Effect of lathyrane-type diterpenoids in neural stem cell physiology: Microbial transformations, molecular docking and dynamics studies

Promoting endogenous neurogenesis for brain repair is emerging as a promising strategy to mitigate the functional impairments associated with various neurological disorders characterized by neuronal death. Diterpenes featuring tigliane, ingenane, jatrophane and lathyrane skeletons, frequently found in Euphorbia plant species, are known protein kinase C (PKC) activators and exhibit a wide variety of pharmacological properties, including the stimulation of neurogenesis. Microbial transformation of these diterpenes represents a green and sustainable methodology that offers a hitherto little explored approach to obtaining novel derivatives and exploring structure-activity relationships. In the present study, we report the biotransformation of euphoboetirane A (4) and epoxyboetirane A (5), two lathyrane diterpenoids isolated from Euphorbia boetica, by Mucor circinelloides MC NRRL3631. Our findings revealed the production of nine biotransformation products (6-14), including jatrophane derivatives originated through an unprecedented rearrangement from the parent lathyranes. The chemical structures and absolute configurations of the new compounds were elucidated through comprehensive analysis using NMR and ECD spectroscopy, as well as MS. The study evaluated how principal metabolites and their derivatives affect TGFα and NRG1 release, as well as their potential to promote proliferation or differentiation in cultures of NSC isolated from the SVZ of adult mice. In order to shed some light on the mechanisms underlying the ability of 12 as a neurogenic compound, the interactions of selected compounds with PKC δ-C1B were analyzed through molecular docking and molecular dynamics. Based on these, it clearly appears that the ability of compound 12 to form both acceptor and donor hydrogen bonds with certain amino acid residues in the enzyme pocket leads to a higher affinity compound-PKC complex, which correlates with the observed biological activity.

13-Oxyingenol-dodecanoate inhibits the growth of non-small cell lung cancer cells by targeting ULK1

Lung cancer is the leading cause of cancer deaths worldwide. Non-small cell lung cancer (NSCLC) accounts for 80-85% of all lung cancers. Euphorbia kansui yielded 13-oxyingenol-dodecanoate (13OD), an ingenane-type diterpenoid, which had a strong cytotoxic effect on NSCLC cells. The underlying mechanism and potential target, however, remained unknown. The study found that 13OD effectively inhibited the cell proliferation and colony formation of NSCLC cells (A549 and H460 cells), with less toxicity in normal human lung epithelial BEAS-2B cells. Moreover, 13OD can cause mitochondrial dysfunction, and apoptosis in NSCLC cells. Mechanistically, the transcriptomics results showed that differential genes were mainly enriched in the mTOR and AMPK signaling pathways, which are closely related to cellular autophagy, the related indicators were subsequently validated. Additionally, bafilomycin A1 (Baf A1), an autophagy inhibitor, reversed the mitochondrial damage caused by 13OD. Furthermore, the Omics and Text-based Target Enrichment and Ranking (OTTER) method predicted ULK1 as a potential target of 13OD against NSCLC cells. This hypothesis was further confirmed using molecular docking, the cellular thermal shift assay (CETSA), and Western blot analysis. Remarkably, ULK1 siRNA inhibited 13OD's toxic activity in NSCLC cells. In line with these findings, 13OD was potent and non-toxic in the tumor xenograft model. Our findings suggested a possible mechanism for 13OD's role as a tumor suppressor and laid the groundwork for identifying targets for ingenane-type diterpenoids.

Rapid Access to Tigliane, Ingenane, and Rhamnofolane Diterpenes from a Lathyrane Precursor via Biomimetic Skeleton Transformation Strategy

Bioinspired skeleton transformation of a tricyclic lathyrane-type Euphorbia diterpene was conducted to efficiently construct a tetracyclic tigliane diterpene on a gram scale via a key aldol condensation. The tigliane diterpene was then respectively converted into naturally rare ingenane and rhamnofolane diterpenes through a semipinacol rearrangement and a visible-light-promoted regioselective cyclopropane ring-opening reaction. This work provides a concise strategy for high-efficiency access to diverse polycyclic Euphorbia diterpene skeletons from abundant lathyrane-type natural products and paves the way for biological activity investigation of naturally rare molecules.

A Biomimetic Approach to Premyrsinane-Type Diterpenoids: Exploring Microbial Transformation to Enhance Their Chemical Diversity

Premyrsinane-type diterpenoids have been considered to originate from the cyclization of a suitable 5,6- or 6,17-epoxylathyrane precursor. Their biological activities have not been sufficiently explored to date, so the development of synthetic or microbial approaches for the preparation of new derivatives would be desirable. Epoxyboetirane A (4) is an 6,17-epoxylathyrane isolated from Euphorbia boetica in a large enough amount to be used in semi-synthesis. Transannular cyclization of 4 mediated by Cp2TiIIICl afforded premyrsinane 5 in good yield as an only diasteroisomer. To enhance the structural diversity of premyrsinanes so their potential use in neurodegenerative disorders could be explored, compound 5 was biotransformed by Mucor circinelloides NRRL3631 to give rise to hydroxylated derivatives at non-activated carbons (6-7), all of which were reported here for the first time. The structures and absolute configurations of all compounds were determined through extensive NMR and HRESIMS spectroscopic studies.

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.

Strophiofimbrins A and B: Two Rearranged Norditerpenoids with Novel Tricyclic Carbon Skeletons from Strophioblachia fimbricalyx

Two rearranged norditerpenoids with novel tricyclic carbon skeletons, strophiofimbrin A (1) and strophiofimbrin B (2), were isolated from Strophioblachia fimbricalyx. Their structures were established by 1D/2D NMR spectroscopy, HRESIMS, quantum chemistry calculations, and X-ray diffraction analyses. 1 and 2 represented the first examples of diterpenoids with unprecedented 5/6/7-fused ring systems. In the proposed biosynthetic pathway, they were suspected to derive from cleistanthane norditerpenoids via ring opening, expansion, cyclization, and rearrangement based on the existence of phenanthrenone and cleistanthane diterpenoids from Strophioblachia and Trigonostemon, two closely related genera of the Euphorbiaceae family. Furthermore, compounds 1 and 2 exhibited significant proliferation inhibition and obvious neuroprotective effects.

Enzyme-like polyene cyclizations catalyzed by dynamic, self-assembled, supramolecular fluoro alcohol-amine clusters

Terpene cyclases catalyze one of the most powerful transformations with respect to efficiency and selectivity in natural product (bio)synthesis. In such polyene cyclizations, structurally highly complex carbon scaffolds are built by the controlled ring closure of linear polyenes. Thereby, multiple C,C bonds and stereocenters are simultaneously created with high precision. Structural pre-organization of the substrate carbon chain inside the active center of the enzyme is responsible for the product- and stereoselectivity of this cyclization. Here, we show that in-situ formed fluorinated-alcohol-amine supramolecular clusters serve as artificial cyclases by triggering enzyme-like reactivity and selectivity by controlling substrate conformation in solution. Because of the dynamic nature of these supramolecular assemblies, a broad range of terpenes can be produced diastereoselectively. Mechanistic studies reveal a finely balanced interplay of fluorinated solvent, catalyst, and substrate as key to establishing nature's concept of a shape-selective polyene cyclization in organic synthesis.

Visible-Light-Promoted Tandem Thiol-Ene Click Reaction/Transannular Cyclization and Regioselective Cyclopropane Ring-Opening to Construct Sulfur-Containing Euphorbia Diterpenes

The biorelevant sulfur-containing Euphorbia diterpenes with scarce 5/7/6/3 premyrsinane- and 5/7/6 myrsinane-type backbones were easily constructed from naturally abundant lathyrane-type Euphorbia factor L₃ by visible-light-triggered tandem thiol-ene click reaction/transannular cyclization and regioselective cyclopropane ring-opening. The selenide diterpene was also successfully obtained to verify the system universality. This concise synthesis route gives an efficient strategy for obtaining structurally diverse Euphorbia diterpenes under very mild conditions and provides a promising anti-HIV bioactive premyrsinane diterpene 3h.

