Phloroglucinol compounds of natural origin

Polycyclic Polyprenylated Acylphloroglucinol Congeners Possessing Diverse Structures from Hypericum henryi

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a class of hybrid natural products sharing the mevalonate/methylerythritol phosphate and polyketide biosynthetic pathways and showing considerable structural and bioactive diversity. In a systematic phytochemical investigation of Hypericum henryi, 40 PPAP-type derivatives, including the new compounds hyphenrones G-Q, were obtained. These compounds represent 12 different structural types, including four unusual skeletons exemplified by 5, 8, 10, and 17. The 12 different core structures found are explicable in terms of their biosynthetic origin. The structure of a known PPAP, perforatumone, was revised to hyphenrone A (5) by NMR spectroscopic and biomimetic synthesis methods. Several compounds exhibited inhibitory activities against acetylcholinesterase and human tumor cell lines. This study deals with the structural diversity, function, and biogenesis of natural PPAPs.

Ion tree-based structure elucidation of acetophenone dimers (AtA) from Acronychia pedunculata and their identification in extracts by liquid chromatography electrospray ionization LTQ-Orbitrap mass spectrometry

Acronychia-type acetophenones (AtA) is a chemical group of compounds of important structural and biological interest, abundant in Acronychia species. However, there are no data available for their characterization using mass spectrometry. In the current work, AtA have been investigated by multistage high resolution mass spectrometry and both electrospray ionization and atmospheric pressure chemical ionization, in positive and negative mode, were utilized for their structure elucidation and identification. The analysis of AtA using a linear ion trap-Orbitrap analyzer enabled the structural determination of key fragment ions and cleavages, which can be used for the structural characterization thereof. A systematic nomenclature based on protonated and deprotonated fragment ions under collision-induced dissociation conditions and decision trees for the structural determination of AtA are proposed. Furthermore, taking advantage of the characteristic fragmentation patterns, a selective Ultra High Performance Liquid Chromatography Electrospray Ionization multistage Mass Spectrometry (UHPLC-ESI(-)-MS(n)) method was developed and successfully applied for the dereplication of known AtA and the identification of potentially new ones in Acronychia extracts. Despite the structure similarity and the presence of isomers, accurate characterization of known and unknown AtA derivatives was possible.

Prenylated benzophenones from Triadenum japonicum

Six new prenylated benzophenones, (-)-nemorosonol (1) and trijapins A-E (2-6), were isolated from the aerial parts of Triadenum japonicum. (-)-Nemorosonol (1) and trijapins A-C (2-4) have a common tricyclo[4.3.1.0(3,7)]decane skeleton, while 1 is an enantiomer of (+)-nemorosonol previously isolated from Clusia nemorosa. The absolute configuration of (-)-nemorosonol (1) was assigned by ECD spectroscopy. Trijapins A-C (2-4) are analogues of 1 possessing an additional tetrahydrofuran ring. Trijapins D (5) and E (6) are prenylated benzophenones with a 1,2-dioxane moiety and a hydroperoxy group, respectively. (-)-Nemorosonol (1) exhibited antimicrobial activity against Escherichia coli (MIC, 8 μg/mL), Staphylococcus aureus (MIC, 16 μg/mL), Bacillus subtilis (MIC, 16 μg/mL), Micrococcus luteus (MIC, 32 μg/mL), Aspergillus niger (IC50, 16 μg/mL), Trichophyton mentagrophytes (IC50, 8 μg/mL), and Candida albicans (IC50, 32 μg/mL), while trijapin D (5) showed antimicrobial activity against C. albicans (IC50, 8 μg/mL).

Hypersubones A and B, new polycyclic acylphloroglucinols with intriguing adamantane type cores from Hypericum subsessile

Hypersubones A and B (1, 2), two adamantane type polycyclic polyprenylated acylphloroglucinols possessing an unprecedented seco-adamantane architecture and a tetracyclo-[6.3.1.1(3,10).0(4,8)]-tridecane core combined with a peroxide ring, respectively, were isolated from Hypericum subsessile together with three analogues (3-5). Their structures were determined by extensive NMR spectroscopic analysis, ECD calculations, and single-crystal X-ray diffraction. Compound 2 exhibited significant cytotoxicities against four human cancer lines in vitro (IC50 0.07-7.52 μM).

