New Phytotoxic Cassane-like Diterpenoids from Eragrostis plana

Chemical Composition, Repellent, and Phytotoxic Potentials of the Fractionated Resin Essential Oil from Araucaria heterophylla Growing in Tunisia

The resin essential oil (REO) of the Tunisian Araucaria heterophylla trunk bark was investigated for its chemical composition. Then, it was evaluated for its insecticidal and allelopathic activities. The REO was obtained by hydrodistillation for 9 h (yield of 4.2 % w/w). Moreover, fractional hydrodistillation was carried out at 3-hour intervals, resulting in 3 fractions (R1-R3), to facilitate chemical identification and localization of the aforementioned biological activities. GC/MS analysis of the obtained samples allowed the identification of 25 compounds, representing between 91.2 and 96.3 % of their total constituents, which consisted predominantly of sesquiterpene hydrocarbons, oxygenated sesquiterpenes and diterpene hydrocarbons. α-Copaene (10.8 %), γ-muurolene (5.8 %), α-copaen-11-ol (7.8 %), spathulenol (10.5 %), 15-copaenol (8.2 %), ylangenal (10.3 %), dehydrosaussurea lactone (7.7 %), and sandaracopimaradiene (11.4 %) were identified as major compounds. The second part aimed to assess the impact of the A. heterophylla EO and its three fractions for their insecticidal and repellent activity against Tribolium castaneum (Herbst), a stored grain pest, of which a strong repellent activity was noted. In addition, the studied samples showed high phytotoxic effects against Lactuca sativa. The third fraction (R3) performed a total inhibitory potential on seed germination and seedling growth of the target plant. Furthermore, alongside this discovery, an estimation was conducted through molecular docking analysis. Wherein the main compounds of the studied samples were docked into the active pocket of protoporphyrinogen IX oxidase (PDB: 1SEZ), a key enzyme in chlorophyll biosynthesis. Thus, it is recommended to use the REO of A. heterophylla as a natural herbicide.

Isolation, Characterization, and Bioherbicidal Potential of the 16-Residue Peptaibols from Emericellopsis sp. XJ1056

Eco-friendly bioherbicides are urgently needed for managing the problematic weed Amaranthus retroflexus. A mass spectrometry- and bioassay-guided screening approach was employed to identify phytotoxic secondary metabolites from fungi for the development of such bioherbicides. This effort led to the discovery of six phytotoxic 16-residue peptaibols, including five new compounds (2-6) and a known congener (1), from Emericellopsis sp. XJ1056. Their planar structures were elucidated through the analysis of tandem mass and NMR spectroscopic data. The absolute configurations of the chiral amino acids were determined by advanced Marfey's method and chiral-phase liquid chromatography-mass spectrometry (LC-MS) analysis. Bioinformatic analysis and targeted gene disruption identified the biosynthetic gene cluster for these peptaibols. Compounds 1 and 2 significantly inhibited the radicle growth of A. retroflexus seedlings, and 1 demonstrated potent postemergence herbicidal activity against A. retroflexus while exhibiting minimal toxicity to Sorghum bicolor. Structure-activity relationship analysis underscored the importance of trans-4-hydroxy-l-prolines at both the 10th and 13th positions for the herbicidal activities of these peptaibols.

Phytochemistry Profile, Antimicrobial and Antitumor Potential of the Methanolic Extract of Tabernaemontana catharinensis A DC and Eragrostis plana NEES