Convergent synthesis of the [5-7-6-3] tetracyclic core of premyrsinane diterpenes

The [5-7-6-3] tetracyclic core of premyrsinane diterpenes was convergently synthesized via the stereoselective three-component coupling of a 2-propenyl unit, an enone, and an aldehyde, followed by the relay ring-closing metathesis with conformation control of the substrate to construct the 7-membered ring.

[2 + 2]-Cycloaddition-derived cyclobutane natural products: structural diversity, sources, bioactivities, and biomimetic syntheses

This review summarizes the structural diversity, bioactivities, and biomimetic synthesis of [2 + 2]-type cyclobutane natural products, along with discussion of their biosynthesis, stereochemical analysis, racemic occurrence, and biomimetic synthesis.

New Cytotoxic Premyrsinane-Type Diterpenes from Euphorbia aleppica Against Breast Cancer Cells

Euphorbia is used in traditional medicine to remove warts, possibly due to its cytotoxic or antiviral effects. This study investigated its phytochemistry and bioactive compounds. Euphorbia aleppica from the Euphorbiaceae family was collected from Kuhdasht, Lorestan, Iran. Plant material was dried and ground. Extraction was performed by maceration using a dichloromethane-acetone solvent. After removing fatty contents, fractionation was done by open column chromatography. Based on the initial H-NMR spectra, fractions containing diterpenoid compounds were identified. The Sephadex column and HPLC performed isolation. The HPLC was done with a regular YMC silica column using a hexane: Ethyl acetate (70: 30) solvent. The selected sub-fractions were identified by one and two-dimensional corelative NMR spectra. Accurate mass spectra confirmed the molecular formula of the obtained structures. Cytotoxicity was assessed using a standard MTT assay against breast cancer cells. The NMR and mass analysis identified compound 1 as a newly described and compound 2 as a pre-defined compound as 3, 7, 15β-triacetyl-5α-tigliate-13(17)-α-epoxy-14-oxopremyrsinane and 3, 7, 14, 15, 17-pentaacetyl-5-tigliate-13(17)-epoxypremyrsinane, respectively. Compound 1 showed moderate cytotoxicity, and compound 2 exhibited a potent cytotoxic effect dose-dependently against MCF-7 and MDA-MB 231 breast cancer cells, probably because of 14-O-acetyl and 17-O-acetylated hemiacetal groups.

Annulations involving 1-indanones to access fused- and spiro frameworks

Indanones are prominent motifs found in number of natural products and pharmaceuticals. Particularly, 1-indanones occupy important niche in chemical landscape due to their easy accessibility and versatile reactivity. In the past few years, significant advancement has been achieved regarding cyclization of 1-indanone core. The present review focuses on recent (2016-2022) annulations involving 1-indanones for the construction of fused- and spirocyclic frameworks. In this context, new strategies for synthesis of various carbocyclic as well as heterocyclic skeletons are demonstrated. Mechanistic aspects of representative reactions are illustrated for better understanding of reaction pathways. A large number of transformations described in this review offer stereoselective formation of desired polycyclic compounds. Importantly, several reactions provide biologically relevant compounds and natural products, such as, plecarpenene/plecarpenone, swinhoeisterol A, cephanolides A-D, diptoindonesin G and atlanticone C.

Euphorbia diterpenoids: isolation, structure, bioactivity, biosynthesis, and synthesis (2013-2021)

Covering: 2013 to 2021As the characteristic metabolites of Euphorbia plants, Euphorbia diterpenoids have always been a hot topic in related science communities due to their intriguing structures and broad bioactivities. In this review, we intent to provide an in-depth and extensive coverage of Euphorbia diterpenoids reported from 2013 to the end of 2021, including 997 new Euphorbia diterpenoids and 78 known ones with latest progress. Multiple aspects will be summarized, including their occurrences, chemical structures, bioactivities, and syntheses, in which the structure-activity relationship and biosynthesis of this class will be discussed for the first time.

