Diterpenes from European Euphorbia Species Serving as Prototypes for Natural-Product-Based Drug Discovery

Total Synthesis of the Euphorbia Diterpenoid Pepluacetal

The first total synthesis of the Euphorbia diterpenoid pepluacetal is disclosed in both racemic and chiral fashions. The synthesis strategically relies on a photo-induced Wolff rearrangement/lactonization cascade (WRLC) reaction to access the cyclobutane moiety, a ring-closing metathesis/cyclopropanation sequence to rapidly forge the 7-3 bicyclic system, and a late-stage Rh-catalyzed transannular carbenoid insertion to C(sp3)-H bond followed by a Baeyer-Villiger oxidation and ring-opening manipulations to install the side chain. The synthetic route demonstrates excellent stereochemical control on the non-classical concave-face bond formation, remote traceless stereochemical relay and high scalability to provide 20 mg of (+)-pepluacetal.

Euphzycopins A - D, macrocyclic diterpenoids with potential anti-inflammatory activity from Euphorbia Helioscopia

Four new diterpenoids (1-4) and four known diterpenoids (5-8) were purified from the whole plant of Euphorbia helioscopia L. Compounds 1 and 2 were jathophanes diterpenoids with a 5/12 polycyclic systems, compound 3 was rhamofolane diterpenoid with a 5/10 bicyclic skeleton and compound 4 was a rare class of euphorbia diterpenes featuring an unusual 5/10 fused ring system. Anti-inflammatory activity tests were conducted on the separated compounds, indicating that compound 4 had significant inhibitory effect on NLRP3 inflammasome with an IC50 value of 7.75 μM. Further, the inhibitory effect of 4 was determined using immunofluorescence assays.

Enhancing Structural Diversity of Lathyrane Derivatives through Biotransformation by the Marine-Derived Actinomycete Streptomyces puniceus BC-5GB.11

Lathyrane-type diterpenes have a wide range of biological activities. Among them, euphoboetirane A (1) exerts neurogenesis-promoting activity. In order to increase the structural diversity of this type of lathyrane and explore its potential use in neurodegenerative disorders, the biotransformation of 1 by Streptomyces puniceus BC-5GB.11 has been investigated. The strain BC-5GB.11, isolated from surface sediments collected from the intertidal zone of the inner Bay of Cadiz, was identified as Streptomyces puniceus, as determined by phylogenetic analysis using 16S rRNA gene sequence. Biotransformation of 1 by BC-5GB.11 afforded five products (3-7), all of which were reported here for the first time. The main biotransformation pathways involved regioselective oxidation at non-activated carbons (3-5) and isomerization of the ∆12,13 double bond (6). In addition, a cyclopropane-rearranged compound was found (7). The structures of all compounds were elucidated on the basis of extensive NMR and HRESIMS spectroscopic studies.

Asymmetric Total Synthesis of Pedrolide

The asymmetric total synthesis of pedrolide (>200 mg) with an unprecedented [5-5-5-6-6-3] hexacyclic core (pedrolane) was achieved. Its unique bicyclo[2.2.1]heptane ring system was efficiently constructed via an enantioselective ene reaction of cyclopentadiene followed by a Wittig reaction, isomerization, and a diastereoselective intramolecular Diels-Alder reaction cascade. The highly oxygenated carane [6-3] ring system was synthesized via a ring-closing metathesis reaction followed by an unusual free carbene cyclopropanation. Furthermore, the 12 contiguous stereocenters of pedrolide were installed diastereoselectively.

Biological activity and structural modification of isosteviol over the past 15 years

Isosteviol is a tetracyclic diterpenoid obtained by hydrolysis of stevioside. Due to its unique molecular skeleton and extensive pharmacological activities, isosteviol has attracted more and more attention from researchers. This review summarized the structural modification, pharmacological activity and microbial transformation of isosteviol from 04/2008 to 10/2023. In addition, the research history, structural characterization, and pharmacokinetics of isosteviol were also briefly reviewed. This review aims to provide useful literature resources and inspirations for the exploration of diterpenoid drugs.

Brønsted Acid-Mediated Conversion of Naturally Abundant Lathyrane Diterpenes: Are Rare 10,11-seco-Lathyrane Diterpenes Artifacts?

The question of whether rare 10,11-seco-lathyranes are natural products or artifacts is thoughtfully considered after a Brønsted acid-mediated chemical conversion of naturally abundant 5/11/3 lathyrane type diterpenes into 10,11-seco-lathyranes was developed. Benefiting from this concise route, a series of 10,11-seco-lathyrane products (1-14) were smoothly synthesized. The conversion may involve an acid promoted cyclopropane ring opening accompanied by a double bond shift with final trapping of carbocation. The ease of this chemical conversion under mildly acidic conditions may imply that the 10,11-seco-lathyranes isolated to date are artifacts. This work not only develops a new modular synthetic strategy for efficient constructing rare 10,11-seco-lathyranes, but also provides a promising bioactive diterpene with excellent effect against the NO production on LPS-induced BV-2 cells.

Myrsinane-Type Diterpenes: A Comprehensive Review on Structural Diversity, Chemistry and Biological Activities

Euphorbia species are important sources of polycyclic and macrocyclic diterpenes, which have been the focus of natural-product-based drug research due to their relevant biological properties, including anticancer, multidrug resistance reversal, antiviral, and anti-inflammatory activities. Premyrsinane, cyclomyrsinane, and myrsinane diterpenes are generally and collectively designated as myrsinane-type diterpenes. These compounds are derived from the macrocyclic lathyrane structure and are characterized by having highly oxygenated rearranged polycyclic systems. This review aims to describe and summarize the distribution and diversity of 220 myrsinane-type diterpenes isolated in the last four decades from about 20 Euphorbia species. Some myrsinane diterpenes obtained from Jatropha curcas are also described. Discussion on their plausible biosynthetic pathways is presented, as well as isolation procedures and structural elucidation using nuclear magnetic resonance spectroscopy. Furthermore, the most important biological activities are highlighted, which include cytotoxic and immunomodulatory activities, the modulation of efflux pumps, the neuroprotective effects, and the inhibition of enzymes such as urease, HIV-1 reverse transcriptase, and prolyl endopeptidase, among other biological effects.

