Prenylated Xanthones Research Articles

Natural Products Targeting the Fungal Unfolded Protein Response as an Alternative Crop Protection Strategy.

Discovering new solutions for crop protection is a major challenge for the next decades as a result of the ecotoxicological impact of classical fungicides, the emergence of fungicide resistances, and the consequence of climate change on pathogen distribution. Previous work on fungal mutants deficient in the unfolded protein response (UPR) supported that targeting this pathway is a promising plant disease control strategy. In particular, we showed that the UPR is involved in fungal virulence by altering cell protection against host defense compounds, such as phytoalexins and phytoanticipins. In this study, we evaluated natural products targeting fungal IRE1 protein (UPR effector) and consequently increasing fungal susceptibility to plant defenses. Developing an in vitro cell-based screening assay allowed for the identification of seven potential IRE1 inhibitors with a focus on polyhydroxylated prenylated xanthones. Inhibition of hac1 mRNA splicing, which is mediated by IRE1, was then validated for the most active compound, namely, γ-mangostin 3. To study the mode of interaction between the binding site of IRE1 and active xanthones, molecular docking was also undertaken, revealing similar and novel interactions between the known inhibitor and the binding site. Eventually, active xanthones applied at subtoxic doses induced a significant reduction in necrosis size for leaves of Brassica oleracea inoculated with Alternaria brassicicola and Botrytis cinerea.

Prenylated xanthones with α-glucosidase and α-amylase inhibitory effects from the pericarp of Garcinia mangostana

Two new prenylated xanthones, mangoxanthones A-B (1-2), together with four known compounds 3-6, were isolated from the ethanol extract of the pericarp of Garcinia mangostana. The structures of these compounds have been elucidated based on spectroscopic analysis. The analysis results of chiral HPLC revealed compounds 1 and 2 were scalemic mixtures respectively. All isolated compounds were biologically evaluated for their α-glucosidase and α-amylase inhibitory effects using in-vitro assays. Compound 1 showed moderate inhibitory activities against α-glucosidase and α-amylase with IC50 of 29.06 ± 1.86 and 22.74 ± 2.07 μM, respectively. Molecular docking predicted the binding sites of compound 1 to α-glucosidase and α-amylase. A preliminary structure-activity relationship was discussed.

In vitro antimalarial activity of Garcinia parvifolia Miq. Stem extracts and fractions on Plasmodium falciparum lactate dehydrogenase (LDH) assay.

The rapid spread of antimalarial drug resistance is becoming a problem in the treatment of malaria. The fact was indicated the importance of finding new antimalarial drugs. The genus Garcinia is well known to be a rich source of bioactive prenylated xanthones and triterpenes reported for their antimalarial activity. Garcinia parvifolia is one of the Garcinia genera that can be explored for the search of new antimalarial drugs. This study was aimed to determine the antimalarial activities of G.parvifolia extracts and fractions. Garcinia parvifolia Miq. stem was collected fromBalikpapan Botanical Garden in East Kalimantan, Indonesia, was extracted gradually with n-hexane, dichloromethane, and methanol by ultrasonic assisted method. The most active extract was further separated using the open column chromatography method. All extracts and fractions were tested against Plasmodium falciparum 3D7 using lactate dehydrogenase (LDH) assay and followed by IC50 determination. The results showed that all extracts inhibit P.falciparum growth by LDH assay. The highest inhibition was showed by dichloromethane stem extract (BP12-S-D) with the IC50 value of 6.61±0.09μg/mL. Further fractionation of BP12-S-D has obtained 10 fractions. All of themwere identified by TLC, and a brownish-yellow spot (fraction-1) appears after spraying with 10% H2SO4. Fraction-1 (F1) performed the highest parasite growth inhibition with the IC50 value of 6.00±0.03μg/mL compared with other fractions. This fraction was classified as having a promising activity of antimalarial. The fraction-1 was identified using HPLC, and two major peaks were observed (A and B). The UV-Vis spectra showed the absorption at wavelengths 250 and 278 (A), 243, 281, and 317nm (B). Based on the profile of TLC, HPLC, and UV-Vis spectra of F1, it was expected that the active compounds are flavonoid (A)and xanthone (B). The fraction-1 of dichloromethane extract of G.parvifolia Miq. stem has the highest antimalarial activity. It might be a potential candidate for the new antimalarial drug.

