Chemical constituents of the plants of the genus Calophyllum

Xanthones: Biosynthesis and Trafficking in Plants, Fungi and Lichens

Xanthones are a class of secondary metabolites produced by plant organisms. They are characterized by a wide structural variety and numerous biological activities that make them valuable metabolites for use in the pharmaceutical field. This review shows the current knowledge of the xanthone biosynthetic pathway with a focus on the precursors and the enzymes involved, as well as on the cellular and organ localization of xanthones in plants. Xanthone biosynthesis in plants involves the shikimate and the acetate pathways which originate in plastids and endoplasmic reticulum, respectively. The pathway continues following three alternative routes, two phenylalanine-dependent and one phenylalanine-independent. All three routes lead to the biosynthesis of 2,3',4,6-tetrahydroxybenzophenone, which is the central intermediate. Unlike plants, the xanthone core in fungi and lichens is wholly derived from polyketide. Although organs and tissues synthesizing and accumulating xanthones are known in plants, no information is yet available on their subcellular and cellular localization in fungi and lichens. This review highlights the studies published to date on xanthone biosynthesis and trafficking in plant organisms, from which it emerges that the mechanisms underlying their synthesis need to be further investigated in order to exploit them for application purposes.

Plant Coumarins with Anti-HIV Activity: Isolation and Mechanisms of Action

This review summarizes and systematizes the literature on the anti-HIV activity of plant coumarins with emphasis on isolation and the mechanism of their antiviral action. This review summarizes the information on the anti-HIV properties of simple coumarins as well as annulated furano- and pyranocoumarins and shows that coumarins of plant origin can act by several mechanisms: inhibition of HIV reverse transcriptase and integrase, inhibition of cellular factors that regulate HIV-1 replication, and transmission of viral particles from infected macrophages to healthy ones. It is important to note that some pyranocoumarins are able to act through several mechanisms or bind to several sites, which ensures the resistance of these compounds to HIV mutations. Here we review the last two decades of research on the anti-HIV activity of naturally occurring coumarins.

Two New Xanthones from the Twigs of Calophyllum membranaceum and Their Anti-Inflammatory Activities in HESC Cells

Two new xanthones, calmemxanthone A (1) and calmemxanthone B (2), along with eleven known compounds were isolated from the dried twigs of Calophyllum membranaceum Gardn. et Champ. The structures of compounds 1 and 2 were established by analysis of spectra and mass spectrometry data. The absolute configuration of compound 1 was confirmed by electronic circular dichroism (ECD) spectral analysis. The anti-inflammation action of these compounds were evaluated on lipopolysaccharide (LPS)-induced inflammatory damage to human endometrial stromal cells (HESCs), and the structure-activities of 1-13 were also discussed. Compound 10 presented the anti-inflammation action with an IC₅₀ value of 20.3 μM, that might be relevant to the regulation of NF-κB signaling pathway via the suppression of TRIF, IKKα, and IκBα.

Pyranochromones with Anti-Inflammatory Activities in Arthritis from Calophyllum membranaceum

Eleven new pyranochromones, calomembranone A-K (1-11), two new pyranocoumarins, calopolyanolide E and F (12 and 13), together with six known analogues (14-19) were isolated from the leaves of Calophyllum membranaceum. Their structures and absolute configurations were elucidated by analysis of spectroscopic data, computational calculations, as well as X-ray crystallography of 4 and 9. The anti-inflammatory activities of all the isolates were evaluated by measuring their NO inhibitory effects in LPS-stimulated RAW 264.7 cells. Structure-activity relationships are also discussed. Compound 7 showed the strongest NO inhibition (IC₅₀ = 0.92 μM). Oral administration of 7 dose-dependently reduced the paw swelling and downregulated neutrophil-to-lymphocyte ratio in the carrageenan-induced acute arthritis mice model. Molecular dynamics simulation and cellular thermal shift assay results indicated that 7 participated in a robust and stable interaction with the active site of TLR4. Compound 7 also suppressed the inflammation in arthritis through the regulation of TLR4 mediated signal transduction via IKK/NF-κB signaling pathway and the consequent reduction of IL-2, IL-4, and IL-5.

