Chemical and Biological Research on Herbal Medicines Rich in Xanthones

Natural xanthones as modulators of the Nrf2/ARE signaling pathway and potential gastroprotective agents

Oxidative stress is implicated in the initiation, pathogenesis, and progression of various gastric inflammatory diseases (GID). The prevalence of these diseases remains a concern along with the increasing risks of adverse effects in current clinical interventions. Hence, new gastroprotective agents capable of inhibiting oxidative stress by modulating cellular defense systems such as the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway are critically needed to address these issues. A candidate to solve the present issue is xanthone, a natural compound that reportedly exerts gastroprotective effects via antioxidant, anti-inflammatory, and cytoprotective mechanisms. Moreover, xanthone derivatives were shown to modulate the Nrf2/ARE signaling pathway to counter oxidative stress in both in vitro and in vivo models. Thirteen natural xanthones have demonstrated the ability to modulate the Nrf2/ARE signaling pathway and have high potential as lead compounds for GID as indicated by their in vivo gastroprotective action-particularly mangiferin (2), α-mangostin (3), and γ-mangostin (4). Further studies on these compounds are recommended to validate the Nrf2 modulatory ability in relation to their gastroprotective action.

Comparative phytochemical studies on the roots of Polygala azizsancarii and P. peshmenii and neuroprotective activities of the two xanthones

Six known sucrose mono-, di- and triesters and five xanthone derivatives were isolated from the roots of Polygala peshmenii Eren, Parolly, Raus & Kürschner which is a narrow species endemic to Türkiye. Among the xanthones, 1,7-dihydroxy-2,3-methylenedioxy-5,6-dimethoxy-xanthone is an undescribed compound isolated for the first time from a natural source. The studies on the roots of P. azizsancarii Dönmez have resulted in the isolation of four known compounds including sucrose mono-, di- and triesters. The structures of the sucrose esters and xanthones isolated from P. azizsancarii and P. peshmenii were established by spectroscopic methods, including 1D-NMR (¹H NMR, ¹³C NMR, DEPT-135), 2D-NMR (COSY, NOESY, HSQC, HMBC). Neuroprotective activities of two xanthones, 1,3,6-trihydroxy-2,5,7-trimethoxyxanthone and 3-O-β-D-glucopyranosyloxy-1,6-dihydroxy-2,5,7-trimethoxyxanthone isolated from the roots of P. azizsancarii were evaluated in vitro using in a cellular model of Alzheimer's disease. SKNAS human neuroblastoma cells were used in the study and treated with different consecrations of Aβ₂₅₋₃₅ oligomer for up to 48 h. Cell viability was evaluated using MTT assay. The distribution of β-amyloid, α-synuclein, tau, JAK2, STAT3, caspase 3 and BMP-2 were investigated using indirect immunoperoxidase staining. Our results suggested that both xanthones control tau aggregation with no effect on β-amyloid plaque formation. In addition, for neuronal pathophysiology in AD cell model, decreased distributions of JAK/STAT3 and BMP2 signaling pathways were demonstrated, therefore they play a role in the protective effect on neurons in neurodegenerative disease. A significant decrease in caspase 3 immunoreactivity was detected after the administration of both compounds in AD cells. Therefore, both compounds control neuronal pathophysiology and rescue cell death in AD disease.

Metabolite Profiling and Bioactivities of Leaves, Stems, and Flowers of Rumex usambarensis (Dammer) Dammer, a Traditional African Medicinal Plant

The comprehensive identification of secondary metabolites represents a fundamental step for the assessment of bioactivities and pharmacological properties of traditional herbal drugs. Rumex usambarensis (Dammer) Dammer has been described as a multipurpose remedy in different African traditional pharmacopoeias, but its phytochemical profile has not been properly investigated. Herein we report a high throughput metabolomic screening, based on ultra-high performance liquid chromatography-travelling wave ion mobility spectrometry quadrupole time-of-flight (UHPLC-TWINS-QTOF), which was performed for the first time on different R. usambarensis plant parts. By applying high-resolution mass spectrometry-based metabolomics and chemometric analysis, a complete discrimination of different aerial parts was obtained, with the annotation of 153 significant metabolites in leaves, stems, and flowers, suggesting an easy authentication and discrimination route. Phytochemical data were correlated to antimicrobial and antioxidant properties. Flavonoids, benzopyranes, chromones, and xanthones derivatives, along with a richer phytocomplex, might be responsible for the stronger bioactivities obtained from flowers.

