Marine Sesquiterpenes for Plant Protection: Discovery of Laurene Sesquiterpenes and Their Derivatives as Novel Antiviral and Antiphytopathogenic Fungal Agents

Antifungal Pseuboyenes A-J, Bergamotene-Derived Sesquiterpenoids from a Cold-Seep-Derived Pseudallescheria boydii

A chemical investigation of a cold-seep-sediment-derived fungus, Pseudallescheria boydii CS-793, resulted in characterization of 10 novel bergamotene-derived sesquiterpenoids, pseuboyenes A-J (1-10). Their structures were elucidated by spectroscopic and X-ray crystallographic analyses as well as using the modified Mosher's method. Compound 1 represents the first example of a β-bergamotene containing a 6-oxobicyclo[3.2.1]octane nucleus adducted with a methyl lactate unit, while 8-10 involve a skeletal rearrangement from bergamotene. Compounds 2-5 showed significant antifungal activities against Colletotrichum gloeosporioides Penz. and Fusarium oxysporum with MICs ranging from 0.5 to 8 μg/mL. Compound 4 exhibited an in vitro anti-F. proliferatum effect with an EC50 value of 1.0 μg/mL.

Design, Synthesis, and Biological Activities of Novel Coumarin Derivatives as Pesticide Candidates

Food security is an important issue in the 21st century; preventing and controlling crop diseases and pests are the key to solve this problem. The creation of new pesticides based on natural products is an important and effective method. Herein, coumarins were selected as parent structures, and a series of their derivatives were designed, synthesized, and evaluated for their antiviral activities, fungicidal activities, and insecticidal activities. We found that coumarin derivatives exhibited good to excellent antiviral activities against tobacco mosaic virus (TMV). The antiviral activities of I-1, I-2a, I-4b, II-2c, II-2g, II-3, and II-3b are better than that of ribavirin at 500 μg/mL. Molecular docking research showed that these compounds had a strong interaction with TMV CP. These compounds also showed broad-spectrum fungicidal activities against 14 plant pathogenic fungi. The EC50 values of I-1, I-2a, I-3c, and II-2d are in the range of 1.56-8.65 μg/mL against Rhizoctonia cerealis, Physalospora piricola, Sclerotinia sclerotiorum, and Pyricularia grisea. Most of the compounds also displayed good insecticidal activities against Mythimna separata. Pesticide-likeness analysis showed that these compounds are following pesticide-likeness and have the potential to be developed as pesticide candidates. The present work lays a foundation for the discovery of novel pesticide lead compounds based on coumarin derivatives.

Myricetin derivatives containing the benzoxazinone moiety discovered as potential anti-tobacco mosaic virus agents

A series of myricetin derivatives containing benzoxazinone were designed and synthesized. The structures of all compounds were characterized by NMR and HRMS. The structure of Y4 had been confirmed by single-crystal X-ray diffraction analysis. The test results of EC50 values of tobacco mosaic virus (TMV) suggested that Y8 had the best curative and protective effects, with EC50 values of 236.8, 206.0 μg/mL, respectively, which were higher than that of ningnanmycin (372.4, 360.6 μg/mL). Microscale thermophoresis (MST) experiments demonstrated that Y8 possessed a strong binding affinity for tobacco mosaic virus coat protein (TMV-CP), with a dissociation constant (Kd) value of 0.045 μM, which was superior to the ningnanmycin (0.700 μM). The findings of molecular docking studies revealed that Y8 interacted with multiple amino acid residues of TMV-CP through the formation of non-covalent bonds, which had an effect on the self-assembly of TMV particles. The malondialdehyde (MDA) and superoxide dismutase assay (SOD) content assays also fully verified that Y8 could stimulate the plant immune system and enhance disease resistance by reducing MDA content and increasing SOD content. In summary, myricetin derivatives containing benzoxazinone could be considered to further research and development as novel antiviral agents.

Design, synthesis, and bioactivity studies of chalcone derivatives containing [1,2,4]-triazole-[4,3-a]-pyridine

In this study, 30 chalcone derivatives containing [1,2,4]-triazole-[4,3-a]-pyridine were designed and synthesized. The results of antibacterial activity showed that EC50 values of N26 against Xoo, Pcb was 36.41, 38.53 μg/mL, respectively, which were better than those of thiodiazole copper, whose EC50 values were 60.62, 106.75 μg/mL, respectively. The bacterial inhibitory activity of N26 against Xoo was verified by SEM. Antibacterial mechanism between N26 and Xoo was preliminarily explored, the experimental results showed that when the drug concentration was 100 mg/L, N26 had a good cell membrane permeability of Xoo, and it can inhibit the production of EPS content and extracellular enzyme content to disrupt the integrity of the Xoo biofilms achieving the effect of inhibiting Xoo. At 200 mg/L, N26 can protect and inhibit the lesions of post-harvested potatoes in vivo. The activities of N1-N30 against TMV were determined with half leaf dry spot method. The EC50 values of the curative and protective activity of N22 was 77.64 and 81.55 μg/mL, respectively, which were superior to those of NNM (294.27, 175.88 μg/mL, respectively). MST experiments demonstrated that N22 (Kd = 0.0076 ± 0.0007 μmol/L) had a stronger binding ability with TMV-CP, which was much higher than that of NNM (Kd = 0.7372 ± 0.2138 μmol/L). Molecular docking results showed that N22 had a significantly higher affinity with TMV-CP than NNM.

