ent-Kaurane diterpenoids from Isodon henryi and their anti-inflammatory activities.

Phytochemical investigation of the 70% ethanol extract of Isodon henryi Kudô afforded fifteen ent-kaurane diterpenoids, including nine previously undescribed compounds, named isohenolides C-K (1-9). Compounds 1-6 featured an unusual 6,7;8,15-diseco-7,20-olide ent-kaurane diterpenoid scaffold, in which 1 also possessed an 11,15-lactone ring while 2-6 all contained a free α-methylene-γ-carboxylic acid. Compound 6 was also a rare 6,8-cyclo-7,20-olide ent-kauranoid. Their structures were elucidated primarily by HRESIMS, 1D and 2D NMR spectroscopy, electronic circular dichroism and X-ray diffraction (Cu Kα) methods. Additionally, most compounds were also screened for anti-inflammatory actions against lipopolysaccharide-induced RAW 264.7 cells, and compounds 9 and 13 exhibited stronger nitric oxide inhibition, with IC50 values of 15.99 ± 0.75 and 18.19 ± 0.42 µM, respectively.

Silvaticusins A-D: ent-kaurane diterpenoids and a cyclobutane-containing ent-kaurane dimer from Isodon silvaticus.

Three new ent-kaurane diterpenoids, silvaticusins A-C (1-3), along with a new ent-kaurane dimer silvaticusin D (4) were isolated from the aerial parts of Isodon silvaticus. The structures of these new compounds were established mainly by comprehensive analysis of their NMR and MS data. The absolute configuration of compounds 1 and 4 were determined using a single-crystal X-ray diffraction and computational methods, respectively. Compounds 2 and 3 were found to exhibit remarkable cytotoxic effects against five human tumor cell lines (HL-60, A-549, SMMC-7721, MDA-MB-231, and SW-480), with IC50 values spanning from 1.27 ± 0.08 to 7.52 ± 0.33 µM.

Design and synthesis of 6,20-epoxy A-ring modified oridonin derivatives with antitumor activity through extrinsic and mitochondrial pathways.

Oridonin is an antitumor ent-kaurane diterpenoid that medicinal chemists have been paying close attention to in recent years. Herein, a novel 6,20-epoxy A-ring modified oridonin derivative 2 was obtained by a 6-step synthesis. A series of 14-O derivatives of 2 (EpskA1-EpskA24) were synthesized to further enhance the activity. Based on their cytotoxicity against MCF-7, A549 and L-02 cells, EpskA9, EpskA10 and EpskA21 were chosen for further screening to obtain a wider antitumor spectrum. Collectively, EpskA21 showed the most potent antiproliferative activity, inhibiting proliferation and migration, and inducing apoptosis and cell cycle arrest in MCF-7 and MIA-PaCa-2 cells. With the help of network pharmacology analysis, apoptosis-related proteins were selected and further tested by western blot assay. The inhibition of PI3K/AKT and an increase in the levels of Bax/Bcl-2 ratio, Cyt-C, cleaved-Caspase-9, cleaved-Caspase-3 and cleaved-PARP was observed, indicating that EpskA21 induced apoptosis through the mitochondrial pathway. Given that an increase in DR5 expression and activated Caspase-8 were also observed, the extrinsic apoptosis pathway might also be related to the antitumor effect.

[Functional characterization of ent-kaurane-type diterpenoid synthases from Stellera chamaejasme].

Sequential catalysis by ent-copalyl diphosphate(CPS) and ent-kaurene synthase(KS) is a critical step for plants to initiate the biosynthesis of gibberellin with geranylgeranyl pyrophosphate(GGPP) as the substrate. This study mined the transcriptome data of Stellera chamaejasme and cloned two key diterpene synthase genes, SchCPS and SchKS, involved in the gibberellin pathway. The two genes had the complete open reading frames of 2 595 bp and 1 701 bp, encoding two hydrophilic proteins composed of 864 and 566 amino acid residues and with the relative molecular mass of 97.9 kDa and 64.6 kDa and the theoretical isoelectric points of 5.61 and 6.12, respectively. Sequence comparison and phylogenetic tree showed that SchCPS contained LHS, PNV, and DxDD motifs conserved in the CPS family and was categorized in the TPS-c subfamily, while SchKS contained DDxxD, NSE/DTE and PIx motifs conserved in the KS family and was categorized in the TPS-e subfamily. Functional validation showed that SchCPS catalyzed the protonation and cyclization of GGPP to ent-CPP, while SchKS acted on ent-CPP dephosphorylation and re-cyclization to ent-kaurene. In this study, the full-length sequences of SchCPS and SchKS were cloned and functionally verified for the first time, which not only enriched the existing CPS and KS gene libraries but also laid a foundation for the cloning and biosynthesis pathway analysis of more genes involved in the synthesis of active components in S. chamaejasme.

