Diterpenoids from Torreya grandis and their cytotoxic activities

Eight previously undescribed diterpenoids, along with eleven previously reported analogues, were obtained from the supercritical CO2 extracts of Torreya grandis aril. The structures of these compounds were elucidated based on HRESIMS, NMR, ECD, and single-crystal X-ray diffraction data. In the MTT assay, compound 18 exhibited significant inhibitory effects on two human colon cancer cell lines, HT-29 and HCT 116 cells, with IC50 values of 7.37 μM and 6.55 μM, respectively. It was found that compound 18 induced apoptosis and significantly inhibited the migration of HCT 116 colon cancer cells in a concentration-dependent manner.

sinensis

Cephalotanes are a rare class of diterpenoids occurring exclusively in Cephalotaxus plants. The intriguing structures and promising biological activities for this unique compound class prompt us to investigate C. fortunei var. alpina and C. sinensis, leading to the isolation of six undescribed cephalotane-type diterpenoids and/or norditerpenoids, ceforloids A-F (1-6). Their structures were elucidated by comprehensive analysis of spectroscopic data, including ECD and single-crystal X-ray diffraction studies, as well as quantum chemical calculations. Compound 1 possesses an unprecedented norditerpenoid skeleton featuring an unusual acetophenone moiety, and originated putatively from a disparate biogenetic pathway. Compounds 4 and 5 incorporate a unique 12,13-p-hydroxybenzylidene acetal motif. Compound 6 is a rare cephalotane-type diterpenoid glycoside. Immunosuppressive assays showed that compounds 2 and 6 exhibited mild suppressive activity against the activated T and B lymphocytes proliferation. These findings not only expanded the structural diversity of this small group of diterpenoids, but also explored their potential as novel structures for the development of immunosuppressive agents.

with potential antioxidant activity

Chemical investigation of Euphorbia wallichii Hook. f. led to the isolation of four undescribed rearranged diterpenoids, euphwanoids I-IV (1-4), and six unreported tigliane diterpenoids walliglianes A-F (5-10). Euphwanoids I-III (1-3) possess a rare 6/6/7/3 ring scaffold, euphwanoid IV (4) is the first spiro[tricyclo[5.4.0.02,4]undecane-8,1'-cyclopentane] skeleton to be found in the tigliane family. The structures of compounds 1-10 were established by utilizing spectroscopic data analysis, experimental electronic circular dichroism measurements, 13C NMR calculations, and single-crystal X-ray diffraction. In the preliminary bioassay, compounds 3, 4, and 7 were found to protect BV-2 cells against H2O2-induced cell injury in a dose-dependent manner by the CCK8 assay.

Br

Four new undescribed halimane- and labdane-type diterpenoids, named zeylleucapenoids E-H (1-4), along with four known analogues (5-8), were isolated from the aerial parts of Leucas zeylanica (L.) R. Br. Their structures were determined by comprehensive spectroscopic analysis and computational calculations. Compounds 1 and 2 are the highly modified halimane diterpenoids featuring a 6/6/6-fused tricyclic system with an unusual six-membered 6,11-ether ring. Compound 8 exhibits nontoxic effects for zebrafish embryo, while it displays efficient reduction against NO production in a dose-dependent manner and strongly suppresses the secretion of LPS-induced TNF-α and IL-6 cytokines in RAW264.7 macrophages. In addition, marked reductions of iNOS and COX-2 expression were observed. Molecular docking analysis indicated that 8 has high affinities with the target amino acid residues on protein-binding sites, which may be a possible mechanism contributing to the anti-inflammatory potential of this molecule.

Diterpenoids from Euphorbia peplus possessing cytotoxic and anti-inflammatory activities

Phytochemical investigation into the medium polar fraction of the ethanol extract of Euphorbia peplus led to the identification of 32 diterpenoids with five structural types. Compounds 1-5 and 7-11 are reported for the first time, while the configuration of 6,7-epoxy group of 6 was revised to be β-oriented. Compounds 1-5 feature a rare structural variation of the double bond at Δ1 migrating to Δ1(10) in the tigliane-type diterpenoid family. Biologically, compound 21 was found to be the only one to show moderate cytotoxic activity, associated with the presence of a benzoyloxy residue at C-16. Besides, compounds 4, 8, 12, 13, 16, and 19 show significant inhibitory activities against NO production induced by LPS in RAW264.7 macrophage cells, with IC50 values within 2-5 μM. Structure-activity relationship (SAR) analysis revealed that the ingenane-type diterpenoids have the best anti-inflammatory activity, and the esterification at 3-OH or 5-OH is crucial. Further biological researches demonstrated that 13, the predominant metabolite in this plant, exerts anti-inflammatory effects by blocking the activation of NF-κB and MAPK signaling pathways.

Total Synthesis of Pallamolides A-E

We have achieved the first total synthesis of pallamolides A-E. Of these compounds, pallamolides B-E possess intriguing tetracyclic skeletons with novel intramolecular transesterifications. Key transformations include highly diastereoselective sequential Michael addition reactions to construct the bicyclo[2.2.2]octane core with the simultaneous generation of two quaternary carbon centers, a one-pot SmI2-mediated intramolecular ketyl-enoate cyclization/ketone reduction to generate the key oxabicyclo[3.3.1]nonane moiety, and an acid-mediated deprotection/oxa-Michael addition/β-hydroxy elimination cascade sequence to assemble the tetracyclic pallamolide skeleton. Kinetic resolution of ketone 14 through Corey-Bakshi-Shibata reduction enabled the asymmetric synthesis of pallamolides A-E.

ex Prokh

Four previously unreported diterpenoids including three ent-atisanes (1-3) and one ent-abietane (4), along with one known linear triterpenoid (5) and five known diterpenoids including four myrsinanes (6-9), and one abietane (10) have been isolated from the roots of Euphorbia spinidens Bornm. ex Prokh. The structures were determined on the basis of extensive spectroscopic analyses including HR-ESI-MS, 1D and 2D NMR and comparison of the data with those reported in the literature. Antimicrobial potential of isolated compounds were also evaluated. Guionianol B (10) showed good antibacterial activity against Staphylococcus aureus and Bacillus subtilis with MIC value of 6.25 μg/mL.

Euphzycopins A - D, macrocyclic diterpenoids with potential anti-inflammatory activity from Euphorbia Helioscopia

Four new diterpenoids (1-4) and four known diterpenoids (5-8) were purified from the whole plant of Euphorbia helioscopia L. Compounds 1 and 2 were jathophanes diterpenoids with a 5/12 polycyclic systems, compound 3 was rhamofolane diterpenoid with a 5/10 bicyclic skeleton and compound 4 was a rare class of euphorbia diterpenes featuring an unusual 5/10 fused ring system. Anti-inflammatory activity tests were conducted on the separated compounds, indicating that compound 4 had significant inhibitory effect on NLRP3 inflammasome with an IC50 value of 7.75 μM. Further, the inhibitory effect of 4 was determined using immunofluorescence assays.

