Lewis acid-mediated skeleton transformation of Euphorbia diterpenes: From lathyrane to euphoractane and myrsinane

A Fast and Efficient Molecular Networking Approach for Reactivity of Natural Products Exploration in Plant Extracts: Application to Diterpene Esters from Euphorbia dendroides

Natural products represent a rich source of bioactive compounds, covering a large chemical space. Even if challenging, this diversity can be extended by applying chemical modifications. However, these studies generally require multigram amounts of isolated natural products and face frequent testing failures. To overcome this limitation, we propose a rapid and efficient approach that uses molecular networking (MN) to visualize the new chemical diversity generated by simple chemical modifications of natural extracts. Moreover, the strategy deployed enables the most appropriate reagents to be defined quickly upstream of a reaction on a pure compound, in order to maximize chemical diversity. This methodology was applied to the latex extract of Euphorbia dendroides to follow the reactivity toward a series of Brønsted and Lewis acids of three class of diterpene esters identified in this species: jatrophane, terracinolide, and phorbol. Through the molecular networking interpretation, with the aim to illustrate our approach, BF3·OEt2 was selected for chemical modification on isolated jatrophane esters. Three rearranged compounds (3-5) were obtained, showing that the most appropriate reagents can be selected by MN interpretation.

Enhancing lathyrane structural diversity and MDR activity by combinatorial modification of lathyrane nucleus and ester side chain: A case study of Euphorbia Factor L1 and Euphorbia Factor L3

The chemical transformation of lathyrane nucleus through reduction and oxidation reactions using Euphorbia Factor L1 (EFL1) and Euphorbia Factor L1 (EFL3) as examples were investigated, along with a co-modification strategy of lathyrane nucleus and its side ester chain. A total of 38 lathyrane derivatives (5-42) including 34 new compounds were obtained, which greatly enriched the structural diversity of the lathyrane-type diterpenoids. Cytotoxicity against drug-sensitive and drug (adriamycin, ADM) resistant MCF-7 cells showed that 23 out of 38 transformed derivatives possessed obvious cytotoxic activity with IC50 values ranging from 7.0 to 41.1 μM and 3.2 to 45.5 μM, respectively, against both cells, compared to the noncytotoxic EFL1 and EFL3. The multidrug resistance (MDR) reversing activities of these lathyrane derivatives were further evaluated in MCF-7/ADM. Three transformed compounds (reversal fold, RF = 151.33, 62.94 and 47.3 for 27, 37 and 42) showed markedly higher activity than EFL1 (RF = 32.92) and EFL3 (RF = 39.68). Structure-activity relationship study revealed an essential role of C-6/17 and C-12/13 double bonds on lathyrane nucleus for exerting MDR reversal activity. Western blotting analysis showed that 42 could reduce the expression level of P-glycoprotein (P-gp) in MCF-7/ADM cells; however, the most active compound 27 with an unnatural 5/7/7/4 fused-ring diterpenoid skeleton, had no inhibitory effect on P-gp expression.

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.

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.

Discovery of myrsinane-type Euphorbia diterpene derivatives through a skeleton conversion strategy from lathyrane diterpene for the treatment of Alzheimer's disease

A series of novel myrsinane-type Euphorbia diterpene derivatives (1-37) were synthesized from the abundant natural lathyrane-type Euphorbia factor L3, using a multi-step chemical process guided by a bioinspired skeleton conversion strategy, with the aim of discovering potential anti-Alzheimer's disease (AD) bioactive lead compounds. The synthesis process involved a concise reductive olefin coupling reaction through an intramolecular Michael addition with a free radical, followed by a visible-light-triggered regioselective cyclopropane ring-opening. The cholinesterase inhibitory and neuroprotective activities of the synthesized myrsinane derivatives were evaluated. Most of the compounds showed moderate to strong potency, highlighting the importance of ester groups in Euphorbia diterpene. In particular, derivative 37 displayed the most potent acetylcholinesterase (AChE) inhibition, with an IC50 value of 8.3 μM, surpassing that of the positive control, tacrine. Additionally, 37 also showed excellent neuroprotective effect against H2O2-induced injury in SH-SY5Y cells, with a cell viability rate of 124.2% at 50 μM, which was significantly higher than that of the model group (viability rate 52.1%). Molecular docking, reactive oxygen species (ROS) analysis, immunofluorescence, and immunoblotting were performed to investigate the mechanism of action of myrsinane derivative 37. The results indicated that derivative 37 may be a promising myrsinane-type multi-functional lead compound for the treatment of Alzheimer's disease. Furthermore, a preliminary SAR analysis was performed to study the acetylcholinesterase inhibitory and neuroprotective activities of these diterpenes.

Scandium-Catalyzed Skeleton Conversion of Lathyrane to Lathyranone-Type Euphorbia Diterpenes

Naturally occurring 1(15 → 14)abeo-lathyrane rearrangement-type diterpene lathyranone A (1) was prepared from lathyrane-type Euphorbia factor L₁₁ (1a) via an efficient Sc(OTf)₃/Et₂NH-catalyzed α-ketol rearrangement, which was also suitable for the synthesis of lathyranones 2 and 3. This skeletal conversion strategy had the characteristic of biogenetically patterned synthesis and provided a convenient method for accessing naturally rare functionalized lathyranones from lathyranes. Moreover, the absolute configuration of the lathyranone skeleton was confirmed for the first time by the X-ray diffraction of 2.

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.

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.

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.

Diterpenoids from the seeds of Euphorbia lathyris and their effects on microglial nitric oxide production

Four new lathyrane-type diterpenoids (1-4) and a novel macrocyclic diterpenoid (5) featuring a 5/7/7/4-fused ring system, together with seventeen known ones (6-22), were isolated from the seeds of Euphorbia lathyris. Their structures were elucidated by extensive spectroscopic analyses and single crystal X-ray crystallography. These isolates were evaluated for their inhibition against nitric oxide (NO) production induced by lipopolysaccharide (LPS) in BV-2 microglial cells. As a result, the inhibitory rates of compounds 1, 3, 4, 6, 7, 9-11, 13-15, 20, and 21 on NO production were more than 40% with the cell viability more than 80% at their effective concentrations. In addition, compounds 6 and 11 markedly reduced the mRNA levels of pro-inflammatory cytokines IL-6 and IL-1β in LPS-stimulated BV-2 cells.

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.