Structurally Diverse Sesquiterpenoids from the Endangered Ornamental Plant Michelia shiluensis

Ent-eudesmane sesquiterpenoids with anti-neuroinflammatory activity from the marine-derived fungus Eutypella sp. F0219

In this study, twenty-three ent-eudesmane sesquiterpenoids (1-23) including fifteen previously undescribed ones, named eutypelides A-O (1-15) were isolated from the marine-derived fungus Eutypella sp. F0219. Their planar structures and relative configurations were established by HR-ESIMS and extensive 1D and 2D NMR investigations. The absolute configurations of the previously undescribed compounds were determined by single-crystal X-ray diffraction analyses, modified Mosher's method, and ECD calculations. Structurally, eutypelide A (1) is a rare 1,10-seco-ent-eudesmane, whereas 2-15 are typically ent-eudesmanes with 6/6/-fused bicyclic carbon nucleus. The anti-neuroinflammatory activity of all isolated compounds (1-23) was accessed based on their ability to NO production in LPS-stimulated BV2 microglia cells. Compound 16 emerged as the most potent inhibitor. Further mechanistic investigation revealed that compound 16 modulated the inflammatory response by decreasing the protein levels of iNOS and increasing ARG 1 levels, thereby altering the iNOS/ARG 1 ratio and inhibiting macrophage polarization. qRT-PCR analysis showed that compound 16 reversed the LPS-induced upregulation of pro-inflammatory cytokines, including iNOS, TNF-α, IL-6, and IL-1β, at both the transcriptional and translational levels. These effects were linked to the inhibition of the NF-κB pathway, a key regulator of inflammation. Our findings suggest that compound 16 may be a potential structure basis for developing neuroinflammation-related disease therapeutic agents.

Identification and structural modification of ent-rosane diterpenoids from Euphorbia milii inhibiting RANKL-induced osteoclastogenesis

Phytochemical study on Euphorbia milii, a common ornamental plant, resulted in the identification of thirteen new ent-rosane diterpenoids (1-13), three new ent-atisane diterpenoids (14-16), and a known ent-rosane (17). Their structures were delineated using spectroscopic data, quantum chemical calculations, and X-ray diffraction experiments. Euphomilone F (1) represented a rare ent-rosane-type diterpenoid with a 5/7/6 skeleton. Euphoainoid G (8) was a rare rosane diterpenic acid. Compounds 9 and 10 carried infrequent tetrahydrofuran rings, and compounds 11-13 was 18-nor-ent-rosane diterpenoids. All isolates were evaluated for their inhibitory effects on RANKL-induced osteoclasts. Notably, compounds with aromatic ester groups (2-7) showed promising activities (IC50 < 10 μM), underscoring the significance of acylated A-ring moieties in the ent-rosane skeleton for anti-osteoclastogenesis. Thirteen synthetic derivatives were obtained through esterification of 17. Of these, compound 27 exhibited remarkable improvement, with an IC50 of 0.8 μM, more than a 12-fold increase in potency compared to the parent compound 17 (IC50 > 10 μM). This work presents a series of new ent-rosane diterpenoids with potential antiosteoporosis agents.

Three rare anti-inflammatory sesquiterpene lactones from Magnolia grandiflora

Four new sesquiterpene lactones (SLs) (1-4), along with a biosynthetically related SL (5), have been isolated from the leaves of Magnolia grandiflora. Magrandate A (1) is notable as the first C18 homogemarane type SL, featuring a unique 1,7-dioxaspiro[4.4]nonan-6-one core. Compounds 2 and 3, representing the first instances of chlorine-substituted gemarane-type SL analogs in natural products, were also identified. The structures of these isolates were elucidated through a combination of spectroscopic data analysis, electronic circular dichroism calculations, and X-ray single-crystal diffraction analysis. All isolates demonstrated anti-inflammatory activity in lipopolysaccharide-stimulated RAW264.7 cells. Notably, 3-5 showed a significant inhibitory effect on nitric oxide production, with IC50 values ranging from 0.79 to 4.73 μmol·L-1. Additionally, 4 and 5 exhibited moderate cytotoxic activities against three cancer cell lines, with IC50 values between 3.09 and 11.23 μmol·L-1.

