Natural and Semisynthetic Tigliane Diterpenoids with New Carbon Skeletons from Euphorbia dracunculoides as a Wnt Signaling Pathway Inhibitor

Diterpenoids with an unusual tricyclo[10.3.0.02,9]pentadecane skeleton from Pedilanthus tithymaloides as multidrug resistance modulators

Three new diterpenoids with an unusual carbon skeleton, pedilanins A-C (1-3), and nine new jatrophane diterpenoids, pedilanins D-L (4-12), along with five known ones (13-17), were isolated from Pedilanthus tithymaloides. Compounds 1-3 characterize an unprecedented tricyclo[10.3.0.02,9]pentadecane skeleton. Compounds 4-8 are rare examples of the jatrophanes bearing a cyclic hemiketal substructure. Their structures were determined by an extensive analysis of HRESIMS, NMR, quantum-chemical calculation, DP4+ probability, and X-ray crystallographic data. In the bioassay, compounds 1-12 dramatically reversed multidrug resistance in cancer cells with the fold-reversals ranging from 17.9 to 396.8 at the noncytotoxic concentration of 10 μM. The mechanism results indicated that compounds 2 and 3 inhibited the P-glycoprotein (Pgp) transporter function, thus reversing the drug resistance.

A new ingol diterpenoid from the seeds of Euphorbia marginata Pursh

A new ingol diterpenoid, namely 3-de-O-acetyleuphornan R (1), along with two known analogues, euphornans E (2) and N (3) were isolated from the seeds of Euphorbia marginata Pursh. The structure of 1 was elucidated by extensive ¹H NMR, ¹³C NMR, HSQC, HMBC, and ¹H-¹H COSY, and HR-MS spectroscopic analyses.

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.

Talaverrucin A, Heterodimeric Oxaphenalenone from Antarctica Sponge-Derived Fungus Talaromyces sp. HDN151403, Inhibits Wnt/β-Catenin Signaling Pathway

The Wnt/β-catenin signaling pathway is an evolutionarily conserved signaling cascade involved in a broad range of biological roles. Dysregulation of the Wnt/β-catenin pathway is implicated in congenital malformations and various kinds of cancers. We discovered a novel Wnt/β-catenin inhibitor, talaverrucin A (1), featuring an unprecedented 6/6/6/5/5/5/6 fused ring system, from an Antarctica sponge-derived fungus Talaromyces sp. HDN151403. Talaverrucin A exhibits inhibitory activity on the Wnt/β-catenin pathway in both zebrafish embryos in vivo and cultured mammalian cells in vitro, providing a naturally inspired small molecule therapeutic lead to target the Wnt/β-catenin pathway.

Diverse diterpenoids with α-glucosidase and β-glucuronidase inhibitory activities from Euphorbia milii

Four undescribed regular rosane-type diterpenoids euphominoids M-P and three undescribed rearranged rosane-type diterpenoids euphomilones C-E were isolated from the whole plants of Euphorbia milii Des Moul., along with nine known compounds. Their structures were elucidated by detailed interpretation of the NMR and mass spectroscopy. The absolute configurations were established by single-crystal X-ray diffraction experiments, as well as comparative analyses of calculated and experimental ECD spectra. Euphominoid M featured a highly oxygenated ring A and a rare four-membered oxygen ring while euphomilones C-E possessed 7/5/6 or 5/7/6 fused ring systems, which were rarely occurring in rosane-type diterpenoids. In the in-vitro bioassays, 19-norrosa-1,3,5(10),15-tetraene-2,3-diol and antiquorin showed more potent α-glucosidase inhibitory activity than the positive control acarbose while euphominoid C exhibited significant inhibitory activity against both α-glucosidase and β-glucuronidase. To the best of our knowledge, it was the first time that rosane-type diterpenoids were reported as β-glucuronidase inhibitors.