Efficient Synthesis of Orphaned Cyclopropanes Using Sulfones as Carbene Equivalents

Small molecules containing 1,1-dimethylcyclopropanes are prevalent throughout nature but are difficult to synthesize using state-of-the-art metal-catalyzed carbene transfer methods without competing 1,2-hydride shifts. Herein, we introduce a mechanistically distinct platform to transfer 1,1-dialkylcarbene units to olefins using carbometalation reactions of dialkyl sulfonyl anions. In the presence of NaNH₂ or n-BuLi in ethereal solvents, dialkyl sulfones react with styrenes and arylbutadienes between 23 and 70 °C to produce the corresponding 1,1-dialkylcyclopropanes. We report 40 examples of this reactivity including 16 different styrenes (up to 89% isolated yield), 9 arylbutadienes (51-88% yield), and 13 different sulfones (46-80% yield). In addition, we report an example of a sequential cyclopropanation reaction using this method. Preliminary mechanistic studies suggest a stepwise anionic process that is initiated by the direct addition of sulfonyl anions to a carbon-carbon double bond.

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.

Gene discovery and virus-induced gene silencing reveal branched pathways to major classes of bioactive diterpenoids in Euphorbia peplus

SignificanceEuphorbia peplus, a member of the Euphorbia genus, is rich in jatrophane and ingenane diterpenoids. Using a metabolomics-guided transcriptomic approach to gene candidate identification, we have discovered a short-chain dehydrogenase gene involved in the production of the lathyrane jolkinol E. We have developed a virus-induced gene-silencing method in E. peplus that has allowed us to demonstrate the direct relationship between casbene and polycyclic diterpenoids and that jolkinol C acts as a key branch point intermediate in the production of ingenanes and jatrophanes. This work contributes both knowledge and tools for engineering production of bioactive diterpenoids in heterologous host systems, thus enabling their further evaluation and development.

Lathyrane and Jatrophane Diterpenoids from Euphorbia helioscopia Evaluated for Cytotoxicity against a Paclitaxel-Resistant A549 Human Lung Cancer Cell Line

A phytochemical investigation on the aerial parts of Euphorbia helioscopia resulted in the isolation of 27 macrocyclic diterpenoids, including three previously unreported lathyrane derivatives, euphohelioscopoids A-C (1-3). Their structures were elucidated by spectroscopic data interpretation. Three jatrophanes, euphoscopin C (4), euphorbiapene D (6), and euphoheliosnoid A (5), showed cytotoxicity against a paclitaxel-resistant A549 human lung cancer cell line with IC₅₀ values of 6.9, 7.2, and 9.5 μM, respectively, but were inactive against the parent A549 human lung cancer cell line (IC₅₀ > 10 μM). It was found that jatrophanes with a benzoyloxy or a nicotinoyloxy substituent at C-7 showed more potent cytotoxic activity than their analogues containing acetyloxy and hydroxy groups at this position.

Diterpenoids with Rearranged 9(10→11)-abeo-10,12-Cyclojatrophane Skeleton and the First (15S)-Jatrophane from Euphorbia helioscopia: Structural Elucidation, Biomimetic Conversion, and Their Immunosuppressive Effects

Two novel diterpenoids, one with a rearranged trans,trans-fused tricyclo[10.3.0.04,6]pentadecane framework (1) and the other with an unprecedented 15S configuration (2), were isolated from Euphorbia helioscopia. Their structures were elucidated by extensive analysis of HR-ESI-MS, NMR, quantum-chemical calculation, and X-ray crystallographic data. Biosynthetically, 1 has a unique "cyclopropane-shift-like" biogenesis involving an oxa-di-π-methane (ODPM) rearrangement, which inspired us to accomplish the biomimetic conversion of 3 to 1. Moreover, compound 1 displayed a potent immunosuppressive effect by inhibiting Kv1.3 voltage-gated channels.

Euphohyrisnoids A and B, Two Highly Rearranged Lathyrane Diterpenoids from Euphorbia lathyris

Euphohyrisnoids A (1) and B (2), two highly rearranged lathyrane diterpenoids featuring a unique tetracyclo[10.2.2.01,10.03,7]cetane and tricyclo[8.4.1.03,7]pentadecane skeleton, respectively, were isolated from the seeds of Euphorbia lathyris. Their structures were determined by detailed spectroscopic analysis and were further confirmed by single-crystal X-ray diffraction. 1 significantly inhibited adipogenesis in 3T3-L1 adipocytes by retarding cell differentiation at the early stage.