New cassane-type alkaloids and diterpenoids from the pericarps of Caesalpinia bonduc

The phytochemical investigation of the pericarps of Caesalpinia bonduc led to the isolation and identification of five new cassane-type alkaloids: caesalminines C - G (1-5) and six new diterpenoids: caesalbonducin K - P (6-11), along with seven known compounds (12-18). Compounds 1-5 were identified as a group of rare alkaloids possessing a tetracyclic cassane-type diterpenoid skeleton with a lactam D-ring instead of a typical furan or lactone moiety. The structures of 1-11 were elucidated on the basis of 1D and 2D NMR including HSQC, HMBC, COSY and NOESY, and other spectroscopic analyses. The cytotoxic activities of the isolated compounds were evaluated in the A431, A549 and U87MG cancer cell lines.

The intramolecular SN2 reaction tautomeric ent-Kauranoids isolated from the aerial parts of Isodon amethystoides

As our ongoing searching for the bioactive natural terpenoids, nine ent-kauranoids (1-9), including three previously undescribed ones (1, 2, and 9), were isolated from the aerial parts of Isodon amethystoides. Their structures were elucidated on the basis of spectroscopic data analysis, including NMR, MS, and ECD. Compounds 1 and 2 were a pair of tautomeric compounds, which was confirmed by the HPLC analysis and low temperature NMR testing. The underlying mechanism of the tautomer was proposed as an intramolecular SN2 reaction, which was explained by quantum chemical calculation. The HOMO-LUMO gap and the free energy revealed the spontaneous of the tautomeric of the 1 and 2. Additionally, the similar phenomena were also found in the two groups of known compounds 3 and 4 and 6 and 7, respectively. Apart from the tautomer, compounds 3 and 4 can be hydrolyzed into 5 through ester hydrolysis in CDCl3, while compounds 6, 7 can be hydrolyzed into 8 through ester hydrolysis. These phenomena were also confirmed through HPLC analysis and low temperature nuclear magnetic resonance tests and the mechanism was studied using quantum chemical calculation.

Structurally diverse analgesic diterpenoids from the flowers of Rhododendron molle

Thirteen diterpenoids (1-13), classified into four structurally diverse carbon skeletons, including 1,5-seco-kalmane (1 and 6), grayanane (2-11), kalmane (12), and rhodomollane (13), were isolated from the flowers extract of Rhododendron molle. Among them, rhodomollinols A - E (1-5) were five new diterpenoids and their structures were elucidated by extensive spectroscopic methods including HRESIMS, UV, IR, 1D and 2D NMR, as well as quantum ECD calculations. Rhodomollinol A (1) is the first representative of a 6-deoxy-1,5-seco-kalmane diterpenoid. The abnormal NMR phenomenon of the presence of only 9 carbon resonances instead of 20 carbons in the 13C NMR spectrum of 1 was observed and elucidated by the quantum NMR calculations. All diterpenoids 1-13 showed significant analgesic activities in an acetic acid-induced writhing model. It's the first time to report the analgesic activity of a rhodomollane-type diterpenoid. At a dose of 1.0 mg/kg, diterpenoids 1-3, 6, 8, 9, and 12 reduced the writhe numbers with inhibition rates over 50%, and 9 exhibited stronger analgesic activity with a writhe inhibition rate of 89.7% than that of the positive control morphine. Importantly, even at the lowest dose of 0.04 mg/kg, rhodomollinols A (1) and B (2), rhodomollein X (7), and 2-O-methylrhodojaponin VI (9) still showed more potent analgesic effects than morphine with the writhe inhibition rates of 51.8%, 48.0%, 61.7%, and 60.0%, respectively. A preliminary structure-activity relationship might provide some clues to design potential analgesics on the basis of structurally diverse Ericaceae diterpenoids.

Bioactive compounds from Vellozia pyrantha A.A.Conc: A metabolomics and multivariate statistical analysis approach

The chemical composition of V. pyrantha resin (VpR) and fractions (VpFr1-7 and VpWS) were assessed by LC-MS and NMR. Twenty-eight metabolites were identified, including 16 diterpenoids, seven nor-diterpenoids, one fatty acid, one bis-diterpenoid, one steroid, one flavonoid, and one triterpenoid. The pharmacological potential of VpR, VpFr1-7, and isolated compounds was assessed by determining their antioxidant, antimicrobial, and cytotoxic activities. VpFr4 (IC50 = 205.48 ± 3.37 μg.mL-1) had the highest antioxidant activity, whereas VpFr6 (IC50 = 842.79 ± 10.23 μg.mL-1) had the lowest. The resin was only active against Staphylococcus aureus (MIC 62.5 μg.mL-1) and Salmonella choleraesius (MIC and MFC 500 μg.mL-1), but fractions were enriched with antibacterial compounds. V. pyrantha resin and fractions showed great cytotoxic activity against HCT116 (IC50 = 20.08 μg.mL-1), HepG2 (IC50 = 20.50 μg.mL-1), and B16-F10 (12.17 μg.mL-1) cell lines. Multivariate statistical analysis was used as a powerful tool to pinpoint possible metabolites responsible for the observed activities.

CYP72D19 from Tripterygium wilfordii catalyzes C-2 hydroxylation of abietane-type diterpenoids

KEY MESSAGE

CYP72D19, the first functional gene of the CYP72D subfamily, catalyzes the C-2 hydroxylation of abietane-type diterpenoids. The abietane-type diterpenoids, e.g., triptolide, tripdiolide, and 2-epitripdiolide, are the main natural products for the anti-tumor, anti-inflammatory, and immunosuppressive activities of Tripterygium wilfordii, while their biosynthetic pathways are not resolved. Here, we cloned and characterized the CYP72D19-catalyzed C-2 hydroxylation of dehydroabietic acid, a compound that has been proven to be a biosynthetic intermediate in triptolide biosynthesis. Through molecular docking and site-directed mutagenesis, L386, L387, and I493 near the active pocket were found to have an important effect on the enzyme activity, which also indicates that steric hindrance of residues plays an important role in function. In addition, CYP72D19 also catalyzed a variety of abietane-type diterpenoids with benzene ring, presumably because the benzene ring of the substrate molecule stabilized the C-ring, allowing the protein and the substrate to form a relatively stable spatial structure. This is the first demonstration of CYP72D subfamily gene function. Our research provides important genetic elements for the structural modification of active ingredients and the heterologous production of other 2-hydroxyl abietane-type natural products.

Identification of Cyclocybe erebia metabolites that affect the circadian rhythm of Eluc expression under control of Bmal1 promoter in mouse fibroblast cells

Pharmacological intervention of circadian rhythms is a potentially useful approach for ameliorating various health problems caused by disturbed circadian rhythms including sleep disorder and metabolic diseases. To find compounds that affect circadian rhythms, we screened mushroom extracts using mouse cells expressing the luciferase gene under the control of the mouse Bmal1 promoter. The culture filtrate extract from the basidiomycete Cyclocybe erebia enhanced the oscillation of bioluminescence caused by the expression of the luciferase gene and prolonged the period of bioluminescence. Bioassay-guided fractionation of the extract resulted in purification of compounds 1 and 2. Spectroscopic analyses along with single-crystal X-ray diffraction analysis, revealed that these compounds were diterpenoids with a unique skeleton and a fused ring system comprising 3-, 7-, and 5-membered rings. Compounds 1 and 2 were named cyclocircadins A and B, respectively. These findings suggested that natural diterpenoids could be a source of compounds with the activity affecting circadian rhythms.

Structure-diversified terpenoids from Salvia prattii and their protective activity against alcoholic liver diseases

Eleven previously unreported compounds (1-11), including five diterpenoids (1-5) and six sesquiterpenoids (6-11), together with two known diterpenoids (12-13), have been isolated from the roots of Salvia prattii. Their structures were comprehensively elucidated through spectroscopic methods, and their configurations were established using computational 13C nuclear magnetic resonance and electronic circular dichroism. Compound 1 was found to be an abietane-type diterpenoid with a novel rearrangement generated from the cleavage of the C-4/5 chemical bond, 20-methyl shift, and the rearrangement of the C-10 side chain. Compounds 2-3 were the third and fourth examples of arrangement seco-norabietanes with a spiro-lactone ring. We evaluated all compounds for their protective effects against alcoholic liver diseases (ALD). Compound 2 exhibited potential protective activity and hence can be used as a novel anti-ALD candidate.

Euphopias G - J, macrocyclic diterpenes with anti-zika virus activity from Euphorbia helioscopia L

Four new diterpenoids (1-4) and sixteen known diterpenoids (5-20) were purified from the whole plant of Euphorbia helioscopia L. Compounds 1 and 2 were rhamofolane diterpenoids with a 5/7/6 tricyclic systems, compound 3 was a lathyranes diterpenoid, and compound 4 was a jathophanes diterpenoid. The isolated compounds were tested for their cytotoxicity and anti-Zika virus properties, and compounds 9 and 15 showed low cytotoxicity and strong anti-Zika virus properties with EC50 2.63 and 5.94 μM, respectively. Further, the inhibitory effects of compounds on protein levels were determined using Western blotting and immunofluorescence assays.

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.

Isolation and identification of 3,4-seco-labdane diterpenoids from Callicarpa nudiflora and investigation of their cytotoxicity against HepG2 cells

Twenty-one previously undescribed compounds, including nineteen 3,4-seco-labdanes (nudiflopenes P-W, Y, A_I-J_I), one 3,4-seco-pimarane (nudiflopene X), and one labdane (nudiflopene Z), along with nine known compounds (one 3,4-seco-pimarane and eight 3,4-seco-labdanes) were isolated from the leaves of Callicarpa nudiflora Hook. Et Arn. The structures of these compounds were elucidated by high-resolution electrospray ionization mass spectrometry and one- and two-dimensional nuclear magnetic resonance spectroscopy. In addition, configurations of the isolated compounds were determined by electronic circular dichroism, DP4+ probability analysis, and single-crystal X-ray diffraction experiments. All undescribed compounds were evaluated for their cytotoxicity against HepG2 cells in vitro, among which compound 12 exhibited a moderate activity with an IC₅₀ value of 27.8 μM.

Structure and anti-inflammatory activity of neo-clerodane diterpenoids from Scutellaria barbata

Herein, 13 previously undescribed neo-clerodane diterpenoids (1-13) and 27 known analogs (14-40) were isolated from the aerial parts of Scutellaria barbata. Absolute configurations of undescribed compounds were assigned based on single-crystal X-ray diffraction analysis and comparison of experimental and circular dichroism. All isolates were evaluated for the inhibition of nitric oxide generation induced by lipopolysaccharide in RAW 264.7 macrophages. Compound 36 was found to be the most active with an IC₅₀ value of 10.6 μM. Structure-activity relations of these neo-clerodane diterpenoids revealed that the α, β-unsaturated-γ-lactone moiety with an exocyclic conjugated double bond was necessary for maintaining and increasing its activity. Further mechanistic studies show that compound 36 suppressed nitric oxide synthase enzymes (iNOS) expression without affecting iNOS activity. Additionally, compound 36 suppresses NF-κB signaling by inhibiting IκBα phosphorylation.

Extending the record of dolabellane-type diterpenoids from the soft coral Clavularia viridis: Structures and stereochemistry

Five undescribed dolabellane-type diterpenoids (1-5), together with three related known ones (6-8), were isolated from the soft coral Clavularia viridis. Their structures and stereochemistry were elucidated by extensive spectroscopic analysis and NMR calculation with DP4+ probability analysis. The absolute configurations of 1 and 5 were unambiguously determined by X-ray crystallographic analysis. A plausible biosynthetic connection between undescribed compounds 1-5 was proposed.

Six new diterpenoids from the resins of Populus euphratica and their anti-inflammatory activities

Six new diterpenoids, identified as two abietane derivatives, euphraticanoids J and K (1 and 2), two pimarane derivatives, euphraticanoids L and M (3 and 4), and two 9,10-seco-abietane derivatives, euphraticanoids N and O (5 and 6) were isolated from Populus euphratica resins. Their structures including absolute configurations were characterized using spectroscopic, quantum chemical NMR, and ECD calculation methods. The anti-inflammatory activity of the compounds was tested and the results revealed that compounds 4 and 6 inhibited the production of iNOS and COX-2 in a dose-dependent manner in lipopolysaccharide (LPS)-induced RAW 264.7 cells.

Effects of centipedic acid on acute lung injury: A dose-response study in a murine model

Centipedic Acid (CPA), a natural diterpene from Egletes viscosa, an endemic species of the Caatinga biome, has shown antioxidant and anti-inflammatory properties. However, no report on the CPA on respiratory system mechanics has been so far advanced. We aimed to investigate the dose-response behavior of CPA on E. coli lipopolysaccharide (LPS)-triggered acute lung injury (ALI). Forty-eight C57BL/6 mice were randomly divided into six groups: control (SS), induced to ALI (LPS), 4 groups induced to ALI pre-treated with 12.5, 25, 50 and 100 mg/kg of CPA (CPA12.5, CPA25, CPA50 and CPA100 groups). CPA 100 mg/kg could prevent inflammatory cell infiltration, alveolar collapse, changes in tissue micromechanics and lung function (airway resistance, tissue elastance, tissue resistance and Static compliance). These results indicate preventive potential of this compound in the installation of ALI.

