Cytotoxic and NF-κB inhibitory constituents of the stems of Cratoxylum cochinchinense and their semisynthetic analogues

Caged xanthone derivatives to promote mitochondria-mediated apoptosis in breast cancer cells

Caged xanthones represent a class of natural secondary metabolites exhibiting significant potential as antitumor agents. These compounds are characterized by their distinct cage-like structures, which offer novel and compelling frameworks for drug design. Nonetheless, there exists a dearth of research focused on the structural modification of these compounds, particularly in relation to their cage-like architectures. This study aims to address this gap by introducing an innovative synthetic method for constructing a novel caged structure that incorporates a widely employed maleimide group. Drawing upon the well-established synthetic approach for dihydroxanthones previously developed within our research group, we successfully synthesized 13 new caged xanthones using the Diels-Alder reaction. Subsequently, we evaluated their anti-proliferative activity against HepG2, A549, and MDA-MB-231 cell lines. The results revealed that compound 10i exhibited IC50 values of 15.86 µM ± 1.29, 19.27 µM ± 1.58, and 12.96 µM ± 0.09 against these cell lines, respectively. Further investigations into the mechanism of action of 10i demonstrated its ability to induce G2/M cell cycle arrest and initiate mitochondria-mediated apoptosis in breast cancer cells.

Caged Xanthones and Biphenyls Isolated from the Tropical Plant Garcinia lateriflora

Four cytotoxic heptacyclic caged-xanthones [gambogefic acids B-E (1-4)], a cytotoxic hexacyclic caged-xanthone [garcilatelic acid (5)], and four biphenyl derivatives [garcilatelibiphenyls A-D (6-9)] were newly isolated in a phytochemical study of a 50% MeOH/CH2Cl2 extract of Garcinia lateriflora (Clusiaceae). The isolated compounds were evaluated for antiproliferative activity against five human tumor cell lines including a vincristine-resistant line. The new caged-xanthones displayed potent activity with IC50 values from 0.5 to 6.7 μM against all tested tumor cell lines.

Structurally Diverse Cytotoxic Polyphenols from Garcinia gracilis

Thirty-five diverse polyphenols, belonging to seven structure classes, were isolated from Garcinia gracilis, a medicinal and edible plant sampled from Laos. The structures of nine new compounds, gargarcilones A-I (1-3, 5-7, 10, 12, and 17), were established using spectroscopic, X-ray diffraction, and experimental and calculated ECD methods. Additionally, we revised the stereochemical assignment of cochinchinoxanthone and cochinchinoxanthone C. The compounds were evaluated for antiproliferative activity against five human tumor cell lines (HL-60, A549, SMMC-7721, MDA-MB-231, and SW480). Compounds 1-4, 7, and 8 exhibited cytotoxic activity with IC50 values of 0.5-8.9 μM. Compound 3 significantly induced apoptosis in SMMC-7721 cells.

Xanthones with Potential Anti-Inflammatory and Anti-HIV Effects from the Stems and Leaves of Cratoxylum cochinchinense

Four new xanthones, cratocochinones A-D (1-4), together with eight known analogues (5-12), were isolated from the stems and leaves of Cratoxylum cochinchinense. The chemical structures of cratocochinones A-D (1-4) were elucidated by comprehensive spectroscopic analyses and the known compounds were identified by comparisons with the spectral data reported in the literature. All isolated compounds 1-12 were evaluated for their anti-inflammatory activities and anti-HIV-1 activities. Compounds 1-12 showed remarkable inhibitory activities on nitric oxide (NO) production induced by lipopolysaccharide in mouse macrophage RAW 264.7 cells in vitro, with IC50 values in the range of 0.86 ± 0.05 to 18.36 ± 0.21 µM. Meanwhile, compounds 1-12 exhibited significant anti-HIV-1 activities with EC50 which ranged from 0.22 to 11.23 µM. These findings indicate that the discoveries of these xanthones, isolated from the stems and leaves of C. cochinchinense, showing significant anti-inflammatory and anti-HIV-1 effects could be of great importance to the research and development of new natural anti-inflammatory and anti-HIV agents.