Developing a Nicotiana benthamiana transgenic platform for high-value diterpene production and candidate gene evaluation

To engineer Nicotiana benthamiana to produce novel diterpenoids, we first aimed to increase production of the diterpenoid precursor geranylgeranyl pyrophosphate (GGPP) by up-regulation of key genes of the non-mevalonate (MEP) pathway sourced from Arabidopsis thaliana. We used transient expression to evaluate combinations of the eight MEP pathway genes plus GGPP synthase and a Jatropha curcas casbene synthase (JcCAS) to identify an optimal combination for production of casbene from GGPP. AtDXS and AtHDR together with AtGGPPS and JcCAS gave a 410% increase in casbene production compared to transient expression of JcCAS alone. This combination was cloned into a single construct using the MoClo toolkit, and stably integrated into the N. benthamiana genome. We also created multigene constructs for stable transformation of two J. curcas cytochrome P450 genes, JcCYP726A20 and JcCYP71D495 that produce the more complex diterpenoid jolkinol C from casbene when expressed transiently with JcCAS in N. benthamiana. Stable transformation of JcCYP726A20, JcCYP71D495 and JcCAS did not produce any detectable jolkinol C until these genes were co-transformed with the optimal set of precursor-pathway genes. One such stable homozygous line was used to evaluate by transient expression the involvement of an 'alkenal reductase'-like family of four genes in the further conversion of jolkinol C, leading to the demonstration that one of these performs reduction of the 12,13-double bond in jolkinol C. This work highlights the need to optimize precursor supply for production of complex diterpenoids in stable transformants and the value of such lines for novel gene discovery.

Iron-Catalyzed Skeletal Conversion of Lathyrane to Premyrsinane Euphorbia Diterpenes and Their Cytotoxic Activities

Two new premyrsinane-type diterpenes (2 and 3) as diastereomers were synthesized from lathyrane-type diterpene euphorbia factor L₃ (1) for the first time via an efficient Fe(acac)₃-catalyzed skeleton conversion process. This conversion features a biogenetically inspired strategy that relies on a concise reductive olefin coupling involving intramolecular Michael addition with free radicals. The structures of 2 and 3 were elucidated by a combination of the interpretation of their spectroscopic data and single-crystal X-ray diffraction analysis. The premyrsinane diterpenes 2 and 3 exhibited cytotoxic activity against the 4T1 breast cancer cell line, while the parent compound euphorbia factor L₃ (1) was inactive. The current results not only confirmed the biogenetic relationship between lathyranes and premyrsinanes for the first time but also suggested a novel method for the preparation of naturally rare premyrsinane diterpenes with high bioactivity from the more abundant natural lathyrane diterpenes.

Unusual polyoxygenated casbane diterpenoids from the South China Sea soft coral Sinularia erecta

A further systematically chemical investigation of the South China Sea soft coral Sinularia erecta led to the discovery of two rare casbane diterpenoids with an uncommon 8,10-peroxide bridge, sinuereperoxides B (1) and C (2), five new casbanes with other oxygenated patterns (3-7), and seven known casbanes (8-14). The structures and absolute configurations of 1-7 were established by extensive spectroscopic data analyses, X-ray diffraction analysis, and/or quantum chemical calculations. In bioassay, compounds 2, 7, 11 and 12 exhibited considerable anti-inflammatory activity by the inhibition of TNF-α release, with IC₅₀ values of 33.8 μM, 5 μM, 9.9 μM and 8 μM.

Collective Total Synthesis of Casbane Diterpenes: One Strategy, Multiple Targets

Of the more than 100 casbane diterpenes known to date, only the eponymous parent hydrocarbon casbene itself has ever been targeted by chemical synthesis. Outlined herein is a conceptually new approach that brings not a single but a variety of casbane derivatives into reach, especially the more highly oxygenated and arguably more relevant members of this family. The key design elements are a catalyst-controlled intramolecular cyclopropanation with or without subsequent equilibration, chain extension of the resulting stereoisomeric cyclopropane building blocks by chemoselective hydroboration/cross-coupling, and the efficient closure of the strained macrobicyclic framework by ring-closing alkyne metathesis. A hydroxy-directed catalytic trans-hydrostannation allows for late-stage diversity. These virtues are manifested in the concise total syntheses of depressin, yuexiandajisu A, and ent-pekinenin C. The last compound turned out to be identical to euphorhylonal A, the structure of which had clearly been misassigned.

