Constituents of the Cuban endemic species Calophyllum pinetorum

Friedelin: Structure, Biosynthesis, Extraction, and Its Potential Health Impact

Pharmaceutical companies are investigating more source matrices for natural bioactive chemicals. Friedelin (friedelan-3-one) is a pentacyclic triterpene isolated from various plant species from different families as well as mosses and lichen. The fundamental compounds of these friedelane triterpenoids are abundantly found in cork tissues and leaf materials of diverse plant genera such as Celastraceae, Asteraceae, Fabaceae, and Myrtaceae. They possess many pharmacological effects, including anti-inflammatory, antioxidant, anticancer, and antimicrobial activities. Friedelin also has an anti-insect effect and the ability to alter the soil microbial ecology, making it vital to agriculture. Ultrasound, microwave, supercritical fluid, ionic liquid, and acid hydrolysis extract friedelin with reduced environmental impact. Recently, the high demand for friedelin has led to the development of CRISPR/Cas9 technology and gene overexpression plasmids to produce friedelin using genetically engineered yeast. Friedelin with low cytotoxicity to normal cells can be the best phytochemical for the drug of choice. The review summarizes the structural interpretation, biosynthesis, physicochemical properties, quantification, and various forms of pharmacological significance.

Prenylated chromones and flavonoids isolated from the roots of Flemingia macrophylla and their anti-lung cancer activity

BACKGROUND

The successful launch of icaritin, a therapeutic drug for liver cancer derived from Epimedium brevicornu, has provided new impetus for the development of prenylated flavonoids in the field of oncology. Flemingia macrophylla is reported to contain characteristic prenylated flavonoids which can regulate the p53 protein. We aimed to isolate these constituents and conduct activity evaluation, structure-activity relationship, and mechanism studies to provide candidate compounds for antitumor drug development.

METHODS

In this study, chromatographic techniques combined with spectroscopic methods were used to separate, purify, and identify the constituents of Flemingia macrophylla methanol extract. The cytotoxic activity of the constituents was evaluated using an MTT assay with A549 and H1975 cells as the model. The binding mechanism between the compounds and the p53 protein was investigated with molecular docking and validated with cellular thermal shift assay (CETSA). Western blotting (WB) was employed to detect the expression of p53 protein and apoptosis-related proteins in cells.

RESULTS

Chiral HPLC separation of racemates 1 and 7 provided two pairs of undescribed enantiomers (1a/1b and 7a/7b), along with eight known compounds (2 - 9) isolated from Flemingia macrophylla roots. Their structures were elucidated by spectroscopic analysis, and the absolute configurations of the enantiomers were determined from experimental and calculated electronic circular dichroism data. Compounds 1 - 7, and the non-prenyl analogues 10 - 13, were evaluated for cytotoxic activity against the human lung cancer A549 and H1975 cell line. Compounds 5 - 7 displayed better cytotoxicity than the positive control icaritin in A549 and H1975, with IC50 values ranging from 4.50 to 19.83 μmol·L-1 and < 5 μmol·L-1, respectively. The structure-activity relationships of the chromone or flavonoid analogues against A549 cells were discussed. Molecular docking results demonstrated that compound 7a has strong interaction with p53 and WB indicated that 7a induced apoptosis by increasing the p53 protein, decreasing the anti-apoptotic protein Bcl-2, and activating the caspase family in A549 cells. These results suggest that prenylated flavonoids are potential p53 protein activators.

CONCLUSION

This study demonstrates that Flemingia macrophylla is rich in prenylated flavonoid constituents, among which compounds 5 and 7 exhibited significant cytotoxic activity against A549 cells and served as reference candidates for the design and development of prenylated compounds as antitumor therapeutic drugs.