Multitarget Action of Xanthones from Garcinia mangostana against α-Amylase, α-Glucosidase and Pancreatic Lipase

Digestive enzymes such α-amylase (AA), α-glucosidase (AG) and pancreatic lipase (PL), play an important role in the metabolism of carbohydrates and lipids, being attractive therapeutic targets for the treatment of type 2 diabetes and obesity. Garcinia mangostana is an interesting species because there have been identified xanthones with the potential to inhibit these enzymes. In this study, the multitarget inhibitory potential of xanthones from G. mangostana against AA, AG and PL was assessed. The methodology included the isolation and identification of bioactive xanthones, the synthesis of some derivatives and a molecular docking study. The chemical study allowed the isolation of five xanthones (1–5). Six derivatives (6–11) were synthesized from the major compound, highlighting the proposal of a new solvent-free methodology with microwave irradiation for obtaining aromatic compounds with tetrahydropyran cycle. Compounds with multitarget activity correspond to 2, 4, 5, 6 and 9, highlighting 6 with IC₅₀ values of 33.3 µM on AA, 69.2 µM on AG and 164.4 µM on PL. Enzymatic kinetics and molecular docking studies showed that the bioactive xanthones are mainly competitive inhibitors on AA, mixed inhibitors on AG and non-competitive inhibitors on PL. The molecular coupling study established that the presence of methoxy, hydroxyl and carbonyl groups are important in the activity and interaction of polyfunctional xanthones, highlighting their importance depending on the mode of inhibition.

Cytotoxic and Antiangiogenetic Xanthones Inhibiting Tumor Proliferation and Metastasis from Garcinia xipshuanbannaensis

Eight prenylated xanthones including four new analogues were extracted and purified from the leaves of Garcinia xipshuanbannaensis. Multiple techniques including UV, 1D and 2D NMR, and HRESIMS were used to determine the structures of the isolated xanthones. These xanthones were evaluated for their cytotoxicity toward human cancer cells, and compound 4 exhibited activity against HeLa cells. A cytotoxic mechanism examination revealed the active compound induced cell apoptosis by arresting the cell cycle, increasing the levels of ROS, and inhibiting the expression of p-STAT3 in HeLa cells. In in vivo zebrafish experiments, compound 4 was found to block tumor proliferation and migration and have antiangiogenetic activity, and thus seems worthy of further laboratory evaluation.

Acmoxanthones A-E, New Lavandulated Xanthones from Hypericum acmosepalum N. Robson

Acmoxanthones A-E (1-5), five new lavandulylated xanthones, were isolated from the aerial parts of Hypericum acmosepalum, together with four known xanthones. Their structures with absolute configurations were elucidated on the basis of analysis of MS, NMR and chiroptical properties. A bioassay against high glucose-induced damage on human umbilical vein endothelial cells (HUVECs) showed ananixanthone (6) and osajaxanthone (7) had potential antioxidative damage activity with EC₅₀ values of 10.5 μg/mL and 7.6 μg/mL, respectively, while 3-hydroxy-2,4-dimethoxyxanthone (8) exhibited cytotoxic effect on the damaged cells with IC₅₀ values of 7.1 μg/mL.

A review on α-mangostin as a potential multi-target-directed ligand for Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive memory loss, declining language skills and other cognitive disorders. AD has brought great mental and economic burden to patients, families and society. However due to the complexity of AD's pathology, drugs developed for the treatment of AD often fail in clinical or experimental trials. The main problems of current anti-AD drugs are low efficacy due to mono-target method or side effects, especially high hepatotoxicity. To tackle these two main problems, multi-target-directed ligand (MTDL) based on "one molecule, multiple targets" has been studied. MTDLs can regulate multiple biological targets at the same time, so it has shown higher efficacy, better safety. As a natural active small molecule, α-mangostin (α-M) has shown potential multi-factor anti-AD activities in a series of studies, furthermore it also has a certain hepatoprotective effect. The good availability of α-M also provides support for its application in clinical research. In this work, multiple activities of α-M related to AD therapy were reviewed, which included anti-cholinesterase, anti-amyloid-cascade, anti-inflammation, anti-oxidative stress, low toxicity, hepatoprotective effects and drug formulation. It shows that α-M is a promising candidate for the treatment of AD.