Two pairs of epimers and three undescribed diterpenoids from Pseudocaryopteris paniculata

A phytochemical investigation on the petroleum ether partition of the whole plant of Pseudocaryopteris paniculata, yield seven new compounds: one phytanes diterpenoid (2Z,6E,10E) 14-keto-2,6,10-trimethyl pentadeca-2,6,10-trien-1-carboxylic acid (1), five clerodane diterpenoids: paniculatins A-E (2, 3a/3b, 4a/4b), one abietane diterpenoid: ent-uncinatone (5), together with 12 known compounds. Their structures were elucidated on the basis of 1D and 2D Nuclear Magnetic Resonance （NMR_, Infrared Radiation (IR), and mass spectroscopic data. Compound 2, 5, and 11 showed weak selective cytotoxic activity of 11 human cancer cell lines.

The pro-apoptotic activity of sinueracasbanone D isolated from Sinularia Leptoclados in hepatocellular carcinoma cells

The soft-bodied corals of the genera Sarcophyton and Sinularia (Alcyoniidae) are known as a warehouse of casbane and cembranoid diterpenoids with remarkable antitumor effects. Two casbane-type diterpenoids (1, 2) along with four cembrane-type diterpenoids (3-6) were isolated from the diethyl ether soluble fraction of the organic extracts of the Red Sea soft corals Sinularia leptoclados and Sarcophyton glaucum, respectively. The antiproliferative activity of all isolated compounds (1-6) against three hepatocellular carcinoma cells, namely, Huh-7, SNU 499, and HepG2, along with the normal cells EA.hy 926, was evaluated. Sinueracabanone D (1) displayed a remarkable antiproliferative effect against the examined cancer cell lines, especially HepG2 cells with IC₅₀ of 4.0 ± 0.37 µM. Cell cycle analysis indicated compound 1 caused the accumulation of HepG2 cells in the G2/M-phase. Further, compound 1 exhibited significant pro-apoptotic activities in HepG2 cells as evidenced by annexin V staining, enhanced mRNA expression of Bax, cytochrome C, and caspase 3, as well as inhibition of Bcl2 expression. Also, challenging HepG2 cells with sinueracabanone D (1) enhanced the active oxygen species generation and decreased mitochondrial membrane potential. In conclusion, compound 1 possesses potent antiproliferative activities against HepG2 cells. These antiproliferative activities are mediated, at least partly, by their ability to induce apoptosis, mitochondrial dysfunction, and oxidative stress.

Offline two-dimensional normal-phase × reversed-phase liquid chromatography coupled with high-resolution mass spectrometry for comprehensive analysis of chemical constituents in Euphorbia kansui

Euphorbia kansui is the dried root of Euphorbia kansui T. N. Liou ex T.P. Wang. Its main chemical components are diterpenoids, triterpenes, and volatile oil. In this study, an offline two-dimensional (2D) normal-phase × reversed-phase liquid chromatography method coupled with quadrupole time-of-flight mass spectrometry was established to comprehensively analyze the chemical constituents in E. kansui. A total of 240 compounds were identified from the E. kansui extract, including 218 diterpenoids (77 known, 141 new), 16 known volatile oils, and six known triterpenes. The relationship between the structural characteristics and tandem mass spectroscopy fragments of diterpenoids was further analyzed. Based on the characteristic fragment ions, 141 new diterpenoids were determined as 118 ingenane diterpenoids and 23 jatrophane diterpenoids. The newly identified diterpenoids may provide lead compounds for drug discovery, improving the medicinal value of E. kansui.

Oryzalexin S biosynthesis: a cross-stitched disappearing pathway

Rice produces many diterpenoid phytoalexins and, reflecting the importance of these natural products in this important cereal crop plant, its genome contains three biosynthetic gene clusters (BGCs) for such metabolism. The chromosome 4 BGC (c4BGC) is largely associated with momilactone production, in part due to the presence of the initiating syn-copalyl diphosphate (CPP) synthase gene (OsCPS4). Oryzalexin S is also derived from syn-CPP. However, the relevant subsequently acting syn-stemarene synthase gene (OsKSL8) is not located in the c4BGC. Production of oryzalexin S further requires hydroxylation at carbons 2 and 19 (C2 and C19), presumably catalyzed by cytochrome P450 (CYP) monooxygenases. Here it is reported the closely related CYP99A2 and CYP99A3, whose genes are also found in the c4BGC catalyze the necessary C19-hydroxylation, while the closely related CYP71Z21 and CYP71Z22, whose genes are found in the recently reported chromosome 7 BGC (c7BGC), catalyze subsequent hydroxylation at C2α. Thus, oryzalexin S biosynthesis utilizes two distinct BGCs, in a pathway cross-stitched together by OsKSL8. Notably, in contrast to the widely conserved c4BGC, the c7BGC is subspecies (ssp.) specific, being prevalent in ssp. japonica and only rarely found in the other major ssp. indica. Moreover, while the closely related syn-stemodene synthase OsKSL11 was originally considered to be distinct from OsKSL8, it has now been reported to be a ssp. indica derived allele at the same genetic loci. Intriguingly, more detailed analysis indicates that OsKSL8(j) is being replaced by OsKSL11 (OsKSL8i), suggesting introgression from ssp. indica to (sub)tropical japonica, with concurrent disappearance of oryzalexin S production.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-022-00092-3.

New chemical structures and liver-protective activity of the diterpenoids from Callicarpa rubella

Callicarpa rubella is a characteristic folk herb in the genus Callicarpa, and has abundant ethnobotanical usage as indigenous medicine in Lingnan area of P. R. China. However, the phytochemical and pharmacological properties of C. rubella was rarely investigated. Now, three new diterpenoids, named rubellapene A-C (1-3), along with five known analogues (4-8), were isolated from C. rubella. Their structures were determined by spectroscopic methods, quantum chemical electronic circular dichroism calculations and single-crystal X-ray diffraction analysis. Notably, the norditerpenoids C₁₈ of clerodane type (rubellapene B) was rarely found in the genus Callicarpa. The liver protective effects of all of the isolates (1-8) were evaluated by the changes of cell viability and transaminase content of AST and ALT in H₂O₂-induced BRL cells. Compound 1, 3-8 exhibited that potent liver protective effects at different levels.

Biosynthesis, enzymology, and future of eunicellane diterpenoids

Eunicellane diterpenoids are a remarkable family of terpene natural products and have been of high interest for over five decades. Widely distributed in soft corals and rare in plants, eunicellanes were also recently identified in actinobacteria. These terpenoids have foundational 6/10-bicyclic frameworks that are frequently oxidized into structures containing transannular ether bridges. Interest in their unique structures and promising biological activities, such as the paclitaxel-like activities of eleutherobin and the sarcodictyins, has led to advancements in natural product isolation, total synthesis, medicinal chemistry, and drug lead development. Until recently, however, there was little known about the biosynthesis and enzymology of these natural products, but several recent studies in both bacteria and coral have opened up the field. This review summarizes recent advancements in the biosynthesis and enzymology of eunicellane diterpenoids and highlights future research prospects in the field.