Trypanocidal and Anti-Inflammatory Effects of Three ent-Kaurane Diterpenoids from Gymnocoronis spilanthoides var. subcordata (Asteraceae).

Chagas disease, caused by the protozoan Trypanosoma cruzi, affects 6-7 million people worldwide. The dichloromethane extract obtained from the aerial parts of Gymnocoronis spilanthoides var subcordata showed trypanocidal activity in vitro. The fractionation of the dewaxed organic extract via column chromatography led to the isolation of three diterpenoids: ent-9α,11α-dihydroxy-15-oxo-kaur-16-en-19-oic acid or adenostemmoic acid B, (16R)-ent-11α-hydroxy-15-oxokauran-19-oic acid and ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic acid. These compounds showed IC50 values of 10.6, 15.9 and 4.8 µM against T. cruzi epimastigotes, respectively. When tested against amastigotes, the diterpenoids afforded IC50 values of 6.1, 19.5 and 60.6 µM, respectively. The cytotoxicity of the compounds was tested on mammalian cells using an MTT assay, resulting in CC50s of 321.8, 23.3 and 14.8 µM, respectively. The effect of adenostemmoic acid B on T. cruzi was examined at the ultrastructural level using transmission microscopy. Treatment with 20 µM for 48 h stimulated the formation of abnormal cytosolic membranous structures in the parasite. This compound also showed an anti-inflammatory effect in murine macrophages stimulated with LPS and other TLR agonists. Treatment of macrophages with adenostemmoic acid B was able to reduce TNF secretion and nitric oxide production, while increasing IL-10 production. The combination of adenostemmoic acid B with benznidazole resulted in greater inhibition of NF-kB and a decrease in nitrite concentration. The administration of adenostemmoic acid B to mice infected with trypomastigotes of T. cruzi at the dose of 1 mg/kg/day for five days produced a significant decrease in parasitemia levels and weight loss. Treatment with the association with benznidazole increased the survival time of the animals. In view of these results, adenostemmoic acid B could be considered a promising candidate for further studies in the search for new treatments for Chagas disease.

Recent Developments in the Syntheses of C-20-Oxygenated ent-Kaurane Diterpenoids.

Ent-kaurane diterpenes are a large group of natural products, with more than 1,000 compounds since their discovery. Due to their excellent biological activities and complex polycyclic structures, these compounds have attracted organic synthesis chemists around the world to be devoted to achieve their total synthesis. At present, the isolated C-20-oxygenated ent-kaurane diterpenes are the most abundant of these natural products, reaching more than 350 in number. However, only total syntheses of 3,20-epoxy, 7,20-epoxy and 19,20-lactone ent-kaurane diterpenes have been reported. In this review, we elaborate the synthesis of these three types of C-20 oxygenated ent-kaurane natural products, discuss these synthetic strategies in detail, and provide good guidance and reference for the synthesis of other C-20 oxygenated compounds.

A partial peroxisome proliferator-activated receptor gamma agonist isolated from the roots of Euphorbia sikkimensis.