Brown algae phlorotannins enhance the tumoricidal effect of cisplatin and ameliorate cisplatin nephrotoxicity

OBJECTIVE

The clinical application of cisplatin is limited due to its drug resistance and side effects. We investigated the effect of a phlorotannin-rich extract from the edible brown alga Ecklonia cava (PREC) and its major phlorotannin (dieckol) on cisplatin responsiveness and side effects.

METHODS

The A2780 and SKOV3 ovarian cancer cell lines and the SKOV3-bearing mouse model were used. The MTT assay was applied to assess cell viability, and the annexin V assay was employed for apoptosis analysis. Reactive oxygen species (ROS) production and protein expression were assessed by H2DCFDA staining and Western blotting, respectively.

RESULTS

We found that PREC enhanced the tumor growth-inhibitory effect of cisplatin and diminished cisplatin-induced nephrotoxicity and weight loss in SKOV3-bearing mice. PREC augmented cisplatin-induced apoptosis by activating caspases in SKOV3 and A2780 ovarian cancer cells. In addition, a combination of PREC and cisplatin-induced ovarian cancer cell apoptosis by downregulating the Akt and NFκB pathways. We further demonstrated that PREC increased intracellular ROS and that antioxidants significantly attenuated Akt-NFκB activation and apoptosis in ovarian cancer cells. In contrast, PREC inhibited cisplatin-induced ROS production and cell death in normal HEK293 kidney cells. Dieckol, a major compound in PREC, significantly enhanced the inhibition of tumor growth by cisplatin with less weight loss and kidney damage in a mouse model.

CONCLUSION

These data suggest that brown algae phlorotannins may improve the efficacy of platinum drugs for ovarian cancer by enhancing cancer cell apoptosis via the ROS/Akt/NFκB pathway and reduce nephrotoxicity by protecting against normal kidney cell damage.

Synthesis and P-glycoprotein induction activity of colupulone analogs

A diprenylated acylphloroglucinol was identified as a potent P-gp inducer and showing ability to increase amyloid-beta transport across BBB, thus it is a potential anti-Alzheimer lead compound.

Calliviminones C–H: six new hetero- and carbon-Diels–Alder adducts with unusual skeletons from the fruits of Callistemon viminalis

Calliviminones C–H (1–6), six novel Diels–Alder adducts of a polymethylated phloroglucinol derivative and acyclic monoterpene (myrcene), were isolated from the fruits of Callistemon viminalis.

8,8'-Bieckol, isolated from edible brown algae, exerts its anti-inflammatory effects through inhibition of NF-κB signaling and ROS production in LPS-stimulated macrophages

Ecklonia cava (E. cava) is an abundant brown alga that contains high levels of phlorotannins, which are unique marine polyphenolic compounds. It has been suggested that E. cava phlorotannins exert anti-inflammatory effects. However, the anti-inflammatory effects and underlying molecular mechanism exerted by 8,8'-bieckol isolated from E. cava have not been reported. Thus, in this study, we examined the anti-inflammatory effects of 8,8'-bieckol on lipopolysaccharide (LPS)-stimulated primary macrophages and RAW 264.7 macrophages. We found that 8,8'-bieckol suppressed key inflammatory mediator [i.e., nitric oxide (NO) and prostaglandin E2 (PGE2)] production in both primary and RAW 264.7 macrophages. 8,8'-Bieckol inhibited NO by suppressing LPS-induced expression of inducible nitric oxide synthase (iNOS) at the mRNA and protein levels in primary macrophages and RAW 264.7 cells. In addition, 8,8'-bieckol decreased the production and mRNA expression of the inflammatory cytokine interleukin-6 (IL-6), but not tumor necrosis factor (TNF)-α, in RAW 264.7 cells. Moreover, 8,8'-bieckol treatment diminished transactivation of nuclear factor-kappa B (NF-κB) and nuclear translocation of the NF-κB p65 subunit and suppressed LPS-induced intracellular reactive oxygen species (ROS) production in macrophages. Furthermore, 8,8'-bieckol markedly reduced mortality in LPS-induced septic mice. Taken together, these data indicate that the anti-inflammatory properties of 8,8'-bieckol are associated with the suppression of NO, PGE2, and IL-6 via negative regulation of the NF-κB pathway and ROS production in LPS-stimulated RAW 264.7 cells. Moreover, 8,8'-bieckol protects mice from endotoxin shock.