Total Synthesis of (+)-Euphorikanin A via an Atropospecific Cascade

A total synthesis of the ingenane-derived diterpenoid (+)-euphorikanin A is described. Key to the strategy is a stereocontrolled one-pot sequence consisting of transannular aldol addition reaction, hemiketal formation, and subsequent semipinacol rearrangement that efficiently leads to the complete euphorikanin skeleton. Atroposelective ring-closing olefin metathesis proved critical for the stereospecific cascade, leading to formation of a (Z)-bicyclo[7.4.1]tetradecenone core. An additional salient feature of the route is pyrolysis of a bis-methylxanthate to cleanly furnish the natural product.

Rearrangement of the Tetra- and Tricyclic Skeletons of Pepluanol B to Access the Core Structures of Tigliane- and Myrsinane-Type Euphorbia Diterpenes

Pepluanol B is a new Euphorbia diterpene with an unprecedented tetracyclic backbone. However, its biogenetic relationship with known Euphorbia diterpenes is unclear. We report herein that its β-hydroxyl ketone motif could undergo a base-promoted retro-aldol/aldol process in two pathways and afford the skeletons of tigliane- and myrsinane-type Euphorbia diterpenes through the formation of the C8-C14 and C7-C13 bonds, respectively. The retro-aldol/aldol cascade indicates that pepluanol B is possibly a biosynthetic precursor of lathyranes and other relevant dipterpenes.

Mukaiyama aldol reaction: an effective asymmetric approach to access chiral natural products and their derivatives/analogues

The Mukaiyama aldol reaction is generally a Lewis-acid catalyzed cross-aldol reaction between an aldehyde or ketone and silyl enol ether. It was first described by Mukaiyama in 1973, almost 5 decades ago, to achieve the enantioselective synthesis of β-hydroxy carbonyl compounds in high percentage yields. Mukaiyama aldol adducts play a pivotal role in the synthesis of various naturally occurring and medicinally important organic compounds such as polyketides, alkaloids, macrolides, etc. This review highlights the significance of the Mukaiyama aldol reaction towards the asymmetric synthesis of a wide range of biologically active natural products reported recently (since 2020).

Photo-induced scandium-catalyzed biomimetic skeleton conversion of lathyrane to naturally rare eupholathone Euphorbia diterpenes

The naturally scarce eupholathone-type euphornin E (1) was efficiently prepared from abundant lathyrane-type Euphorbia factor L1via a visible-light-induced Sc(OTf)3-catalyzed tandem process. Eupholathones 2 and 3 were also smoothly obtained by changing the reaction solvent. This route provides a convenient method for easily constructing scarce eupholathone- from lathyrane-type Euphorbia diterpenes, and confirms the biogenetic relationship between them from a chemical standpoint. Notably, compound 1 exhibited good anti-HIV activity.

Sesquiterpenes from Carpesium faberi triggered ROS-induced apoptosis and protective autophagy in hepatocellular carcinoma cells

Ten previously undescribed sesquiterpenes, carpespenes A-J (1-10), and eight known compounds (11-18), were isolated from the whole plants of Carpesium faberi. Their structures were established by extensive analysis of HRESIMS, NMR, and ECD spectra. Carpespene A (1) is eudesmanolide-type sesquiterpene lactone with an open five membered ring involving C-2 and C-3. Furthermore, compound 1 showed significant cytotoxic effects against four cancer cell lines with IC50 values from 8.20 to 18.45 μM, compared with the positive controls cisplatin and doxorubicin. Mechanistically, compound 1 induced apoptosis in the HepG2 cells by triggering excessive ROS accumulation. The latter however induced cytoprotective autophagy, which impaired the cytotoxicity of compound 1. Simultaneous antophagy inhibition with compound 1 treatment augmented the cytotoxic effects of the latter on HepG2 cells. Our findings further establish the structural diversity and bioactivity of sesquiterpenes, and provide an experimental basis for targeting cytoprotective autophagy as a potential chemotherapeutic strategy.

Euphopias G - J, macrocyclic diterpenes with anti-zika virus activity from Euphorbia helioscopia L

Four new diterpenoids (1-4) and sixteen known diterpenoids (5-20) were purified from the whole plant of Euphorbia helioscopia L. Compounds 1 and 2 were rhamofolane diterpenoids with a 5/7/6 tricyclic systems, compound 3 was a lathyranes diterpenoid, and compound 4 was a jathophanes diterpenoid. The isolated compounds were tested for their cytotoxicity and anti-Zika virus properties, and compounds 9 and 15 showed low cytotoxicity and strong anti-Zika virus properties with EC50 2.63 and 5.94 μM, respectively. Further, the inhibitory effects of compounds on protein levels were determined using Western blotting and immunofluorescence assays.

Finding activity through rigidity: syntheses of natural products containing tricyclic bridgehead carbon centers

Covering: up to 2022Tricyclic bridgehead carbon centers (TBCCs) are a synthetically challenging substructure found in many complex natural products. Here we review the syntheses of ten representative families of TBCC-containing isolates, with the goal of outlining the strategies and tactics used to install these centers, including a discussion of the evolution of the successful synthetic design. We provide a summary of common strategies to inform future synthetic endeavors.

Chemical Constituents of Euphorbia stracheyi Boiss (Euphorbiaceae)

Euphorbia stracheyi Boiss was used for hemostasis, analgesia, and muscular regeneration in traditional Chinese medicine. To study the chemical constituents of E. stracheyi, the ethyl acetate part of the methanol extract of the whole plant was separated by silica gel, sephadex LH-20 column chromatography, and semi-preparative HPLC. The isolation led to the characterization of a new lathyrane type diterpenoid, euphostrachenol A (1), as well as eleven known compounds (2-11), including a lathyrane, three ingenane-type and two abietane-type diterpenoids, two ionones, and two flavonoids. The structures of these compounds were established using 1D- and 2D-NMR experiments, mass spectrometry, and X-ray crystallographic experiments. The MTT method was used to determine the cytotoxic activity of five cancer cell lines (Leukemia HL-60, lung cancer A-549, liver cancer SMMC-7721, breast cancer MCF-7, and colon cancer SW480) on the isolated compounds. However, only compound 4 showed moderate cytotoxicity against these cell lines, with IC₅₀ values ranging from 10.28 to 29.70 μM, while the others were inactive. Our chemical investigation also confirmed the absence of jatrophane-type diterpenoids in the species, which may be related to its special habitat.

Defensive Specialized Metabolites from the Latex of Euphorbia jolkinii

Plant latex is sequestered in laticiferous structures and exuded immediately from damaged plant tissues. The primary function of plant latex is related to defense responses to their natural enemies. Euphorbia jolkinii Boiss. is a perennial herbaceous plant that greatly threaten the biodiversity and ecological integrity of northwest Yunnan, China. Nine triterpenes (1-9), four non-protein amino acids (10-13) and three glycosides (14-16) including a new isopentenyl disaccharide (14), were isolated and identified from the latex of E. jolkinii. Their structures were established on the basis of comprehensive spectroscopic data analyses. Bioassay revealed that meta-tyrosine (10) showed significant phytotoxic activity, inhibiting root and shoot growth of Zea mays, Medicago sativa, Brassica campestris, and Arabidopsis thaliana, with EC50 values ranging from 4.41 ± 1.08 to 37.60 ± 3.59 µg/mL. Interestingly, meta-tyrosine inhibited the root growth of Oryza sativa, but promoted their shoot growth at the concentrations below 20 µg/mL. meta-Tyrosine was found to be the predominant constituent in polar part of the latex extract from both stems and roots of E. jolkinii, but undetectable in the rhizosphere soil. In addition, some triterpenes showed antibacterial and nematicidal effects. The results suggested that meta-tyrosine and triterpenes in the latex might function as defensive substances for E. jolkinii against other organisms.

Enantioselective Total Synthesis of (+)-Pedrolide

The first total synthesis of (+)-pedrolide, a tigliane-derived diterpenoid featuring an unprecedented 5-5-6-6-3 carbon skeleton, is reported. Key to the approach is the construction of the bicyclo[2.2.1]heptane core via an intramolecular cyclopentadiene-Diels-Alder cycloaddition. To this end, a norbornadiene serves as an effective surrogate for cyclopentadiene, which is unmasked under mild conditions involving a complex Diels-Alder reaction cascade. In addition, the synthesis provides a novel approach to a densely functionalized carane in an efficient and enantioselective manner.

An overview of the traditional use, phytochemistry, and biological activity of the genus Homalanthus

Homalanthus species are native to tropical Asia and the Pacific region. This genus, comprising 23 accepted species, received less scientific attention compared to other genera of the Euphorbiaceae family. Seven Homalanthus species, such as H. giganteus, H. macradenius, H. nutans, H. nervosus, N. novoguineensis, H. populneus, and H. populifolius, have been reported to treat various health problems in traditional medicine. Only a few Homalanthus species have been investigated for their biological activities, including antibacterial, anti-HIV, anti-protozoal, estrogenic, and wound-healing activities. From a phytochemical point of view ent-atisane, ent-kaurane, and tigliane diterpenoids, triterpenoids, coumarins, and flavonol glycosides were found to be characteristic metabolites of the genus. The most promising compound is prostratin, isolated from H. nutans, with anti-HIV activity and the ability to eradicate the HIV reservoir in infected patients by mechanism of protein kinase C (PKC) agonist. This review provides information on traditional usage, phytochemistry, and biological activity of the genus Homalanthus with the aim to delineate future research directions.

Euphejolkinolide A, a new ent-abietane lactone from Euphorbia peplus L. with promising biological activity in activating the autophagy-lysosomal pathway

A new ent-abietane diterpenoid, named Euphejolkinolide A (1), was isolated from the whole plant of Euphorbia peplus L. Its structure, including absolute configurations, was determined by spectroscopic analyses and was corroborated by single-crystal X-ray diffraction analysis. This new compound was assessed for its activity to induce lysosome biogenesis through Lyso-Tracker Red staining, in which compound 1 could significantly induce lysosome biogenesis. In addition, quantitative real-time PCR (qRT-PCR) analysis demonstrated a direct correlation between the observed lysosome biogenesis and the transcriptional activation of the lysosomal genes after treatment with the compound 1. Moreover, compound 1 promoted autophagic flux by upregulating LC3-II and downregulating SQSTM1 in both human microglia cells and U251 cells, which is required for cellular homeostasis. Further results suggested 1 induced lysosome biogenesis and autophagy which was mediated by TFEB (transcription factor EB). The structure activity relationships (SAR) analysis suggested that the carbony1 at C-7 in 1 might be a key active group. Overall, the current data suggested that 1 could be a potential compound for lysosome disorder therapy by induction of autophagy.