Liriogerphines E-U, further unique sesquiterpene-alkaloid hybrids from the rare Chinese tulip tree

Seventeen undescribed sesquiterpene-alkaloid hybrids (liriogerphines E-U, 1-17) were isolated and identified during a further phytochemical investigation on the branches and leaves of Chinese tulip tree (Liriodendron chinense), a rare medicinal and ornamental plant endemic to China. These unique heterodimers are conjugates of germacranolide-type sesquiterpenoids with structurally diverse alkaloids [i.e., aporphine- (1-15), proaporphine- (16), and benzyltetrahydroisoquinoline-type (17)] via the formation of a C-N bond. The previously undescribed structures were elucidated by comprehensive spectroscopic data analyses and electronic circular dichroism calculations. Such a class of sesquiterpene-alkaloid hybrids presumably biosynthesized via an aza-Michael addition is quite rare from terrestrial plants. In particular, the sesquiterpene-benzyltetrahydroisoquinoline hybrid skeleton has never been reported until the present study. All the isolates were evaluated for their cytotoxic effects against a small panel of leukemia cell lines (Raji, Jeko-1, Daudi, Jurkat, MV-4-11 and HL-60), and some of them exhibited considerable activities.

Discovery of plant-derived anti-tumor natural products: Potential leads for anti-tumor drug discovery

Natural products represent a paramount source of novel drugs. Numerous plant-derived natural products have demonstrated potent anti-tumor properties, thereby garnering considerable interest in their potential as anti-tumor drugs. This review compiles an overview of 242 recently discovered natural products, spanning the period from 2018 to the present. These natural products, which include 69 terpenoids, 42 alkaloids, 39 flavonoids, 21 steroids, 14 phenylpropanoids, 5 quinolines and 52 other compounds, are characterized by their respective chemical structures, anti-tumor activities, and mechanisms of action. By providing an essential reference and fresh insights, this review aims to support and inspire researchers engaged in the fields of natural products and anti-tumor drug discovery.

Discovery of diverse sesquiterpenoids from Magnolia grandiflora with cytotoxic activities by inducing cell apoptosis

Phytochemical study of Magnolia grandiflora led to the isolation of 39 sesquiterpenoids, including 15 new compounds (1-15). Compounds 1 and 2 are discovered to be the first 13-norgermacrane type sesquiterpenoids in natural products. Compound 15 is a rare 5,6-seco-guaiane type sesquiterpene and its possible biogenic precursor is presumed to be compound 20. Subsequent structural modification for compound 28 led to 21 derivatives, among which 15 derivatives were new compounds. All compounds were tested for the inhibitory effects on three tumor cell lines, and 17 compounds were active with the IC50 values ranging from 1.91 ± 0.39 μM to 12.29 ± 1.68 μM. The structure-activity relationships implied that an α, β-unsaturated lactone group was an important active group for the cytotoxicity. Two most active compounds (19 and 29) with low toxicity on normal human liver cell line were selected for further mechanism study. Compound 29 could induce apoptosis on Colo320DM cells through influencing the key apoptotic related proteins, such as PARP, Cleaved PARP, cleaved Caspase-3, and pro-Caspase 3. In addition, compound 19 with the best cytotoxic activity on HEL cells also could induce the apoptosis in dose- and time-dependent manners. In summary, our investigation implied that compounds 19 and 29 are two new potential anti-cancer candidates for ongoing study in the future.

Comparison of Composition, Free-Radical-Scavenging Capacity, and Antibiosis of Fresh and Dry Leave Aqueous Extract from Michelia shiluensis

Numerous plants of medicinal value grow on Hainan Island (China). Given the lack of knowledge on the phytochemical and pharmacological properties of Michelia shiluensis Chun and Y. F. Wu (M. shiluensis), the application of natural antioxidants and antimicrobials in the food industry has attracted increasing interest. This study aimed to compare the chemical composition, free-radical-scavenging capacity, and antibiosis of aqueous extracts of the fresh and dried leaves of M. shiluensis. The aqueous extract of the leaves of M. shiluensis was obtained using steam distillation, and its chemical components were separated and identified via gas chromatography-mass spectrometry (GC-MS). The free-radical-scavenging capacity and antibiosis were determined. Further, 28 and 20 compounds were isolated from the fresh leaf aqueous extract of M. shiluensis (MSFLAE) and dried leaf aqueous extract of M. shiluensis (MSDLAE), respectively. The free-radical-scavenging capacity of MSFLAE and MSDLAE was determined by the 2,2-diphenyl-1 picrylhydrazyl (DPPH) method, which was 43.43% and 38.74%, respectively. The scavenging capacity of MSFLAE and MSDLAE determined by the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonate (ABTS)) method was 46.90% and 25.99%, respectively. The iron ion reduction capacity of MSFLAE and MSDLAE was determined by the ferric-reducing antioxidant power (FRAP) method as 94.7 and 62.9 μmol Fe2⁺/L, respectively. This indicated that the two leaf aqueous extracts had a certain free-radical-scavenging capacity, and the capacity of MSFLAE was higher than that of MSDLAE. The antibiosis of the two leaf aqueous extracts on the three foodborne pathogenic bacteria was low, but the antimicrobial effects on Gram-positive bacteria were better than those on Gram-negative bacteria. The antibiosis of MSFLAE on Escherichia coli and Staphylococcus aureus was greater than that of MSDLAE. Finally, MSFLAE and MSDLAE both had certain free-radical-scavenging capacities and antibiosis, confirming that the use of this plant in the research and development of natural antioxidants and antibacterial agents was reasonable. Plant aqueous extracts are an essential source of related phytochemistry and have immense pharmacological potential.