A multitasking vanadium-dependent chloroperoxidase as an inspiration for the chemical synthesis of the merochlorins

The vanadium-dependent chloroperoxidase Mcl24 was discovered to mediate a complex series of unprecedented transformations in the biosynthesis of the merochlorin meroterpenoid antibiotics. In particular, a site-selective naphthol chlorination is followed by an oxidative dearomatization/terpene cyclization sequence to build up the stereochemically complex carbon framework of the merochlorins in one step. Inspired by the enzyme reactivity, a chemical chlorination protocol paralleling the biocatalytic process was developed. These chemical studies led to the identification of previously overlooked merochlorin natural products.

Padina arborescens extract protects high glucose-induced apoptosis in pancreatic β cells by reducing oxidative stress

BACKGROUND/OBJECTIVES

This study investigated whether Padina arborescens extract (PAE) protects INS-1 pancreatic β cells against glucotoxicity-induced apoptosis.

MATERIALS/METHODS

Assays, including cell viability, lipid peroxidation, generation of intracellular ROS, NO production, antioxidant enzyme activity and insulin secretion, were conducted. The expressions of Bax, Bcl-2, and caspase-3 proteins in INS-1 cells were evaluated by western blot analysis, and apoptosis/necrosis induced by high glucose was determined by analysis of FITC-Annexin V/PI staining.

RESULTS

Treatment with high concentrations of glucose induced INS-1 cell death, but PAE at concentrations of 25, 50 or 100 µg/ml significantly increased cell viability. The treatment with PAE dose dependently reduced the lipid peroxidation and increased the activities of antioxidant enzymes reduced by 30 mM glucose, while intracellular ROS levels increased under conditions of 30 mM glucose. PAE treatment improved the secretory responsiveness following stimulation with glucose. The results also demonstrated that glucotoxicity-induced apoptosis is associated with modulation of the Bax/Bcl-2 ratio. When INS-1 cells were stained with Annexin V/PI, we found that PAE reduced apoptosis by glucotoxicity.

CONCLUSIONS

In conclusion, the present study indicates that PAE protects against high glucose-induced apoptosis in pancreatic β cells by reducing oxidative stress.

Anti-HIV-1 activity of phlorotannin derivative 8,4‴-dieckol from Korean brown alga Ecklonia cava

8,4‴-dieckol is a natural product which has been isolated from brown alga, Ecklonia cava. This polyphenolic compound is a phlorotannin derivative with a broad range of bioactivities. Its inhibitory activity on human immunodeficiency virus type-1 (HIV-1) was tested and the results indicated that 8,4‴-dieckol inhibited HIV-1 induced syncytia formation, lytic effects, and viral p24 antigen production at noncytotoxic concentrations. Furthermore, it was found that 8,4‴-dieckol selectively inhibited the activity of HIV-1 reverse trancriptase (RT) enzyme with 91% inhibition ratio at the concentration of 50 μM. HIV-1 entry was also inhibited by 8,4‴-dieckol. According to data from this study, 8,4‴-dieckol is an effective compound against HIV-1 with high potential for further studies. These results suggest that it might be used as a drug candidate for the development of new generation therapeutic agents, although further studies on the mechanism of inhibition should be addressed.

Antimicrobial prenylated benzoylphloroglucinol derivatives and xanthones from the leaves of Garcinia goudotiana

Bioassay-guided fractionation using antimicrobial assay of the crude acetonic extract of Garcinia goudotiana leaves and of its five partitions led to the isolation of two new prenylated benzoylphloroglucinol derivatives, goudotianone 1 (1) and goudotianone 2 (2), in addition to two known compounds including one xanthone, 1,3,7-trihydroxy-2-isoprenylxanthone (3), and one triterpenoid, friedelin (4). Their structures were elucidated on the basis of different spectroscopic methods, including extensive 1D- and 2D-NMR spectroscopy and mass spectrometry. The crude acetonic extract, the methylene chloride and ethyl acetate partitions, and some tested compounds isolated from this species (1-3) demonstrated selective significant antimicrobial activities against Gram-positive bacteria, in particular Staphylococcus lugdunensis, Enterococcus faecalis and Mycobacterium smegmatis. The potential cytotoxic activities of these extracts and compounds were evaluated against human colon carcinoma HT29 and human fetal lung fibroblast MRC5 cells.