Ingol, ent-atisane, and stachane-type diterpenoids from Euphorbia deightonii with multidrug resistance reversing activity

Nine previously undescribed ingol-type diterpenoid polyesters with eighteen known ingol esters, two ent-atisane, and one stachane diterpenoid were isolated from the methanol extract of Euphorbia deightonii Croizat. The structures were established by extensive spectroscopic analysis involving 1D (1H, 13C J-modulation) and 2D NMR experiments, HRESIMS measurements, and the comparison of the spectroscopic data with reported literature values. The cytotoxic concentrations of 13 isolated compounds were determined, and the compounds were investigated for multidrug resistance modulating activity on an L5178 mouse lymphoma cell line using a rhodamin 123 accumulation assay. Six ingol esters demonstrated the significant inhibition of P-glycoprotein, while the two ent-atisane diterpenoids were found to be inactive. The measured activities allowed to establish some structure-activity relationships. Notably, lower and higher-type diterpenoids simultaneously occurred in E. deightonii.

Pharmacological Potential of Lathyrane-Type Diterpenoids from Phytochemical Sources

Lathyrane diterpenoids are one of the primary types of secondary metabolites present in the genus Euphorbia and one of the largest groups of diterpenes. They are characterized by having a highly oxygenated tricyclic system of 5, 11 and 3 members. These natural products and some synthetic derivatives have shown numerous interesting biological activities with clinical potential against various diseases, such as cytotoxic activity against cancer cell lines, multi-drug resistance reversal, antiviral properties, anti-inflammatory activity and their capability to induce proliferation or differentiation into neurons of neural progenitor cells. The structure of the lathyrane skeleton could be considered privileged because its framework is able to direct functional groups in a well-defined space. The favorable arrangement of these makes interaction possible with more than one target. This review aims to highlight the evidence of lathyranes as privileged structures in medicinal chemistry. Chemical structures of bioactive compounds, the evaluation of biological properties of natural and semisynthetic derivatives, and the exploration of the mechanisms of action as well as target identification and some aspects of their targeted delivery are discussed.

Identification of Gene Biomarkers for Tigilanol Tiglate Content in Fontainea picrosperma

Tigilanol tiglate (EBC-46) is a small-molecule natural product under development for the treatment of cancers in humans and companion animals. The drug is currently produced by purification from the Australian rainforest tree Fontainea picrosperma (Euphorbiaceae). As part of a selective-breeding program to increase EBC-46 yield from F. picrosperma plantations, we investigated potential gene biomarkers associated with biosynthesis of EBC-46. Initially, we identified individual plants that were either high (>0.039%) or low EBC-46 (<0.008%) producers, then assessed their differentially expressed genes within the leaves and roots of these two groups by quantitative RNA sequencing. Compared to low EBC-46 producers, high-EBC-46-producing plants were found to have 145 upregulated genes and 101 downregulated genes in leaves and 53 upregulated genes and 82 downregulated genes in roots. Most of these genes were functionally associated with defence, transport, and biosynthesis. Genes identified as expressed exclusively in either the high or low EBC-46-producing plants were further validated by quantitative PCR, showing that cytochrome P450 94C1 in leaves and early response dehydration 7.1 and 2-alkenal reductase in roots were consistently and significantly upregulated in high-EBC-46 producers. In summary, this study has identified biomarker genes that may be used in the selective breeding of F. picrosperma.

Bioinspired Total Synthesis of (+)-Euphorikanin A

We have achieved a bioinspired total synthesis of (+)-euphorikanin A, which possesses an intriguing and complex 5/6/7/3-fused tetracyclic skeleton bearing a bridged [3.2.1]-γ-lactone moiety. Key transformations include stereoselective alkylation and aldol condensation to install the main stereocenters, an intramolecular nucleophile-catalyzed aldol lactonization of carboxylic acid-ketone to assemble the five-membered ring, a McMurry coupling to construct the seven-membered ring, and a biomimetic benzilic acid type rearrangement to form the bridged [3.2.1]-γ-lactone moiety.

Natural Plant Compounds: Does Caffeine, Dipotassium Glycyrrhizinate, Curcumin, and Euphol Play Roles as Antitumoral Compounds in Glioblastoma Cell Lines?

Many plant-derived compounds are shown to be promising antitumor therapeutic agents by enhancing apoptosis-related pathways and cell cycle impairment in tumor cells, including glioblastoma (GBM) cell lines. We aimed to review four natural plant compounds effective in GBM cell lines as caffeine, dipotassium glycyrrhizinate (DPG), curcumin, and euphol. Furthermore, antitumoral effect of these plant compounds on GBM cell lines through microRNAs (miRs) modulation was investigated. However, only DPG and curcumin were found as effective on miR modulation. Caffeine arrests GBM cell cycle in G0/G1 phase by cyclin-dependent kinases (CDK) complex inhibition and by decreasing BCL-2 and increasing FOXO1 expression levels causing greater apoptotic activity. Caffeine can also directly inhibit IP3R3, p38 phosphorylation, and rho-associated protein kinase (ROCK), decreasing cell invasion and migration capacity or indirectly by inhibiting the tissue inhibitor metalloproteinase-1 (TIMP-1) and integrins β1 and β3, leading to lower matrix metalloproteinases, MMP-2 and MMP-9. DPG presents antitumoral effect in GBM cells related to nuclear factor kappa B (NF-κB) pathway suppression by IRAK2 and TRAF6-mediating miR-16 and miR-146a, respectively. More recently, it was observed that DPG upregulated miR-4443 and miR-3620, responsible for post-transcriptional inhibition of the NF-κB pathway by CD209 and TNC modulation, respectively leading to lower MMP-9 and migration capacity. Curcumin is able to increase miR-223-3p, miR-133a-3p, miR-181a-5p, miR-34a-5p, miR-30c-5p, and miR-1290 expression leading to serine or threonine kinase (AKT) pathway impairment and also it decreases miR-27a-5p, miR-221-3p, miR-21-5p, miR-125b-5p, and miR-151-3p expression causing p53-BCL2 pathway inhibition and consequently, cellular apoptosis. Interestingly, lower expression of miR-27a by curcumin action enhanced the C/EBP homologous protein(CHOP) expression, leading to paraptosis. Curcumin can inhibit miR-21 expression and consequently activate apoptosis through caspase 3 and death receptor (DR) 4 and 5 activation. Autophagy is controlled by the LC-3 protein that interacts with Atg family for the LC3-II formation and autophagy activation. Euphol can enhance LC3-II levels directly in GBM cells or inhibits tumor invasion and migration through PDK1 modulation.