A Study of Gentianae Radix et Rhizoma Class Differences Based on Chemical Composition and Core Efficacy

(1) Background: Establishment of a method for evaluating Gentianae Radix et Rhizoma (GRR) classes based on chemical composition and core efficacy; (2) Methods: Liquid chromatography-mass spectrometry (LC-MS) was used to determine the chemical constituents of GRR-first class (GF) and GRR-second class (GS). The cell viability, liver function, oxidative stress enzyme activity, and inflammatory factor levels of GF and GS on H2O2-induced HepG2 cells were determined with CCK-8, ELISA, and biochemical methods, and the antioxidant activity of the two was evaluated using bioefficacy; ELISA, biochemical methods, real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) method, and Western blot (WB) were used to determine the liver function, oxidative stress enzyme activity, inflammatory factor levels, and expression of related genes and proteins in mice with acute liver injury (ALI) model induced with 0.3% CCl4 olive oil solution after gavage administration; (3) Results: GF and GS had the same types of components, but the cyclic enol ether terpenes such as morinlon goside c, loganin, gentiopicroside, and swertiamarin differed significantly between the two; the effect of GF on CCl4-induced acute hepatic injury in C57BL/6 mice was stronger compared to GS. It helped alleviate weight loss, increase hepatic and splenic indices, improve hepatic lobular structure and hepatocyte status, inhibit collagen deposition, enhance oxidative stress and anti-inflammatory-related genes and protein expression, and decrease apoptotic genes and proteins more significantly than GS; (4) Conclusions: In this study, we established a GRR class evaluation method combining chemical composition and core medicinal effects, which can rapidly determine the differential composition of GF and GS, detect the quality of GRR through antioxidant bioefficacy, and validate it with in vivo experiments, which provides references for the evaluation of the class of GRR and the rational use of medication in the clinic.

Tissue-Specific Profiling of Biflavonoids in Ginkgo (Ginkgo biloba L.)

Biflavonoids are flavonoid dimers that are much less studied than monomeric flavonoids. Their precise distribution among plants and their role in plants is still unknown. Here, we have developed a HPLC-DAD method that allows us to separate and simultaneously determine the five major biflavonoids (amentoflavone, bilobetin, ginkgetin, isoginkgetin, and sciadopitysin) in ginkgo (Ginkgo biloba L.). We performed tissue-specific profiling of biflavonoids in ten different plant parts: tree bark, twigs bark, twigs without bark, buds, leaf petioles, leaf blades, seed stalks, sarcotesta, nutshells, and kernels. We did not detect biflavonoids in plant parts not in direct contact with the environment (twigs without bark, nutshells, and kernels). We found the highest total biflavonoids content in leaves, where sciadopitysin was predominant. In contrast, in the bark, amentoflavone was the predominant biflavonoid, suggesting that more methylated biflavonoids accumulate in leaves and seeds. This is probably related to their biological function, which remains to be determined.

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.

Caloforines A-G, coumarins from the bark of Calophyllum scriblitifolium

Bioactivity-guided separation of the methanol extract of Calophyllum scriblitifolium bark led to the isolation of five new pyranocoumarins, caloforines A–E (1–5) and two new coumarins, caloforines F and G (6 and 7). Their structures were elucidated by 1D and 2D NMR spectroscopy, and their absolute configurations were investigated by a combination of CD spectroscopy and DFT calculation. Caloforines A–F (1–6) showed moderate antimalarial activity against Plasmodium falciparum 3D7 strain.

Metabolic Engineering of Saccharomyces cerevisiae for High-Level Friedelin via Genetic Manipulation