Design, Synthesis, and Biological Evaluation of Novel Derivatives of the Marine Natural Product Laurene

Plant pathogenic fungi and viruses are seriously threatening agricultural production. There is an urgent need to develop novel fungicides and antiviral agents with low toxicity and high efficiency. In this study, we designed and synthesized 32 thiazole-, hydrazone-, and amide-containing derivatives of laurene and systematically evaluated their antiviral activities and fungicidal activities. Structure-simplified compounds 5a-5c, 5i, 5k, 5l, 11a, 11j, and 12c displayed higher antiviral activities than that of ningnanmycin. Compound 11a with a simple chemical structure, convenient synthetic route, and excellent antiviral activity emerged as a secondary lead compound. The docking results show that compounds 5i, 5k, and 11a have strong interactions with the tobacco mosaic virus coat protein (TMV CP). These compounds also exhibited significant fungicidal activities. Compounds 5g, 5k, 11j, and 11l displayed 9.15-17.45 μg/mL EC50 values against Pyricularia grisea, and compounds 5h (EC50: 8.01 μg/mL) and 11i (EC50: 15.23 μg/mL) exhibited a similar level of EC50 values with chlorothalonil (EC50: 7.33 μg/mL) against Physalospora piricola. Preliminary fungicidal mechanism research indicated that compound 5h has a certain destructive effect on the hyphae of P. piricola. This work lays a foundation for the application of laurene derivatives in plant protection.

Furofuran Lignans for Plant Protection: Discovery of Sesamolin and Its Derivatives as Novel Anti-Tobacco Mosaic Virus and Antibacterial Agents

Natural products have been a valuable source of efficient and low-risk pesticides. In this work, a series of novel sesamolin derivatives A0-A31 and B0-B4 were designed and synthesized via structural simplification of furofuran lignan phrymarolin II, and their antiviral and antibacterial activities were systematically evaluated. The bioassay results showed that compound A24 displayed remarkable inactivation activity against tobacco mosaic virus (TMV) with an EC₅₀ value of 130.4 μg/mL, which was superior to that of commercial ningnanmycin (EC₅₀ = 202.0 μg/mL). The antiviral mode of action assays suggested that compound A24 may obstruct self-assembly by binding to TMV coat protein (CP), thus resisting the TMV infection. In addition, compound A25 possessed prominent antibacterial activities, especially against Ralstonia solanacearum with an EC₅₀ value of 43.8 μg/mL, which is better than those of commercial bismerthiazol and thiodiazole copper. This research lays a solid foundation for the utilization of furofuran lignans in crop protection.

Design, Synthesis and Fungicidal Activity of Ester Derivatives of 4-(3,4-Dichloroisothiazole) 7-Hydroxy Coumarin

The development of new fungicides is vital for safeguarding crops and ensuring sustainable agriculture. Building on our previous finding that 4-(3,4-dichloroisothiazole)-7-hydroxy coumarins can be used as fungicidal leads, 44 novel coumarin ester derivatives were designed and synthesized to evaluate whether esterification could enhance their fungicidal activity. In vitro fungicidal bioassays indicated that compound 2ai displayed good activity against Alternaria solani, Botrytis cinereal, Cercospora arachidicola, Physalospora piricola and Sclerotinia sclerotiorum, with an EC₅₀ value ranging from 2.90 to 5.56 μg/mL, comparable to the lead compound 1a, with its EC₅₀ value ranging from 1.92 to 9.37 μg/mL. In vivo bioassays demonstrated that compounds 1a, 2ar and 2bg showed comparable, excellent efficacy against Pseudoperonospora cubensis at a dose of 25 µg/mL. Our research shows that the esterification of 4-(3,4-dichloroisothiazole) 7-hydroxycoumarins results in a fungicidal activity equivalent to that of its lead compounds. Furthermore, our density functional theory (DFT) calculations and 3D-QSAR modeling provide a rational explanation of the structure-activity relationship and offer valuable insights to guide further molecular design.