XANTHONES AND OTHER COMPOUNDS FROM THE LATEX OF GARCINIA COWA

From our ongoing study on the latex of Garcinia cowa Roxb. ex Choisy collected in Quy Chau, Nghe An province, seven compounds were isolated including four prenylated xanthones: norcowanin (1), kaennacowanol A (2), garcinone D (3), fuscaxanthone I (4); one tocotrienol: parvifoliol F (5) and two triterpenes: stigmasterol (6), lupeol (7). The structures of the isolated compounds were elucidated by physico-chemical spectroscopic analysis and by comparison with reported data. To the best of our knowledge, garcinone D (3), fuscaxanthone I (4) and parvifoliol F (5) were first reported as components of Garcinia cowa.

Staprexanthones, Xanthone-Type Stimulators of Pancreatic β-Cell Proliferation from a Mangrove Endophytic Fungus.

This project was focused on the discovery of novel compounds that promote endogenous β-cell regeneration. Screening of extracts identified the fungus Stachybotrys chartarum as a promising candidate. After fermentation and extraction of S. chartarum, we isolated five new prenylated xanthones, namely, staprexanthones A-E (1-5), with staprexanthone A (1) being the first natural xanthone bearing a rare 4,5-dimethyl-1,3-dioxolane moiety. Compounds 1, 2, and 5 significantly increased β-cell numbers in vivo in a zebrafish model. Further analysis revealed that 2 and 5 promoted β-cell mass expansion by increasing proliferation of existing β-cells though promotion of cell-cycle progression at the G1/S transition. These findings indicate that prenylated xanthones are potential new drug leads for antidiabetes therapy by stimulating β-cell regeneration.

Inhibitory Effect of Cudratrixanthone U on RANKL-Induced Osteoclast Differentiation and Function in Macrophages and BMM Cells.

Cudratrixanthone U (CTU) is a prenylated xanthone compound isolated from Maclura tricuspidata Bureau (Moraceae). Prenylated xanthones have been reported to exhibit a variety of biological activities. However, the effects of prenylated xanthone on osteoclast differentiation and function are still unclear. Excessive bone resorption by osteoclasts is considered a major cause of diseases such as osteoporosis. Accordingly, suppression of excessive osteoclast formation and function is one of strategies for treating osteoclast related bone diseases. In this study, CTU inhibited osteoclast differentiation and function in RAW264.7 macrophages and BMM cells induced by receptor activator of nuclear factor-κB ligand (RANKL). CTU regulated the formation of TRAF6-TAK1 complex in RANKL-induced RAW264.7 macrophages and BMM cells. Osteoclast-specific genes including those encoding matrix metallopeptidase 9 (MMP-9), dendritic cell-specific transmembrane proteins (DC-STAMP), cathepsin K (CTSK) and chemokine CC motif ligand 4 (CCL4) play an important role in bone resorption and migration, and were effectively regulated by CTU. These results suggest that CTU is a potential therapeutic agent in osteoporosis.

The acute diuretic effects with low-doses of natural prenylated xanthones in rats

The diuretic effect of 3-demethyl-2-geranyl-4-prenylbellidypholine xanthone (DGP) and 1,5,8-trihydroxy-4′,5′-dimethyl-2H-pyrano(2,3:3,2)-4-(3-methylbut-2-enyl) xanthone (TDP), two natural prenylated xanthones, was investigated in female normotensive (NTR) and spontaneously hypertensive rats (SHR). The rats received a single treatment with DGP, TDP, hydrochlorothiazide (HCTZ), or vehicle (VEH) after an oral load of physiological saline. The effects of DGP and TDP in combination with diuretics of clinical use, as well as with L-NAME, atropine and indomethacin were also explored. The urinary parameters were measured at the end of the 8-h experiment. When orally given to rats, DGP was able to increase the urine volume, at doses of 0.03–0.3 mg/kg, associated with a K+-sparing effect. TDP, in turn, at doses of 0.03–0.3 mg/kg, induced diuresis and saluresis (i.e. augmented urinary levels of Na+ and Cl−) in NTR, while decreased the urinary content of Ca2+ in both NTR and SHR. The combination with HCTZ, but not with furosemide or amiloride, significantly enhanced DGP and TDP induced diuresis, which was accompanied by an increase of the electrolytes content in the urine. Instead, amiloride in combination with DGP or TDP enhanced urinary Na+ and Cl− and decreased K+ elimination. Furthermore, the effect of DGP and TDP were heightened after pretreatment with L-NAME. While atropine was able to prevent DGP-induced diuresis, the pretreatment with indomethacin precluded TDP-induced diuresis. Besides, TDP exerted protective effects against urinary calcium oxalate crystals formation. Taken together, our data revealed the diuretic effect of two xanthones in rats and their possible underlying mode of action.

Cytotoxic Xanthones from Hypericum stellatum, an Ethnomedicine in Southwest China.