Modulation of LPS-induced inflammation in RAW264.7 murine cells by novel isoflavonoids from Millettia pulchra

Millettia pulchra is a renowned anti-inflammatory herbal medicine in southeast provinces of China. However, the underlying anti-inflammation mechanism remained incompletely understood. Herein, four new isoflavones, pulvones A-D and eleven reported constituents were isolated from the stems of Millettia pulchra with their structures being elucidated by HRMS and NMR analysis. The anti-inflammatory activities of pulvones A and C were further evaluated due to the better inhibitory activity on nitric oxide production in LPS-stimulated RAW264.7 cells and no obvious cytotoxicity to RAW264.7 cells. Western blot showed that pulvones A significantly decreased the levels of iNOS and COX-2 proteins and pulvones C only decreased the level of iNOS protein. ELISA analysis demonstrated that pulvones A inhibited the production of both interleukin-6 (IL-6) and IL-1β while pulvones C showed better suppression effect on IL-1β production in LPS-stimulated RAW264.7 cells. Then, their potential inhibitory effects on NF-κB pathway were tested in LPS-stimulated RAW264.7 cells. Immunofluorescence and western blot assay showed that pulvones A and C reduced the nuclear translocation of NF-κB(p65) and interrupted IκB phosphorylation. The ADP-Glo™ kinase assay showed pulvones A and C could directedly inhibit the IKKβ kinase activity with the inhibitory rate of 40%, which were also verified by docking study. Collectively, these results suggested that pulvones A and C's anti-inflammatory effects were relevant to the interruption of NF-κB activation by inhibiting IKKβ kinase.

Two new xanthones from the roots of Cratoxylum cochinchinense and their cytotoxicity

Two new xanthones namely cratochinone A (1) and cratochinone B (2), along with 16 known xanthones, were isolated from the roots of Cratoxylum cochinchinense. Their structures were characterized by spectroscopic methods, especially 1D and 2D NMR as well as comparison with those reported in the literature for known xanthones. All isolated compounds were evaluated for their cytotoxicity against five human cancer cell lines (KB, HeLa S-3, HT-29, MCF-7 and Hep G2 cell lines). Compounds 2, 5, and 7 showed significant cytotoxic effects against all cell lines with IC₅₀ values in the range of 0.91-9.93 μM, while 10 exhibited cytotoxicity against the KB, HeLa S-3, and HT-29 cells with IC₅₀ values of 7.39, 6.07, and 8.11 μM, respectively. Compound 12 exhibited cytotoxicity against both KB and HeLa S-3 cells with IC₅₀ values of 7.28 and 9.84 μM.

Tetrandraxanthones A-I, Prenylated and Geranylated Xanthones from the Stem Bark of Garcinia tetrandra

Nine new xanthones, tetrandraxanthones A-I (1-9), and 22 known xanthones (10-31) were isolated from Garcinia tetrandra stem bark. The structures of 1-9 were characterized through detailed spectroscopic analysis, including HRESIMS and 2D NMR data. Among the compounds tested for their cytotoxicity, 26 showed significant cytotoxic effects against five human cancer cell lines, including MCF-7, HT-29, KB, Hep G2, and HeLa S3, with IC₅₀ values in the range of 1.6-3.4 μM, while 10 and 11 were cytotoxic against the MCF-7, HeLa S3, and KB cell lines, with IC₅₀ values of 4.3-9.0 μM.

Phytochemical analysis of Vietnamese propolis produced by the stingless bee Lisotrigona cacciae

Propolis produced by the stingless bee Lisotrigona cacciae was studied for the first time. Using different chromatographic procedures, a total of eighteen constituents (phenols and triterpenes) were isolated, among which flavane 1, homoisoflavanes 2-4, and xanthones 5 and 6 were new for propolis. Propolis extract was also characterized by gas chromatography/mass spectrometry and other fifteen constituents were identified. The xanthone α-mangostin (8) demonstrated significant activity against Staphylococcus aureus with MIC and MBC 0.31 μg/ml, followed by 7,4'-dihydroxy-5-methoxy-8-methylflavane (1) with MIC 78 μg/ml and MBC 156 μg/ml. 10,11- Dihydroxydracaenone C (4), a component bearing ortho-hydroxyl groups, was the only compound displaying radical scavenging ability. Triple botanical origin of the sample was defined, consisting of Dracaena cochinchinensis, Cratoxylum cochinchinense and Mangifera indica. D. cochinchinensis is a new resin source of propolis.

A pair of new enantiomers of xanthones from the stems and leaves of Cratoxylum cochinchinense

Background

The simple and caged xanthones from Clusiaceae showed significant antineoplastic activity. This study aims to identify structural diverse xanthones and search for novel antitumor natural products from this family plants.

Methods

The structures of new compounds 1a and 1b were elucidated mainly through comprehensive NMR and MS spectroscopic data, and their absolute configurations were determined by the comparison of the experimental and calculated electronic circular dichroism.