Natural Products for Pesticides Discovery: Structural Diversity Derivation and Biological Activities of Naphthoquinones Plumbagin and Juglone

Plant diseases and insect pests seriously affect the yield and quality of crops and are difficult to control. Natural products are an important source for the discovery of new pesticides. In this work, naphthoquinones plumbagin and juglone were selected as parent structures, and a series of their derivatives were designed, synthesized and evaluated for their fungicidal activities, antiviral activities and insecticidal activities. We found that the naphthoquinones have broad-spectrum anti-fungal activities against 14 types of fungus for the first time. Some of the naphthoquinones showed higher fungicidal activities than pyrimethanil. Compounds I, I-1e and II-1a emerged as new anti-fungal lead compounds with excellent fungicidal activities (EC₅₀ values: 11.35-17.70 µg/mL) against Cercospora, arachidicola Hori. Some compounds also displayed good to excellent antiviral activities against the tobacco mosaic virus (TMV). Compounds I-1f and II-1f showed similar level of anti-TMV activities with ribavirin, and could be used as new antiviral candidates. These compound also exhibited good to excellent insecticidal activities. Compounds II-1d and III-1c displayed a similar level of insecticidal activities with matrine, hexaflumuron and rotenone against Plutella xylostella. In current study, plumbagin and juglone were discovered as parent structures, which lays a foundation for their application in plant protection.

Design, Synthesis, Antiviral and Fungicidal Activities of Novel Polycarpine Simplified Analogues

Fungal and viral diseases account for 70-80% of agricultural production losses caused by microbial diseases. Synthetic fungicides and antiviral agents have been used to treat plant diseases caused by plant pathogenic fungi and viruses, but their use has been criticized due to their adverse side effects. As alternative strategies, natural fungicides and antiviral agents have attracted many researchers' interest in recent years. Herein, we designed and synthesized a series of novel polycarpine simplified analogues. Antiviral activity research against tobacco mosaic virus (TMV) revealed that most of the designed compounds have good antiviral activities. The virucidal activities of 4, 6d, 6f, 6h, and 8c are higher than that of polycarpine and similar to that of ningnanmycin. The structure simplified compound 8c was selected for further antiviral mechanism research which showed that compound 8c could inhibit the formation of 20S protein discs by acting on TMV coat protein. These compounds also displayed broad-spectrum fungicidal activities against 7 kinds of plant fungi. This work lays the foundation for the application of polycarpine simplified analogues in crop protection.

Synthesis and biological activities of novel chalcone derivatives containing pyrazole oxime ethers

A series of novel chalcone derivatives containing pyrazole oxime ethers were designed and synthesized. The structures of all the target compounds were determined by NMR and HRMS. The structure of H5 was further confirmed via single-crystal X-ray diffraction analysis. The results of biological activity test showed that some of the target compounds exhibited significant antiviral and antibacterial activities. The test results of EC₅₀ value against tobacco mosaic virus showed that H9 had the best curative and protective effect, and the EC₅₀ value of curative activity of H9 was 166.9 μg/mL, which was superior to ningnanmycin (NNM) 280.4 μg/mL, the EC₅₀ value of protective activity of H9 was 126.5 μg/mL, which was superior to ningnanmycin 227.7 μg/mL. Microscale thermophoresis (MST) experiments demonstrated that H9 (K_d = 0.0096 ± 0.0045 μmol/L) exhibited a strong binding ability with tobacco mosaic virus capsid protein (TMV-CP), which was far superior to ningnanmycin (K_d = 1.2987 ± 0.4577 μmol/L). In addition, molecular docking results showed that the affinity of H9 to TMV protein was significantly higher than ningnanmycin. The results of against bacterial activity showed that H17 has a good inhibiting effect against Xanthomonas oryzae pv. oryzae (Xoo), the EC₅₀ value of H17 was 33.0 μg/mL, which was superior to the commercial drugs thiodiazole copper (68.1 μg/mL) and bismerthiazol (81.6 μg/mL), and the antibacterial activity of H17 was verified by scanning electron microscopy (SEM).

Sesquiterpenoids with Phytotoxic and Antifungal Activities from a Pathogenic Fungus Aspergillus alabamensis

Five new carotane sesquiterpenoids (asperalacids A-E (1-5)), one new tricyclic sesquiterpenoid (4-hydroxy-5(6)-dihydroterrecyclic acid A (6)), and two known analogues (7-8) were obtained from a seagrass-derived fungus Aspergillus alabamensis, which was speculated to be a phytopathogenic fungus, isolated from the necrotic leaves of Enhalus acoroides. The structures of 1-6 were established by a combination of spectroscopic methods, including comprehensive NMR analysis, mass spectrometry, conformational analysis, NMR computational methods, and ECD calculations. Compound 4, with higher inhibitory activity on wheat (Triticum aestivum L.) root and shoot elongation than the positive control terbutryn, a broad-spectrum systemic herbicide, is a new natural plant growth inhibitor. Compound 5, belonging to the rare glycosylated sesquiterpenoid class, represents the first example of glycosylated carotane sesquiterpenoid whose sugar moiety was identified as α-d-glucose. Compounds 1-4 and 6 displayed weak to potent antimicrobial activity against the plant pathogenic fungi Fusarium oxysporum, Fusarium graminearum, and Penicillium italicum and the Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus.