Sesquiterpenoids and further diterpenoids from the rare Chloranthaceae plant Chloranthus sessilifolius

Phytochemical and biological studies on rare and endangered plants endemic to China. Part XXXVI. Tsugaforrestiacids A-O: Structurally diverse C-18 carboxylated diterpenoids from the twigs and needles of the 'vulnerable' conifer Tsuga forrestii and their inhibitory effects on ATP-citrate lyase

An extensive phytochemical investigation on the EtOAc-soluble fraction of the 90% MeOH extract from the twigs and needles of the 'vulnerable' Chinese endemic conifer Tsuga forrestii (Forrest's hemlock) led to the isolation and characterization of 50 structurally diverse diterpenoids, including 15 unreported C-18 carboxylated ones (tsugaforrestiacids A-O, 1-15, resp.). Among them, compounds 1-7 are abieten-18-oic acids, compound 8 is an abieten-18-succinate, and compounds 10-12 are podocarpen-18-oic acids, whereas compounds 13-15 are pimarane-type, isopimarane-type, and totarane-type diterpenoid acids, respectively. Their structures and absolute configurations were determined by a combination of spectroscopic methods, GIAO NMR calculations and DP4+ probability analyses, electronic circular dichroism (ECD) data, and single crystal X-ray diffraction analyses. All the isolates were evaluated for their inhibitory activities against the ATP-citrate lyase (ACL), a key enzyme in cellular metabolism. Tsugaforrestiacids E (5) and H (8) were found to have significant inhibitory effects against ACL, with IC50 values of 5.3 and 6.2 μM, respectively. The interactions of the bioactive molecules with the ACL enzyme were examined by molecular docking studies. The isolated diterpenoids also provide chemotaxonomic evidence to support the delimitation of Tsuga from its closest sister group (Nothotsuga). The above findings highlight the importance of protecting plant species with unique and diverse secondary metabolites, which may be potential sources of new therapeutic agents for the treating ACL-associated diseases.

Terpenoids of plants from Chloranthaceae family: chemistry, bioactivity, and synthesis

Covering: 1976 to December 2023Chloranthaceae is comprised of four extant genera (Chloranthus, Sarcandra, Hedyosmum, and Ascarina), totaling about 80 species, many of which have been widely used as herbal medicines for diverse medical purposes. Chloranthaceae plants represent a rich source of structurally interesting and diverse secondary metabolites, with sesquiterpenoids and diterpenoids being the predominant structural types. Lindenane sesquiterpenoids and their oligomers, chemotaxonomical markers of the family Chloranthaceae, have shown a wide spectrum of bioactivities, attracting significant attention from organic chemists and pharmacologists. Recent achievements also demonstrated the research value of two unique structural types in this plant family, sesquiterpenoid-monoterpenoid heterodimers and meroterpenoids. This review systematically summarizes 682 structurally characterized terpenoids from 22 Chloranthaceae plants and their key biological activities as well as the chemical synthesis of selected terpenoids.

Chemistry and bioactivity of lindenane sesquiterpenoids and their oligomers

Covering: 1925 to July 2023Among the sesquiterpenoids with rich structural diversity and potential bioactivities, lindenane sesquiterpenoids (LSs) possess a characteristic cis, trans-3,5,6-carbocyclic skeleton and mainly exist as monomers and diverse oligomers in plants from the Lindera genus and Chloranthaceae family. Since the first identification of lindeneol from Lindera strychnifolia in 1925, 354 natural LSs and their oligomers with anti-inflammatory, antitumor, and anti-infective activities have been discovered. Structurally, two-thirds of LSs exist as oligomers with interesting skeletons through diverse polymeric patterns, especially Diels-Alder [4 + 2] cycloaddition. Fascinated by their diverse bioactivities and intriguing polycyclic architectures, synthetic chemists have engaged in the total synthesis of natural LSs in recent decades. In this review, the research achievements related to LSs from 1925 to July of 2023 are systematically and comprehensively summarized, focusing on the classification of their structures, chemical synthesis, and bioactivities, which will be helpful for further research on LSs and their oligomers.

A Comprehensive Review of the Classification, Sources, Phytochemistry, and Pharmacology of Norditerpenes

Norditerpenes are considered to be a common and widely studied class of bioactive compounds in plants, exhibiting a wide array of complex and diverse structural types and originating from various sources. Based on the number of carbons, norditerpenes can be categorized into C19, C18, C17, and C16 compounds. Up to now, 557 norditerpenes and their derivatives have been found in studies published between 2010 and 2023, distributed in 51 families and 132 species, with the largest number in Lamiaceae, Euphorbiaceae, and Cephalotaxaceae. These norditerpenes display versatile biological activities, including anti-tumor, anti-inflammatory, antimicrobial, and antioxidant properties, as well as inhibitory effects against HIV and α-glucosidase, and can be considered as an important source of treatment for a variety of diseases that had a high commercial value. This review provides a comprehensive summary of the plant sources, chemical structures, and biological activities of norditerpenes derived from natural sources, serving as a valuable reference for further research development and application in this field.

Lindenane sesquiterpenoid monomers and oligomers: Chemistry and pharmacological activities

Lindenane sesquiterpenoid monomers and oligomers, characterized by a sterically congested cyclopentane and an unusual trans-5/6 ring junction, are mainly found in Chloranthaceae species and the genus Lindera Thunb (Lauraceae). Numerous studies have shown that lindenane sesquiterpenoid monomers and oligomers exhibit a broad range of biological activities, such as cytotoxicity, anti-inflammation, neuroprotection, antifungal, and anti-malarial activities. This review covers publications from the first identification of lindeneol in 1925-2023 and classifies the lindenane sesquiterpenoid derivatives into sesquiterpenoid monomers, sesquiterpenoid-monoterpene conjugates, sesquiterpenoid homodimers, sesquiterpenoid heterodimers, and trimeric sesquiterpenoids. In addition, their biological activities are summarized. This review will establish a scientific basis and provide guidance for utilizing this unique class of natural products as potential lead compounds to develop their application in treating diseases corresponding to inflammation, cancer, and plasmodium.

Lindenane sesquiterpenoid dimers from Chloranthus holostegius with anti-neuroinflammatory activities in BV-2 microglia

Fifteen undescribed lindenane-type sesquiterpenoid dimers, designated chloranholides F-T (1-15), together with twenty-five known analogs (16-40), were isolated from the whole plants of Chloranthus holostegius. The isolate structures were elucidated by analysis of spectroscopic data and chemical methods, and their absolute configurations were determined by X-ray crystallography and electronic circular dichroism spectra. In anti-neuroinflammatory assays, all isolates were evaluated by examination of their inhibitory effect on nitric oxide (NO) in LPS-stimulated BV-2 cells, and the results showed that 21-24, 26, 30, 32 and 36 significantly inhibited the production of the inflammatory mediator NO, with IC50 values ranging from 3.18 to 11.46 μM, which was better than that of quercetin. Structure-activity relationship analysis revealed that two essential functional groups played an indispensable role in the anti-inflammatory effects. Moreover, 22 and 24 inhibited the LPS-induced upregulation of iNOS and COX-2 enzymes in BV-2 microglia at the protein level.

Further terpenoids from the Chloranthaceae plant Chloranthus multistachys and their anti-neuroinflammatory activities

Three labdane-type [multisins A-C (1-3)], two guaiane-type [multisins D (4) and E (5)], and one eudesmane-type [multisin F (6)] previously undescribed terpenoids, together with 14 mono- (7-20) and seven dimeric- (21-27) known terpenoids, were isolated from the 90% MeOH extract of the whole plant of Chloranthus multistachys. Their structures and absolute configurations were determined by extensive spectroscopic methods and electronic circular dichroism (ECD) calculations. Compounds 4 and 5 are rare trinor-sesquiterpenes with a de-isopropyl guaiane skeleton, whereas compound 6 is a rearranged dinor-eudesmene featuring an uncommon octahydro-1H-indene ring system. Among the isolates, the dimeric lindenane sesquiterpenoid shizukaol C (25) exhibited the most potent (IC₅₀ = 8.04 μM) anti-neuroinflammatory activity by inhibiting the nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated murine BV-2 microglial cells.