Results

A pair of new xanthone enantiomers, (+)- and (-)-cracochinxanthone A (1a and 1b), along with thirty known analogues (2-31), were isolated from extracts of the stems and leaves of C. cochinchinense. Preliminary biological assay of some isolates against HL-60, PC-3, and MDA-MB-231 cancer cell lines.

Conclusion

Some isolated xanthones exhibited high sensitivity against three human malignant cell lines and the structure-activity relationship study showed that the prenyl and geranyl units may play an important role in antitumor activity.

Potential Anticancer Agents Characterized from Selected Tropical Plants

Higher plants are well known for their value in affording clinically useful anticancer agents, with such compounds acting against cancer cells by a range of mechanisms of action. There remains a strong interest in the discovery and development of plant secondary metabolites as additional cancer chemotherapeutic lead compounds. In the present review, progress on the discovery of plant-derived compounds of the biflavonoid, lignan, sesquiterpene, steroid, and xanthone structural types is presented. Several potential anticancer leads of these types have been characterized from tropical plants collected in three countries as part of our ongoing collaborative multi-institutional project. Preliminary structure-activity relationships and work on in vivo testing and cellular mechanisms of action are also discussed. In addition, the relevant work reported by other groups on the same compound classes is included herein.

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.

Cytotoxic and NF-κB and mitochondrial transmembrane potential inhibitory pentacyclic triterpenoids from Syzygium corticosum and their semi-synthetic derivatives

Syzygium is a large genus of flowering plants, with several species, including the clove tree, used as important resources in the food and pharmaceutical industries. In our continuing search for anticancer agents from higher plants, a chloroform extract of the leaves and twigs of Syzygium corticosum collected in Vietnam was found to be active toward the HT-29 human colon cancer cell line. Separation of this extract guided by HT-29 cells and nuclear factor-kappa B (NF-κB) inhibition yielded 19 known natural products, including seven triterpenoids, three ellagic acid derivatives, two methylated flavonoids, a cyclohexanone, four megastigmanes, a small lactone, and an aromatic aldehyde. The full stereochemistry of (+)-fouquierol (2) was defined for the first time. Biological investigations showed that (+)-ursolic acid (1) is the major cytotoxic component of S. corticosum, which exhibited also potent activities in the NF-κB and mitochondrial transmembrane potential (MTP) inhibition assays conducted, with IC50 values of 31 nM and 3.5 µM, respectively. Several analogues of (+)-ursolic acid (1) were synthesized, and a preliminary structure-activity relationship (SAR) study indicated that the C-3 hydroxy and C-28 carboxylic acid groups and 19,20-dimethyl substitution are all essential in the mediation of the bioactivities observed for this triterpenoid.

Synthesis and antiproliferative activity of derivatives of the phyllanthusmin class of arylnaphthalene lignan lactones

A series of arylnaphthalene lignan lactones based on the structure of the phyllanthusmins, a class of potent natural products possessing diphyllin as the aglycone, has been synthesized and screened for activity against multiple cancer cell lines. SAR exploration was performed on both the carbohydrate and lactone moieties of this structural class. These studies have revealed the importance of functionalization of the carbohydrate hydroxy groups with both acetylated and methylated analogues showing increased potency relative to those with unsubstituted sugar moieties. In addition, the requirement for the presence and position of the C-ring lactone has been demonstrated through reduction and selective re-oxidation of the lactone ring. The most potent compound in this study displayed an IC₅₀ value of 18 nM in an HT-29 assay with several others ranging from 50 to 200 nM. In an effort to elucidate their potential mechanism(s) of action, the DNA topoisomerase IIa inhibitory activity of the most potent compounds was examined based on previous reports of structurally similar compounds, but does not appear to contribute significantly to their antiproliferative effects.

Caged xanthones displaying protein tyrosine phosphatase 1B (PTP1B) inhibition from Cratoxylum cochinchinense

Four new caged xanthones (1-4) and two known compounds (5, 6) were isolated from the roots of Cratoxylum cochinchinense, a polyphenol rich plant, collected in China. The structures of the isolated compounds (1-6) were characterized by obtaining their detailed spectroscopic data. In particular, compounds 1 and 6 were fully identified by X-ray crystallographic data. The isolated compounds (1-6) were evaluated against protein tyrosine phosphatase 1B (PTP1B), which plays an important role in diabetes, obesity, and cancer. Among these compounds, 3, 4, and 6 displayed significant inhibition with IC₅₀ values of 76.3, 43.2, and 6.6 µM, respectively. A detailed kinetic study was conducted by determining K_m, V_max, and the ratio of K_ik and K_iv, which revealed that all the compounds behaved as competitive inhibitors.