Diterpenoids from the genus Euphorbia: Structure and biological activity (2013-2019)

Euphorbiaceae is one of the largest families of higher plants, including 7500 species, and many of them are used as medicines in China. From 2013 to 2019, a total of 455 previously undescribed diterpenoids were isolated from 53 species of Euphorbia, and some skeleton types were first discovered from the genus Euphorbia. Most of the diterpenoids isolated from Euphorbia spp. have been tested for their biological activity, and some of them were first reported for Euphorbia diterpenoids in recent years, such as neuroprotection, antimalarial activity and inhibition of osteoclast formation. In this review, we summarize all the isolated diterpenoids from the genus Euphorbia according to their skeleton types, classify all these diterpenoids into 26 normal classes and 37 novel skeleton types, and summarize their biological activity.

Bioactive Compounds from Euphorbia usambarica Pax. with HIV-1 Latency Reversal Activity

Euphorbia usambarica is a traditional medicine used for gynecologic, endocrine, and urogenital illnesses in East Africa; however, its constituents and bioactivities have not been investigated. A variety of compounds isolated from Euphorbia species have been shown to have activity against latent HIV-1, the major source of HIV-1 persistence despite antiretroviral therapy. We performed bioactivity-guided isolation to identify 15 new diterpenoids (1–9, 14–17, 19, and 20) along with 16 known compounds from E. usambarica with HIV-1 latency reversal activity. Euphordraculoate C (1) exhibits a rare 6/6/3-fused ring system with a 2-methyl-2-cyclopentenone moiety. Usambariphanes A (2) and B (3) display an unusual lactone ring constructed between C-17 and C-2 in the jatrophane structure. 4β-Crotignoid K (14) revealed a 250-fold improvement in latency reversal activity compared to crotignoid K (13), identifying that configuration at the C-4 of tigliane diterpenoids is critical to HIV-1 latency reversal activity. The primary mechanism of the active diterpenoids 12–14 and 21 for the HIV-1 latency reversal activity was activation of PKC, while lignans 26 and 27 that did not increase CD69 expression, suggesting a non-PKC mechanism. Accordingly, natural constituents from E. usambarica have the potential to contribute to the development of HIV-1 eradication strategies.

Cytotoxic tigliane diterpenoids from Euphorbia neorubella

Two new tigliane diterpenes, named eupneonoids A (1) and B (2), together with four known analogues (3-6) were isolated from the whole plant of Euphorbia neorubella Bruyns. Their structures were deduced based on the detailed spectroscopic analysis. All the isolates displayed cytotoxic effects against A549 human tumor cell lines with IC₅₀ values ranging from 1.318 to 7.042 μM.

Pedrolane, a Polycyclic Diterpene Scaffold Containing a Bicyclo[2.2.1]heptane System, from Euphorbia pedroi

Pedrolide (1), a diterpenoid with an unprecedented carbon skeleton, pedrolane, containing a bicycle[2.2.1]heptane system, is reported. This structural feature is hypothesized to involve an intramolecular cyclization, via Michael addition, and a ring contraction, via 1,2-alkyl shift or a Pinacol rearrangement of rings A and B, from a tigliane-type 5/7/6/3-tetracyclic ring precursor. The structure of 1 was established using spectroscopic techniques, single-crystal X-ray diffraction, and ab initio calculations. Pedrolide reversed multidrug resistance mediated by P-glycoprotein.

Small Molecule Wnt Pathway Modulators from Natural Sources: History, State of the Art and Perspectives

The Wnt signaling is one of the major pathways known to regulate embryonic development, tissue renewal and regeneration in multicellular organisms. Dysregulations of the pathway are a common cause of several types of cancer and other diseases, such as osteoporosis and rheumatoid arthritis. This makes Wnt signaling an important therapeutic target. Small molecule activators and inhibitors of signaling pathways are important biomedical tools which allow one to harness signaling processes in the organism for therapeutic purposes in affordable and specific ways. Natural products are a well known source of biologically active small molecules with therapeutic potential. In this article, we provide an up-to-date overview of existing small molecule modulators of the Wnt pathway derived from natural products. In the first part of the review, we focus on Wnt pathway activators, which can be used for regenerative therapy in various tissues such as skin, bone, cartilage and the nervous system. The second part describes inhibitors of the pathway, which are desired agents for targeted therapies against different cancers. In each part, we pay specific attention to the mechanisms of action of the natural products, to the models on which they were investigated, and to the potential of different taxa to yield bioactive molecules capable of regulating the Wnt signaling.