Natural compounds that have the potential to act as antimicrobials and antitumors are a constant search in the field of pharmacotherapy. Eragrostis plana NEES (Poaceae) is a grass with high allelopathic potential. Allelopathy is associated with compounds generated in the primary and secondary metabolism of the plant, which act to protect it from phytopathogens. Tabernaemontana catharinensis A DC (Apocynaceae), a tree in which its leaves and bark are used for the preparation of extracts and infusions that have anti-inflammatory and antinociceptive effects, is attributed to its phytochemical constitution. The objective of this study was to elucidate the phytochemical constitution, the antibacterial potential, the toxicity against immune system cells, hemolytic potential, and antitumor effect of methanolic extracts of E. plana and T. catharinensis. The phytochemical investigation was carried out using the UHPLC-QTOF MS equipment. The antibacterial activity was tested using the broth microdilution plate assay, against Gram-negative and Gram-positive strains, and cytotoxicity assays were performed on human peripheral blood mononuclear cells (PBMC) and in vitro hemolysis. Antitumor activity was performed against the colon cancer cell line (CT26). Results were expressed as mean and standard deviation and analyzed by ANOVA. p < 0.05 was considered significant. More than 19 possible phytochemical constituents were identified for each plant, with emphasis on phenolic compounds (acids: vanillic, caffeic, and quinic) and alkaloids (alstovenine, rhyncophylline, amezepine, voacangine, and coronaridine). Both extracts showed antibacterial activity at concentrations below 500 µg/mL and were able to decrease the viability of CT26 at concentrations below 2000 µg/mL, without showing cytotoxic effect on PBMCs and in vitro hemolysis at the highest concentration tested. This is the first report of the activity of E. plana and T. catharinensis extracts against colon cancer cell line (CT26). Studies should be carried out to verify possible molecular targets involved in the antitumor effect in vivo.

Selective Phytotoxic Effects of Sesquiterpenoids from Sonchus arvensis as a Preliminary Approach for the Biocontrol of Two Problematic Weeds of Wheat

The objective of this study is to find new selective allelochemicals for managing two problematic weeds redroot pigweed (Amaranthus retroflexus) and common lambsquarters (Chenopodium album) with minimal negative effects on wheat, thereby facilitating the development of eco-friendly botanical herbicide. Three new sesquiterpenoids, sonarvenolide A-C (1-3), and nine known sesquiterpenoids (4-12) were isolated from Sonchus arvensis. Compound 1 was a rare peroxide-substituted eudesmane-type sesquiterpenoid, and compound 3 was a rare iphionane-type sesquiterpenoid. Notably, compounds 1, 3, 4, 6-8, and 11 showed selectivity phytotoxic activity. In particular, compounds 1, 3, and 4 exhibited excellent germination inhibitory effect on A. retroflexus (IC₅₀ = 32.0-129.0 μM), higher than that of the positive control triasulfuron (IC₅₀ = 141.7 μM), and compound 4 showed excellent inhibition on C. album (IC₅₀ = 82.0 μM), higher than that of triasulfuron (IC₅₀ = 100.9 μM). In addition, compounds 1, 3, and 4 showed allelopathy to the growth of two weeds, which were more potent than or close to that of triasulfuron. Furthermore, these compounds were not toxic to wheat even at a high concentration (1000 μM). Structure-activity relationships (SARs) revealed that the presence of peroxides or the absence of hydroxyl at C-5 in the eudesmane-type sesquiterpenoids could strengthen the inhibitory activities. The discovery of selective allelochemicals provides not only a new choice to control two problematic weeds of wheat but also new natural lead compounds for herbicides.

Cassane diterpenoids from the aerial parts of Caesalpinia pulcherrima and their antibacterial and anti-glioblastoma activity

Sixteen cassane diterpenoids (CAs), including four undescribed lactam-type, four unreported lactone-type, along with eight known ones, were isolated from the aerial parts of Caesalpinia pulcherrima (L.) Sw. Their structures were characterized by comprehensive spectroscopic analyses (including NMR and HRESIMS). The absolute configuration of pulcherritam A was finally established by single-crystal X-ray diffraction with Cu Kα radiation. Notably, pulcherritam s A-D were elucidated as a group of rare CAs bearing an α, β-unsaturated γ-lactam ring rather than a typical lactone moiety. Almost all compounds were examined for their antibacterial. The results reveal that pulcherritam H exhibited significant antibacterial activities against Bacillus cereus, Staphylococcus aureus, as well as Pseudomonas syringae pv. actinidae (Psa) with the MIC from 6.25 to 12.5 μM, while pulcherritams A and C displayed potent antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA). Then, all isolates were evaluated for their anti-glioblastoma activities. Pulcherritam A and Pulcherrimin G illustrated moderate inhibitory activity against glioblastoma multiforme (GBM) U87MG cell, and the other compounds did not show obvious inhibitory activity against GBM U87MG cell. Furthermore, the preliminary structure-activity relationship and their biosynthetic pathway were also discussed.