Characterization, antioxidant, and cytotoxic effects of some Egyptian wild plant extracts

Background

Natural products from plants are very safe as compared to synthetic ones, so the aim of this study was to assess the in vitro antioxidant and antitumor activities of the ethanolic extracts of four Egyptian wild plant species (Varthemia candicans, Peganum harmala, Suaeda vermiculata, and Conyza dioscoridis), as well as polyphenols and flavonoid contents with gas chromatography–mass spectrometry (GC-MS). The antioxidant activity of the four plant extracts was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) to determine 50% inhibition of DPPH radical scavenging activity and reducing power by phosphomolybdate assay. In addition, the chemical composition of the four sample extracts was investigated using GC-MS. The total phenolic and flavonoid levels were also determined. Then, the antitumor activity of the plant extracts against HepG2 cells was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

Results

The results showed that Varthemia candicans extract was the highest one regarding both polyphenols and flavonoid contents. Moreover, the extract of Suaeda vermiculata exhibited the lowest half maximum inhibitory concentration (IC50) against DPPH, thus indicating its highest effectiveness. All studied plant extracts decreased the viability of HepG2 cells, in a dose- and time-dependent manner, and the lowest IC50 was for Suaeda vermiculata.

Conclusion

The investigated plant extracts showed potent antioxidant and antitumor activities in vitro due to their phytochemical contents.

Two lathyrane diterpenoid stereoisomers containing an unusual trans-gem-dimethylcyclopropane from the seeds of Euphorbia lathyris

Two novel lathyrane-type diterpenoids, which possess a trans-gem-dimethylcyclopropane were obtained from seeds of Euphorbia lathyris. The Euphorbia factor L_2b exhibited an inhibitory effect against U937 cell line with an IC₅₀ value of 0.87 μM.

Bond reactivity indices approach analysis of the [2+2] cycloaddition of jatrophane skeleton diterpenoids from Euphorbia gaditana Coss to tetracyclic gaditanone

The reaction mechanism of the intramolecular [2 + 2] cycloaddition from a jatrophane precursor to the gaditanane skeleton, an unprecedented 5/6/4/6-fused tetracyclic ring framework recently isolated from Euphorbia spp., was studied using the bond reactivity indices approach. Furthermore, six diterpenoids, including three undescribed jatrophanes isolated from E. gaditana Coss, were described. The structures of these compounds were deduced by a combination of 2D NMR spectroscopy and ECD data analysis.

Lathyrane, Premyrsinane, and Related Diterpenes from Euphorbia boetica: Effect on in Vitro Neural Progenitor Cell Proliferation

Lathyrane-type diterpenes previously have been proven to promote proliferation of neural precursor cells (NPCs) by targeting and activating one or more protein kinase C (PKC) isozymes. Aiming to find new drug candidates with a lathyrane skeleton to modulate adult neurogenesis through PKC activation, a phytochemical study of a methanol extract of the aerial parts of Euphorbia boetica was carried out. Seven new diterpenes, representing the premyrsinane (1-3), myrsinane (4, 5), and cyclomyrsinane types (6, 7), along with three known diterpenes, belonging to the cyclomyrsinane (8) and lathyrane types (9, 10), were isolated. The chemical structures and relative configurations of the new compounds were determined by extensive NMR spectroscopic studies and comparison with known compounds. The absolute configurations for compounds 2, 3, 6, and 7 were proposed, based on a comparison of the experimental ECD spectra of compounds 2 and 7 with those of known related compounds. The activity of lathyrane compounds 9 and 10 as promoters of NPC proliferation was evaluated using a neurosphere assay. Both compounds increased the size of neurospheres in a dose-dependent manner when proliferation was stimulated by the epidermal growth factor and the basic fibroblast growth factor.