ONE-SENTENCE SUMMARY

A summary of recent advancements in the biosynthesis and enzymology of eunicellane diterpenoids, a structurally unique and biologically active family of natural products found in coral, plants, and bacteria.

Further undescribed cembranoids from South China Sea soft coral Sarcophyton ehrenbergi: Structural elucidation and biological evaluation

A detailed chemical investigation of the South China Sea soft coral Sarcophyton ehrenbergi has yield seven undescribed cembranoids, namely isoehrenbergol D and sarcoehrenolides F-K embodying a rare α,β-unsaturated-lactone moiety at C-6 to C-19, along with two known related compounds, ehrenbergol D and sarcoehrenolide A. Their structures and absolute configurations were unambiguously established in the light of extensive spectroscopic data analysis, modified Mosher's method, X-ray diffraction analysis, and quantum chemical computation method. In a bioassay for α-glucosidase inhibition, ehrenbergol D was evaluated as α-glucosidase inhibitor with an IC₅₀ value of 13.57 μM.

Bioactive diterpenoids and sesquiterpenoids with different skeletons from Salvia digitaloides Diels

Salvia has been regarded as a beneficial healing herb in ancient Egypt, Rome and Greece, and is listed as an official medicine in the pharmacopoeias of many countries worldwide. Currently, Salvia is widely used to flavor and preserve food. Here, two undescribed norabietane-type diterpenoids, sadigitaloides A and B, two undescribed germacrane-type sesquiterpenoids, sadigitaloides C and D, five undescribed guaiane-type sesquiterpenoid lactones, sadigitaloides E-I, two undescribed noreudesmane-type sesquiterpenoids, sadigitaloides J and K, one known diterpenoid, three known sesquiterpenoids, and three other types of known compounds were isolated from the 95% ethanol extract of the whole plants of Salvia digitaloides. Their structures and absolute configurations were characterized using 1D and 2D NMR spectroscopic techniques, electronic circular dichroism (ECD) calculations, HRESIMS experiments, and single-crystal X-ray diffraction analysis. Some compounds were evaluated for their anti-inflammatory activities against lipopolysaccharide (LPS)-induced TNF-α production in rat macrophage NR8383 cells. Sadigitaloide A showed noticeable anti-inflammatory activity at a concentration of 100.0 μM. At a concentration of 60 μM, sadigitaloide B exhibited better protection of dopaminergic neurons than the positive control n-butylidenephthalide in the Caenorhabditis elegans model injured by 6-OHDA. The phytotoxic activities of some compounds were attributed to considerable inhibitory effects on the growth of the roots and hypocotyls of Raphanus sativus L seedlings, especially cis, trans-abscisic acid, whose inhibition rates were much higher than those of glyphosate at concentrations ranging from 50 to 400 ppm. These results indicated that abietane-type diterpenoids possessed excellent anti-inflammatory and neuroprotective activities and further suggested that the low-molecular-weight compounds exhibited outstanding phytotoxic activities.

Diterpenoids from Sigesbeckia glabrescens with anti-inflammatory and AChE inhibitory activities

Fourteen previously undescribed diterpenoids, including seven ent-pimarane-type diterpenoids and seven phytane-type diterpenes, together with five known ones, were isolated from the aerial parts of Sigesbeckia glabrescens. The structures and absolute configurations of undescribed compounds were elucidated based on extensive spectroscopic techniques, ECD calculations, Mo₂(OAC)₄-induced ECD, Rh₂(OCOCF₃)₄-induced ECD, calculated ¹³C NMR, and chemical methods. In the anti-inflammatory bioassay, siegetalis H showed potent inhibitory effect on LPS-induced NO production in RAW264.7 murine macrophages with an IC₅₀ value at 17.29 μM. Furthermore, siegetalis H suppressed the protein expression of iNOS and COX-2 in LPS-stimulated RAW264.7 cells. Mechanistically, siegetalis H suppressed the phosphorylation and degradation of IκBα, as well as the activation of the NF-κB signaling pathway. In addition, the AChE inhibition assay displayed that 3-O-acetyldarutigenol had a remarkable inhibitory effect against AChE with an IC₅₀ value at 7.02 μM. Kinetic study on 3-O-acetyldarutigenol indicated that it acted as a mixed-type inhibitor, and the binding mode was explored by molecular docking.

COX-2 and iNOS inhibitory abietane diterpenoids from Pinus yunnanensis exudates

Pinuskesiols A-F (1-6), six new structurally diverse abietane diterpenoids were isolated from Pinus yunnanensis resins. Their structures including absolute configurations were characterized by using spectroscopic and computational methods. All the compounds bear a carbonyl functionality at C-4 with 1 and 2 behaving as a lactone thereof. The isopropyl group is attached to C-13 via O-atom in 3. In addition, the presence of a Δ⁵⁽⁶⁾ double bond and a ketone at C-7 makes 2 a large conjugated system. Biological evaluation revealed that 1, 2, and 4 could concentration-dependently inhibit iNOS and COX-2 expression in lipopolysaccharide-induced RAW 264.7 cells with 2 to be the most active toward COX-2 inhibition.

Unprecedented diterpene skeletons isolated from vascular plants in the last twenty years (2001-2021)

Every year there are hundreds of reports about the isolation of undescribed terpenoids based on novel functionalizations of known carbocyclic skeletons series. However, on some occasions the compounds obtained have a carbocyclic skeleton that does not correspond with the series established, in these peculiar opportunities, in addition to finding an undescribed natural product, is obtained an unprecedented carbocyclic skeleton, whose biogenesis must necessarily involve other additional steps that explain its formation. This review accounts for the reports of seventy-nine unprecedented diterpene skeletons (corresponding to one-hundred-three undescribed diterpenoids) isolated from vascular plants in the last two decades. According to the genus, Euphorbia and Salvia are the most prolific in reports of unprecedented diterpene skeletons with a total of twenty, and nine skeletons, respectively. If the findings are expressed in terms of the family, Euphorbiaceae and Lamiaceae have the highest number of reports of undescribed diterpene skeletons, with twenty-seven and twenty-two, respectively. Finally, fifty-three skeletons are derived from higher diterpenoids (2-12, 68, 69, 86, 104-109, 158-161, 186, 189, 222, 250-255, 285-298, 403-404, 415, 416, and 436), twenty are derived from lower diterpenoids (135, 136, 192-194, 225-229, 363-370, 397, and 425), and six (96, 97, 147, 148, 205, and 206) are derived from skeletons whose biogenesis has not yet been established, or at least, cannot be formally included within the groups mentioned above. This article comprehensively highlights the hypothetical biosynthetic pathway for each of the one-hundred-three undescribed compounds with unprecedented diterpene skeletons and summarizes their most significant biological activities.

Ingol, ent-atisane, and stachane-type diterpenoids from Euphorbia deightonii with multidrug resistance reversing activity

Nine previously undescribed ingol-type diterpenoid polyesters with eighteen known ingol esters, two ent-atisane, and one stachane diterpenoid were isolated from the methanol extract of Euphorbia deightonii Croizat. The structures were established by extensive spectroscopic analysis involving 1D (1H, 13C J-modulation) and 2D NMR experiments, HRESIMS measurements, and the comparison of the spectroscopic data with reported literature values. The cytotoxic concentrations of 13 isolated compounds were determined, and the compounds were investigated for multidrug resistance modulating activity on an L5178 mouse lymphoma cell line using a rhodamin 123 accumulation assay. Six ingol esters demonstrated the significant inhibition of P-glycoprotein, while the two ent-atisane diterpenoids were found to be inactive. The measured activities allowed to establish some structure-activity relationships. Notably, lower and higher-type diterpenoids simultaneously occurred in E. deightonii.

Cytotoxic abietane diterpenoids from Salvia leriifolia Benth

The Phytochemical profiling of the root extract of Salvia leriifolia, an endemic plant of Iran, was investigated and 16 abietane diterpenes were isolated, and three were original compounds. 1D and 2D NMR and HRMS performed structural elucidation. The absolute configuration of the previously unreported compounds was determined by circular dichroism (ECD). The cytotoxicity of the isolated compounds was investigated against AGS, MIA PaCa-2, HeLa, and MCF-7 cell lines by the MTT assay. The known diterpene pisiferal possesses high cytotoxicity against all investigated cell lines at a concentration between 9.3 ± 0.6 and 14.38 ± 1.4 μM.

Exploring optimal Taxol® CYP725A4 activity in Saccharomyces cerevisiae

Background

CYP725A4 catalyses the conversion of the first Taxol® precursor, taxadiene, to taxadiene-5α-ol (T5α-ol) and a range of other mono- and di-hydroxylated side products (oxygenated taxanes). Initially known to undergo a radical rebound mechanism, the recent studies have revealed that an intermediate epoxide mediates the formation of the main characterised products of the enzyme, being T5α-ol, 5(12)-oxa-3(11)-cyclotaxane (OCT) and its isomer, 5(11)-oxa-3(11)-cyclotaxane (iso-OCT) as well as taxadienediols. Besides the high side product: main product ratio and the low main product titre, CYP725A4 is also known for its slow enzymatic activity, massively hindering further progress in heterologous production of Taxol® precursors. Therefore, this study aimed to systematically explore the key parameters for improving the regioselectivity and activity of eukaryotic CYP725A4 enzyme in a whole-cell eukaryotic biocatalyst, Saccharomyces cerevisiae.

Results

Investigating the impact of CYP725A4 and reductase gene dosages along with construction of self-sufficient proteins with strong prokaryotic reductases showed that a potential uncoupling event accelerates the formation of oxygenated taxane products of this enzyme, particularly the side products OCT and iso-OCT. Due to the harmful effect of uncoupling products and the reactive metabolites on the enzyme, the impact of flavins and irons, existing as prosthetic groups in CYP725A4 and reductase, were examined in both their precursor and ready forms, and to investigate the changes in product distribution. We observed that the flavin adenine dinucleotide improved the diterpenoids titres and biomass accumulation. Hemin was found to decrease the titre of iso-OCT and T5α-ol, without impacting the side product OCT, suggesting the latter being the major product of CYP725A4. The interaction between this iron and the iron precursor, δ-Aminolevulinic acid, seemed to improve the production of these diterpenoids, further denoting that iso-OCT and T5α-ol were the later products. While no direct correlation between cellular-level oxidative stress and oxygenated taxanes was observed, investigating the impact of salt and antioxidant on CYP725A4 further showed the significant drop in OCT titre, highlighting the possibility of enzymatic-level uncoupling event and reactivity as the major mechanism behind the enzyme activity. To characterise the product spectrum and production capacity of CYP725A4 in the absence of cell growth, resting cell assays with optimal neutral pH revealed an array of novel diterpenoids along with higher quantities of characterised diterpenoids and independence of the oxygenated product spectra from the acidity effect. Besides reporting on the full product ranges of CYP725A4 in yeast for the first time, the highest total taxanes of around 361.4 ± 52.4 mg/L including 38.1 ± 8.4 mg/L of T5α-ol was produced herein at a small, 10-mL scale by resting cell assay, where the formation of some novel diterpenoids relied on the prior existence of other diterpenes/diterpenoids as shown by statistical analyses.

Conclusions

This study shows how rational strain engineering combined with an efficient design of experiment approach systematically uncovered the promoting effect of uncoupling for optimising the formation of the early oxygenated taxane precursors of Taxol®. The provided strategies can effectively accelerate the design of more efficient Taxol®-producing yeast strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01922-1.

Study on components with neuroinflammation inhibitory activities from Croton tiglium L. var. xiaopadou

An undescribed tigliane diterpenoid 12- O -tiglyl-13-acetyl-17- O -tiglyl-phorbol, together with thirty-three known components, were isolated from the stems of Croton tiglium L. var. xiaopadou (Euphorbiaceae). Their structures were established based on spectroscopic data and calculated ECD spectra. Their anti-neuroinflammatory effects were evaluated in LPS-induced BV-2 microglia. Thirteen tested compounds showed significant inhibitory activities, especially compounds 10 , 16 , 18 and 21 exhibited an inhibitory effect with IC 50 values in the range of 12.39 to 17.80 μM, which are comparable with that of the positive control (minocycline, IC 50 13.92 μM).

Anhuienoside C inhibits human ovarian cancer cell growth by inducing apoptosis, suppression of cell migration and invasion, and targeting PI3K/AKT/mTOR signaling pathway

The present study was initiated to examine the anticancer effects of Anhuienoside C (AC) against ovarian cancer and postulates the possible molecular mechanism of its action. 3-[4,5-Dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay was implemented for determination of the effects of AC on cell viability of the ovarian cancer OVACAR-3 cell line. To study cellular morphology, phase contrast microscopy was performed. Apoptosis was examined via acridine orange/ethidium bromide used staining assays. Flow cytometry was used to check the different phases of the cell cycle. Cell migration and invasion assays were performed via transwell chamber assay. The effects of AC on expression of phosphoinositide 3-kinases (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) protein in ovarian cell were assessed using western blotting assay. The results indicated that the cell proliferation rate lowered in AC-treated OVACAR-3 cells as compared to the untreated controls in a dose-dependent manner. Cell morphology changed substantially by the exposure to AC and remained dose dependent. These morphological changes were indicative of apoptotic cell death. Apoptosis analysis showed dose-dependent increase of apoptosis. The cell migration and invasion of OVACAR-3 cells was reduced to a minimum by AC in a dose-dependent manner. Finally, western blotting assay showed blocking of PI3K/AKT/mTOR signaling pathway with increasing AC doses. Taking all together, AC is a potential ovarian cancer inhibitor. It induces its anti-ovarian cancer effects via induction of apoptosis, delaying cell migration and invasion, and blocking PI3K/AKT/mTOR signaling pathway.