Xanthones and Xanthone O-β-D-glucosides from the Roots of Polygala azizsancarii Dönmez

Nine xanthone derivatives (1-9) were isolated from the roots of Polygala azizsancarii, which is a narrow endemic species for the flora of Türkiye. Based on all of the evidence, the structures of 1-9 were established as two previously undescribed xanthone O-glucosides, 3-O-β-D-glucopyranosyloxy-1,6-dihydroxy-2,5,7-trimethoxyxanthone (1), 3-O-β-D-glucopyranosyloxy-1,6-dihydroxy-2,7-dimethoxyxanthone (2), and seven previously described xanthones, 1,3,6-trihydroxy-2,5,7-trimethoxyxanthone (3), 1,3,6-trihydroxy-2,7-dimethoxyxanthone (4), 1,2,3,4,7-pentamethoxyxanthone (5), 1,3-dihydroxy-2,5,6,7-tetramethoxyxanthone (6), 1,3-dihydroxy-4,7-dimethoxyxanthone (7), 1,7-dihydroxy-3-methoxyxanthone (8), 1,7-dihydroxy-2,3-methylenedioxy-xanthone (9). The structures of the compounds were determined by spectroscopic methods, including 1D-NMR (1H NMR, 13C NMR, DEPT-135), 2D-NMR (COSY, NOESY, HSQC, HMBC, INADEQUATE), and HRMS. The solid-state structures of 1-4, including the absolute configurations of the stereogenic carbons of the sugar moiety in 1 and 2, were established by X-ray crystal-structure analyses. For the newly described compounds, the trivial names sancarosides A (1) and B (2) are proposed.

Isolation, Characterization and In Silico Studies of Secondary Metabolites from the Whole Plant of Polygala inexpectata Peşmen & Erik

Polygala species are frequently used worldwide in the treatment of various diseases, such as inflammatory and autoimmune disorders as well as metabolic and neurodegenerative diseases, due to the large number of secondary metabolites they contain. The present study was performed on Polygala inexpectata, which is a narrow endemic species for the flora of Turkey, and resulted in the isolation of nine known compounds, 6,3'-disinapoyl-sucrose (1), 6-O-sinapoyl,3'-O-trimethoxy-cinnamoyl-sucrose (tenuifoliside C) (2), 3'-O-(O-methyl-feruloyl)-sucrose (3), 3'-O-(sinapoyl)-sucrose (4), 3'-O-trimethoxy-cinnamoyl-sucrose (glomeratose) (5), 3'-O-feruloyl-sucrose (sibiricose A5) (6), sinapyl alcohol 4-O-glucoside (syringin or eleutheroside B) (7), liriodendrin (8), and 7,4'-di-O-methylquercetin-3-O-β-rutinoside (ombuin 3-O-rutinoside or ombuoside) (9). The structures of the compounds were determined by the spectroscopic methods including 1D-NMR (¹H NMR, ¹³C NMR, DEPT-135), 2D-NMR (COSY, NOESY, HSQC, HMBC), and HRMS. The isolated compounds were shown in an in silico setting to be accommodated well within the inhibitor-binding pockets of myeloperoxidase and inducible nitric oxide synthase and anchored mainly through hydrogen-bonding interactions and π-effects. It is therefore plausible to suggest that the previously established anti-inflammatory properties of some Polygala-derived phytochemicals may be due, in part, to the modulation of pro-inflammatory enzyme activities.