Euphzycopias A-I, macrocyclic diterpenes with NLRP3 inflammasome inhibitory activity from Euphorbia helioscopia L

A phytochemical investigation was conducted on Euphorbia helioscopia, resulting in the isolation of thirteen compounds, including nine undescribed diterpenoids, Euphzycopias A - I (1-9), of which the skeletons of compounds 1-4 were found in E. helioscopia L. Compounds 1-3 had 5/7/6 cyclic systems, while compound 4 had a 4/11 polycyclic system with a 4,7-cyclic ether between C-4 and C-7. The anti-inflammasome test using the isolated compounds (1-6, 8-13) showed that the diterpenes from E. helioscopia L. had a strong inhibitory effect on NLRP3 inflammasomes with IC₅₀ values of 3.34-14.92 μM.

Macrocyclic Diterpenoid Constituents of Euphorbia deflexa, an Endemic Spurge from Greece

Euphorbia deflexa, an endemic spurge from Greece, was investigated for the occurrence of its diterpene constituents. Through continuous monitoring by ¹H NMR, 22 diterpenoids were isolated, including 16 previously undescribed compounds (euphodeflexins A-P), which belong to the jatrophane, ingenane, segetane, and pepluane diterpene types. Their chemical structures were elucidated through a combination of HRESIMS, NMR spectroscopy, and X-ray data. The isolated diterpenoids were tested against a panel of human cancer cell lines, as well as against two bacterial strains. Compounds 1, 13, and 17 were active against the HeLa cell line with IC₅₀ values 9.9, 9.8, and 5.8 μM, respectively.

Euphorbia Diterpenes: An Update of Isolation, Structure, Pharmacological Activities and Structure-Activity Relationship

Euphorbia species have a rich history of ethnomedicinal use and ethnopharmacological applications in drug discovery. This is due to the presence of a wide range of diterpenes exhibiting great structural diversity and pharmacological activities. As a result, Euphorbia diterpenes have remained the focus of drug discovery investigations from natural products. The current review documents over 350 diterpenes, isolated from Euphorbia species, their structures, classification, biosynthetic pathways, and their structure-activity relationships for the period covering 2013-2020. Among the isolated diterpenes, over 20 skeletal structures were identified. Lathyrane, jatrophane, ingenane, ingenol, and ingol were identified as the major diterpenes in most Euphorbia species. Most of the isolated diterpenes were evaluated for their cytotoxicity activities, multidrug resistance abilities, and inhibitory activities in vitro, and reported good activities with significant half-inhibitory concentration (IC50) values ranging from 10-50 µM. The lathyranes, isopimaranes, and jatrophanes diterpenes were further found to show potent inhibition of P-glycoprotein, which is known to confer drug resistance abilities in cells leading to decreased cytotoxic effects. Structure-activity relationship (SAR) studies revealed the significance of a free hydroxyl group at position C-3 in enhancing the anticancer and anti-inflammatory activities and the negative effect it has in position C-2. Esterification of this functionality, in selected diterpenes, was found to enhance these activities. Thus, Euphorbia diterpenes offer a valuable source of lead compounds that could be investigated further as potential candidates for drug discovery.

New Insights on Euphorbia dendroides L. (Euphorbiaceae): Polyphenol Profile and Biological Properties of Hydroalcoholic Extracts from Aerial Parts

Euphorbia dendroides L. is a rounded shrub commonly found in the Mediterranean area well-known, since ancient times, for its traditional use. The aim of the present study was to investigate the phytochemical profile as well as the antioxidant and anti-inflammatory properties of flower (FE), leaf (LE), fruit (FrE), and branch (BE) hydroalcoholic extracts. For this purpose, a preliminary phytochemical screening followed by RP-LC-DAD-ESI-MS analysis, as well as several in vitro cell-free colorimetric assays, were carried out. Moreover, the toxicity of the extracts was investigated by the brine shrimp lethality assay. All extracts showed a high content of polyphenols, in particular phenolic acids (chlorogenic acid 0.74-13.80 g/100 g) and flavonoids (rutin 0.05-2.76 g/100 g and isovitexin 8.02 in BE). All the extracts showed strong and concentration-dependent antioxidant and anti-inflammatory activity with, on average, the following order of potency: FE, LE, FrE, and BE. Interestingly, all the extracts investigated did not show any toxicity on Artemia salina. Moreover, the only LD50 found (BE, 8.82 mg/mL) is well above the concentration range, which has been shown the biological properties. Considering this, this study offers the first evidence of the possible use of the polyphenol extracts from the aerial parts of E. dendroides as promising antioxidant and anti-inflammatory agents.

Enantioselective Total Synthesis of (+)-Euphorikanin A

We disclose the first total synthesis of (+)-euphorikanin A, an ingenane-derived natural product featuring an unprecedented 5/6/7/3-fused tetracyclic skeleton. Key to the approach is a SmI₂-mediated ketyl-enoate reaction that leads to the formation of two rings in a single step. The polarity-reversed cyclization proceeds in excellent yield and high diastereoselectivity. Access to ring B is effected late in the synthesis by implementation of a number of chemoselective transformations, including in situ generation of a vinyl lithium species and subsequent intramolecular attack onto an α-ketolactone.