Macrocyclic Diterpenoids from Euphorbia helioscopia and Their Potential Anti-inflammatory Activity

Guided by ¹H NMR spectroscopic experiments using the aromatic protons as probes, 11 macrocyclic diterpenes (1-11) were isolated from the aerial parts of Euphorbia helioscopia. Their full three-dimensional structures, including absolute configurations, were established unambiguously by spectroscopic analysis and single-crystal X-ray crystallographic experiments. Among the isolated compounds, compound 1 is the third member thus far of a rare class of Euphorbia diterpenes featuring an unusual 5/10 fused ring system, and 2-4 are new jatrophane diterpenes. Based on the NMR data of the jatrophane diterpenes obtained in this study as well as those with crystallographic structures reported in the literature, the correlations of the chemical shifts of the relevant carbons and the configurations of C-2, C-13, and C-14 of their flexible macrocyclic ring were considered. Moreover, the anti-inflammatory activities of 1-11 were investigated by monitoring their inhibitory effects on nitric oxide production in lipopolysaccharide-stimulated RAW 264.7 cells. Compound 1 showed an IC₅₀ of 7.4 ± 0.6 μM, which might be related to the regulation of the NF-κB signaling pathway by suppressing the translocation of the p65 subunit and the consequent reduction of IL-6 and TNF-α secretions.

Bioactive Diterpenoids from the Stems of Euphorbia antiquorum

A total of 18 diterpenoids, including 10 new analogues (1-10), were isolated from Euphorbia antiquorum. The structures were characterized by spectroscopic techniques, and circular dichroism data analysis was adopted to confirm the absolute configurations of 1-10. Compounds 1-9 were classified as ent-atisane diterpenoids, and 10 was assigned as an ent-kaurane diterpenoid. The biological evaluation of nitric oxide (NO) production inhibition was conducted, and all of these isolates showed the property of inhibiting NO generation in lipopolysaccharide-induced BV-2 cells. Further research on molecular docking disclosed the affinities between the diterpenoids obtained and inducible nitric oxide synthase.

Cassiabudanols A and B, Immunostimulative Diterpenoids with a Cassiabudane Carbon Skeleton Featuring a 3-Oxatetracyclo[6.6.1.02,6.010,14]pentadecane Scaffold from Cassia Buds

Two novel diterpenoids, cassiabudanols A (1) and B (2), were isolated from cassia buds. Their structures were determined by comprehensive spectroscopic analysis and single-crystal X-ray diffraction. Compounds 1 and 2 possess an unprecedented 11,14- cyclo-8,14:12,13-di- seco-isoryanodane (cassiabudane) carbon skeleton featuring a unique 3-oxatetracyclo[6.6.1.0^2,6.0^10,14]pentadecane bridged system, and their biosynthetic pathways are proposed. Compounds 1 and 2 exhibited significant immunostimulative activity, and the mode of action of 2 involves upregulating CD4⁺ and CD8⁺ T cells and downregulating Tregs.

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial sources from 2017.

Crotonols A and B, two rare tigliane diterpenoid derivatives against K562 cells from Croton tiglium

Crotonol B (2) represents the first example of 13,14-seco-tigliane diterpenoids.

Survey of natural products reported by Asian research groups in 2017

The new natural products reported in 2017 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2017 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as caesalpinflavin A from Caesalpinia enneaphylla.