Total syntheses of hyperforin and papuaforins A-C, and formal synthesis of nemorosone through a gold(I)-catalyzed carbocyclization

The remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane-2,4,9-trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A-C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)-catalyzed 6-endo-dig carbocyclization of cyclic enol ethers for late-stage functionalization.

Two new polyprenylated acylphloroglucinols from Hypericum scabrum

Two new polyprenylated acylphloroglucinols, (1S,32R,5S,6R,7R)-6-((R)-3,4-di-hydroxy-4-methylpentyl)-2-(2-hydroxypropan-2-yl)-7-isobutyryl-6-methyl-5,9-bis(3-methylbut-2-en-1-yl)-4,5,6,7-tetrahydro-2H-32,7-methanocycloocta[b]furan-8,10(3H)-dione (1) and (4R,5R,7R)-4-((R)-3,4-dihydroxy-4-methylpentyl)-2,2,4-trimethyl-5,7-bis(3-methyl-but-2-en-1-yl)-7-(5-methylhex-4-enoyl)-4,5,6,7-tetrahydrobenzofuran-3(2H)-one (2) were isolated from Hypericum scabrum. The structures were elucidated by means of spectroscopic methods, including MS, IR, NMR, OR, and CD.

Potential matrix metalloproteinase inhibitors from edible marine algae: a review

Matrix metalloproteinases are endopeptidases which belong to the group of metalloproteinases that contribute for the extra-cellular matrix degradation, and several tissue remodeling processes. An imbalance in the regulation of these endopeptidases eventually leads to several severe pathological complications like cancers, cardiac, cartilage, and neurological related diseases. Hence inhibitory substances of metalloproteinases (MMPIs) could prove beneficial in the management of above specified pathological conditions. The available synthetic MMPIs that have been reported until now have few shortcomings and thus many of them could not make to the final clinical trials. Hence a growing interest among researchers on screening of MMPIs from different natural resources is evident and especially natural products from marine origin. As there has been an unparalleled contribution of several biologically active compounds from marine resources that have shown profound applications in nutraceuticals, cosmeceuticals, and pharmaceuticals, we have attempted to discuss the various MMPIs from edible sea-weeds.

Hypercohones D-G, New Polycyclic Polyprenylated Acylphloroglucinol Type Natural Products from Hypericum cohaerens

Four new polycyclic polyprenylated acylphloroglucinol type metabolites, hypercohones D-G (1-4), along with four known analogues (5-8), were isolated from the aerial parts of Hypericum cohaerens. The structures of these isolates were elucidated by extensive spectroscopic methods. The inhibitory activities of these isolates against five human cancer cell lines in vitro were also tested.

Volatile Organic Compounds of six French Dryopteris Species: Natural Odorous and Bioactive Resources

Aerial parts of six Dryopteris species collected in France were investigated for volatile organic compounds (VOC) for the first time. Fifty-three biosynthesized VOC from the shikimic, lipidic and terpenic pathways were identified using gas chromatography/mass spectrometry. Many bioactive polyketide compounds as filicinic derivatives (from 8.5 to 23.5%) and phloroglucinol derivatives (from 8.2 to 53.8%) with various pharmacological activities were detected in high amount from five analysed Dryopteris species, in particular D. oreades and D. borreri, i.e., propionylfilicinic acid (> 10% in D. affinis and D. ardechensis) and 2,6-dihydroxy-4-methoxy-3-methylbutyrophenone (aspidinol) (19.1% and 14.6% in D. oreades and D. borreri, respectively). Several terpenic derivatives with a low odor threshold were identified, i.e., carota-5,8-diene (from 2.5 to 18.4%: floral, woody or fresh bark note), ( E)-nerolidol (> 10% for D. borreri and D. cambrensis; floral or woody odor), α-selinene (> 7% for D. ardechensis; woody-spicy odor), and aristolene (12.8% in D. affinis; flower, sweet odor). The main isoprenoid derivatives were 4-hydroxy-5,6-epoxyionol, 3-oxo-α-ionol and 4-oxo-7,8-dihydro-β-ionone (essentially in D. remota), whereas the main aromatic compound was 4-hydroxy-3-methoxyacetophenone (20.6% and 12.6% in D. cambrensis and D. borreri, respectively) and the main lipid derivative was 1-octen-3-ol with a mushroom-like odor (from 0.4 to 8.3%). Dryopteris species resources are of great interest as a reservoir of odorous and bioactive compounds.