Design, synthesis and structure–activity relationships of mangostin analogs as cytotoxic agents

A series xanthone derivatives were synthesized and cytotoxicity results indicated that the isopentene group at C-8 is essential.

Highly Cytotoxic Xanthones from Cratoxylum cochinchinense Collected in Myanmar

Eight xanthones and one anthraquinone, together with four common triterpenoids, have been isolated from the barks of Cratoxylum cochinchinense, collected in Myanmar. The structures of the metabolites were elucidated by spectroscopic data analysis and their antiproliferative activities were measured against six human tumor cell lines, by using the MTT assay. Pruniflorone N (1) showed a significant cytotoxicity against all cancer cells with IC50 values in the range 3-9 μM, on average higher than the anticancer drug cisplatin. Instead, compounds 2 and 3 exhibited high antiproliferative activity against some specific cell lines.

Antibiofilm activity of α-mangostin extracted from Garcinia mangostana L. against Staphylococcus aureus

OBJECTIVE

To isolate α-mangostin (AMG) from the peels of mangosteen (Garcinia mangostana L.), grown in Vietnam, and to investigate antibiofilm activity of this compound against three Staphylococcus aureus (S. aureus) strains, one of which was methicillin-resistant S. aureus (MRSA) and the other two strains were methicillin-sensitive S. aureus (MSSA).

METHODS

AMG in n-hexane fraction was isolated on a silica gel column and chemically analyzed by HPLC and NMR. The antibiofilm activity of this compound was investigated by using a 96-well plate model for the formation of biofilms. Biofilm biomass was quantified using crystal violet. The viability of cells was observed under confocal microscopy using LIVE/DEAD BacLight stains. Biofilm composition was determined using specific chemical and enzyme tests for polysaccharide, protein and DNA. Membrane-damaging activity was assayed by measuring the hemolysis of human red blood cells in presence of AMG.

RESULTS

The results indicated that the isolated AMG, with a purity that exceeded 98%, had minimal inhibitory concentrations in the range of 4.6-9.2 μmol/L for the three strains tested. Interestingly, the MSSA strains were more sensitive to AMG than the MRSA strain. Minimal bactericidal concentrations were 2-fold higher than the minimal inhibitory concentration values for the three strains, indicating that AMG was a bactericidal compound. AMG also prevented biofilm formation effectively, albeit that again the MRSA strain was the most resistant. Interestingly, biofilms of the MRSA strain contained protein as a main component of the extracellular matrix, whereas this was polysaccharide in the MSSA strains. This might relate to the resistance of the MRSA 252 strain to AMG. Assays using human red blood cells indicated that AMG caused significant membrane damage with 50% of cell lysis occurred at concentration of about 36 μmol/L.

CONCLUSIONS

Our results provide evidence that the isolated AMG has inhibitory activity against biofilm formation by S. aureus, including MRSA. Thus, isolated AMG proposes a high potential to develop a novel phytopharmaceutical for the treatment of MRSA.

Scalemic Caged Xanthones Isolated from the Stem Bark Extract of Garcinia propinqua

Seven new caged xanthones, doitunggarcinones E-K (1-7), all as scalemic mixtures and 10 known compounds (8-17), were isolated from the stem bark extract of Garcinia propinqua. The structures were elucidated on the basis of spectroscopic methods. The separation of the enantiomers of 1-6 was achieved by semipreparative chiral HPLC. The absolute configuration of compound (+)-1 was determined by single-crystal X-ray crystallographic analysis using Cu Kα radiation. The absolute configurations of the other related compounds were determined from comparisons of their ECD spectra with that of compound (+)-1. Compounds (-)-6 and 7 showed cytotoxicity against a colon cancer cell line with IC₅₀ values of 14.23 and 23.95 μM, respectively.

Pharmacology of mangostins and their derivatives: A comprehensive review

Mangosteen (Garcinia mangostana Linn.) is a well-known tropical tree indigenous to Southeast Asia. Its fruit's pericarp abounds with a class of isoprenylated xanthones which are referred as mangostins. Numerous in vitro and in vivo studies have shown that mangostins and their derivatives possess diverse pharmacological activities, such as antibacterial, antifungal, antimalarial, anticarcinogenic, antiatherogenic activities as well as neuroprotective properties in Alzheimer's disease (AD). This review article provides a comprehensive review of the pharmacological activities of mangostins and their derivatives to reveal their promising utilities in the treatment of certain important diseases, mainly focusing on the discussions of the underlying molecular targets/pathways, modes of action, and relevant structure-activity relationships (SARs). Meanwhile, the pharmacokinetics (PK) profile and recent toxicological studies of mangostins are also described for further druggability exploration in the future.