Xanthones and benzophenones isolated from the endophytic fungus Penicillium sp. ct-28 of Corydlis tomentella and their cytotoxic activity

One new xanthone, griseophenexanthone A (1), one new benzophenone, digriseophene A (2), and 14 previously reported compounds were isolated from the culture of Penicillium sp. ct-28, an endophytic fungus of Corydlis tomentella. The structures of the isolated compounds were identified by an extensive analysis of HRESIMS, 1D and 2D NMR. MTT assay showed that six xanthones (1 and 3-7) significantly inhibited cell proliferation in four cancer cell lines, with IC₅₀ values ranging from 18.12 ± 2.42 to 85.55 ± 7.66 μM. Our results showed that slight structural changes led to obvious activity differences among these compounds. We also investigated the effects of the six xanthones on cell cycle and apoptosis in human hepatoma HepG2 cells. Compound 7 caused cell cycle arrest at G1 phase, compounds 5 and 6 caused cell cycle arrest at S phase, whereas compounds 1, 3 and 4 had no effects on cell cycle distribution. All six xanthones induced apoptosis in dose-dependent manners in HepG2 cells accompanied by degradation of PARP and activation of caspase 3. The structure-activity relationship analysis revealed that the effects of these xanthones on cell cycle and apoptosis in HepG2 cells were closely related to the substituent groups on their skeleton. Our studies provide novel insights for the structural optimization of xanthones in the development of new anticancer drugs.

A Review on the Ethnomedicinal Usage, Phytochemistry, and Pharmacological Properties of Gentianeae (Gentianaceae) in Tibetan Medicine

Gentianaceae is a large plant family and is distributed worldwide. As the largest tribe in Gentianaceae, Gentianeae contains 939-968 species, and the Qinghai-Tibet Plateau and adjacent areas are the main centers of diversity for Gentianeae. Species from the Gentianeae are widely used in traditional Tibetan medicine. In this review, a systematic and constructive overview of the information on botany, ethnomedicinal usage, phytochemistry, and pharmacological properties of Gentianeae in Tibetan medicine is provided. The results of this study are based on a literature search, including electronic databases, books, websites, papers, and conference proceedings. Botanical studies showed that Gentianeae includes the subtribe Gentianeae and Swertiinae, and several new genera and taxa have been identified. Approximately 83 species from Gentianeae were used in Tibetan medicine, among which Gentiana and Swertia constituted the largest number of species with 42 and 24 species, respectively. The species from Gentianeae are mainly used as Bangjian (སྤང་རྒྱན།), Jieji (ཀྱི་ལྕེ།), Dida (ཏིག་ཏ།), and Ganggaqiong (གང་གྰཆུང་།) in Tibetan medicine with different clinical applications. More than 240 formulas were found containing Gentianeae species with different attending functions. Phytochemical studies showed that the main active components of Gentianeae species are iridoids, xanthones, flavonoids, and triterpenoids. The bioactivities of plants from Gentianeae include hepatic protection, upper respiratory tract protection, joint and bone protection, glucose regulation, antibacterial, antioxidant, anticancer, and antiviral effects. This review will provide a reference for future research on natural resource protection, plant-based drug development, and further clinical investigation.

Xanthones Active against Multidrug Resistance and Virulence Mechanisms of Bacteria

The emergence of multidrug and extensively drug-resistant pathogenic bacteria able to resist to the action of a wide range of antibiotics is becoming a growing problem for public health. The search for new compounds with the potential to help in the reversion of bacterial resistance plays an important role in current medicinal chemistry research. Under this scope, bacterial efflux pumps are responsible for the efflux of antimicrobials, and their inhibition could reverse resistance. In this study, the multidrug resistance reversing activity of a series of xanthones was investigated. Firstly, docking studies were performed in the AcrAB-TolC efflux pump and in a homology model of the NorA pump. Then, the effects of twenty xanthone derivatives on bacterial growth were evaluated in Staphylococcus aureus 272123 and in the acrA gene-inactivated mutant Salmonella enterica serovar Typhimurium SL1344 (SE03). Their efflux pump inhibitory properties were assessed using real-time fluorimetry. Assays concerning the activity of these compounds towards the inhibition of biofilm formation and quorum sensing have also been performed. Results showed that a halogenated phenylmethanamine xanthone derivative displayed an interesting profile, as far as efflux pump inhibition and biofilm formation were concerned. To the best of our knowledge, this is the first report of xanthones as potential efflux pump inhibitors.