Eucalmaidials A and B, phloroglucinol-coupled sesquiterpenoids from the juvenile leaves of Eucalyptus maideni

Eucalmaidials A and B, representing a new skeleton of phloroglucinol-coupled iphionane, were isolated from the juvenile leaves of Eucalyptus maideni.

Semisynthesis of mallotus B from rottlerin: evaluation of cytotoxicity and apoptosis-inducing activity

Mallotus B (2d) is a prenylated dimeric phloroglucinol compound isolated from Mallotus philippensis. There have been no reports on the synthesis or biological activity of this compound. In the present paper, a semisynthetic preparation of mallotus B is reported via base-mediated intramolecular rearrangement of rottlerin (1), which is one of the major constituents of M. philippensis. The homodimer "rottlerone" was also formed as one of the products of this base-mediated intramolecular reaction. Rottlerin (1), along with rottlerone (2c) and mallotus B (2d), was evaluated for cytotoxicity against a panel of cancer cell lines including HEPG2, Colo205, MIAPaCa-2, PC-3, and HL-60 cells. Mallotus B (2d) displayed cytotoxicity for MIAPaCa-2 and HL-60 cells with IC₅₀ values of 9 and 16 μM, respectively. Microscopic studies in HL-60 cells indicated that mallotus B (2d) induces cell cycle arrest at the G1 phase and causes defective cell division. It also induces apoptosis, as evidenced by distinct changes in cell morphology.

Evaluation of inhibitory effect of phlorotannins from Ecklonia cava on triglyceride accumulation in adipocyte

In the present study, a methanolic extract of Ecklonia cava and its solvent-partitioned fractions were evaluated for their antiadipogenic effect in 3T3-L1 adipocytes. One of them, the n-BuOH fraction, effectively reduced lipid accumulation and glucose consumption. In addition, the presence of the n-BuOH fraction in adipocytes suppressed the regulations of adipogenic transcription factors, PPARγ and SREBP1c, and adipogenic specific genes, FABP4, FABP1, FAS, LPL, HSL, and ACS1. Further purification of n-BuOH fractions led to the isolation of six phlorotannins (1-6). The six phlorotannins effectively suppressed triglyceride accumulation. Comparative analysis showed that lipid accumulation in adipocytes was dramatically attenuated in the presence of eckstolonol (4).

Determination of major phlorotannins in Eisenia bicyclis using hydrophilic interaction chromatography: seasonal variation and extraction characteristics

In this study, a hydrophilic interaction chromatography (HILIC) condition was developed for the simultaneous determination of five major phlorotannins from an extract of Eisenia bicyclis (Kjellman) Setchell with good linearity (r(2)>0.999). Based on this method, the seasonal variations and extraction characteristics, in terms of total extraction yield and the content of the phlorotannins, were investigated under various extraction conditions. In results, the yields and phlorotannins were increased two-to-four times in summer (June-October) and then, were decreased to normal levels in winter (November-March). In the extraction of E. bicyclis, ethanol percentage in water, extraction time and washing time significantly affected the yield of the extract and the phlorotannins, whereas the temperature and the sample/solvent ratio impacted the extraction to a lesser degree. These results will be useful information in the application of this macroalga in the commercial areas related to nutraceuticals, pharmaceuticals, and cosmeceuticals.