Diterpenoid Compounds Isolated from Chloranthus oldhamii Solms Exert Anti-Inflammatory Effects by Inhibiting the IKK/NF-κB Pathway

Chloranthus oldhamii Solms (CO) is a folk medicine for treating infection and arthritis pain but its pharmacological activity and bioactive compounds remain mostly uncharacterized. In this study, the anti-inflammatory compounds of C. oldhamii were identified using an LPS-stimulated, NF-κB-responsive RAW 264.7 macrophage reporter line. Three diterpenoid compounds, 3α-hydroxy-ent-abieta-8,11,13-triene (CO-9), 3α, 7β-dihydroxy-ent-abieta-8,11,13-triene (CO-10), and decandrin B (CO-15) were found to inhibit NF-κB activity at nontoxic concentrations. Moreover, CO-9 and CO-10 suppressed the expression of IL-6 and TNF-α in LPS-stimulated RAW 264.7 cells. The inhibitory effect of CO-9 on TNF-α and IL-6 expression was further demonstrated using LPS-treated bone marrow-derived macrophages. Furthermore, CO-9, CO-10, and CO-15 suppressed LPS-triggered COX-2 expression and downstream PGE2 production in RAW 264.7 cells. CO-9 and CO-10 also reduced LPS-triggered iNOS expression and nitrogen oxide production in RAW 264.7 cells. The anti-inflammatory mechanism of the most effective compound, CO-9, was further investigated. CO-9 attenuated LPS-induced NF-κB activation by reducing the phosphorylation of IKKα/β (Ser176/180), IκBα (Ser32), and p65 (Ser534). Conversely, CO-9 did not affect the LPS-induced activation of MAPK signaling pathways. In summary, this study revealed new anti-inflammatory diterpenoid compounds from C. oldhamii and demonstrated that the IKK-mediated NK-κB pathway is the major target of these compounds.

Natural Terpenoids as Neuroinflammatory Inhibitors in LPS-stimulated BV-2 Microglia

Neuroinflammation is a typical feature of many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Microglia, the resident immune cells of the brain, readily become activated in response to an infection or an injury. Uncontrolled and overactivated microglia can release pro-inflammatory and cytotoxic factors and are the major culprits in neuroinflammation. Hence, research on novel neuroinflammatory inhibitors is of paramount importance for the treatment of neurodegenerative diseases. Bacterial lipopolysaccharide, widely used in the studies of brain inflammation, initiates several major cellular activities that critically contribute to the pathogenesis of neuroinflammation. This review will highlight the progress on terpenoids, an important and structurally diverse group of natural compounds, as neuroinflammatory inhibitors in lipopolysaccharidestimulated BV-2 microglial cells over the last 20 years.

Three pairs of sesquiterpene enantiomers from Chloranthus multistachys pei

Phytochemical investigation on the whole plant of Chloranthus multistachys pei (Chloranthaceae) afforded three pairs of new sesquiterpene enantiomers (+)/(-)-chlorantene M [(+)/(-)-1], (+)/(-)-chlorantene M1 [(+)/(-)-2] and (+)/(-)-chlorantene N [(+)/(-)-3]. The structures of new compounds were determined through spectroscopic techniques (HR-ESI-MS, 1 D and 2 D NMR), besides, their absolute and relative configurations were established by using Single-crystal X-ray diffraction analysis and CD spectrum. The anti-inflammatory potential of all compounds was evaluated by applying LPS induced RAW 264.7 macrophage inflammatory model, and the results were that none of these compounds showed activity (IC₅₀ > 100 μM).

Natural disesquiterpenoids: an update

This review highlights the progress on the isolation, bioactivity, biogenesis and total synthesis of dimeric sesquiterpenoids since 2010.

Reanalysis of Lindenatriene, a Building Block for the Synthesis of Lindenane Oligomers

Lindenane oligomers isolated from Chloranthus pose significant challenges for chemical synthesis. The structure of a proposed biosynthetic monomer, lindenatriene, was recently called into question. Its attempted synthesis produced a compound whose 1H NMR spectrum differed significantly from the spectrum of a monomer produced by oligomer pyrolysis. Here we propose that the original structural assignment after pyrolysis was correct and instead the spectra of synthetic materials were misinterpreted. Reanalysis of 2D NMR data suggest that lindenatriene isomerizes (formal [1,7]-hydrogen shift) upon treatment with base.