Jatrophane Diterpenoids from the Seeds of Euphorbia peplus with Potential Bioactivities in Lysosomal-Autophagy Pathway

Euphopepluanones F - K (1 - 4), four new jatrophane type diterpenoids were isolated from the seeds of Euphorbia peplus, along with eight known diterpenoids (5 - 12). Their structures were established on the basis of extensive spectroscopic analysis and X-ray crystallographic experiments. The new compounds 1 - 4 were assessed for their activities to induce lysosomal biogenesis through LysoTracker Red staining. Compound 2 significantly induced lysosomal biogenesis. In addition, compound 2 could increase the number of LC3 dots, indicating that it could activate the lysosomal-autophagy pathway.

Structurally diverse triterpenoids with cytotoxicity from Euphorbia hypericifolia

Extensive phytochemical investigation on the whole herbs of Euphorbia hypericifolia led to the isolation of 18 structurally diverse tetracyclic and pentacyclic triterpenoids, including four 4α,14α-dimethyl-5α-ergostanes (1-4), two seco-adiananes (5 and 6), three dammaranes (7-9), four cycloartanes (10-13), one tirucallane (14), two fernanes (15 and 16), one ursane (17), and one oleanane (18). Among them, euphypenoids A (1) and B (5) were new triterpenoids. Their structures were elucidated on the basis of extensive spectroscopic analysis, single-crystal X-ray diffraction, and chemical transformation. All isolates were screened for their cytotoxic activities against the colorectal cancer cell line HCT-116, and compounds 1, 12, and 15 showed remarkable activities with IC50 values of 12.8 ± 1.6, 7.4 ± 0.2, and 10.6 ± 1.2 μM, respectively.

Diterpenoids with an unprecedented ring system from Euphorbia peplus and their activities in the lysosomal-autophagy pathway

Three novel jatrophane diterpenes, cyclojatrophanes A-C (1-3), were isolated from the seeds of Euphorbia peplus. Compounds 1-3 featured an unprecedented 5/5/5/11 tetracyclic ring system incorporating ditetrahydropyran rings. Their structures including their absolute configurations were established by extensive spectroscopic analysis, X-ray crystallographic experiments and chemical transformations. In addition, these compounds could significantly activate the lysosomal-autophagy pathway.

Antioxidant activity and enzyme inhibitory potential of Euphorbia resinifera and E. officinarum honeys from Morocco and plant aqueous extracts

Natural products may be applied in a wide range of domains, from agriculture to food and pharmaceutical industries. In this study, the antioxidant properties and the capacity to inhibit some enzymatic activities of Euphorbia resinifera and Euphorbia officinarum aqueous extracts and honeys were assessed. The physicochemical characteristics were also evaluated. Higher amounts of iron, copper and aluminium were detected in E. officinarum honey, which may indicate environmental pollution around the beehives or inadequate storage of honey samples. This honey sample showed higher amounts of total phenols and better capacity for scavenging superoxide anion free radicals and DPPH free radicals as compared with E. resinifera honey, but poorer capacity for inhibiting lipoxygenase, acetylcholinesterase, tyrosinase and xanthine oxidase. The ratio plant mass:solvent volume (1:100) and extraction time (1 - 2 h) were associated with higher total phenols and better antioxidant activities and lipoxygenase, acetylcholinesterase and tyrosinase inhibitory activities, regardless of the plant species. The aqueous extracts had systematically higher in vitro activities than the respective honey samples.

Stereoselective Construction of the Methylcyclopentane Core of Peditithins B-H with Five Continuous Stereocenters

A stereoselective construction of the methylcyclopentane core (3) of jatrophane diterpenoids peditithins B-H was achieved in 14 steps from commercially available d-(+)-ribono-1,4-lactone (9). The linear 5-ene-heptanal derived from 9 was cyclized to the five-membered ring by an intramolecular carbonyl ene reaction, and five continuous stereocenters on 3 were stereoselectively introduced via a successive substrate-controlled manner, involving diastereoselective 1,4-addition, MoOPH-induced hydroxylation, and stereospecific epoxidation.

Macrocyclic diterpenoids from the seeds of Euphorbia peplus with potential activity in inducing lysosomal biogenesis

The first phytochemical investigation of the seeds of Euphorbia peplus led to the isolation and characterization of five new (1-5), named euphopepluanones A-E, and five known diterpenoids (6-10). Their structures were established by extensive spectroscopic analysis and X-ray crystallographic experiments. Euphopepluanones A-E (1-3) feature a very rare 5/11/5-tricyclic skeleton, and euphopepluanones D-E (4-5) represent the first report of lathyrane type diterpenoids found in E. peplus. The new compounds 1-5 were assessed for their activities to induce lysosomal biogenesis through LysoTracker Red staining, in which compounds 1 and 3 could significantly induce lysosomal biogenesis. In addition, compounds 1 and 3 could promote the nuclear translocation of TFEB, a master transcriptional factor of lysosomal genes, indicating that compounds 1 and 3 induced lysosomal biogenesis through activation of TFEB.

Bioactive diterpenoid metabolism and cytotoxic activities of genetically transformed Euphorbia lathyris roots

Plants in the genus Euphorbia produce a wide variety of pharmacologically active diterpenoids with anticancer, multidrug resistance reversal, and antiviral properties. Some are the primary industrial source of ingenol mebutate, which is approved for treatment of the precancerous skin condition actinic keratosis. Similar to other high value phytochemicals, Euphorbia diterpenoids accumulate at low concentrations in planta and chemical synthesis produces similarly low yields. We established genetically transformed root cultures of Euphorbia lathryis as a strategy to gain greater access to diterpenoids from this genus. Transformed roots produced via stem explant infection with Agrobacterium rhizogenes strain 15834 recapitulated the metabolite profiles of field-grown plant roots and aerial tissues. Several putative diterpenoids were present in transformed roots, including ingenol and closely related structures, indicating that root cultures are a promising approach to Euphorbia-specific diterpenoid production. Treatment with methyl jasmonate led to a significant, albeit transient increase in mRNA levels of early diterpenoid biosynthetic enzymes (farnesyl pyrophosphate synthase, geranylgeranyl pyrophosphate synthase, and casbene synthase), suggesting that elicitation could prove useful in future pathway characterization and metabolic engineering efforts. We also show the potential of transformed E. lathyris root cultures for natural product drug discovery applications by measuring their cytotoxic activities using a panel of human carcinoma cell lines derived from prostate, cervix, breast, and lung.