(Zingiberaceae): Structural assignment of saraburol and their biological activities

Five undescribed compounds, including three diterpenoids namely, saraburol, saraburanes A and B, and two p-methoxycinnamic acid monoterpene diol esters, named E/Z-saraburinic esters, together with ten known oxygenated isopimarane diterpenoids, were isolated from the whole plant of Kaempferia saraburiensis Picheans. Among these compounds, saraburol possesses an unusual 6/9/6 tricyclic ring system bearing a 1,3-dioxonane-4-one scaffold, which is rarely found in natural products. The structure of isolated compounds was elucidated by spectroscopic methods, including HRESIMS, FTIR, 1D and 2D-NMR, and by comparison with published data, and their absolute configurations were determined by comparison of experimental with calculated ECD spectra and hydrolysis reaction. Using gauge-independent atomic orbital (GIAO) NMR shift calculations coupled with DP4+ probability analyses, biogenetic considerations, and optical rotation allowed for the complete characterization of saraburol. A plausible biosynthetic pathway for saraburol and saraburane A was proposed. The cytotoxicity result indicated that E-saraburinic ester exhibited the most potent activity with an IC₅₀ value of 12.0 μM against MOLT-3 cells with a selectivity index of 12.5. Saraburane B exhibited the most potent activity against Gram-positive bacteria strain Staphylococcus epidermidis with MIC (MBC) value of 25 (50) μg/mL.

Engineering a powerful green cell factory for robust photoautotrophic diterpenoid production

Diterpenoids display a large and structurally diverse class of natural compounds mainly found as specialized plant metabolites. Due to their diverse biological functions they represent an essential source for various industrially relevant applications as biopharmaceuticals, nutraceuticals, and fragrances. However, commercial production utilizing their native hosts is inhibited by low abundances, limited cultivability, and challenging extraction, while the precise stereochemistry displays a particular challenge for chemical synthesis. Due to a high carbon flux through their native 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway towards photosynthetically active pigments, green microalgae hold great potential as efficient and sustainable heterologous chassis for sustainable biosynthesis of plant-derived diterpenoids. In this study, innovative synthetic biology and efficient metabolic engineering strategies were systematically combined to re-direct the metabolic flux through the MEP pathway for efficient heterologous diterpenoid synthesis in C. reinhardtii. Engineering of the 1-Deoxy-D-xylulose 5-phosphate synthase (DXS) as the main rate-limiting enzyme of the MEP pathway and overexpression of diterpene synthase fusion proteins increased the production of high-value diterpenoids. Applying fully photoautotrophic high cell density cultivations demonstrate potent and sustainable production of the high-value diterpenoid sclareol up to 656 mg L^-1 with a maximal productivity of 78 mg L^-1 day^-1 in a 2.5 L scale photobioreactor, which is comparable to sclareol titers reached by highly engineered yeast. Consequently, this work represents a breakthrough in establishing a powerful phototrophic green cell factory for the competetive use in industrial biotechnology.

Structurally diverse diterpenoids from the leaves and twigs of the endangered conifer Torreya jackii and their bioactivities

A phytochemical investigation on the MeOH extract of the leaves and twigs of the endangered conifer Torreya jackii Chun led to the isolation and characterization of 21 structurally diverse diterpenoids. Among them, six are previously undescribed, including four abietane-type (torreyins A-D, resp.) and two labdane-type diterpenoids (torreyins E and F). Their structures and absolute configurations were determined by a combination of spectroscopic methods, calculated/experimental electronic circular dichroism (ECD) data, and single-crystal X-ray diffraction analyses. In particular, torreyins A-C are rare 11,12-seco-abietane type diterpenoids possessing a dilactone moiety, and their biosynthetic pathway starting from a co-occurring abietane derivative (i.e., cyrtophyllone B) was briefly proposed. Among the isolates, 7-oxo-dehydroabietic acid and 15-methoxy-7,13-abietadien-18-oic acid showed considerable inhibitory effects against acetyl-coenzyme A carboxylase 1 (ACC1) and protein tyrosine phosphatase 1 B (PTP1B), with IC₅₀ values of 3.1 and 6.8 μM, respectively.

A strategy for rapid discovery and validation of active diterpenoids as quality markers in different habitats of Langdu using ultra-high performance liquid chromatography-tandem mass spectrometry with multivariate statistical analysis

Langdu known as a Traditional Chinese Medicine was identified as the roots of species of Euphorbia ebracteolata Hayata and Euphorbia fischeriana Steud, displaying anti-tuberculosis activity. In order to clarify the potent quality markers of Langdu, this research firstly developed a fast and sensitive ultra-high performance liquid chromatography-tandem mass spectrometry method for the quantification of thirteen diterpenoids existed in Langdu. The developed method was further applied in the analyses of 12 authentic E. ebracteolata and E. fischeriana samples collected in the North and Southeast of China. Then, the anti-tuberculosis evaluation of 12 batches of Langdu samples was performed in vitro. Finally, Partial least squares discrimination analysis was used in the discrimination of E. ebracteolata and E. fischeriana from different origins and processing methods. Jolkinolide A (1), jolkinolide E (3), yuexiandajisu D (6), Ebractenone A (11) were identified as the key, potent diterpenoids for quality control of E. ebracteolata Hayata and E. fischeriana Steud. The present study established a qualitative chemical analysis method for Langdu (E. ebracteolata and E. fischeriana), and suggested the key bioactive components which will improve qualitative control methodology for this important medicine. This article is protected by copyright. All rights reserved.

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.

Euphzycopias A-I, macrocyclic diterpenes with NLRP3 inflammasome inhibitory activity from Euphorbia helioscopia L

A phytochemical investigation was conducted on Euphorbia helioscopia, resulting in the isolation of thirteen compounds, including nine undescribed diterpenoids, Euphzycopias A - I (1-9), of which the skeletons of compounds 1-4 were found in E. helioscopia L. Compounds 1-3 had 5/7/6 cyclic systems, while compound 4 had a 4/11 polycyclic system with a 4,7-cyclic ether between C-4 and C-7. The anti-inflammasome test using the isolated compounds (1-6, 8-13) showed that the diterpenes from E. helioscopia L. had a strong inhibitory effect on NLRP3 inflammasomes with IC₅₀ values of 3.34-14.92 μM.