Using 13 C-NMR dereplication to aid in the identification of xanthones present in the stem bark extract of Calophyllum brasiliense

INTRODUCTION

Xanthones are metabolites with a variety of biological properties. The Clusiaceae family, which until recently included the genus Calophyllum, is recognised for its production of monohydroxylated and polyhydroxylated xanthones. Presently, C. brasiliense is the only Calophyllum spp. known to occur in the Yucatan peninsula.

OBJECTIVE

To use a combination of traditional phytochemical methods and carbon-13 nuclear magnetic resonance (¹³ C-NMR) dereplication analysis to identify xanthones in the stem bark of C. brasiliense.

MATERIAL AND METHODS

Initial fractionation and purification of the stem bark extract of C. brasiliense produced macluraxanthone (1). Additional xanthones, together with chromanones and terpenoids, were identified using ¹³ C-NMR dereplication analysis in different semipurified fractions obtained from the low and medium polarity fractions of the stem bark extract of C. brasiliense.

RESULTS

Initial identification of macluraxanthone (1) was confirmed by ¹³ C-NMR dereplication analysis; additionally, ¹³ C-NMR dereplication analysis allowed the identification of a number of monohydroxylated and polyhydroxylated xanthones, together with chromanones and terpenoids.

CONCLUSION

This study confirms C. brasiliense as a rich source of xanthones and the ¹³ C-NMR dereplication analysis as a suitable method to quickly identify the presence of different families of secondary metabolites in semipurified fractions.

Stigmasterol and Stigmasterone from Methanol Extract of Calophyllum soulattri Burm. F. Stem Bark

Stigmasterol and Stigmasterone from Methanol Extract of Calophyllum soulattri Burm. F. Stem Bark. Calophyllum soulattri Burm. F. has been widely used for herbal medicine. Phytochemical investigation of C. soulattri contains a secondary metabolite of the steroid class. Steroid compounds have various biological activities, such as anti-inflammatory, antioxidant, antiproliferative, antibacterial, antimalarial, and anticancer. Two secondary metabolites steroids have been isolated and identified from the stem bark extract of C. soulattri. Isolation was carried out through the extraction (maceration), fractionation, and purification stages. Maceration is carried out using methanol as a solvent. Fractionation was carried out by vacuum liquid chromatography (VLC), and purification was by flash column chromatography. Identification of combined fractions and determination of pure isolates were used through thin-layer chromatography (TLC). The solvent used in the chromatography methods was a mixture of n-hexane and ethyl acetate. The structure isolates were identified by FTIR, 1H NMR, and 13C NMR and compared with literature data. Secondary metabolites steroids that have been isolated are identical compounds to stigmasterol and stigmasterone.

Additional Insights into Hypericum perforatum Content: Isolation, Total Synthesis, and Absolute Configuration of Hyperbiphenyls A and B from Immunomodulatory Root Extracts

Phytochemical investigation of the root extracts of Hypericum perforatum led to the isolation of two biphenyl derivatives named hyperbiphenyls A and B (1 and 2) and four known xanthones (3-6). These structures were elucidated by spectroscopic and spectrometric methods including UV, NMR, and HRMS. The absolute configuration of the biphenyl derivatives was defined by two different approaches: biomimetic total synthesis of racemic hyperbiphenyl A followed by ¹H and ¹⁹F NMR Mosher's esters analysis and stereoselective total synthesis of hyperbiphenyl B, permitting assignment of the S absolute configuration for both compounds. The bioactivity of compounds 1-6 toward a set of biomolecules, including major histocompatibility complex (MHC) molecules expressed on vascular endothelial cells, was measured. The results showed that the major xanthone, i.e., 5- O-methyl-2-deprenylrheediaxanthone B (3), is a potent inhibitor of MHC that efficiently reduces HLA-E, MHC-II, and MICA biomolecules on cell surfaces.