In vitro antioxidant properties of crude extracts and compounds from brown algae

Research on the bioactives from seaweeds has increased in recent years. Antioxidant activity is one of the most studied, due to the interest of these compounds both as preservatives and protectors against oxidation in food and cosmetics and also due to their health implications, mainly in relation to their potential as functional ingredients. Brown algae present higher antioxidant potential in comparison with red and green families and contain compounds not found in terrestrial sources. In vitro antioxidant chemical methods, used as a first approach to evaluate potential agents to protect from lipid oxidation in foods, confirmed that the brown algae crude extracts, fractions and pure components are comparatively similar or superior to synthetic antioxidants. Particular emphasis on the fucoidan and phlorotannin polymeric fractions is given, considering variations associated with the species, collection area, season, and extraction and purification technologies.

Application of ionic liquid-based surfactants in the microwave-assisted extraction for the determination of four main phloroglucinols from Dryopteris fragrans

An ionic liquid-based surfactant combined with microwave-assisted extraction method, followed by RP-HPLC-diode array detection (DAD) with a core shell column, was successfully applied in extracting and quantifying four major phloroglucinols from Dryopteris fragrans. Eight ionic liquids with different cation and anion were investigated, and 1-octyl-3-methylimidazolium bromide presented the best relative extraction efficiency for four phloroglucinols. The optimum conditions of this method were as follows: ionic liquid concentration 0.75 M, liquid/solid ratio 12:1 mL/g, extraction time 7 min, extraction temperature 50°C, and irradiation power 600 W. The quality analytical parameters of the method were obtained based on the linearity, precision, accuracy, detection, and quantification limits. The recoveries were between 96.90 and 103.5% with standard deviations not higher than 4.7%. Compared with ionic liquid-based heat reflux extraction, ultrasonic-assisted extraction, negative-pressure cavitation extraction, and conventional microwave-assisted extraction, the relative extraction efficiencies of the proposed method for four phloroglucinols increased 1.5-40.4%. The method was successfully applied for the quantification of four major phloroglucinols from D. fragrans. All these results suggest that the developed method represents an excellent alternative for the extraction and quantification of phloroglucinols in other plant materials.

The impact and mode of action of phenolic compounds extracted from brown seaweed on mixed anaerobic microbial cultures

AIMS

This study discusses the effect of phenolic compounds extracted from brown seaweed (phlorotannins) on mixed microbial cultures found in anaerobic systems.

METHODS AND RESULTS

Assays were conducted with phloroglucinol as the nonpolymerized form of phlorotannin and with phlorotannins extracted from the brown seaweed Laminaria digitata. Electron micrographs revealed that phlorotannins induce significant extra- and intracellular effects upon cells, with the disruption of cell membranes observed with most micro-organisms. Microscopy results were further confirmed by cell membrane leakage assays demonstrating that phloroglucinol strongly affects cell membrane permeability. However, cell membrane leakage could not be observed with phlorotannins as the cell suspension immediately started to coagulate and impaired spectrophotometric measurements.

CONCLUSIONS

Results suggest that the bactericidal activity of phlorotannins is a function of the level of polymerization of the compounds. By monitoring intermediary compounds during the anaerobic digestion of phlorotannins, it was also found that higher energy consumption is required by micro-organisms for survival under stress induced by phlorotannins.

SIGNIFICANCE AND IMPACT OF THE STUDY

The successful anaerobic degradation of brown seaweed is thus likely to be dependant on the concentration of phenolic compounds present and their bactericidal effect on micro-organisms. This is the first article to posit a probable mode of action for the antimicrobial effect of phlorotannins.

Anti-diabetic effects of brown algae derived phlorotannins, marine polyphenols through diverse mechanisms

Marine algae are popular and abundant food ingredients mainly in Asian countries, and also well known for their health beneficial effects due to the presence of biologically active components. The marine algae have been studied for biologically active components and phlorotannins, marine polyphenols are among them. Among marine algae, brown algae have extensively studied for their potential anti-diabetic activities. Majority of the investigations on phlorotannins derived from brown algae have exhibited their various anti-diabetic mechanisms such as α-glucosidase and α-amylase inhibitory effect, glucose uptake effect in skeletal muscle, protein tyrosine phosphatase 1B (PTP 1B) enzyme inhibition, improvement of insulin sensitivity in type 2 diabetic db/db mice, and protective effect against diabetes complication. In this review, we have made an attempt to discuss the various anti-diabetic mechanisms associated with phlorotannins from brown algae that are confined to in vitro and in vivo.