Synthetic applications of type II intramolecular cycloadditions

Type II intramolecular cycloadditions ([4+2], [4+3], [4+4] and [5+2]) have emerged recently as an efficient and powerful strategy for the construction of bridged ring systems. In general, type II cycloadditions provide access to a wide range of bridged bicyclo[m.n.1] ring systems with high regio- and diastereoselectivity in an easy and straightforward manner. In each section of this review, an overview of the corresponding type II cycloadditions is presented, which is followed by highlights of method development and synthetic applications in natural product synthesis. The goal of this review is to provide a survey of recent advances in the field covering literature up to 2020. The review will serve as a useful reference for organic chemists engaged in the total synthesis of natural products containing bridged bicyclo[m.n.1] ring systems and provide strong stimulus for invention and further advances in this exciting research field.

Enriched Terpenes Fractions of the Latex of Euphorbia umbellata Promote Apoptosis in Leukemic Cells

The current study was carried out by a bioguided fractionation of a hexane extract of the latex of Euphorbia umbellata against leukemic cells. Samples were analyzed by NMR, GC/MS, triterpenes quantification, and MTT reduction assay. Morphological, cell cycle, mitochondrial membrane potential and caspases 3/7 analyses were performed for the dichloromethane and ethanol fractions, and selectivity index for the dichloromethane fraction. NMR analysis presented characteristic signals of terpenes and steroids, data were confirmed by the quantification of triterpenes and GC/MS analysis. MTT reduction assay demonstrated that HL-60 was the most sensitive cell lineage against dichloromethane and ethanol fractions. Compounds of these matrices caused morphological changes compatible with apoptosis induction, altered cell cycle, increment of depolarized population cells and activation of caspases 3/7. Selectivity indices were higher than 22.44. Bioguided-fractionation study showed that samples of the latex of E. umbellata raised the activity of the phytocomplex against leukemic cells, and the cytotoxicity can be associated with an apoptosis pathway.

Antimicrobial Terpenoids as a Potential Substitute in Overcoming Antimicrobial Resistance

There was a golden era where everyone thought that microbes can no longer establish threat to humans but the time has come where microbes are proposing strong resistance against the majority of antimicrobials. Over the years, the inappropriate use and easy availability of antimicrobials have made antimicrobial resistance (AMR) to emerge as the world's third leading cause of death. Microorganisms over the time span have acquired resistance through various mechanisms such as efflux pump, transfer through plasmids causing mutation, changing antimicrobial site of action, or modifying the antimicrobial which will lead to become AMR as the main cause of death worldwide by 2030. In order to overcome the emerging resistance against majority of antimicrobials, there is a need to uncover drugs from plants because they have proved to be effective antimicrobials due to the presence of secondary metabolites such as terpenoids. Terpenoids abundant in nature are produced in response to microbial attack have huge potential against various microorganisms through diverse mechanisms such as membrane disruption, anti-quorum sensing, inhibition of protein synthesis and ATP. New approaches like combination therapy of terpenoids and antimicrobials have increased the potency of treatment against various multidrug resistant microorganisms by showing synergism to each other.

Three new diterpenoids from Euphorbia peplus

Three new diterpenoids (1-3) (two abietane type diterpenoids and a paralianone type diterpenoid), together with four known compounds (4-7) were isolated from the whole plants of Euphorbia peplus. Their structures were elucidated through spectroscopic analysis and physicochemical characteristics. The cytotoxic activities of compounds 1-7 against five human tumour cell lines were evaluated, however, they were inactive at the concentration of 40 μM. The compound 3 enhanced lysosomal biogenesis with Lyso Tracker staining intensity of 132.6%.

Jatrophane and rearranged jatrophane-type diterpenes: biogenesis, structure, isolation, biological activity and SARs (1984-2019)

Diterpene compounds specially macrocyclic ones comprising jatrophane, lathyrane, terracinolide, ingenane, pepluane, paraliane, and segetane skeletons occurring in plants of the Euphorbiaceae family are of considerable interest in the context of natural product drug discovery programs. They possess diverse complex skeletons and a broad spectrum of therapeutically relevant biological activities including anti-inflammatory, anti-chikungunya virus, anti-HIV, cytotoxic, and multidrug resistance-reversing activities as well as curative effects on thrombotic diseases. Among macrocyclic diterpenes of Euphorbia, the discovery of jatrophane and modified jatrophane diterpenes with a wide range of structurally unique polyoxygenated polycyclic derivatives and as a new class of powerful inhibitors of P-glycoprotein has opened new frontiers for research studies on this genus. In this review, an attempt has been made to give in-depth coverage of the articles on the naturally occurring jatrophanes and rearranged jatrophane-type diterpenes isolated from species belonging to the Euphorbiaceae family published from 1984 to March 2019, with emphasis on the biogenesis, isolation methods, structure, biological activity, and structure-activity relationship.