Biotechnological production of hyperforin for pharmaceutical formulation

Hyperforin is a major active constituent of Hypericum perforatum (St. John's wort). It has amazing pharmacological activities, such as antidepressant properties, but it is labile and difficult to synthesize. Its sensitivity and lipophilicity are challenges for processing and formulation. Its chemical complexity provokes approaches of biotechnological production and modification. Dedifferentiated H. perforatum cell cultures lack appropriate storage sites and hence appreciable hyperforin levels. Shoot cultures are capable of forming hyperforin but less suitable for biomass up-scaling in bioreactors. Roots commonly lack hyperforin but a recently established adventitious root line has been demonstrated to produce hyperforin and derivatives at promising levels. The roots also contained lupulones, the typical constituents of hop (Humulus lupulus). Although shear-sensitive, these root cultures provide a potential production platform for both individual compounds and extracts with novel combinations of constituents and pharmacological activities. Besides in vitro cultivation techniques, the reconstruction of hyperforin biosynthesis in microorganisms is a promising alternative for biotechnological production. The biosynthetic pathway is under study, with omics-technologies being increasingly implemented. These biotechnological approaches may not only yield hyperforin at reasonable productivity but also allow for modifications of its chemical structure and pharmacological profile.

Cardiac Glycoside Constituents of Streblus asper with Potential Antineoplastic Activity

Three new (1-3) and two known (4 and 5) cytotoxic cardiac glycosides were isolated and characterized from a medicinal plant, Streblus asper Lour. (Moraceae), collected in Vietnam, with six new analogues and one known derivative (5a-g) synthesized from (+)-strebloside (5). A preliminary structure-activity relationship study indicated that the C-10 formyl and C-5 and C-14 hydroxy groups and C-3 sugar unit play important roles in the mediation of the cytotoxicity of (+)-strebloside (5) against HT-29 human colon cancer cells. When evaluated in NCr nu/nu mice implanted intraperitoneally with hollow fibers facilitated with either MDA-MB-231 human breast or OVCAR3 human ovarian cancer cells, (+)-strebloside (5) showed significant cell growth inhibitory activity in both cases, in the dose range 5-30 mg/kg.

New Benzophenones and Xanthones from Cratoxylum sumatranum ssp. neriifolium and Their Antibacterial and Antioxidant Activities

Two new benzophenones (1 and 2) and four new xanthones (4-6 and 17) together with 24 known compounds (3, 7-16, and 18-30) were isolated from the roots and twigs of Cratoxylum sumatranum ssp. neriifolium. Their structures were elucidated by spectroscopic methods. Compounds 5 and 26 showed antibacterial activity against Micrococcus luteus, Bacillus cereus, and Staphylococcus epidermis with minimum inhibitory concentrations ranging from 4 to 8 μg/mL, whereas compounds 7, 20, and 26 displayed selective antibacterial activities against Staphylococcus aureus (8 μg/mL), Salmonella typhimurium (4 μg/mL), and Pseudomonas aeruginosa (4 μg/mL), respectively. The radical scavenging effects of some isolated compounds were investigated. Compounds 11 and 21 exhibited potent activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) with IC₅₀ values of 7.0 ± 1.0 and 6.0 ± 0.2 μM, respectively.

Recent developments in the pharmacology of prenylated xanthones

Prenylated xanthones are secondary metabolites that are particularly common in plants belonging to the Clusiaceae family. Such compounds have been the focus intensive research because of their potential as biologically active agents. Here, we survey data published over the past decade relating to the properties of prenylated xanthones to provide a more detailed view of the potential of these naturally occurring compounds as therapeutic agents.