Xanthones as P-glycoprotein modulators and their impact on drug bioavailability

Introduction: P-glycoprotein (P-gp) is an important efflux pump responsible for the extruding of many endogenous and exogenous substances out of the cells. P-gp can be modulated by different molecules - including xanthone derivatives - to surpass the multidrug resistance (MDR) phenomenon through P-gp inhibition, or to serve as an antidotal strategy in intoxication scenarios through P-gp induction/activation.Areas covered: This review provides a perspective on P-gp modulators, with particular focus on xanthonic derivatives, highlighting their ability to modulate P-gp expression and/or activity, and the potential impact of these effects on the pharmacokinetics, pharmacodynamics and toxicity of P-gp substrates.Expert opinion: Xanthones, of natural or synthetic origin, are able to modulate P-gp, interfering with its protein synthesis or with its mechanism of action, by decreasing or increasing its efflux capacity. These modulatory effects make the xanthonic scaffold a promising source of new derivatives with therapeutic potential. However, the mechanisms beyond the xanthones-mediated P-gp modulation and the chemical characteristics that make them more potent P-gp inhibitors or inducers/activators are still understudied. Furthermore, a new window of opportunity exists in the neuropathologies field, where xanthonic derivatives with potential to modulate P-gp should be further explored to optimize the prevention/treatment of brain pathologies.

Construction of Highly Functionalized Xanthones via Rh-Catalyzed Cascade C-H Activation/O-Annulation

A facile and efficient strategy for obtaining functionalized and multihydroxylated xanthones via Rh catalysis under redox-neutral conditions is developed. Diverse salicylaldehydes bearing heterocycles, aromatics, and fused aromatics can be rapidly coupled with 1,4-benzoquinones or 1,4-hydroquinones to afford valuable xanthones via cascade C-H/O-H functionalization and annulation. This protocol provides a rapid synthetic approach to obtain biologically active materials through late-stage functionalization and prepares natural products such as subelliptenone, pruniflorone N, and ravenelin.

Chemical-informatics approach to COVID-19 drug discovery: Exploration of important fragments and data mining based prediction of some hits from natural origins as main protease (Mpro) inhibitors

As the world struggles against current global pandemic of novel coronavirus disease (COVID-19), it is challenging to trigger drug discovery efforts to search broad-spectrum antiviral agents. Thus, there is a need of strong and sustainable global collaborative works especially in terms of new and existing data analysis and sharing which will join the dots of knowledge gap. Our present chemical-informatics based data analysis approach is an attempt of application of previous activity data of SARS-CoV main protease (Mpro) inhibitors to accelerate the search of present SARS-CoV-2 Mpro inhibitors. The study design was composed of three major aspects: (1) classification QSAR based data mining of diverse SARS-CoV Mpro inhibitors, (2) identification of favourable and/or unfavourable molecular features/fingerprints/substructures regulating the Mpro inhibitory properties, (3) data mining based prediction to validate recently reported virtual hits from natural origin against SARS-CoV-2 Mpro enzyme. Our Structural and physico-chemical interpretation (SPCI) analysis suggested that heterocyclic nucleus like diazole, furan and pyridine have clear positive contribution while, thiophen, thiazole and pyrimidine may exhibit negative contribution to the SARS-CoV Mpro inhibition. Several Monte Carlo optimization based QSAR models were developed and the best model was used for screening of some natural product hits from recent publications. The resulted active molecules were analysed further from the aspects of fragment analysis. This approach set a stage for fragment exploration and QSAR based screening of active molecules against putative SARS-CoV-2 Mpro enzyme. We believe the future in vitro and in vivo studies would provide more perspectives for anti-SARS-CoV-2 agents.