Chemical constituents of the Euphorbia sikkimensis roots was investigated and twelve known compounds were isolated, including three ent-atisane diterpenes: ent-(13S)-hydroxyatis-16-ene-3,14-dione (1), ent-(5ß,8α,9ß,10α,11α,12α)-11-hydroxyatis-16-ene-3,14-dione (2), ent-atisane-3-oxo-16α,17-diol (3); two kaurene diterpenes: ent-kaurane-3-oxo-16α,17-diol (4), ent-kaurane-3-oxo-16ß,17-diol (5); one lathyane diterpene of latilagascene B (6); two flavonoids: quercetin (7), luteolin (8); one lignin d-pinoresinol (9); one coumarin scopoletin (10); together with ethyl gallate (11), p-hydroxybenzaldehyde (12). Their structures were identified based on the extensive spectroscopic analysis in comparison with the literature data. Compounds 1, 2, 4, 6 and 9 were isolated from Euphorbia sikkimensis for the first time. The agonistic activity of peroxisome proliferator-activated receptor gamma (PPARγ) for compounds 1, 7, 8, 9 and 11 was evaluated. Compound 1 exhibited moderate agonistic activity for PPARγ receptor with relative fluorescence intensity of 10.19 at 30.0 µM, in comparison with that of the positive control of rosiglitazone (28.50 at 2.0 µM).

Ent-16ß,17-dihydroxy-kauran-19-oic acid (DKA), a kaurane diterpenoid from Sigesbeckia pubescens(Makino) Makino, inhibits the migration of MDA-MB-231 breast cancer.

Ent-kaurane diterpenoids were studied as a biologically active ingredient group of Sigesbeckia pubescens (Makino) Makino. Here, five known ent-kaurane diterpenoids were isolated and identified, named ent-16ß,17-dihydroxy-kauran-19-oic acid (1), ent-16ß,17-dihydroxy-kauran-19-oate (2), ent-18-acetoxy-17-hydroxykauran-19-oic acid (3), ent-16ß,17,18-trihydroxy-kauran-19 -oic acid (4), and ent-17-hydroxy-kauran-16ßH-19-oic acid (5). Their inhibitory effects of these compounds on MDA-MB-231 breast cancer migration were firstly tested in a chemotaxis invasion assay. Among them, compound 1 (DKA) showed superior inhibitory activities with IC50 value of 1.96 µM. Then, a wound healing assay and BALB/c nude mice were used for further studying the inhibitory activity of DKA on MDA-MB-231 breast cancer migration in vitro and in vivo, respectively. The wound healing assay showed that DKA (1, 5, and 25 µM) can significantly inhibit cell migration and the mouse model of lung metastasis showed that DKA (2.5, 5, and 10 mg/kg) could strongly suppress the lung metastasis of MDA-MB-231 breast cancer cells.

Diterpenoid and phenolic constituents from corn silk (Zea mays) with PTP1B inhibitory activity.

Chemical investigation of corn silk resulted in the isolation of nine secondary metabolites, including a new ent-kaurane diterpenoid, zeamaysditerpene A (1) and eight known compounds, stigmaydene A (2), stigmaydene J (3), stigmaydene L (4), stigmane D (5), demethyltorosaflavone D (6), chrysoeriol 6-C-ß-boivinopyranosyl-7-O-ß-D-glucopyranoside (7), deoxypodophyllotoxin (8), and α-peltatin glucoside (9). Their structures were elucidated using a combination of spectroscopic methods, including 1D and 2D NMR and HRESIQTOF mass spectra. The absolute configuration of 1 was deduced by applying electronic circular dichroism (ECD) calculation method. Among the isolates, only 6 displayed significant inhibition against PTP1B activity in a dose-dependent manner, with an IC50 value of 10.7 ± 0.1 µM. Furthermore, molecular docking simulation was carried out to explore the action perspective of 6 inside the enzyme PTP1B. This finding suggests that 6 might be a potential lead for the development of a new anti-diabetic agent.

Design and synthesis of oridonin derivatives as cytotoxic agents.

Oridonin is one of the ent-kaurane diterpenes that have been studied extensively for various bioactivities. In an effort to expand natural scaffold-based library as anticancer agents, we have designed and synthesised a number of novel oridonin derivatives and evaluated their bioactivities on a panel of human cancer cell lines (HCT116, A375, MCF-7, HepG2, and A549). Compound 4b bearing a 4-fluorophenyl moiety was found to be the most active compound with an IC50 value of 0.3 µM against MCF-7 cells, which was 7.4-fold more active than oridonin. This study could provide some insightful information for further synthesis of oridonin derivatives as anticancer agents.

ent-Kaurane-Type Diterpenes Induce ROS-Mediated Mitochondrial Dysfunction and Apoptosis by Suppress the Homologous Recombination DNA Repair in Triple-Negative Breast Cancer Cells.