Hypericum stellatum, a species endemic to China, is used to treat hepatitis by several ethnic groups in Guizhou Province. This research was inspired by the traditional medicinal usage of H. stellatum, and aims to explore the phytochemistry and bioactivity of H. stellatum to explain why local people in Guizhou widely apply H. stellatum for liver protection. In this study, two new prenylated xanthones, hypxanthones A (8) and B (9), together with seven known compounds, were isolated from the aerial parts of the plant. Spectroscopic data as well as experimental and calculated ECD spectra were used to establish the structures of these compounds. Six xanthones isolated in this study, together with four xanthones previously isolated from H. stellatum, were evaluated for their growth-inhibitory activities against five human liver carcinoma cell lines to analyze the bioactivity and structure-activity relationship of xanthones from H. stellatum. Isojacareubin (6) showed significant cytotoxicity against five human liver carcinoma cell lines, with an IC50 value ranging from 1.41 to 11.83 μM, which was stronger than the positive control cisplatin (IC50 = 4.47–20.62 μM). Hypxanthone B (9) showed moderate cytotoxicity to three of the five cell lines. Finally, structure-activity analysis revealed that the prenyl and pyrano substituent groups of these xanthones contributed to their cytotoxicity.

Cytotoxic Prenylated Xanthones from the Leaves of Garcinia bracteata.

Six new prenylated xanthones (1: -6: ) and seventeen known xanthones were isolated from extracts of Garcinia bracteata leaves. Their structures were determined by extensive NMR and MS spectroscopic data analysis. The inhibitory activities of the isolates were assayed on HeLa, A549, PC-3, HT-29, and WPMY-1 cell lines. Compounds 1: and 15: -17: showed moderate inhibitory effects on tumor cell growth, with IC50s ranging from 3.7 to 14.7 µM.

Non-destructive chemical analysis of a Garcinia mangostana L. (Mangosteen) herbarium voucher specimen

Herbarium voucher specimens are used primarily for taxonomic confirmation. However, they also afford a record of the metabolic profile of a plant, potentially at the time it was collected, or at the very least, at the time of analysis. Even with the enhanced sensitivity of modern analytical techniques, analysis of the metabolites of a herbarium voucher requires removal and consumption of at least part of an entire specimen. We present herein a non-destructive method to analyze the metabolites of herbarium voucher specimens with the droplet-liquid microjunction-surface sampling probe (droplet probe) coupled to ultra-performance liquid chromatography and high-resolution mass spectrometry. As proof of concept, a herbarium voucher specimen of Garcinia mangostana (mangosteen) was utilized due to the well-characterized xanthones biosynthesized by this plant, which are of interest as potential anticancer agents. Also, the juice of the fruits of this plant is used widely in the United States and in other countries as a botanical dietary supplement. Metabolite profiles of the sampled surfaces were compared to a subset of xanthone standards. Using this innovative method on the herbarium voucher specimen, we were able to readily identify cytotoxic prenylated xanthones while maintaining the integrity of the entire specimen.

Garcixanthones B and C, new xanthones from the pericarps of Garcinia mangostana and their cytotoxic activity

Two new prenylated xanthones, garcixanthones B (1) and C (2) and six known metabolites: gartanin (3), 1,3,8-trihydroxy-2-(3-methyl-2-butenyl)-4-(3-hydroxy-3-methylbutanoyl)-xanthone (4), rubraxanthone (5), 1,3,6,7-tetrahydroxy-8-prenylxanthone (6), garcinone C (7), and xanthone I (9-hydroxycalabaxanthone) (8) were separated from the EtOAc-soluble fraction of the air-dried pericarps of Garcinia mangostana (Clusiaceae). Their structures were verified on the basis of spectroscopic data analysis as well as by comparison with the literature. The cytotoxic activity of the new compounds was assessed against MCF7, A549, and HCT116 cell lines using sulforhodamine B (SRB) assay. Compounds 1 and 2 showed significant cytotoxic potential against MCF7 (human breast adenocarcinoma) and A549 (lung carcinoma) cell lines with IC50s 4.27 and 2.65 and 3.08 and 3.91 μM, respectively compared to doxorubicin (0.06 and 0.44 μM, respectively). However, they exhibited moderate activity towards HCT116 (colon carcinoma) cell line.