Cancer Chemopreventive Activity of Xanthones from Calophyllum elatum

In our continuing search for compounds with antitumor-promoting activity, we screened eight xanthones isolated from Calophyllum elatum Bedd. (Guttiferae) by examining their possible inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12- O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. Several compounds tested in this study showed inhibitory activity against EBV, without showing any cytotoxicity. Isogarciniaxanthone E (2) showed more potent activity than any of the other compounds tested. Furthermore, isogarciniaxanthone E (2) exhibited a marked inhibitory effect on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.

Bioactive Coumarins and Xanthones From Calophyllum Genus and Analysis of Their Druglikeness and Toxicological Properties

Calophyllum spp. (Calophyllaceae) is a genus of tropical trees valued in the chemopharmacological industry as an important source of biogenetically related coumarins and xanthones, which can lead to the development of new drugs due to their relevant pharmacological activities and diversity of molecular structural. These compounds have relevant pharmacological activities, such as: cytotoxicity against human tumor cell lines (especially leukemia), parasites (Plasmodium, Leshmania, and Trypanosoma), retroviruses (e.g., HIV), and Mycobacterium tuberculosis. Chemoinformatic and toxicoinformatic tools were used here to perform a computational analysis of 70 coumarins and 70 xanthones isolated from this genus in order to explore their potential as new drugs. Most coumarins from this genus possess similar patterns of druglikeness with differences in its physicochemical properties. Xanthones, on the other hand, show quite similar physicochemical properties and druglikeness. It is interesting to note that the vast majority of these compounds (57 coumarins and 59 xanthones) are in compliance with Lipinski´s Rule of Five. Remarkably, two xanthones (2-hydroxyxanthone and caledonixanthone-B) have leadlikeness potential that accordingly with chemoinformatic analysis may target MAO A and B, respectively, and therefore may exhibit antidepressant potential. These compounds also target tyrosine-phosphorilation-regulated kinase 1A (DYRK1A) which is over-expressed in a variety of hematological and brain cancers, therefore they could act as anticancer compounds. Several toxicological predictions were also depicted. Coumarins could be an irritant and may affect the reproductive system, while xanthones may have mutagenic results. To our knowledge, this is the first chemoinformatic report on the main active compounds of this genus and its potential for drug development.

Trends in the chemical and pharmacological research on the tropical trees Calophyllum brasiliense and Calophyllum inophyllum, a global context

Tropical trees of Calophyllum genus (Calophyllaceae) have chemical and biological importance as potential source of secondary active metabolites which can lead to the development of new drugs. Research on this species has been rising since 1992 due to the discovering of anti-HIV properties of Calanolide A found in Calophyllum inophyllum leaves. This compound is the most important natural product for potential development of new anti-HIV drugs and phytomedicines. The scientometric analysis (1953–2014) here performed revealed that the most studied species of Calophyllum genus are: C. inophyllum and C. brasiliense, distributed in the Asian, and American continents, respectively. Current research on these species is carried out mainly in India and Brazil, respectively, where these species grow. Research on C. brasiliense is focused mainly on ecological, antiparasitic, cytotoxic properties, and isolation of new compounds. Chemical studies and biodiesel development are the main topics in the case of C. inophyllum. Text mining analysis revealed that coumarins, and xanthones are the main secondary active metabolites responsible for most of the reported pharmacological properties, and are potential compounds for the treatment of leukemia and against intracellular parasites causing American Trypanosomiasis and Leshmaniasis. On the other hand, C. inophyllum represents an important source for the development of 2nd generation biodiesel. Medicinal and industrial applications of these species may impulse sustainable forest plantations. To our knowledge this is the first scientometric and text mining analysis of chemical and biomedical research on Calophyllum genus, C. brasiliense and C. inophyllum.

Antifilarial Activity of Constituents of Calophyllum inophyllum and their Derivatives

Elephantiasis is a classic sign of late-stage lymphatic filariasis. Although the infection can be treated with drugs, the chronic conditions may not be curable by currently available antifilarial drugs. In continuation of our drug discovery program, we identified potent antifilarial activity in a calophyllic acid and isocalophllic acid mixture, which was isolated from the leaves of Calophyllum inophyllum. The mixture inhibited the motility of adult Brugia malayi worms and microfilariae stage parasites at a concentration of 15.6 μg/mL with an IC50 of 2.1 and 5.5 μg/mL, respectively, in in vitro studies. The diastereomeric mixture also exhibited moderate in vivo antifilarial activity in the jird ( Meriones unguiculatus) model. A few derivatives of calophyllic acid and isocalophyllic acid were prepared and one of the amide derivatives turned out to be the most promising compound against the adult (MIC: 3.9 and IC50: 0.32 μg/mL) and microfilariae stage (MIC:1.9 and IC50: 0.26 μg/mL) parasites with a high selectivity index. The amide derivative has superior activity than the parent natural product, as well as the standard antifilarial drug, ivermectin.