Isolation and Absolute Configurations of Diversiform C17, C21 and C25 Terpenoids from the Marine Sponge Cacospongia sp

Chemical investigation of MeOH extract of a South China Sea sponge Cacospongia sp. yielded 15 terpenoids belonging to three different skeleton-types, including the unusual C₁₇γ-lactone norditerpenoids (1–3), the rare C₂₁ pyridine meroterpenoid (7), and the notable C₂₅ manoalide-type sesterterpenoids (4–6, 8–10). Compounds 1–5 were initially obtained as enantiomers, and were further separated to be optically pure compounds (1a, 1b, 2a, 2b, 3a-r, 3b-r, 4a, 4b, 5a and 5b) by chiral HPLC, with a LiAlH₄ reduction aid for 3. Compounds 3a/3b (a pair of inseparable enantiomers), 4a, 5a, 6, and 7 were identified as new compounds, while 1a/1b and 2a/2b were obtained from a natural source and were determined for their absolute configurations for the first time. This is also the first time to encounter enantiomers of the well-known manoalide-type sesterterpenoids from nature. The structures with absolute configurations of the new compounds were unambiguously determined by comprehensive methods including HR-ESI-MS and NMR data analysis, optical rotation comparison, experimental and calculated electronic circular dichroism (ECD), and Mo₂(OAc)₄ induced circular dichroism (ICD) methods. The cytotoxicity of the isolates against selected human tumor cell lines was evaluated, however, the tested compounds showed no activity against selected cell lines.

Total Syntheses of Aromatic Abietane Diterpenoids Utilizing Advances in the Pummerer Rearrangement

The first total syntheses of triptobenzene T, vitexifolin C, 4- epi-triptobenzene L, triptobenzene L, and nepetaefolin F have been accomplished through an enantioselective, common intermediate approach and have enabled the confirmation and/or establishment of the absolute stereochemistry of each natural product synthesized. Application of three new and/or underutilized Pummerer reaction pathways proved critical to the synthetic work. A proline sulfonamide-catalyzed Yamada-Otani reaction was used to access the highly functionalized cyclohexane A ring core, including the C₁₀ all-carbon quaternary stereocenter. Additionally, the importance of the A ring unsaturation for controlling the stereoselectivity during the C₄ alkylation is showcased.

LC-MS guided isolation of sinodamines A and B: Chimonanthine-type alkaloids from the endangered ornamental plant Sinocalycanthus chinensis

Two previously undescribed chimonanthine-type [sinodamines A and B] and five related known dimeric tryptamine-derived alkaloids were isolated and characterized from the leaves of the endangered ornamental plant Sinocalycanthus chinensis under the guidance of LC-MS detection and dereplication analyses, along with conventional isolation procedures. Their structures were established on the basis of spectroscopic methods and chemical transformations. Sinodamine A can be regarded as the naturally occurring N-oxide derivative of its pseudo-mesomer sinodamine B. An acid-catalyzed Meisenheimer rearrangement from sinodamine A to its oxazine-form with a final equilibrium of 1:2 was observed by monitoring their NMR spectra. (-)-Folicanthine showed significant cytotoxicity against human lung carcinoma A549 and colorectal carcinoma HT29 cells, with IC₅₀ values of 7.76 and 6.16 μM, respectively.

Camellianols A-G, Barrigenol-like Triterpenoids with PTP1B Inhibitory Effects from the Endangered Ornamental Plant Camellia crapnelliana

Seven new naturally occurring barrigenol-like compounds, camellianols A-G (1-7), and 10 known triterpenoids were isolated from the twigs and leaves of the cultivated endangered ornamental plant Camellia crapnelliana. According to the ECD octant rule for saturated cyclohexanones, the absolute configurations of camellianols D (4) and E (5) were defined. The backbones of the remaining new isolates are assumed to have the same absolute configuration as compounds 4, 5, and harpullone (12). Compounds 2, 3, 9, 10, 13, and 16 exhibited inhibitory effects on the protein tyrosine phosphatase 1B (PTP1B) enzyme, with IC₅₀ values less than 10 μM.