Semi-Synthetic Ingenol Derivative from Euphorbia tirucalli Inhibits Protein Kinase C Isotypes and Promotes Autophagy and S-phase Arrest on Glioma Cell Lines

The identification of signaling pathways that are involved in gliomagenesis is crucial for targeted therapy design. In this study we assessed the biological and therapeutic effect of ingenol-3-dodecanoate (IngC) on glioma. IngC exhibited dose-time-dependent cytotoxic effects on large panel of glioma cell lines (adult, pediatric cancer cells, and primary cultures), as well as, effectively reduced colonies formation. Nevertheless, it was not been able to attenuate cell migration, invasion, and promote apoptotic effects when administered alone. IngC exposure promoted S-phase arrest associated with p21CIP/WAF1 overexpression and regulated a broad range of signaling effectors related to survival and cell cycle regulation. Moreover, IngC led glioma cells to autophagy by LC3B-II accumulation and exhibited increased cytotoxic sensitivity when combined to a specific autophagic inhibitor, bafilomycin A1. In comparison with temozolomide, IngC showed a mean increase of 106-fold in efficacy, with no synergistic effect when they were both combined. When compared with a known compound of the same class, namely ingenol-3-angelate (I3A, Picato^®), IngC showed a mean 9.46-fold higher efficacy. Furthermore, IngC acted as a potent inhibitor of protein kinase C (PKC) activity, an emerging therapeutic target in glioma cells, showing differential actions against various PKC isotypes. These findings identify IngC as a promising lead compound for the development of new cancer therapy and they may guide the search for additional PKC inhibitors.

Effective MDR reversers through phytochemical study of Euphorbia boetica

INTRODUCTION

Macrocyclic diterpenes from Euphorbia species were found to be promising modulators of multidrug resistance (MDR), a complex phenomenon that hampers the effectiveness of cancer therapy.

OBJECTIVE

To find new effective MDR reversers through the phytochemical study of E. boetica, including isolation and molecular derivatisation.

MATERIAL AND METHODS

The phytochemical study of E. boetica was performed through chromatographic techniques. Preliminary analysis of crude chromatographic fractions from the methanol extract was carried out by ¹ H-NMR in order to prioritise the study of those having macrocyclic diterpenes. Polyamide resin was used to remove chlorophylls. Molecular derivatisation of isolated compounds comprised hydrolysis, reduction and acylation reactions. The structural identification of compounds was performed through analysis of spectroscopic data, mainly one-dimensional- and two-dimensional-NMR. The MDR reversing activity was assessed using a combination of transport and chemosensitivity assays, in mouse lymphoma (L5178Y-MDR) and Colo320 cell models.

RESULTS

The ¹ H-NMR study of crude fractions and application of a straightforward method to remove chlorophylls, allowed the effortless isolation of two lathyrane-type diterpenes in large amounts, including the new polyester, euphoboetirane B (1). Taking advantage of the chemical functions of 1, 13 new derivatives were prepared. Several compounds showed to be promising modulators of P-glycoprotein (P-gp), in resistant cancer cells. Most of the compounds tested revealed to interact synergistically with doxorubicin.

CONCLUSION

These results corroborate the importance of macrocyclic lathyrane diterpenes as effective lead compounds for the reversal of MDR.

Isolation and Pharmacological Investigation of Compounds From Euphorbia matabelensis

This work deals with the isolation and pharmacological investigations of compounds of Euphorbia matabelensis. After multiple separation process, including thin layer chromatography (TLC), vacuum liquid chromatography, preparative TLC, and high-performance liquid chromatography, 1 diterpene (ingenol) and 2 flavonoids (naringenin and eriodictyol) were obtained from the methanol extracts prepared from the stems and roots of the plant. The structures of the isolated compounds were determined by nuclear magnetic resonance (NMR) and MS measurements and comparison with literature data. All compounds were isolated for the first time from the plant. Eriodictyol was detected for the first time from a Euphorbia species. The compounds were tested for their antiproliferative (on HeLa, C33a, MCF-7, and MDA-MB-231 cell lines) and GIRK channel blocking activities. None of the compounds proved to be active in these test systems.

Investigation of Premyrsinane and Myrsinane Esters in Euphorbia cupanii and Euphobia pithyusa with MS2LDA and Combinatorial Molecular Network Annotation Propagation

The species Euphorbia pithyusa and Euphorbia cupanii are two closely related Mediterranean spurges for which their taxonomic relationships are still being debated. Herein, the diterpene ester content of E. cupanii was investigated using liquid chromatography coupled to tandem mass spectrometry. The use of molecular networking coupled to unsupervised substructure annotation ( MS2LDA) indicated the presence of new premyrsinane/myrsinane diterpene esters in the E. cupanii fractions. A structure-guided isolation procedure yielded 16 myrsinane (11a-h, 12, and 13) and premyrsinane esters (14a-c and 15a-c), along with four 4β-phorbol esters (16a-c and 17) that showed inhibitory activity against chikungunya virus replication. The structures of the 16 new compounds (11a-c, 11h, 12, 13, 14a-c, 15a-c, 16a-c, and 17) were characterized by NMR spectroscopy and X-ray crystallography. To further uncover the diterpene ester content of these two species, the concept of combinatorial network annotation propagation (C-NAP) was developed. By leveraging the fact that the diterpene esters of Euphorbia species are made up of limited building blocks, a combinatorial database of theoretical structures was created and used for C-NAP that made possible the annotation of 123 premyrsinane or myrsinane esters, from which 74% are not found in any compound database.

Macrocyclic Diterpenoids from Euphorbiaceae as A Source of Potent and Selective Inhibitors of Chikungunya Virus Replication

Macrocyclic diterpenoids produced by plants of the Euphorbiaceae family are of considerable interest due to their high structural diversity; and their therapeutically relevant biological properties. Over the last decade many studies have reported the ability of macrocyclic diterpenoids to inhibit in cellulo the cytopathic effect induced by the chikungunya virus. This review; which covers the years 2011 to 2019; lists all macrocyclic diterpenoids that have been evaluated for their ability to inhibit viral replication. The structure-activity relationships and the probable involvement of protein kinase C in their mechanism of action are also detailed.