Prenylated xanthones from the stem bark of Garcinia dulcis

Three new prenylated xanthones, named dulcisxanthone J (1), dulcisxanthone K (2), and dulcisxanthone L (3), along with 38 known compounds have been isolated from the stem bark of Garcinia dulcis. Their structures were elucidated mainly by analysis of 1D and 2D spectroscopic data. 12b-Hydroxy-des-D-garcigerrin A (12) and dulcisxanthone J (1) displayed moderate antibacterial activity against both penicillin-susceptible Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) with minimum inhibitory concentration (MIC) values of 4 and 16μg/mL, respectively.

UPLC-PDA-QTOFMS-guided isolation of prenylated xanthones and benzoylphloroglucinols from the leaves of Garcinia oblongifolia and their migration-inhibitory activity.

A UPLC-PDA-QTOFMS-guided isolation strategy was employed to screen and track potentially new compounds from Garcinia oblongifolia. As a result, two new prenylated xanthones, oblongixanthones D and E (1–2), six new prenylated benzoylphloroglucinol derivatives, oblongifolins V–Z (3–7) and oblongifolin AA (8), as well as a known compound oblongifolin L (9), were isolated from the EtOAc-soluble fraction of an acetone extract of the leaves of Garcinia oblongifolia guided by UPLC-PDA-QTOFMS analysis. The structures of the new compounds were elucidated by 1D- and 2D-NMR spectroscopic analysis and mass spectrometry. Experimental and calculated ECD spectra were used to determine the absolute configurations. The results of wound healing and transwell migration assay showed that oblongixanthones D (1), E (2), and oblongifolin L (9) have the ability to inhibit cancer cell migration in lower cytotoxic concentrations. Western blotting results showed that these compounds exhibited an anti-metastasis effect mainly through downregulating RAF protein levels. In addition, 2 and 9 could inhibit phospho-MEK and phospho-ERK at downstream. Moreover, 1, 2, and 9 could inhibit snail protein level, suggesting that they could regulate the EMT pathway.

Antimalarial polyoxygenated and prenylated xanthones from the leaves and branches of Garcinia mckeaniana

The first phytochemical investigation of the leaf and branch extracts of Garcinia mckeaniana has led to the isolation and characterization of five new polyoxygenated and prenylated xanthones, mckeanianones A-E (1–5), and one new biflavone, mckeaniabiflavone (6), together with 13 known compounds (7–19). The diprenylated pyrano-xanthones (1–3) and the biflavone (6) were isolated from the leaves while the monoprenylated xanthones (4 and 5) were isolated from the branches. The structures of all isolated compounds were elucidated based on spectroscopic methods and were evaluated for their antimalarial activities against the Plasmodium falciparum strains, TM4 (drug sensitive strain) and K1 (a multidrug resistant strain), and cytotoxicity against a Vero cell line (African green monkey kidney epithelial cells). The pyrano-xanthones (1–3, 7 and 8), having two isoprene units, were generally the most active compounds with IC50 values in the range of 6.0±1.1 _ 8.5±1.2 and 3.6±1.7 _ 7.3±1.2 μM, respectively against the TM4 and K1 strains. Of these compounds 2, 3 and 8 were 2–5 times less cytotoxic against a Vero cell line (IC50 values of 12.6±0.9, 29.5±3.9 and 13.2±4.6 μM, respectively) in comparison with their antiplasmodial activities.

Regiospecific Prenylation of Hydroxyxanthones by a Plant Flavonoid Prenyltransferase.

C-Prenylated xanthones are pharmacologically attractive specialized metabolites that are distributed in plants and microorganisms. The prenylation of xanthones often contributes to the structural diversity and biological activities of these compounds. However, efficient regiospecific prenylation of xanthones is still challenging. In this study, the regiospecific prenylation of a number of structurally different hydroxyxanthones (3-10) by MaIDT, a plant flavonoid prenyltransferase with substrate flexibility from Morus alba, is demonstrated. Among the enzymatic products, 2-dimethylallyl-1,3,7-trihydroxyxanthone (3a) effectively attenuated glutamate-induced injury in SK-N-SH neuroblastoma cells. These results suggest a potential approach for the synthesis of bioactive prenylated xanthones by a substrate-relaxed flavonoid prenyltransferase.

Xanthones from the green branch of Garcinia dulcis

Two new prenylated xanthones, namely dulcisxanthone H and dulcisxanthone I along with garciniaxanthone C, were isolated from the dichloromethane extract of the green branch of Garcinia dulcis. Their structures were elucidated by the analysis of 1-D and 2-D NMR spectral data. Their antibacterial activities were also examined.

Antifungal New Oxepine-Containing Alkaloids and Xanthones from the Deep-Sea-Derived Fungus Aspergillus versicolor SCSIO 05879.