Phytotoxic bioassays and Fingerprinting by HPLC-DAD of Eragrostis plana Nees Root Extracts - application of chemometrics

Eragrostis plana (Nees) (Tough Lovegrass) shows ability to interfere with other plants, a phenomenon known as allelopathy. This chemical interaction between plants occurs due to the release of compounds into the environment. Thus, a phytotoxicity study was carried out with E. plana roots collected during each season throughout the year, and the compounds were extracted with solvents of increasing polarity. The data from the bioassays were analyzed by GLM and PCA. In addition, a fingerprint of these extracts was obtained by HPLC-DAD. The extracts in petroleum ether from roots collected in the winter and summer showed greater phytotoxicity on Ipomoea grandifolia germination and growth. The PCA obtained from the chromatogram of the crude extract showed that the extracts in petroleum ether were chemically different from the extracts in ethyl acetate and methanol. Thus, continuing this study in order to develop a new generation of bio-herbicides is essential.

Phytotoxic Neocassane Diterpenes from Eragrostis plana

Five new neocassane-like diterpenes (1-5) were isolated from the roots of Eragrostis plana. Their structures were elucidated by spectroscopic data, and the absolute configurations of the representative compounds neocassa-12(17),15-dien-3-one (2) and neocassa-12(13),15-diene-3,14-dione (5) were assigned by vibrational circular dichroism. The phytotoxic activity of compounds 3, 4, and 5 was evaluated against the germination and growth of Ipomoea grandifolia and Euphorbia heterophylla. Compound 4 exhibited the most potent activity for growth variables, resulting in the smallest radicle length of I. grandifolia and in the smallest aerial part length of E. heterophylla. Compound 5 reduced the germination speed index more effectively than the herbicide glyphosate (Roundup).

Bioactive Constituents from the Bryophyta Hypnum plumaeforme

Chemical investigation of the secondary metabolites of the whole plant of bryophyte Hypnum plumaeforme Wilson led to the isolation of a new pimarane-type diterpenoid, momilactone F (1), along with seventeen known compounds. Their chemical structures were elucidated based on massive spectroscopic data. The allelopathic and antifungal properties were evaluated. Among them, momilactone F (1), acrenol (2),^[11] momilactones A (3) and B (4) showed significant allelopathic activity against Samolus parviflorus Raf. and Lactuca sativa L. var. angustana Irish, as well as selected antifungal property against crop pathogenic fungi strains. On the other hand, 8(14)-podocarpen-13-on-18-oic acid (8) exhibited strong promoting activity on the growth of L. sativa L. var. angustana Irish. The present investigation provided new insights for developing of H. plumaeforme for further application as a potential agricultural tool.

Synthesis of Pyranopyrans Related to Diplopyrone and Evaluation as Antibacterials and Herbicides

Stereoselective syntheses of new pyranopyrans that are related to the natural product diplopyrone, which is a phytotoxin implicated in cork oak decline, have been achieved from carbohydrate starting materials in two approaches that are based on C-glycosides as key intermediates. A C-alkynyl glycoside prepared by Ferrier rearrangement was used as the precursor to a new pyranopyran alkyne that showed potent antibacterial activity against the common bacterial pathogen Edwardsiella ictaluri that causes enteric septicemia in catfish. The C-alkynyl glycoside also showed herbicidal activity. New bioassay data for the pyranopyran nitrile (4aR,6S,8aR)-6-cyano-6,8a-dihydropyrano-[3,2-b]pyran-2(4aH)-one, the most potent of the pyranopyrans synthesized to date, were obtained in greenhouse studies that revealed additional herbicidal activity. Other new analogues that were synthesized included desmethylpyranopyrans that were prepared by Isobe C-alkynylation-rearrangement/reduction and RCM-based pyranopyran construction. The antibiotic and phytotoxic activities of the new pyranopyrans synthesized in this study highlight the importance of substituents on the nonlactone ring and demonstrate the potential of such compounds as antibiotics and herbicides.