Friedelin, the most rearranged pentacyclic triterpene, also exhibits remarkable pharmacological and anti-insect activities. In particular, celastrol with friedelin as the skeleton, which is derived from the medicinal plant Tripterygium wilfordii, is a promising drug due to its anticancer and antiobesity activities. Although a previous study achieved friedelin production using engineered Saccharomyces cerevisiae, strains capable of producing high-level friedelin have not been stably engineered. In this study, a combined strategy was employed with integration of endogenous pathway genes into the genome and knockout of inhibiting genes by CRISPR/Cas9 technology, which successfully engineered multiple strains. After introducing an efficient TwOSC1^T502E, all strains with genetic integration (tHMG1, ERG1, ERG20, ERG9, POS5, or UPC2.1) showed a 3.0∼6.8-fold increase in friedelin production compared with strain BY4741. Through further double knockout of inhibiting genes, only strains GD1 and GD3 produced higher yields. Moreover, strains GQ1 and GQ3 with quadruple mutants (bts1; rox1; ypl062w; yjl064w) displayed similar increases. Finally, the dominant strain GQ1 with TwOSC1^T502E was cultured in an optimized medium in shake flasks, and the final yield of friedelin reached 63.91 ± 2.45 mg/L, which was approximately 65-fold higher than that of the wild-type strain BY4741 and 229% higher than that in ordinary SD-His-Ura medium. It was the highest titer for friedelin production to date. Our work provides a good example for triterpenoid production in microbial cell factories and lays a solid foundation for the mining, pathway analysis, and efficient production of valuable triterpenoids with friedelin as the skeleton.

NMR and X-ray studies of apetalic acid isolated from Calophyllum brasiliense and of its chiral amides

The tropical tree Calophyllum brasiliense Cambess. (Clusiaceae) grows in rain forests from Brazil to Mexico. Its leaves, as well as those of other Calophyllum species, are rich sources of chromanone acids, such as apetalic acid, isoapetalic acid, and their derivatives. Apetalic acid has shown significant antimycobacterial activity. The biological activity of apetalic acid has been related to the configuration of three asymmetric centers and the stereochemistry of the molecule; however, the C-19 configuration in the acidic side chain has not been fully resolved. For this reason, the unequivocal determination of the absolute configuration by means of X-ray crystallography in a sample of unique homogeneous apetalic acid stereoisomer was the most important point to start this study. Chiral amides were prepared using the carboxyl group. We determined the C-19 stereochemistry of apetalic acid and its specific chiral derivatives using NMR, X-ray diffraction, and molecular mechanics. Finally, we observed that steric hindrance in the side chain of apetalic acid leads to restriction of rotation around the pivotal linkage C-10–C-19, establishing chiral centers at C2(R), C3(S), and C19(R). We were able to separate the derivatives of these two high-rotatory-barrier conformers of apetalic acid by forming diastereoisomeric amides with phenylglycine methyl ester having a chiral center at C-2′. Our results confirmed the existence of atropisomerism in the apetalic acid molecule.

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.

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.

Functional characterization of an oxidosqualene cyclase (PdFRS) encoding a monofunctional friedelin synthase in Populus davidiana

An oxidosqualene cyclase (PdFRS) from Populus davidiana was characterized as a monofunctional friedelin synthase by its heterologous expression in yeast and overexpression in plants. Triterpenes are one of the largest classes of plant chemical compounds composed of three terpene units, which form the basic skeleton of all sterols and saponins. Friedelin (friedelan-3-one), a pentacyclic triterpene, occurs in many plant families and is particularly present in rich amounts in cork tissues from trees. The biosynthesis of friedelin occurs through the oxidosqualene cyclase (OSC) enzyme that generates friedelin from 2,3-oxidosqualene after the maximum rearrangement of a triterpene skeleton. Populus davidiana is called Korean aspen and grows in northern East Asia. From 57,322 unique sequences generated from the P. davidiana transcriptome database, one complete coding sequence (PdFRS) was obtained from a contig, which showed 74% identity to Betula platyphylla β-amyrin synthase and 73% identity with friedelin synthase from Maytenus ilicifolia. The open reading frame (ORF) region of the PdFRS sequence was 2280 bp long and composed a 759 amino acid protein with a predicted molecular mass of 87.81 kDa. qPCR analysis revealed that methyl jasmonate treatments strongly upregulated PdFRS gene expression and resulted in enhanced friedelin accumulation in leaves. Heterologous expression of the PdFRS gene in yeast resulted in the production of friedelin triterpene as a single product, which was confirmed by comparison with the mass fragmentation pattern from an authentic friedelin standard by GC/MS analysis. Transgenic P. davidiana overexpressing the PdFRS gene was constructed via Agrobacterium-mediated transformation. Overexpression of PdFRS in transgenic P. davidiana lines resulted in enhanced friedelin production.