Anti-inflammatory and PTP1B inhibitory sesquiterpenoids from the twigs and leaves of Aglaia lawii

Twelve sesquiterpenoids with seven different carbon skeletons, including four isodaucanes (1-4), an aromadendrane (5), a guaiane (6), a cadalane (7), two eudesmanes (8 and 9), two bisabolanes (10 and 11), and a megastigmane (12), were isolated from the twigs and leaves of Aglaia lawii (Wight) C. J. Saldanha et Ramamorthy. Of these compounds, amouanglienoids A (1) and B (2) are new isodaucane sesquiterpenoids. This is the first report of isodaucanes from the genus Aglaia, and amouanglienoid A (1) represents the first isodaucane containing a Δ⁷⁽⁸⁾ double bond. Their structures were discerned from extensive spectroscopic analyses, single-crystal X-ray diffraction, and comparison of the experimental and calculated ECD data. In in vitro bioassays, compounds 1, 10, and 11 showed potent inhibitory effects against lipopolysaccharide (LPS)-induced inflammation in BV-2 microglial cells, while compound 11 exhibited considerable inhibition of PTP1B with an IC₅₀ value of 16.05 ± 1.09 μM.

Liriogerphines A-D, a Class of Sesquiterpene-Alkaloid Hybrids from the Rare Chinese Tulip Tree Plant

Liriogerphines A-D (1-4, respectively), an unprecedented class of hybrids of germacranolide-type sesquiterpenoids and aporphine-type alkaloids, were isolated from the rare medicinal plant Liriodendron chinense. Their structures were elucidated by comprehensive spectroscopic analyses combined with electronic circular dichroism calculations and X-ray crystallographic data. Biosynthetically, an aza-Michael addition reaction is proposed to be involved in the assemblies of this class of hybrids. Compound 4 exhibited cytotoxicity against leukemia cells via inducing apoptosis and inhibiting Bcl-2 expression.

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.

Guaiane-type sesquiterpenoids from Cinnamomum migao H. W. Li: And their anti-inflammatory activities

The phytochemical assessment of Cinnamomum migao H. W. Li fruits illustrated the isolation and identification of ten undescribed guaiane-type sesquiterpenoids "miganoids A-J″ and one undescribed sesquiterpene "7(S)-(hydroxypropanyl)-3-methyl-2-(4-oxopentyl) cyclohex-2-en-1-one". The extensive analysis of HRESIMS, 1D NMR, 2D NMR, experimental circular dichroism (ECD), and calculated (ECD) analysis entirely corroborated the configuration and confirmation of these isolated compounds. Moreover, the anti-inflammatory properties of the reported compounds were established by determining the LPS induced nitric oxide production. In the current study, miganoid C is testified the most active compound with about 89% NO inhibition. Additionally, miganoids C, E, and G also exhibited moderate inhibitory effects against the pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6). The IC₅₀ values for miganoid C and miganoid G were determined as 19.4 and 14.5 μΜ against TNF-α mRNA, respectively.

Guaiane-type sesquiterpenoids from the roots of Stellera chamaejasme L. and their neuroprotective activities

Nine undescribed guaiane-type sesquiterpenoids stelleraterpenoids A‒I, along with seven reported congeners, were isolated and identified from the 70% EtOH extract of the roots of Stellera chamaejasme L. Their chemical structures were elucidated on the basis of various spectral data. The relative configurations were determined by their NOESY spectra and comparison between their experimental and calculated NMR data. The absolute configurations were established by the comparison between the experimental and calculated ECD spectra and further by X-ray single-crystal diffraction analysis. The neuroprotective effects of these compounds on the H₂O₂-induced damage in human neuroblastoma SH-SY5Y cells were evaluated. Stelleraguaianone B exhibited the better activity with 71.62% cell viability compared to the positive control Trolox (65.05%) at 12.5 μM, which might be achieved by inhibiting the apoptosis of SH-SY5Y cells based on an annexin V-FITC/PI staining experiment.