Six ent-kaurane-type diterpenes were isolated from the roots of Isodon ternifolia. Previous studies have shown that compounds 1 and 2 exhibited cytotoxicity against three human cancer cell lines (MCF-7, A549, and HCT116), but its molecular mechanism has not been studied yet. In the present study, the inhibited proliferation of compounds 1 and 2 of two triple-negative breast cancer (TNBC) cell lines (4T1 and MDA-MB-231) have been demonstrated by MTT and colony formation assay. Flow cytometry, western blotting, and qPCR were used to further demonstrate the apoptosis process in TNBCs. Importantly, the following mitochondrial membrane potential (MMP) decrease during apoptosis was demonstrated to correlate to reactive oxygen species (ROS) production. In addition, DNA damage induced by compounds 1 and 2 was illustrated by detect of homologous recombination (HR) DNA repair genes and proteins expression, such as RAD51. These results indicated that compounds 1 and 2 could trigger the TNBCs apoptosis mediated by ROS-induced mitochondrial dysfunction and induce DNA double-strand breaks (DSBs) by down regulating HR DNA repair. Furthermore, this research reveals that the mechanism between mitochondria dysfunction and DNA damage is deserved to be investigated for elucidating the dynamic signal transduction between the nucleus and the cellular matrix during apoptosis.

Ent-kaurane diterpenoids from the Annonaceae family: a review of research progress and call for further research.

The Annonaceae is one of the plant families with members that are credited with numerous pharmacological functions. Among the group of compounds responsible for these bioactivities are the ent-kaurane diterpenoids. The ent-kauranes are a group of 20-Carbon, tetracyclic diterpenoids that are widely distributed in other plant families including the Annonaceae family. This mini-review focuses mainly on the ent-kaurane diterpenoids isolated from the Annonaceae family, delineates the various biological activities of these compounds, and highlights the research gaps that exist for further scientific scrutiny.

Anti-inflammatory kaurane diterpenoids of Erythroxylum bezerrae.

Five unusual kaurane diterpenes, designated as bezerraditerpenes A-E (1-5), along with six known ones (6-11), were isolated from the hexane extract of the stems of Erythroxylum bezerrae. Their structures were elucidated based on the interpretation of the NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis. The anti-inflammatory potential of the diterpenes 1-11 was screened through cellular viability and lipopolysaccharide (LPS)-induced nitric oxide (NO) production on murine macrophage-like cells RAW 264.7. Diterpene 6 (cauren-6ß-ol) showed potent cytotoxicity and increased ability to inhibit NO production. Diterpenes 1 (bezerraditerpene A), 2 (bezerraditerpene B), and 8 (ent-kaur-16-ene-3ß,15ß-diol) exhibited the same significant anti-inflammatory activity with NO CI50 inhibition (3.21-3.76 µM) without cytotoxicity, in addition to decreasing the levels of pro-inflammatory cytokines TNF-α and IL-6 in LPS-induced RAW264.7 cells.

Two new ent-kaurane-type diterpene diastereomers isolated from Coffea canephora.

Phytochemical investigation of the trunks of Coffea canephora yielded two new ent-kaurane diterpene diastereomers, which have been named coffecanepholide A, ent-3ß,16ß,17-trihydroxykauran-18-al (1) and coffecanepholide B, ent-3ß,16ß,17-trihydroxykauran-19-al (2). Structural elucidation and configurational assignment were deduced from extensive spectroscopic NMR/HRESIMS analysis and by comparison with the spectral data of the literature relevant structures. The isolated compounds were assayed for in vitro inhibitory activities against α-glucosidase. Structure 2 showed the α-glucosidase inhibitory activity with an IC50 value of 294.7 ± 0.9 µM, while compound 1 exhibited inactivity. In addition, the docking results revealed that structure 2 can form more interactions with amino acid residues at the active site of α-glucosidase, which gave a more negative binding energy (-9.56 kcal/mol) compared with 1 (-8.60 kcal/mol). This observation might be responsible for a better activity of 2 against α-glucosidase.

