Dimeric Sesquiterpenoids

A comprehensive review on the chemical constituents, sesquiterpenoid biosynthesis and biological activities of Sarcandra glabra

Sarcandra glabra (Thunb.) Nakai is a perennial evergreen herb categorised within the Sarcandra Gardner genus under the Chloranthaceae family. Indigenous to tropical and subtropical regions of East Asia and India, this species is extensively distributed across China, particularly in the southern regions (Sichuan, Yunnan, and Jiangxi). In addition to its high ornamental value, S. glabra has a rich history of use in traditional Chinese medicine, evident through its empirical prescriptions for various ailments like pneumonia, dysentery, fractures, bruises, numbness, amenorrhea, rheumatism, and other diseases. Besides, modern pharmacological studies have revealed various biological activities, such as antitumour, anti-bacterial, anti-viral anti-inflammatory and immunomodulatory effects. The diverse chemical constituents of S. glabra have fascinated natural product researchers since the 1900s. To date, over 400 compounds including terpenoids, coumarins, lignans, flavonoids, sterols, anthraquinones, organic acids, and organic esters have been isolated and characterised, some featuring unprecedented structures. This review comprehensively examines the current understanding of S. glabra's phytochemistry and pharmacology, with emphasis on the chemistry and biosynthesis of its unique chemotaxonomic marker, the lindenane-type sesquiterpenoids.

Weizhouochrones: Gorgonian-Derived Symmetric Dimers and Their Structure Elucidation Using Anisotropic NMR Combined with DP4+ Probability and CASE-3D

Natural product dimers have intriguing structural features and often have remarkable pharmacological activities. We report here two uncommon marine gorgonian-derived symmetric dimers, weizhouochrones A (1) and B (2), with indenone-derived monomers, that were isolated from the coral Anthogorgia ochracea collected from the South China Sea. These dimers are difficult targets for structure elucidation that solely relies upon conventional NMR data such as NOEs and J-couplings. Here, to explore the application of emerging methods on the structure elucidation of challenging molecules, we explored a number of different anisotropic and computational NMR approaches. The measurements of anisotropic NMR parameters of weizhouochrone A, including residual dipolar couplings (RDCs) and residual chemical shift anisotropy (RCSA), allowed us to successfully determine the planar structure and its relative configuration. This result was corroborated by a computational NMR analysis based on DP4+ probability and computer-assisted 3D structure elucidation (CASE-3D).

Horienoids A and B, Two Heterocoupled Sesquiterpenoid Dimers from Hedyosmum orientale

Two eudesmane-guaiane/lindenane heterocoupled sesquiterpenoid dimers, horienoids A (1) and B (2) with new carbon skeletons, from Hedyosmum orientale were characterized by a combined method. Compound 1 featured a unique 2,10-dioxabicyclo[6.2.1]undecane core moiety with an anti-Bredt bridgehead double bond. Their biogenetic pathways were proposed to involve Diels-Alder and cascade rearrangement reactions as the key steps. Compound 2 exhibited a potent anti-inflammatory effect on LPS-induced BV-2 microglial cells.

Natural Nitrogenous Sesquiterpenoids and Their Bioactivity: A Review

Nitrogenous sesquiterpenoids fromnatural sourcesare rare, so unsurprisingly neither the potentially valuable bioactivity nor thebroad structural diversity of nitrogenous sesquiterpenoids has been reviewed before. This report covers the progressduring the decade from 2010 to February 2020 on the isolation, identification, and bioactivity of 391 nitrogen-containing natural sesquiterpenes from terrestrial plant, marine organisms, and microorganisms. This complete and in-depth reviewshouldbe helpful for discovering and developing new drugs of medicinal valuerelated to natural nitrogenous sesquiterpenoids.

Dodelates A-E: Five dimeric eudesmane sesquiterpenoids from Dobinea delavayi

Dodelates A-E (1-5), five angeloylated eudesmane sesquiterpenoid dimers were isolated from the roots of Dobinea delavayi. Their structures were elucidated by extensive spectroscopic data and single-crystal X-ray diffraction analyses. A possible biosynthetic pathway of these five compounds was proposed. Compounds 1 and 3 exhibited moderate antimalarial activities against Plasmodium yoelii BY265RFP.