Herbicidal Polyketides and Diketopiperazine Derivatives from Penicillium viridicatum

Herbicidal activity-guided isolation from the fermentation extract of Penicillium viridicatum had obtained two herbicidal series of polyketides (1-7) and diketopiperazine derivatives (8-11), especially including three novel polyketides (1-3). The structures and absolute configurations of new polyketides 1-3 were elucidated by extensive spectroscopic analyses, as well as comparisons between measured and calculated ECD spectra. Novel polyketides 1-3 and known 4, all bearing the heptaketide skeleton with a trans-fused decalin ring of 8-CH₃ substitution, could significantly inhibit the radicle growth of Echinochloa crusgalli seedlings with a dose-dependent relationship. Especially at the concentration of 10 μg/mL, 1-4 exhibited the inhibition rates with 81.5% ± 2.0, 76.4% ± 0.8, 79.6% ± 1.1, and 80.0 ± 1.8%, respectively, even better than the commonly used synthetic herbicide of acetochlor with 76.1 ± 1.4%. Further greenhouse bioassay revealed that 4 showed pre-emergence herbicidal activity against E. crusgalli with the fresh-weight inhibition rate of 74.1% at a dosage of 400 g ai/ha, also better than acetochlor, while the other isolated metabolites (5-11) exhibited moderate herbicidal activities. The structure-activity differences of isolated polyketides indicated that the heptaketide skeleton, characterized by a trans-fused decalin ring with 8-CH₃ substitution, should be the key factor of their herbicidal activities, which could give new insights for the bioherbicide developments.

Syntheses and Phytotoxicity of All Stereoisomers of 6-(2-Hydroxy-6-phenylhex-1-yl)-5,6-dihydro-2H-pyran-2-one and Determination of the Effect of the α,β-Unsaturated Carbonyl Structure and Hydroxy Group Bonding to Chiral Carbon

All four stereoisomers of naturally occurring 6-(2-hydroxy-6-phenylhex-1-yl)-5,6-dihydro-2H-pyran-2-one (1) were synthesized by employing yeast-reduction products with high optical purity [from 95% enantiomeric excess (ee) to more than 99% ee], and then their phytotoxicities against lettuce and Italian ryegrass were evaluated. In the Italian ryegrass seedlings test, (6S,2'R)-1 showed the most potent and stereospecific activity against the shoots (IC50 = 260 μM) and roots (IC50 = 43.2 μM), with a significant difference from other stereoisomers. The highest seed germination inhibitory activity against Italian ryegrass seed was also observed in (6S,2'R)-1, showing a 53% germination ratio from the control at 1000 μM. This advantageous (6S,2'R) stereochemistry was employed in the syntheses of α,β-dihydro, 2'-dehydroxy, and 2'-methoxy derivatives 13-15. By the test using these derivatives, the importance of the α,β-unsaturated double bond and hydroxy group bonding to a chiral center on the 6-alkyl chain of 5,6-dihydro-α-pyrone for phytotoxicity was determined. In the test against lettuce, the 6S configuration and (6S,2'S) configuration were necessary for growth inhibition (IC50 = ca. 60 μM) and germination inhibition (63% germination ratio at 1000 μM), respectively.

Phytotoxic Diterpenoids from Plants and Microorganisms

Phytotoxic natural products with either unique or various structures are one of the most abundant sources for the discovery of potential allelochemicals, natural herbicides, and plant growth regulators. Phytotoxic diterpenoids, a relatively large class of natural products, play an important role in the plant-plant or plant-microorganism interactions. This article argues that the phytotoxic diterpenoids isolated from the plants and microorganisms can either inhibit the seed germination and the growth of plant seedlings or lead to some disease symptoms on the tested plant tissues and plant seedlings.