Phytopathogenic fungi remain a continuous and huge threat in the agricultural fields. The agrochemical industry has made great development of the use of microbial natural products, which has been regarded as an effective strategy against phytopathogenic fungi. Antifungal bioassay-directed fractionation was used to isolate two new oxepine-containing alkaloids (1 and 2), two new 4-aryl-quinolin-2-one alkaloids (3 and 4), and four new prenylated xanthones (5-8) from the deep-sea-derived fungus Aspergillus versicolor SCSIO 05879. Extensive NMR spectroscopic analysis, quantum mechanical calculations, and X-ray single-crystal diffraction were used to elucidate their structures, including their absolute configurations. Versicoloids A and B, versicone A, and cottoquinazoline A showed antifungal activities against three phytopathogenic fungi. The antifungal activities of these bioactive compounds strongly depend on the fungal species. Especially versicoloids A and B showed strong fungicidal effect (MIC of 1.6 μg/mL) against Colletotrichum acutatum, compared with that of the positive control cycloheximide (MIC of 6.4 μg/mL). The results of antifungal experiments indicated that versicoloids A and B may be regarded as candidate agents of antifungal agrochemicals.

Three new xanthones from the leaves of Garcinia lancilimba.

Three new prenylated xanthones, garcinexanthones G-I (1-3), together with fifteen known ones (4-18) were identified from the leaves of Garcinia lancilimba. Their structures were determined by extensive spectroscopic analyses. Most of the compounds exhibited inhibitory effects against HL-60 (human leukemia), A549 (human lung cancer), and MCF-7 (human breast cancer) cell lines. Among them, compounds 7, 17, and 13 exhibited the most pronounced growth inhibitory activity against HL-60, A549, and MCF-7 cell lines with GI50 values of 1.68, 4.88, and 6.28 μM, respectively.

The natural compound nujiangexanthone A suppresses mast cell activation and allergic asthma

Mast cells play an important role in allergic diseases such as asthma, allergic rhinitis and atopic dermatitis. The genus Garcinia of the family Guttiferae is well known as a prolific source of polycyclic polyprenylated acylphloroglucinols and bioactive prenylated xanthones, which exhibit various biological activities including antibacterial, antifungal, anti-inflammatory, antioxidant, and cytotoxic effects. Nujiangexanthone A (N7) is a novel compound isolated from the leaves of Garcinia nujiangensis. In this paper, we sought to determine the anti-allergic and anti-inflammation activity of N7 in vivo and its mechanism in vitro. We found N7 suppressed IgE/Ag induced mast cell activiation, including degranulation and production of cytokines and eicosanoids, through inhibiting Src kinase activity and Syk dependent pathways. N7 inhibited histamine release, prostaglandin D2 and leukotriene C4 generation in mast cell dependent passive cutaneous anaphylaxis animal model. We also found N7 inhibited the IL-4, IL-5, IL-13 and IgE levels in ovalbumin-induced asthma model. Histological studies demonstrated that N7 substantially inhibited OVA-induced cellular infiltration and increased mucus production in the lung tissue. Our study reveals the anti-allergic function of N7, thereby suggesting the utility of this compound as a possible novel agent for preventing mast cell-related immediate and delayed allergic diseases.

Search for Structurally Unique Bioactive Natural Products

In our continuing search for structurally and biologically interesting metabolites from marine organisms and plants, we investigated the constituents of Okinawan marine sponges and Hypericum plants, resulting in the isolation of several new and unique natural products. Their structures were elucidated on the basis of spectroscopic analyses and chemical conversions. Novel bromopyrrole alkaloids, nagelamides X-Z, were isolated from a sponge Agelas sp. Heteroaromatic alkaloids, hyrtimomines A and B, were isolated from a sponge Hyrtios sp. together with bisindole alkaloids, hyrtimomines C-E. An oxylipin with a trimeric structure, manzamenone O, was obtained from a sponge Plakortis sp. Dimeric eudesmane sesquiterpenes connected through various linker moieties, halichonadins K-L, were isolated from a sponge Halichondria sp., and isomalabaricane triterpenes, stelliferins J-N, were obtained from a sponge Rhabdastrella sp. The investigation for the extracts of Hypericum plants gave new meroterpenes, acylphloroglucinols, and xanthones. Biyoulactones A-E are meroterpenoids from the roots of Hypericum chinense. Acylphloroglucinols, chipericumines A-D, and highly prenylated xanthones, biyouxanthones A-D, were also isolated from the same origin. Tricyclic meroterpenes, yezo'otogirins A-C, and liner meroterpenos, yojironins A and B, were isolated from Hypericum yezoense and Hypericum yojiroanum, respectively.