Tetramerized Sesquiterpenoid Ainsliatetramers A and B from Ainsliaea fragrans and Their Cytotoxic Activities

Two guaianolide sesquiterpenoid tetramers named ainsliatetramers A and B were separated from Ainsliaea fragrans. Through spectroscopic analyses, especially the band-selective CT-HSQC and CT-HMBC techniques, the complex skeleton was constructed from four sesquiterpene units via three different linkages. A biosynthetic pathway was proposed featuring a Michael addition and a regular and a hetero-Diels-Alder cycloaddition. Both exhibited potent cytotoxicity against human cancer cell lines with IC₅₀ values ranging from 2 to 15 μM.

New terpenoids from the fermentation broth of the edible mushroom Cyclocybe aegerita

The strophariaceous basidiomycete Cyclocybe aegerita (synonyms Agrocybe aegerita and A. cylindracea) is one of the most praised cultivated edible mushrooms and is being cultivated at large scale for food production. Furthermore, the fungus serves as a model organism to study fruiting body formation and the production of secondary metabolites during the life cycle of Basidiomycota. By studying the secondary metabolite profiles of C. aegerita, we found several terpenoids in submerged cultures. Aside from the main metabolite, bovistol (1), two new bovistol derivatives B and C (2, 3) and pasteurestin C as a new protoilludane (4) were isolated by preparative HPLC. Their structures were elucidated by mass spectrometry and NMR spectroscopy. The relative configurations of 2–4 were assigned by ROESY correlations, and ³J_H,H coupling constants in the case of 4. Applying quantitative PCR for gene expression validation, we linked the production of bovistol and its derivatives to the respective biosynthesis gene clusters.

Rare dimeric guaianes from Xylopia vielana and their multidrug resistance reversal activity

Thirteen undescribed dimeric guaianes were isolated from the leaves of Xylopia vielana Pierre. Their structures were elucidated by NMR spectroscopy and mass spectrometry, and the absolute configurations of vielanins G-Q were determined by a combination of the circular dichroism (CD) exciton chirality method, chemical conversion, and electronic CD (ECD) spectroscopy analysis. Vielaninors A and B are the first examples of trinor-guaiane-dimers. Multidrug resistance reversal activity assay of the isolates was evaluated in doxorubicin-resistant human breast cancer cells. Vielanins H, K-M, P, and Q were noncytotoxic and enhanced the cytotoxicity of doxorubicin by 2.1-41.6-fold at 10 μM.

Novel Terpenoids with Potent Cytotoxic Activities from Resina Commiphora

A novel sesquiterpene dimer, spirocommiphorfuran A (1); two new cadinane sesquiterpenoids, commiphorenes A (2) and B (3); along with three known terpenoids (4–6), were isolated from ResinaCommiphora. The structures of these new compounds were characterized by NMR, HRESIMS, quantum chemical computation, and X-ray diffraction analysis. Compound 1 features a 7-oxabicyclo[2.2.1]heptane-2-ene core, representing the first example of germacrane-type sesquiterpene dimer fused via a spiro ring system. Compound 2 is a novel sesquiterpene with a completely new carbon skeleton, which is characteristic of an additional carbon attaching to the cadinane backbone via a carbon–carbon bond. Additionally, compounds 2 and 4 exert acceptable cytotoxicity toward normal cells and high selectivity in cancer cells, especially in HepG2 cells.

Vlasouliolides A-D, four rare C17/C15 sesquiterpene lactone dimers with potential anti-inflammatory activity from Vladimiria souliei

Vlasouliolides A-D (1–4), four rare sesquiterpene lactone dimers, were isolated from Vladimiria souliei. The common structural characteristic of 1–4 is the C₃₂ skeleton comprising two sesquiterpene lactone units linked by a C11-C13′ single bond with one acetyl connected to the C-13 position of one of the two sesquiterpene lactone units. The stereochemistries of 1–4 were assigned by a combination of NOESY correlations and Cu-Κα X-ray crystallographic analyses. Compounds 1–4 strongly inhibited the production of NO in LPS-stimulated RAW 264.7 cells. Furthermore, 1 and 2 inhibited the activation of NF-κB in LPS-induced 293T cells.