Cratoxylum formosum Extracts Inhibit Growth and Metastasis of Cholangiocarcinoma Cells by Modulating the NF-κB and STAT3 Pathways

Cratoxylum formosum Dyer has been used in Southeast Asian countries both for food and folk medicine. In this study, the leaf extracts of C. formosum were evaluated for anticancer effects on human cholangiocarcinoma (CCA) KKU-M156 cells. The results showed that the plant extracts possessed potent cytotoxicity against CCA cells. The cytotoxic activity was associated with an induction of cell apoptosis. Moreover, the colony forming ability of CCA cells was also inhibited by C. formosum extracts. Consistent with growth inhibitory effects, the plant extracts induced cell cycle arrest at the G2/M phase and downregulated cyclin A and Cdc25A protein expression. The extracts potently suppressed the migration and invasion properties of CCA cells. The effects were associated with the suppression of NF-κB and STAT3 nuclear translocation and transcriptional activity, and downregulation of genes involving in cancer progression and metastasis. Furthermore, the possible bioactive compounds in the extracts were analyzed by HPLC. Taken together, the potent anticancer activity of C. formosum against CCA indicates the plant promising use for CCA prevention and therapy.

Bioactive Xanthones from Cratoxylum cochinchinense

Chemical investigation of Cratoxylum cochinchinense stem bark has led to the isolation and identification of a new xanthone, cochinchinone M (1), together with 12 known compounds. Their structures were elucidated on the basis of spectroscopic methods, including UV, IR, NMR and MS. Some compounds were evaluated for their antibacterial and acetylcholinesterase inhibitory activities.

Bioactive prenylated xanthones from the stems of Cratoxylum cochinchinense

Cochinchinones M-U (1-9), together with 12 known compounds (10-21), were isolated from the stems of Cratoxylum cochinchinense (Lour.) Blume. Their structures were determined on the basis of extensive spectroscopic data analyses. In addition, their retinoid X receptor-α transcriptional activities were evaluated using an in vitro assay.

Cytotoxic and natural killer cell stimulatory constituents of Phyllanthus songboiensis

A dichapetalin-type triterpenoid and a dibenzylbutyrolactone-type lignan, together with five known lignans, a known aromatic diterpenoid, and a known acylated phytosterol, were isolated from the aerial parts of Phyllanthus songboiensis, collected in Vietnam. Their structures were determined by interpretation of the spectroscopic data, and the inhibitory activity toward HT-29 human colon cancer cells of all isolates was evaluated by a cytotoxicity assay. The known arylnaphthalene lignan, (+)-acutissimalignan A, was highly cytotoxic toward HT-29 cells, with an IC50 value of 19 nM, but this compound was inactive as a DNA topoisomerase IIα (topo IIα) poison. The known phytosterol, (-)-β-sitosterol-3-O-β-D-(6-O-palmitoyl)glucopyranoside, was found to stimulate natural killer (NK) cells at a concentration of 10μM in the presence of interleukin 12 (IL-12).

Investigation of Vietnamese plants for potential anticancer agents

Higher plants continue to afford humankind with many new drugs, for a variety of disease types. In this review, recent phytochemical and biological progress is presented for part of a collaborative multi-institutional project directed towards the discovery of new antitumor agents. The specific focus is on bioactive natural products isolated and characterized structurally from tropical plants collected in Vietnam. The plant collection, identification, and processing steps are described, and the natural products isolated from these species are summarized with their biological activities.

Potent cytotoxic arylnaphthalene lignan lactones from Phyllanthus poilanei

Two new (1 and 2) and four known arylnaphthalene lignan lactones (3-6) were isolated from different plant parts of Phyllanthus poilanei collected in Vietnam, with two further known analogues (7 and 8) being prepared from phyllanthusmin C (4). The structures of the new compounds were determined by interpretation of their spectroscopic data and by chemical methods, and the structure of phyllanthusmin D (1) was confirmed by single-crystal X-ray diffraction analysis. Several of these arylnaphthalene lignan lactones were cytotoxic toward HT-29 human colon cancer cells, with compounds 1 and 7-O-[(2,3,4-tri-O-acetyl)-α-L-arabinopyranosyl)]diphyllin (7) found to be the most potent, exhibiting IC50 values of 170 and 110 nM, respectively. Compound 1 showed activity when tested in an in vivo hollow fiber assay using HT-29 cells implanted in immunodeficient NCr nu/nu mice. Mechanistic studies showed that this compound mediated its cytotoxic effects by inducing tumor cell apoptosis through activation of caspase-3, but it did not inhibit DNA topoisomerase IIα activity.