In Vivo Screening of Xanthones from Garcinia oligantha Identified Oliganthin H as a Novel Natural Inhibitor of Convulsions

Epilepsy is a chronic neurological disorder, characterized by recurrent, spontaneous, and transient seizures, and affects more than 70 million people worldwide. Although two dozen antiepileptic drugs (AEDs) are approved and available in the market, seizures remain poorly controlled in one-third of epileptic patients who are suffering from drug resistance or various adverse effects. Recently, the xanthone skeleton has been regarded as an attractive scaffold for the discovery and development of emerging anticonvulsants. We had isolated several dihydroxanthone derivatives previously, including oliganthin H, oliganthin I, and oliganthin N, whose structures were similar and delicately elucidated by spectrum analysis or X-ray crystallographic data, from extracts of leaves of Garcinia oligantha. These xanthone analogues were evaluated for anticonvulsant activity, and a novel xanthone, oliganthin H, has been identified as a sound and effective natural inhibitor of convulsions in zebrafish in vivo. A preliminary structure-activity relationship analysis on the relationship between structures of the xanthone analogues and their activities was also conducted. Oliganthin H significantly suppressed convulsant behavior and reduced to about 25% and 50% of PTZ-induced activity, in 12.5 and 25 μM treatment groups (P < 0.01 and 0.001), respectively. Meanwhile, it reduced seizure activity, velocity, seizure duration, and number of bursts in zebrafish larvae (P < 0.05). Pretreatment of oliganthin H significantly restored aberrant induction of gene expressions including npas4a, c-fos, pyya, and bdnf, as well as gabra1, gad1, glsa, and glula, upon PTZ treatment. In addition, in silico analysis revealed the stability of the oliganthin H-GABAA receptor complex and their detailed binding pattern. Therefore, direct interactions with the GABAA receptor and involvement of downstream GABA-glutamate pathways were possible mechanisms of the anticonvulsant action of oliganthin H. Our findings present the anticonvulsant activity of oliganthin H, provide a novel scaffold for further modifications, and highlight the xanthone skeleton as an attractive and reliable resource for the development of emerging AEDs.

Natural Xanthones and Skin Inflammatory Diseases: Multitargeting Mechanisms of Action and Potential Application

The pathogenesis of skin inflammatory diseases such as atopic dermatitis, acne, psoriasis, and skin cancers generally involve the generation of oxidative stress and chronic inflammation. Exposure of the skin to external aggressors such as ultraviolet (UV) radiation and xenobiotics induces the generation of reactive oxygen species (ROS) which subsequently activates immune responses and causes immunological aberrations. Hence, antioxidant and anti-inflammatory agents were considered to be potential compounds to treat skin inflammatory diseases. A prime example of such compounds is xanthone (xanthene-9-one), a class of natural compounds that possess a wide range of biological activities including antioxidant, anti-inflammatory, antimicrobial, cytotoxic, and chemotherapeutic effects. Many studies reported various mechanisms of action by xanthones for the treatment of skin inflammatory diseases. These mechanisms of action commonly involve the modulation of various pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor α (TNF-α), as well as anti-inflammatory cytokines such as IL-10. Other mechanisms of action include the regulation of NF-κB and MAPK signaling pathways, besides immune cell recruitment via modulation of chemokines, activation, and infiltration. Moreover, disease-specific activity contributed by xanthones, such as antibacterial action against Propionibacterium acnes and Staphylococcus epidermidis for acne treatment, and numerous cytotoxic mechanisms involving pro-apoptotic and anti-metastatic effects for skin cancer treatment have been extensively elucidated. Furthermore, xanthones have been reported to modulate pathways responsible for mediating oxidative stress and inflammation such as PPAR, nuclear factor erythroid 2-related factor and prostaglandin cascades. These pathways were also implicated in skin inflammatory diseases. Xanthones including the prenylated α-mangostin (2) and γ-mangostin (3), glucosylated mangiferin (4) and the caged xanthone gambogic acid (8) are potential lead compounds to be further developed into pharmaceutical agents for the treatment of skin inflammatory diseases. Future studies on the structure-activity relationships, molecular mechanisms, and applications of xanthones for the treatment of skin inflammatory diseases are thus highly recommended.