Spatiotemporal expression profile of novel and known small RNAs throughout rice plant development focussing on seed tissues

Background

Small RNAs (sRNAs) regulate numerous plant processes directly related to yield, such as disease resistance and plant growth. To exploit this yield-regulating potential of sRNAs, the sRNA profile of one of the world’s most important staple crops – rice – was investigated throughout plant development using next-generation sequencing.

Results

Root and leaves were investigated at both the vegetative and generative phase, and early-life sRNA expression was characterized in the embryo and endosperm. This led to the identification of 49,505 novel sRNAs and 5581 tRNA-derived sRNAs (tsRNAs). In all tissues, 24 nt small interfering RNAs (siRNAs) were highly expressed and associated with euchromatic, but not heterochromatic transposable elements. Twenty-one nt siRNAs deriving from genic regions in the endosperm were exceptionally highly expressed, mimicking previously reported expression levels of 24 nt siRNAs in younger endosperm samples. In rice embryos, sRNA content was highly diverse while tsRNAs were underrepresented, possibly due to snoRNA activity. Publicly available mRNA expression and DNA methylation profiles were used to identify putative siRNA targets in embryo and endosperm. These include multiple genes related to the plant hormones gibberellic acid and ethylene, and to seed phytoalexin and iron content.

Conclusions

This work introduces multiple sRNAs as potential regulators of rice yield and quality, identifying them as possible targets for the continuous search to optimize rice production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08264-z.

Diterpenoids from Euphorbia helioscopia and their enhancement of NK cell-mediated killing of NSCLC cells

Fourteen previously undescribed diterpenoids, including an unusual diterpenoid (1) with a 9,10-seco-jatrophane skeleton, ten jatrophane-type diterpenoids (2-11), two lathyrane-type diterpenoids (12, 13), and an abietane-type diterpenoid (14), together with thirty-six known ones (15-50), were isolated from the whole plants of Euphorbia helioscopia L. The structures of the new isolates were characterized by spectroscopic methods, single-crystal X-ray diffraction analysis, and computational prediction of ECD and chemical shifts. Thirty-nine abundant diterpenoids were evaluated for their enhancement of NK cell-mediated killing of NSCLC cells. As a result, compounds 24, 33, and 41 were found to significantly enhance the killing activity of NK cells towards H1299-luci cells and A549-luci cells at the concentration of 2.5 μM.

Diterpenoids from the whole plants of Croton yunnanensis and their bioactivities

Four new 19-nor-clerodane diterpenoids (1-4), one new 15,16-dinor-ent-pimarane diterpenoid (5) together with four known diterpenoids (6-9) were isolated from whole plants of Croton yunnanensis. The structures of these compounds were determined by extensive spectroscopic methods including 1D, 2D NMR, HR-ESI-MS, and by comparing their NMR data with those of previously reported compounds. The experimental and calculated electronic circular dichroism data were used to define their absolute configurations. The ¹H and ¹³C NMR spectra of 6 were completely assigned for the first time. All isolated compounds (1-9) were evaluated for their cytotoxic activities against five human cancer cell lines (including SMMC-7721, HL-60, A-549, MCF-7, and SW-480), and anti-inflammatory activities in LPS-induced RAW264.7 macrophages. Crotonyunnan E (5) exhibited selective cytotoxicities against three tumor cell lines, SMMC-7721 (human hepatoma cells, IC₅₀ 4.47 ± 0.39 μM), HL-60 (human premyelocytic leukemia, IC₅₀ 14.38 ± 1.19 μM), and A-549 (human lung cancer cells, IC₅₀ 27.42 ± 0.48 μM), while none of the compounds showed obviously anti-inflammatory activities at 50 μM level.

Euphorfinoids E-L: Diterpenoids from the roots of Euphorbia fischeriana with acetylcholinesterase inhibitory activity

Eight undescribed diterpenoids, euphorfinoids E-L, together with twelve known analogues, were isolated from the roots of wild Euphorbia fischeriana. Their structures and absolute configurations were elucidated by a combination of NMR, MS, ECD, and X-ray diffraction analyses. The plausible biosynthetic pathway of 1 was also proposed. The isolated compounds displayed moderate inhibitory activity against acetylcholinesterase (AChE) with 50% inhibiting concentration (IC₅₀) values of 6.23-192.38 μM.

Antifeedant, cytotoxic, and anti-inflammatory neo-clerodane diterpenoids in the peltate glandular trichomes and fresh leaves of Ajuga forrestii

The Lamiaceae plant Ajuga forrestii Diels is a traditional Chinese herbal medicine with abundant glandular trichomes (GTs), but their chemistry and biological functions remain uninvestigated. Here, a panel of six highly functionalized neo-clerodane diterpenoids was localized to the peltate GTs of A. forrestii using laser microdissection coupled with HPLC analysis, indicating that the GTs of A. forrestii are an excellent material for the elucidation of the yet unclear biosynthetic pathway of natural neo-clerodane diterpenoids. In addition, four undescribed neo-clerodane diterpenoids with an acyclic C-9 side chain including two pairs of 1:1 mixture of inseparable diastereomers, ajuforrestins D-G, were isolated from the fresh leaves of A. forrestii together with six known compounds. The structures of the undescribed compounds were elucidated by spectroscopic (including 1D and 2D NMR and HR-ESI-MS) analyses. Biological assays indicated that the major GT compound ajugacumbin B and undescribed ajuforrestins D/E showed antifeedant activity against Helicoverpa armigera, suggesting that neo-clerodanes in A. forrestii should be involved in plant defence against insects. Moreover, the abietane diterpenoid ajuforrestin B exhibited significant anti-inflammatory activity on the secretion of interleukin-2 (IL-2) and cytotoxicity against three cancer cell lines, NCI-H1975, HepG2 and MCF-7, suggesting that ajuforrestin B could positively contribute to the therapeutic effects of this traditional Chinese medicine.

Diterpenoids from Zhumeria majdae roots as potential heat shock protein 90 (HSP90) modulators

Four undescribed and 17 known diterpenoids were isolated from the roots of Zhumeria majdae Rech.f. & Wendelbo. Using 1D and 2D NMR spectroscopy, ECD spectroscopy, and HRESIMS data analysis, the structures of the undescribed compounds were elucidated. The anti-proliferative activity of isolated compounds was evaluated against HeLa and MCF7 cancer cell lines. The binding affinity of all compounds to HSP90, one of the targets for the modern anticancer therapy, was investigated using surface plasmon resonance. The results demonstrated that lanugon Q interacted with the chaperone. To explain its mechanism of action, experimental and computational tests were also conducted.