.7 μM, respectively. Compounds 1-10 were also tested for their anti-HIV-1 activity; compounds 2, 3, and 6 displayed anti-HIV-1 activity with therapeutic index values above 100:1.

Synthesis of polyhydroxylated flavonoids bearing a lipophilic decyl tail as potential therapeutic antioxidants

Antioxidants have potential for the treatment of stroke and neurodegeneration, and chimeric compounds that combine a flavon-3-ol head group related to myricetin and a lipophilic decyl tail are known to protect membranes from oxidative damage at least as well as vitamin E. New flavon-3-ols that are highly hydroxylated in the B ring in ways not found in natural flavon-3-ols and bearing a lipophilic decyl tail have been prepared from trimethoxy- and tetramethoxybenzoic acids accessed by lithiation–carboxylation reactions. Direct enolate acylation was preferred over Baker–Venkataraman rearrangement when there were methoxy groups at both the 2- and the 6-position of the benzoic acid derivatives.

Oxidative Dimerisation of Isoflavones: Synthesis of Kudzuisoflavone A and Related Compounds

Kudzuisoflavone-A was successfully synthesised via oxidative dimerisation of daidzein in the presence of cuprous chloride. Appropriately substituted isoflavones also undergo regioselective oxidative dimerisation when treated with thallium trifluoroacetate to give novel 6′,6′″-biisoflavones in good yield. A rationale for the regioselectivity is proposed.

Antithrombotic phenolic compounds from Glycyrrhiza uralensis

A new coumestan, named glycyrurol, and nine phenolic compounds were isolated from the ethyl acetate extract of the roots and rhizomes of Glycyrrhiza uralensis. Their structures were elucidated based on spectroscopic analysis and literature data, and anticoagulative assay found significant antithrombotic activity of compounds 4, 8 and 10.

Iron-catalyzed rearrangements and cycloaddition reactions of 2H-chromenes

Iron(III) salts catalyze the tandem rearrangement/hetero-Diels-Alder reaction of 2H-chromenes to yield tetrahydrochromeno heterocycles. The process can occur as a homodimerization and cycloaddition process using electron-rich dienophiles. Deuterium labeling and mechanistic studies revealed a hydride shift and ortho-quinone methide cycloaddition reaction pathway.

Reinvestigation of the synthesis of isoliquiritigenin: application of Horner-Wadsworth-Emmons reaction and Claisen-Schmidt condensation

Isoliquiritigenin [ILG, (E)-1] was readily prepared via the Horner-Wadsworth-Emmons reactions using β-ketophosphonates 5a, b. An improved protocol for the synthesis of (E)-1 via the Claisen-Schmidt condensation was also presented.

An Efficient Catalytic Synthesis of Flavanones under Green Conditions

An efficient and “green” catalytic conversion of 2'-hydroxychalcones to flavanones in 15 min in the presence of a simple amino acid and a base at room temperature is reported. Liquiritigenin was also efficiently synthesised under these conditions.

Candenatenins A-F, phenolic compounds from the heartwood of Dalbergia candenatensis

Chemical investigation of the CH2Cl2 extract of the heartwood of Dalbergia candenatensis affored six new phenolic compounds, designated candenatenins A-F (1-6), as well as four known compounds, (2R,3R)-3,5-dihydroxy-7-methoxyflavanone (7), 4-hydroxy-3-methoxy-8,9-methylenedioxypterocarpan (8), nutiducol (9), and sophoraflavanone A (10). The structures of the new compounds were determined by 1D- and 2D-NMR spectroscopic studies as well as by MS analysis. The cytotoxic activities of the isolated compounds are also reported.

Phytochemical analysis of young fustic (Cotinus coggygria heartwood) and identification of isolated colourants in historical textiles

Young fustic (Cotinus coggygria Scop.; Anacardiaceae) has been used as a dyestuff since antiquity. Phytochemical investigation of the methanol extract of the heartwood has led to the isolation and structure elucidation by nuclear magnetic resonance and mass spectrometry (MS) of 3',4',6-trihydroxyaurone (sulfuretin) and 3',4',7-trihydroxyflavonol (fisetin) as well as 3',4',7-trihydroxyflavanol (fustin), 3',4',5,7-tetrahydroxyflavonol (quercetin), 3',4',5,7-tetrahydroxyflavanol (taxifolin), 4',7-dihydroxyflavanol, 3',4',7-trihydroxyflavanone (butin), 4',7-dihydroxyflavanone (liquiritigenin), trans-2',3,4,4'-tetrahydroxychalcone (butein), 4',5,7-trihydroxyflavanone and trans-2',4,4'-trihydroxychalcone (isoliquiritigenin). The isolated compounds were used as reference materials for the development of a high-performance liquid chromatography-diode array detector-MS method, which was then applied to analyse (1) fresh silk samples dyed with young fustic, (2) dyed silk subjected to artificially accelerated light ageing and (3) historical silk micro-samples, extracted from ecclesiastical post-Byzantine garments (fifteenth to eighteenth century), which belong to monasteries of Mount Athos. Sulfuretin and fisetin, which are usually used as markers for the identification of the yellow dye and, for the first time, some of the aforementioned flavonoid components of young fustic were identified in the historical extracts. Furthermore, preliminary experiments suggested that although the amounts of the dye components decrease with light ageing, the relative ratio of fisetin and sulfuretin, after a first step of ageing, seems to be almost unaffected by such degradation processes raised by light. The effect of the latter on the morphology of the dyed silk fibres is briefly investigated by scanning electron microscopy.