Three new guaiane-type sesquiterpenoids and a monoterpenoid from Litsea lancilimba Merr

Three undescribed guaiane-type sesquiterpenes (1-3), and a monoterpenoid (4) along with eleven known compounds (5 - 15) were isolated from the crude extract of Litsea lancilimba Merr. The structures of all the isolated compounds were extensively elucidated on the basis of comprehensive spectroscopic techniques (HRESIMS, 1 D NMR, and 2 D NMR). Their relative and absolute configurations were comprehensively established by NOESY spectroscopy, circular dichroism (ECD) and the calculated ECD analysis. All the isolates were tested for anti-inflammatory activity by measuring the amount of nitric oxide production. Amongst tested compounds, compounds 1 - 3 exhibited moderate inhibitory activities against the production of nitric oxide with IC₅₀ value of 35.5, 32.1, 46.7 μM in RAW264.7 cells stimulated by LPS, respectively.

Chromenopyridin A, a new N-methoxy-1-pyridone alkaloid from the endophytic fungus Penicillium nothofagi P-6 isolated from the critically endangered conifer Abies beshanzuensis

A new N-methoxy-1-pyridone alkaloid [chromenopyridin A (1)] and four known compounds (2-5) were isolated and identified from the endophytic fungus Penicillium nothofagi P-6, which was derived from the bark of the critically endangered conifer Abies beshanzuensis. Their structures were elucidated by extensive spectroscopic analyses and single-crystal X-ray diffraction. Among the isolates, compound 1 showed considerable cytotoxicities against the A549 and Hela human cancer cell lines, with IC₅₀ values of 14.7 and 11.3 μM. In addition, compounds 1 and 4 exhibited potent antibacterial activity against Staphylococcus aureus with MIC values of 62.5 and 15.6 μg/mL, respectively.

Amentotaxins C-V, Structurally Diverse Diterpenoids from the Leaves and Twigs of the Vulnerable Conifer Amentotaxus argotaenia and Their Cytotoxic Effects

A phytochemical investigation of the MeOH extract of the leaves and twigs of Amentotaxus argotaenia, a relict vulnerable coniferous species endemic to China, led to the isolation and characterization of 35 diterpenoids/norditerpenoids. Twenty of these are new, including 11 ent-kaurane-type (amentotaxins C-M, 1-11, respectively), three icetexane-type [= 9(10→20)abeo-abietane-type (amentotaxins N-P, 12-14, respectively)], four ent-labdane-type (amentotaxins Q-T, 15-18, respectively), and two isopimarane-type [amentotaxins U (19) and V (20)] compounds. Their structures were elucidated on the basis of spectroscopic data, single-crystal X-ray diffraction, the modified Mosher's method, and electronic circular dichroism data analyses. Compounds 1-9 are rare 18-nor-ent-kaurane-type diterpenoids featuring a 4β,19-epoxy ring. All the isolates were evaluated for their cytotoxic effects against a small panel of cultured human cancer cell lines (HeLa, A-549, MDA-MB-231, SKOV3, Huh-7, and HCT-116), and some of them exhibited cytotoxicities with IC₅₀ values ranging from 1.5 to 10.0 μM.

A new coumarin derivative from the stems of the endangered plant Ulmus elongata

A preliminary phytochemical investigation of the stems of the endangered plant Ulmus elongata led to the isolation of a new coumarin derivative (named ulmuselactone A, 1) and eight known compounds (2-9). The new structure was elucidated by detailed analysis of comprehensive spectroscopic methods, and its absolute configuration was established by comparing experimental and calculated electronic circular dichroism (ECD) spectra. The isolated compounds were evaluated for their antibacterial activities.