Antidyslipidemic and antioxidant activity of the constituents isolated from the leaves of Calophyllum inophyllum

In continuation of our drug discovery program on Indian medicinal plants, we isolated bioactive compounds (1-5) from the leaves of Calophyllum inophyllum and evaluated their antidyslipidemic activity in triton induced hyperlipidemia model. The calophyllic acid (1A) and isocalophyllic acid (1B) mixture, canophyllic acid (4) and amentoflavone (5) showed dose dependent lipid lowering activity in in vivo experiments. The compounds 1A+1B mixture and 3 also showed good in vitro antioxidant activity.

Bioguided fractionation and isolation of natural inhibitors of advanced glycation end-products (AGEs) from Calophyllum flavoramulum

Advanced glycation end-products (AGEs) are associated with many pathogenic disorders such as Alzheimer's disease, pathogenesis of diabetes, atherosclerosis or endothelial dysfunction leading to cardiovascular events. Clusiaceae and Calophyllaceae families are rich in compounds like polyphenols which are able to inhibit their formation and are therefore of great interest. Calophyllum flavoramulum Hend. & Wyatt-Sm., a native Malaysian plant, was selected after an anti-AGEs screening conducted on DCM and MeOH extracts from plants belonging to these aforementioned families. In a first study, bioguided fractionation of the MeOH leaf extract of C. flavoramulum afforded amentoflavone, 3-methoxy-2-hydroxyxanthone, 3,4-dihydroxy-tetrahydrofuran-3-carboxylic acid, quercitrin, 3,4-dihydroxybenzoic acid, canophyllol and apetalactone. Amentoflavone and 3-methoxy-2-hydroxyxanthone were found to be very potent (IC(50)=0.05 and 0.06 mM respectively), while anti-AGEs activities of quercitrin and 3,4-dihydroxybenzoic acid appeared as moderately strong (IC(50)=0.5 mM). In a second study, a systematic phytochemical study of the cyclohexane, DCM and EtOAc extracts obtained from the same plant was conducted to isolate the following products: flavoramulone, 6-deoxyjacareubin, rheediachromenoxanthone, 2,3-dihydroamentoflavone and benzoic acid. 3,4-Dihydroxy-tetrahydrofuran-3-carboxylic acid and flavoramulone were isolated for the first time and their structures were identified by means of IR, MS and NMR spectrometries.

Phenolic compounds from Selaginella moellendorfii

Chemical investigation of the leaves and roots of Selaginella moellendorfii Hieron has resulted in the isolation and characterization of two new flavone glucosides, 7-O-(β-glucopyranosyl(1→2)-[β-glucopyranosyl(1→6)]-β-glucopyranosyl)flavone-3',4',5,7-tetraol (1) and 7-O-(β-glucopyranosyl(1→2)-[β-glucopyranosyl(1→6)]-β-glucopyranosyl)flavone-4',5,7-triol (2), two new biflavonoids, 2,3-dihydroflavone-5,7,4'-triol-(3'→8″)-flavone-5″,6″,7″,4'''-tetraol (3) and 6-methylflavone-5,7,4'-triol-(3'→O→4''')-6″-methylflavone-5″,7″-diol (4), two new lignans, (7'E)-3,5,3',5'-tetramethoxy-8 : 4'-oxyneolign-7'-ene-4,9,9'-triol (5) and 3,3'-dimethoxylign-8'-ene-4,4',9-triol (6), together with two known monolignans, four known lignans, and four known biflavonoids. Their structures were established by spectroscopic means and by comparison with literature values.