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.

Cytotoxicity and nitric oxide inhibitory activities of Xanthones isolated from Calophyllum hosei Ridl

Previous studies on Calophyllum species have shown the existence of a wide variety of bioactive xanthones and coumarins. Phytochemical investigations carried out on the plant, Calophyllum hosei led to the isolation of eleven known xanthones, ananixanthone (1), 9-hydroxycalabaxanthone (2), dombakinaxanthone (3), thwaitesixanthone (4), caloxanthone B (5), trapezifolixanthone (6), β-mangostin (7), osajaxanthone (8), caloxanthone A (9), calozeyloxanthone (10) and rubraxanthone (11). The structures of these compounds were identified and elucidated using spectroscopic techniques such as NMR and MS. The cytotoxicity and nitric oxide production inhibitory activities of selected xanthones as well as the extracts were tested against HL-60 cells and RAW 264.7 murine macrophages, respectively. Among all tested compounds, β-mangostin exhibited appreciable cytotoxicity against HL-60 cells with the IC₅₀ value of 7.16 ± 0.70 µg/mL and rubraxanthone exhibited significant nitric oxide inhibitory activity against LPS induced RAW 264.7 murine macrophages with the IC₅₀ value of 6.45 ± 0.15 µg/mL.

Gambogic acid: A shining natural compound to nanomedicine for cancer therapeutics

The United States Food and Drug Administration has permitted number of therapeutic agents for cancer treatment. Most of them are expensive and have some degree of systemic toxicity which makes overbearing in clinical settings. Although advanced research continuously applied in cancer therapeutics, but drug resistance, metastasis, and recurrence remain unanswerable. These accounts to an urgent clinical need to discover natural compounds with precisely safe and highly efficient for the cancer prevention and cancer therapy. Gambogic acid (GA) is the principle bioactive and caged xanthone component, a brownish gamboge resin secreted from the of Garcinia hanburyi tree. This molecule showed a spectrum of biological and clinical benefits against various cancers. In this review, we document distinct biological characteristics of GA as a novel anti-cancer agent. This review also delineates specific molecular mechanism(s) of GA that are involved in anti-cancer, anti-metastasis, anti-angiogenesis, and chemo-/radiation sensitizer activities. Furthermore, recent evidence, development, and implementation of various nanoformulations of gambogic acid (nanomedicine) have been described.

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.

Effects of Benzophenones from Mango Leaves on Lipid Metabolism

The mango tree (Mangifera indica L.) is a tropical, perennial, woody evergreen plant belonging to the Anacardiaceae. In traditional medicine, dried mango tree leaves were considered useful in treating diabetes and respiratory infections. In this paper, we review the phytochemical research on mango leaves and the mechanisms of benzophenones in lipid metabolism regulation. Thirty-six benzophenones have been isolated from mango leaves; among them, mangiferin is the major compound. Structure-activity relationships of benzophenones in lipid accumulation and the mechanisms of action of mangiferin in lipid metabolism are summarized. After oral administration, mangiferin is partly converted to its active metabolite, northyariol, which contributes to the activation of sirtuin-1 and liver kinase B1 and increases the intracellular AMP level and AMP/adenosine triphosphate ratio, followed by AMP-activated protein kinase phosphorylation, leading to increased phosphorylation of sterol regulatory element-binding protein-1c. Current evidence supports ethnopharmacological uses of mango leaves in diabetes and points toward potential future applications.