Phytochemical and biological studies on rare and endangered plants endemic to China. Part XV. Structurally diverse diterpenoids and sesquiterpenoids from the vulnerable conifer Pseudotsuga sinensis

An extensive phytochemical investigation on the chemical constituents from the needles and twigs of the vulnerable conifer Pseudotsuga sinensis yielded 19 diterpenoids and 21 sesquiterpenoids with various carbocyclic skeletons. Among them, 13 (named pseudosinins A-M, resp.) were undescribed compounds. Their structures with absolute configurations were characterized by a combination of spectroscopic methods, calculated and experimental electronic circular dichroism (ECD) data, quantum chemical calculations of the chemical shifts, and single crystal X-ray diffraction analyses. In particular, an array of labdane-derived norditerpenoids with C₁₉-, C₁₈-, and C₁₆-skeletons, and related drimane-type sesquitepenoids with C₁₅- and C₁₃-skeletons were found in the title plant. The possible biogenetic relationships of these degraded terpenoids were briefly discussed. Among the isolates, pseudosinin D, cis-communic acid, and 4β,15-dihydroxy-19-norabieta-8,11,13-trien-7-one showed moderate inhibitory activities against the enzyme ATP-citrate lyase (ACL), a potential drug target for the treatment of hyperlipidemia and hypercholesterolemia.

Stewartiacids A–N, C-23 carboxylated triterpenoids from Chinese Stewartia and their inhibitory effects against ATP-citrate lyase and NF-κB

Fourteen previously undescribed naturally occurring C-23 carboxylated triterpenoids, stewartiacids A–N (1–14), were isolated and characterized from the twigs and leaves of the ornamental and medicinal plant Stewartia sinensis (Chinese Stewartia), a ‘vulnerable’ species endemic to China. The new structures were elucidated on the basis of spectroscopic data, single crystal X-ray diffraction, and electronic circular dichroism (ECD) analyses. Stewartiacids A (1) and B (2) are isoursenol derivatives. Stewartiacid C (3) is a 12-oxo-γ-amyrin analogue. Both isoursenol and γ-amyrin derivatives are quite rare in nature. Stewartiacids D (4) and E (5) are 13,27-cycloursane-type compounds. Stewartiacids K (11) and L (12) are ursane-type triterpene and phenylpropanol adducts built through a 1,4-dioxane ring, which are also seldom reported in the literature. The rest are common C-23 carboxylated ursane-type (6–10) and oleanane-type (13, 14) pentacyclic triterpenoids. Stewartiacids G (7), K (11), and L (12) showed moderate inhibitory effects against ATP-citrate lyase (ACL), with IC₅₀ values of 12.5, 2.8, and 10.6 μM, respectively. Stewartiacid K (11) also exhibited moderate inhibition (IC₅₀: 16.8 μM) of NF-κB.

Fourteen new C-23 carboxylated triterpenoids (stewartiacids A–N, 1–14) were obtained from the ‘vulnerable’ plant Stewartia sinensis. 11 and 12 showed inhibitory effects against ACL.

Phytochemical and biological studies on rare and endangered plants endemic to China. Part XIV. Structurally diverse terpenoids from the twigs and needles of the endangered plant Picea brachytyla

A phytochemical investigation on the MeOH extract of the twigs and needles of the endangered plant Picea brachytyla led to the isolation and characterization of thirty-eight structurally diverse terpenoids. Seven of these molecules are previously undescribed, including three abietane-type (brachytylins A-C) and one labdane-type (brachytylin D) diterpenoids, an unseparated C-24 epimeric mixture of cycloartane-type triterpenoids (brachytylins E/F, ratio: 1:1), and a rare rearranged 12(1 → 6)-abeo-megastigmane glycoside (brachytylins G). Their structures and absolute configurations were determined by extensive spectroscopic (e.g., detailed 2D NMR and ECD) methods and/or X-ray diffraction analyses. All the isolates were evaluated for their inhibitory activities against the adenosine triphosphate (ATP)-citrate lyase (ACL) and the Src homology-2 domain containing protein tyrosine phosphatase-2 (SHP2). Among them, abiesadine J showed inhibitory effect against ACL, displaying an IC₅₀ value of 17 μM. 3S,23R-Dihydroxycycloart-24-en-26-oic acid exhibited inhibitory effect on SHP2, with an IC₅₀ value of 19 μM. Meanwhile, 3R*,23S*-dihydroxycycloart-24-en-26-oic acid was found to have inhibitory effects against both ACL and SHP2, with IC₅₀ values of 16 and 12 μM, respectively.

Aflatoxins from the endophytic fungus Aspergillus sp. Y-2 isolated from the critically endangered conifer Abies beshanzuensis

Two new [asperxins A (1) and B (2)] and four known (3-6) aflatoxins were isolated and identified from the endophytic fungus Aspergillus sp. Y-2, which was derived from the needles of the critically endangered conifer Abies beshanzuensis. Their structures were elucidated by extensive spectroscopic methods. Among the isolates, compounds 1 and 5 showed considerable cytotoxicities against the A549 and Hela human cancer cell lines, with IC₅₀ values in the range of 7.5-16.8 μM.