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.

7-Step total synthesis of (+)-EBC-329: Photoisomerisation reveals new seco-casbane family member

The first seco-casbane, EBC-329, isolated from the Australian rainforest, was synthesised from (+)-2-carene in seven steps. This endeavour not only established the absolute stereochemical assignment as (8R,9S)-EBC-329, but also identified, via photoisomerisation, a new seco-casbane family member.

Isolation of Premyrsinane, Myrsinane, and Tigliane Diterpenoids from Euphorbia pithyusa Using a Chikungunya Virus Cell-Based Assay and Analogue Annotation by Molecular Networking

Six new premyrsinol esters (1-6) and one new myrsinol ester (8) were isolated from an aerial parts extract of Euphorbia pithyusa, together with a known premyrsinol (7) and two known dideoxyphorbol esters (9 and 10), following a bioactivity-guided purification procedure using a chikungunya virus (CHIKV) cell-based assay. The structures of the new diterpene esters (1-6 and 8) were elucidated by MS and NMR spectroscopic data interpretation. Compounds 1-10 were evaluated against CHIKV replication, and results showed that the 4β-dideoxyphorbol ester 10 was the most active compound, with an EC₅₀ value of 4.0 ± 0.3 μM and a selectivity index of 10.6. To gain more insight into the structural diversity of diterpenoids produced by E. pithyusa, the initial extract and chromatographic fractions were analyzed by LC-MS/MS. The generated data were annotated using a molecular networking procedure and revealed that dozens of unknown premyrsinane, myrsinane, and tigliane analogues were present.

Gaditanone, a Diterpenoid Based on an Unprecedented Carbon Skeleton Isolated from Euphorbia gaditana

A novel diterpenoid, gaditanone (2), which possesses an unprecedented 5/6/4/6-fused gaditanane tetracyclic ring skeleton, and a new jatrophane (1) were isolated from the aerial parts of Euphorbia gaditana. The chemical structures and absolute configurations were determined by extensive spectroscopic NMR studies and ECD data analysis. A proposed biosynthetic pathway is presented for compound 2.

Terpenoids from Euphorbia soongarica and Their Multidrug Resistance Reversal Activity

Ten new terpenoids, including five diterpenoids (1-5), three nortriterpenoids (6-8), and two triterpenoids (9, 10), and 15 known terpenoids (11-25) were isolated from an acetone extract of Euphorbia soongarica. Sooneuphoramine (1) is the first example of a euphoractine B-type diterpenoid alkaloid, while sooneuphanones A-C (6-8) are rare nortriterpenoids from the Euphorbia genus. The isolated terpenoids were tested for their cytotoxicity and multidrug resistance (MDR) reversal activity, 10 of which showed moderate cytotoxicity against the KB and KBv200 cell lines, while 11 compounds exhibited P-gp modulating potential. The triterpenoid sooneuphanone D (9) possessed a remarkable MDR reversal activity much higher than the positive control, verapamil.

Lathyrane Diterpenes from the Latex of Euphorbia laurifolia

Two new macrocyclic diterpenes, 2- epi-latazienone (4) and 15β-acetoxy-7β-nicotinoyloxy-3β8α-di-(2-methylpropanoyloxy)–4αH,9αH,11αH-lathyra-5 E,12 E-dien-14-one (5), and three known lathyrane-type diterpenes (1-3) were isolated from Euphorbia laurifolia latex. Their structures were determined on the basis of a detailed analysis of their 1D and 2D NMR spectroscopic and mass spectral data.