Cratoxylum formosum (Jack) Dyer ssp. pruniflorum (Kurz) Gogel. (Hóng yá mù) extract induces apoptosis in human hepatocellular carcinoma HepG2 cells through caspase-dependent pathways

BACKGROUND

Cratoxylum formosum (Jack) Dyer ssp. pruniflorum (Kurz) Gogel. (Hóng yá mù) (CF) has been used for treatment of fever, cough, and peptic ulcer. Previously, a 50% ethanol-water extract from twigs of CF was shown highly selective in cytotoxicity against cancer cells. This study aims to investigate the molecular mechanisms underlying the apoptosis-inducing effect of CF.

METHODS

The cytotoxicity of CF was evaluated in the human hepatocellular carcinoma (HCC) HepG2 cell line in comparison with a non-cancerous African green monkey kidney epithelial cell line (Vero) by a neutral red assay. The apoptosis induction mechanisms were investigated through nuclear morphological changes, DNA fragmentation, mitochondrial membrane potential alterations, and caspase enzyme activities.

RESULTS

CF selectively induced HepG2 cell death compared with non-cancerous Vero cells. A 1.5-fold higher apoptotic effect compared with melphalan was induced by 120 μg/mL of the 50% ethanol-water extract of CF. The apoptotic cell death in HepG2 cells occurred via extrinsic and intrinsic caspase-dependent pathways in dose- and time-dependent manners by significantly increasing the activities of caspase 3/7, 8, and 9, decreasing the mitochondrial membrane potential, and causing apoptotic body formation and DNA fragmentation.

CONCLUSIONS

CF extract induced a caspase-dependent apoptosis in HepG2 cells.

New isoflavonoids from Erythrina arborescens and structure revision of anagyroidisoflavone A

Five hitherto unknown isoflavonoids, namely erythrinins D-H (1–5), were isolated from the ethanol extract of Erythrina arborescens. Their structures were elucidated on the basis of extensive spectroscopic studies. In addition, the structure of anagyroidisoflavone A (6a) has been revised as 1″-O-methylerythrinin F (6) by re-analysis of the original spectroscopic data.

Cytotoxic and NF-κB inhibitory sesquiterpene lactones from Piptocoma rufescens

Six new (1-6) and eight known germacranolide-type sesquiterpene lactones, along with several known phenylpropanol coumarates and methylated flavonoids, were isolated from the leaves of Piptocoma rufescens, collected in the Dominican Republic. The new compounds were identified by analysis of their spectroscopic data, with the molecular structure of 3 being established by single-crystal X-ray diffraction. The absolute configurations of the sesquiterpene lactones isolated were determined from their CD and NOESY NMR spectra, together with the analysis of Mosher ester reactions. Bioassay screening results showed the majority of the sesquiterpene lactones isolated (1-13) to be highly cytotoxic toward the HT-29 human colon cancer cell line, with the most potent compound being 15-deoxygoyazensolide (10, IC(50), 0.26 µM). In addition, several of the sesquiterpene lactones exhibited NF-κB (p65) inhibitory activity.

Prenylated caged xanthones: chemistry and biology

CONTEXT

Prenylated caged xanthones are "privileged structure" characterized by the presence of the unusual 4-oxo-tricyclo[4.3.1.0(3,7)]dec-8-en-2-one scaffold. The natural sources of these compounds confines mainly in the Garcinia genus in the family of Guttiferae. Gambogic acid is the most abundant substance and most of the studies have been done on this compound, particularly as a new potential antitumor agent. The history, sources, structural diversity, and biological activities of these compounds are covered.

OBJECTIVE

This review is written with the intention to provide additional aspects from what have been published of prenylated caged xanthones, including history, sources, structural diversity, and biological activities.

METHODS

This review has been compiled using information from a number of reliable references mainly from major databases including SciFinder, ScienceDirect, and PubMed.

RESULTS

More than 120 prenylated caged xanthones have been found in the plant genera Garcinia, Cratoxylum, and Dascymaschalon. These compounds exhibited various potentially useful biological activities such as anticancer, anti-HIV-1, antibacterial, anti-inflammatory, and neurotrophic activities.

CONCLUSIONS

Prenylated caged xanthones, both naturally occurring and synthetic analogues, have been identified as promising bioactive compounds, especially for anticancer agents. Gambogic acid has been demonstrated to be a highly valuable lead compound for antitumor chemotherapy. The structure activity relationship (SAR) study of its analogues is still the subject of intensive research. Apoptosis cytotoxic mechanism has been identified as the major pathway. Research on the delineation of the in-depth mechanism of action is still on-going. Analogues of gambogic acid had been identified to be effective against a rare and special form of liver cancer, cholangiocarcinoma for which currently there is no chemotherapeutic treatment available.