Development and Validation of a Stability-Indicating HPLC Method for the Quantification of α-Mangostin in Dietary Supplements

Xanthones are the main active constituents isolated from Garcinia mangostana L. (Hypericaceae). Among these, α-mangostin (1) is reported as the principal component of the species, with remarkable pharmacological activities. In this work, a reverse-phase high-performance liquid chromatography (HPLC) method was developed as a suitable stability-indicating procedure for the quantification of 1 in the presence of degradation products. Chromatographic analysis was performed on a Purospher STAR C18 column with a mobile phase containing 0.1% trifluoroacetic acid in water and ACN (20:80) at a flow rate of 1.0 mL/min. The method was linear over the concentration range of 10 to 100 μg/mL. The limits of detection and quantification were 0.13 and 0.4 μg/mL, respectively. Stability studies were carried out at temperature/relative humidity of 30°C/60% and 40°C/75% during 6 months; and no significant changes were observed. According to the global results, a simple HPLC method was developed and fully validated for quantifying 1 in mangosteen dietary supplements.

Chiral Derivatives of Xanthones with Antimicrobial Activity

According to the World Health Organization, the exacerbated use of antibiotics worldwide is increasing multi-resistant infections, especially in the last decade. Xanthones are a class of compounds receiving great interest in drug discovery and development that can be found as natural products or obtained by synthesis. Many derivatives of xanthones are chiral and associated with relevant biological activities, including antimicrobial. The aim of this review is to compile information about chiral derivatives of xanthones from natural sources and their synthesized examples with antimicrobial activity.

Structures, Activities and Drug-Likeness of Anti-Infective Xanthone Derivatives Isolated from the Marine Environment: A Review

Marine organisms represent almost half of total biodiversity and are a very important source of new bioactive substances. Within the varied biological activities found in marine products, their antimicrobial activity is one of the most relevant. Infectious diseases are responsible for high levels of morbidity and mortality and many antimicrobials lose their effectiveness with time due to the development of resistance. These facts justify the high importance of finding new, effective and safe anti-infective agents. Among the variety of biological activities of marine xanthone derivatives, one that must be highlighted is their anti-infective properties. In this work, a literature review of marine xanthones with anti-infective activity, namely antibacterial, antifungal, antiparasitic and antiviral, is presented. Their structures, biological activity, sources and the methods used for bioactivity evaluation are described. The xanthone derivatives are grouped in three sets: xanthones, hydroxanthones and glycosylated derivatives. Moreover, molecular descriptors, biophysico-chemical properties, and pharmacokinetic parameters were calculated, and the chemical space occupied by marine xanthone derivatives is recognized. The chemical space was compared with marketed drugs and framed accordingly to the drug-likeness concept in order to profile the pharmacokinetic of anti-infective marine xanthone derivatives.

Structure Elucidation of the Main Tetrahydroxyxanthones of Hypericum Seeds and Investigations into the Testa Structure

Seeds from Hypericum species have recently been identified as an interesting source of xanthone derivatives. Extraction of seeds from H. perforatum with MeOH and subsequent concentration via polyamide adsorption yielded a fraction enriched in tetrahydroxyxanthones (THX), which were further semipurified by silica gel chromatography. Based on tentative structure assignment of the two main THX X1 and X2 by NMR a total synthesis was performed for both compounds (THX 1 and 2, respectively), starting with an Ullmann ether synthesis. The synthesized 1 and 2 were characterized via 1D- and 2D-NMR methods as well as by LC/HR-MS analysis and proven to be 1,4,6,7-THX (1) and 1,2,6,7-THX (2). Final structure assignment of the natural Hypericum THX constituents was accomplished by comparing chromatographic and spectroscopic data (LC/MSⁿ and GC/MS) with those of 1 and 2 which were obtained by synthesis. Beyond, investigations into the seeds of H. perforatum and H. tetrapterum by scanning electron microscopy (SEM) provided insights of the structure of the testa (seed coat), which is established by two cell layers, with the lignified sclerenchyma presumably being the depository of the xanthones.