Structure-based modelling, scoring, screening, and in vitro kinase assay of anesthetic pkc inhibitors against a natural medicine library

Protein kinase C (PKC) is an intracellular effector of the inositol phosphate-mediated signal transduction pathway. Evidence is emerging that certain general anaesthetics can influence the activity of PKC by interacting with the regulatory domain of the enzyme, and targeting PKC kinase domain is considered as a strategy to modulate the anaesthetic effects. Here, an integrated method was used to perform virtual screening against a large library of natural compounds for the discovery of new and potent PKC modulators. A number of hits were identified and their inhibitory activity against PKC kinase domain was measured by using a standard kinase assay protocol. Three and five compounds were determined to have high and moderate activities with IC₅₀ values at nanomolar and micromolar levels, respectively. These compounds can be considered as promising lead molecular entities to develop efficacious anaesthetic modulators. Structural examination revealed a variety of nonbonded interactions such as hydrogen bonds, cation-π contacts, and hydrophobic forces across the complex interface of PKC with the identified compounds. This study helps to establish an integrative approach to rational kinase inhibitor discovery by efficiently exploiting various existing natural products.

Euphorbia dendroides Latex as a Source of Jatrophane Esters: Isolation, Structural Analysis, Conformational Study, and Anti-CHIKV Activity

An efficient process was used to isolate six new jatrophane esters, euphodendroidins J (3), K (5), L (6), M, (8), N (10), and O (11), along with seven known diterpenoid esters, namely, euphodendroidins A (4), B (9), E (1), and F (2), jatrophane ester (7), and 3α-hydroxyterracinolides G and B (12 and 13), and terracinolides J and C (14 and 15) from the latex of Euphorbia dendroides. Their 2D structures and relative configurations were established by extensive NMR spectroscopic analysis. The absolute configurations of compounds 1, 11, and 15 were determined by X-ray diffraction analysis. Euphodendroidin F (2) was obtained in 18% yield from the diterpenoid ester-enriched extract after two consecutive flash chromatography steps, making it an interesting starting material for chemical synthesis. Euphodendroidins K and L (5 and 6) showed an unprecedented NMR spectroscopic behavior, which was investigated by variable-temperature NMR experiments and molecular modeling. The structure-conformation relationships study of compounds 1, 5, and 6, using DFT-NMR calculations, indicated the prominent role of the acylation pattern in governing the conformational behavior of these jatrophane esters. The antiviral activity of compounds 1-15 was evaluated against Chikungunya virus (CHIKV) replication.

Metabolic changes in Euphorbia palusrtis latex after fungal infection

The variations of metabolic profile of the latex of wild-growing Euphorbia palustris was carried out using multivariate analysis of ¹H NMR spectral data. One population was infected with fungi Fusarium sporotrichioides, Fusarium proliferatum and Alternaria alternata, while the other consisted of healthy plant species. The non-polar metabolites of latex extracts such as benzoyl ingenol-laurate, amyrin decadienoate esters, cis-1,4-polyisoprene, and 24-methylenecycloartanol were identified using ¹H and 2D NMR spectra. Principal component analysis of ¹H NMR data provided a clear discrimination between the latex of infected and healthy plants. Minimum inhibitory concentration and minimum fungicidal concentration values of the latex extracts of healthy and infected plants were determined. The latex of infected plants was found to contain higher levels of benzoyl ingenol-laurate and 24-methylenecycloartanol, of which concentrations were strongly correlated with the antifungal activities of the latex.

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.

A Cytochrome P450-Mediated Intramolecular Carbon-Carbon Ring Closure in the Biosynthesis of Multidrug-Resistance-Reversing Lathyrane Diterpenoids

The Euphorbiaceae produce a wide variety of bioactive diterpenoids. These include the lathyranes, which have received much interest due to their ability to inhibit the ABC transporters responsible for the loss of efficacy of many chemotherapy drugs. The lathyranes are also intermediates in the biosynthesis of range of other bioactive diterpenoids with potential applications in the treatment of pain, HIV and cancer. We report here a gene cluster from Jatropha curcas that contains the genes required to convert geranylgeranyl pyrophosphate into a number of diterpenoids, including the lathyranes jolkinol C and epi-jolkinol C. The conversion of casbene to the lathyranes involves an intramolecular carbon-carbon ring closure. This requires the activity of two cytochrome P450s that we propose form a 6-hydroxy-5,9-diketocasbene intermediate, which then undergoes an aldol reaction. The discovery of the P450 genes required to convert casbene to lathyranes will allow the scalable heterologous production of these potential anticancer drugs, which can often only be sourced in limited quantities from their native plant.