New ent-kaurene and germacrene derivatives from Mesona procumbens Hemseley and their biological activity.

Mesona procumbens Hemseley is a well-known traditional herbal medicine used for heat-related ailments. In Taiwan, boiled extracts of M. procumbens are also used as desserts called grass jelly. In this study, the hexane extract from 75% EtOH of M. procumbens showed potent activities on inhibition of E. coli ß-glucuronidase (eßG) and NO production and cytotoxicity against MCF-7 and HepG2 cancer cell lines. Furthermore, using various flash columns and HPLC chromatography on the bioactive layer led to the isolation of twelve compounds (1-12), including a new ent-kaurene, mesokaurol A (1), and a new germacrene derivative, mesogermapene A (2). Their structures were elucidated by extensive spectroscopic analyses, especially 2 D NMR and mass data. Biological assays showed that compound 9 (linolenic acid) had specific activity on inhibition of eßG (68.27%) at 100 µg/mL but was non-inhibitory to human ß-glucuronidase. Compound 1 possessed significant cytotoxicity against MCF-7 (EC50 = 9.76 µM) and HepG2 (EC50 = 8.64 µM) cancer cell lines.

Caracasine, An ent-kaurane Diterpene with Proapoptotic and Pro-differentiator Activity in Human Leukaemia Cell Lines.

BACKGROUND: Kaurane-type diterpenoids, obtained from various natural sources, have shown many biological activities, including anti-inflammatory and antitumor effects. Caracasine, an ent-kaurane diterpenoid isolated from the flowers of Croton micans, was shown to induce apoptosis in leukaemia cell lines. OBJECTIVE: The present study aimed to ascertain the compound's mechanism of cell death induction using two leukaemia cell lines, Jurkat E6.1 (T cell) and HL-60 (promyeloblast cells). METHODS: Cell death in Jurkat and HL60 cells were evaluated by flow cytometry for apoptosis with annexin-V/PI, mitochondrial membrane potential disturbance, changes in cell cycle, CD95 expression, caspase activation, Nuclear Factor kappa B inhibition, and differentiation into a neutrophil-like cell (dHL60). RESULTS: Caracasine (10 µM) increased the G0/G1 phase in Jurkat and arrested the cell cycle in the S phase in HL60. Caracasine increased CD95 expression (p<0.01 in Jurkat and p<0.05 in HL60) and caspase-8 activation (p<0.001 in Jurkat and p<0.05 in HL60). Caspase-9 was activated in both cell lines (p<0.001) along with the decline in mitochondrial Δψm (p<0.05 in Jurkat and p<0.001 in HL60). In HL60 cells, the kaurane induced neutrophil differentiation was assessed by CD40 expression and reactive oxygen species production. In Jurkat cells, caracasine inhibited the NF-κB pathway in cells pretreated with PHA to activate the NF-κB pathway, suggesting a possible role in inflammatory diseases. CONCLUSION: Caracasine induced apoptosis through the intrinsic and extrinsic pathways in both cell lines were evaluated which could be the leading structure for new anti-leukemic and anti-inflammatory drugs.

Diterpenes of Coffea seeds show antifungal and anti-insect activities and are transferred from the endosperm to the seedling after germination.

Species of the genus Coffea accumulate diterpenes of the ent-kaurane family in the endosperm of their seeds, of which cafestol and kahweol are the most abundant. The diterpenes are mainly stored in esterified form with fatty acids, mostly palmitate. In contrast to the numerous studies on their effects on human health and therapeutic applications, nothing was previously known about their biological and ecological role in planta. The antifungal and anti-insect activities of cafestol and cafestol palmitate were thus investigated in this study. Cafestol significantly affected the mycelial growth of five of the six phytopathogenic fungi tested. It also greatly reduced the percentage of pupation of larvae and the pupae and adult masses of one of the two fruit flies tested. By contrast, cafestol palmitate had no significant effect against any of the fungi and insects studied. Using confocal imaging and oil body isolation and analysis, we showed that diterpenes are localized in endosperm oil bodies, suggesting that esterification with fatty acids enables the accumulation of large amounts of diterpenes in a non-toxic form. Diterpene measurements in all organs of seedlings recovered from whole seed germination or embryos isolated from the endosperm showed that diterpenes are transferred from the endosperm to the cotyledons during seedling growth and then distributed to all organs, including the hypocotyl and the root. Collectively, our findings show that coffee diterpenes are broad-spectrum defence compounds that protect not only the seed on the mother plant and in the soil, but also the seedling after germination.