Chemical Constituents from the Root Bark of Calophyllum inophyllum

A new chromanone derivative, namely caloinophyllin B (1), along with seventeen known compounds 2–18 were isolated from the root bark of Calophyllum inophyllum. The structures of all isolated compounds (1–18) were determined by spectroscopic methods as well as comparison with previous reports in the literature. To the best of our knowledge, compounds 1, 3, 6, 8, 11–14 and 16 were isolated from this plant for the first time. Moreover, all isolated compounds (1–18) were evaluated for their cytotoxicity against KB and Hela S-3 cell lines. Compound 8 exhibited moderate activity toward KB and Hela S-3cells with the IC50 values of 25.8 and 18.1μM, respectively.

Chemical and Biological Research on Herbal Medicines Rich in Xanthones

Xanthones, as some of the most active components and widely distributed in various herb medicines, have drawn more and more attention in recent years. So far, 168 species of herbal plants belong to 58 genera, 24 families have been reported to contain xanthones. Among them, Calophyllum, Cratoxylum, Cudrania, Garcinia, Gentiana, Hypericum and Swertia genera are plant resources with great development prospect. This paper summarizes the plant resources, bioactivity and the structure-activity relationships (SARs) of xanthones from references published over the last few decades, which may be useful for new drug research and development on xanthones.

Calofolic acids A-F, chromanones from the bark of Calophyllum scriblitifolium with vasorelaxation activity

Vasorelaxation activity guided separation of the methanol extract of Calophyllum scriblitifolium bark led to the isolation of 6 chromanones (calofolic acids A-F, 1-6). Their structures were elucidated by 1D and 2D NMR spectroscopy, and their absolute configurations were investigated by a combination of CD spectroscopy and DFT calculation. All isolated chromanones showed dose-dependent vasorelaxation activity on isolated rat aorta.

A Review on the Phytochemistry, Pharmacology, and Pharmacokinetics of Amentoflavone, a Naturally-Occurring Biflavonoid

Amentoflavone (C30H18O10) is a well-known biflavonoid occurring in many natural plants. This polyphenolic compound has been discovered to have some important bioactivities, including anti-inflammation, anti-oxidation, anti-diabetes, and anti-senescence effects on many important reactions in the cardiovascular and central nervous system, etc. Over 120 plants have been found to contain this bioactive component, such as Selaginellaceae, Cupressaceae, Euphorbiaceae, Podocarpaceae, and Calophyllaceae plant families. This review paper aims to profile amentoflavone on its plant sources, natural derivatives, pharmacology, and pharmacokinetics, and to highlight some existing issues and perspectives in the future.

A fast and efficient HPLC-PDA-MS method for detection and identification of pyranochromanone acids in Calophyllum species

Pyranochromanone acids isolated from Calophyllum species have shown a variety of biological potentialities including antioxidant, antiulcer, anticancer and anti-Helicobacter pylori activities. These compounds seem to be the main constituents of Cuban Calophyllum species together xanthones and biflavonoids. Recently, the pyranochromanone acids calophyllic acid, isocalophyllic acid, apetalic acid, calolongic acid, isoapetalic acid, pinetoric acid I, pinetoric acid II, were isolated from Calophyllum pinetorum, a Cuban endemic species. The objective of the present work was the development of a rapid and efficient HPLC-DAD-MS method for fast screening of pyranochromanones in the leaves and resins of different endemic Calophyllum spp of Cuba, without clean-up procedures. For this purpose, a generalized fragmentation pathway was proposed and used to characterize, by HPLC-DAD-MS, the pyranochromanone acids in leaves and resins of different Calophyllum species. The developed method enables to detect also minor compounds in Calophyllum spp. The structures proposed by MS data for these compounds were unambiguous confirmed by 1D and 2D-NMR analysis and three new pyranochromanone acids, isocalolongic acid, pinetoric acid III and isopinetoric acid III, were reported here for the first time.