Cytotoxic ent-Kaurane Diterpenoids from Rabdosia Rubescens.

One new (1) and 11 reported ent-kaurane diterpenoids (2-12) were received from the ethanol extract of the air-dried aerial parts of Rabdosia rubescens collected in Jiyuan. Their structures were determined in accordance with high resolution electrospray ionization mass spectroscopy, one dimensional (1D) and two-dimensional (2D) NMR spectroscopy and the data published in the literature. The cytotoxic activity of these isolated compounds was assessed against SMMC-7721, A-549, H-1299 and SW-480 cancer cell lines. Compounds 2-6 revealed significant cytotoxic activity on lung cancer cell lines A549 with IC50 values from 6.2 to 28.1 µM. Analysis of structure-activity relationship of these tested compounds indicated the carbonyl at C-15 and hydroxy at C-1 together could be crucial groups for inhibiting lung cancer cell lines A549 proliferation.

Maizediterpene D from the roots of Zea mays L. alleviates hydrogen peroxide induced oxidative stress and improves cell survival by activation of TrkB/IGF-1R crosstalk pathways.

The ent-kaurane diterpenoid enriched fraction (EDEF) of maize root was isolated and purified, and 10 compounds, including 4 ent-kaurane diterpenoids, were isolated and identified. We evaluated their neuroprotective properties in vitro for the first time using an H2O2-induced oxidative damage model in SH-SY5Y cells. The results showed that pretreatment with maizediterpene D, a new ent-kaurane diterpenoid isolated from the EDEF, significantly attenuated H2O2-induced apoptosis by improving cell survival, reducing ROS production and increasing mitochondrial membrane potential. Mechanistically, the neuroprotective effect of maizediterpene D was confirmed to be related to the dual activation of IGF-1R and BDNF/TrkB crosstalk pathways. Our findings suggest that the EDEF and its active constituent maizediterpene D had good neuroprotective properties and could serve as potential candidates for the development of therapeutic drugs for oxidative stress-related diseases.

New Terpenoids from Potentilla freyniana Bornm. and Their Cytotoxic Activities.

Two new A-ring contracted triterpenoids, madengaisu A and madengaisu B, and one undescribed ent-kaurane diterpenoid, madengaisu C, along with 20 known compounds were isolated from the roots of Potentilla freyniana Bornm. The structures were elucidated using extensive spectroscopic techniques, including 1D and 2D-NMR, HR-ESI-MS, ECD spectra, IR, and UV analysis. Moreover, all isolated constituents were evaluated for their anti-proliferative activity against RA-FLS cells and cytotoxic activities against the human cancer cell lines Hep-G2, HCT-116, BGC-823, and MCF-7. Ursolic acid and pomolic acid displayed moderate inhibitory activity in RA-FLS cells with IC50 values of 24.63 ± 1.96 and 25.12 ± 1.97 µM, respectively. Hyptadienic acid and 2α,3ß-dihydroxyolean-12-en-28-oic acid 28-O-ß-d-glucopyranoside exhibited good cytotoxicity against Hep-G2 cells with IC50 values of 25.16 ± 2.55 and 17.66 ± 1.82 µM, respectively. In addition, 2α,3ß-dihydroxyolean-13(18)-en-28-oic acid and alphitolic acid were observed to inhibit HCT-116 cells (13.25 ± 1.65 and 21.62 ± 0.33 µM, respectively), while madengaisu B and 2α,3ß-dihydroxyolean-13(18)-en-28-oic acid showed cytotoxic activities against BGC-823 cells with IC50 values of 24.76 ± 0.94 and 26.83 ± 2.52 µM, respectively, which demonstrated that triterpenes from P. freyniana may serve as therapeutic agents for RA and cancer treatment.