Structural Simplification of Marine Natural Products: Discovery of Hamacanthin Derivatives Containing Indole and Piperazinone as Novel Antiviral and Anti-phytopathogenic-fungus Agents

Design, Synthesis, and Antiviral and Fungicidal Activities of 4-Oxo-4H-quinolin-1-yl Acylhydrazone Derivatives

To discover novel antiviral agents, based on the high antiviral activity of (4-oxo-4H-quinolin-1-yl)-acetic acid hydrazide (C), a series of 4-oxo-4H-quinoline acylhydrazone derivatives were designed, synthesized, and first evaluated for their antiviral and fungicidal activities. Most acylhydrazone derivatives exhibited moderate to good antiviral activities in vivo. The inactive, curative, and protective activities of compounds 4 (51.2, 47.6, and 46.3%), 11 (49.6, 43.0, and 45.2% at 500 mg/L), and 17 (47.1, 49.2, and 44.1%) were higher than those of ribavirin (39.2, 38.0, and 40.8%) at 500 mg/L. Molecular docking showed that compound 4 exhibited a stronger affinity to TMV coat protein (TMV-CP) than ribavirin, with a binding energy (-6.89 kcal/mol) slightly lower than that of ribavirin (-6.08 kcal/mol). Microscale thermophoresis showed that compound 4 (K d = 0.142 ± 0.060 μM) exhibited a strong binding ability to TMV-CP, superior to that of ribavirin (K d = 0.512 ± 0.257 μM). The results of transmission electron microscopy showed that compound 4 hindered the self-assembly and growth of TMV. The antifungal activities of most compounds were moderate at 50 mg/L, among which compounds 12 and 21 exhibited a 72.1 and 76.5% inhibitory rate against Physalospora piricola, respectively. Meanwhile, compound 16 exhibited a 60% inhibitory rate against Cercospora arachidicola Hori at 50 mg/L.

Discovery of Novel Oxathiapiprolin Derivatives as Potent Fungicide Candidates

Oxathiapiprolin (OXA), which targets the oxysterol-binding protein (OSBP), is an outstanding piperidinyl thiazole isoxazoline (PTI) fungicide that can be used to control oomycetes diseases. In this study, starting from the structure of OXA, a series of novel OSBP inhibitors were designed and synthesized by introducing an indole moiety to replace the pyrazole in OXA. Finally, compound b24 was found to exhibit the highest control effect (82%) against cucumber downy mildew (CDM) in the greenhouse at a very low dosage of 0.069 mg/L, which was comparable to that of OXA (88%). Furthermore, it showed better activity against potato late blight (PLB) than other derivatives of indole. The computational results showed that the R-conformation of b24 should be the dominant conformation binding to PcOSBP. The results of the present work indicate that the 3-fluorine-indole ring is a favorable fragment to increasing the electronic energy when binding with PcOSBP. Furthermore, compound b24 could be used as a lead compound for the discovery of new OSBP inhibitors.

Design and synthesis of bis(indolyl)-hydrazide-hydrazone derivatives and their antifungal activities against plant pathogen fungi

A series of bis(indolyl)-hydrazide-hydrazone derivatives were synthesised, and their structures were characterised using 1H-NMR and HRMS. The antifungal activity of the prepared compounds was evaluated against Pyricularia oryzae Cav., Colletotrichum -gloeosporioides Penz., Botrytis cinerea Pers.: Fr. and Rhizoctonia solani Kühn using the mycelial growth rate method. The preliminary bioassays revealed that most of the synthesised compounds exhibited antifungal activity against the four tested fungi and displayed a remarkable inhibitory effect on the mycelium growth of R. solani. In particular, compounds 3b, 3c, and 3k demonstrated significant antifungal activity against R. solani, with EC50 values of 26.42, 20.74, and 22.41 μM, respectively, outperforming the positive control shenqinmycin (47.18 μM) and carvacrol (49.13 μM).

Innovative Arylimidazole-Fused Phytovirucides via Carbene-Catalyzed [3+4] Cycloaddition: Locking Viral Cell-To-Cell Movement by Out-Competing Virus Capsid-Host Interactions

The control of potato virus Y (PVY) induced crop failure is a challengeable issue in agricultural chemistry. Although many anti-PVY agents are designed to focus on the functionally important coat protein (CP) of virus, how these drugs act on CP to inactivate viral pathogenicity, remains largely unknown. Herein, a PVY CP inhibitor -3j (S) is disclosed, which is accessed by developing unusually efficient (up to 99% yield) and chemo-selective (> 99:1 er in most cases) carbene-catalyzed [3+4] cycloaddition reactions. Compound -3j bears a unique arylimidazole-fused diazepine skeleton and shows chirality-preferred performance against PVY. In addition, -3j (S) as a mediator allows ARG191 (R191) of CP to be identified as a key amino acid site responsible for intercellular movement of virions. R191 is further demonstrated to be critical for the interaction between PVY CP and the plant functional protein NtCPIP, enabling virions to cross plasmodesmata. This key step can be significantly inhibited through bonding with the -3j (S) to further impair pathogenic behaviors involving systemic infection and particle assembly. The study reveals the in-depth mechanism of action of antiviral agents targeting PVY CP, and contributes to new drug structures and synthetic strategies for PVY management.

Identification of Novel Bisamide-Decorated Benzotriazole Derivatives as Anti-Phytopathogenic Virus Agents: Bioactivity Evaluation and Computational Simulation

As a notorious phytopathogenic virus, the tobacco mosaic virus (TMV) severely reduced the quality of crops worldwide and caused critical constraints on agricultural production. The development of novel virucides is a persuasive strategy to address this predicament. Herein, a series of novel bisamide-decorated benzotriazole derivatives were elaborately prepared and screened. Biological tests implied that the optimized compound 7d possessed the most brilliant antiviral inactive profile (EC50 = 157.6 μg/mL) and apparently surpassed that of commercial ribavirin (EC50 = 442.1 μg/mL) 2.8-fold. The preliminary antiviral mechanism was elaborately investigated via transmission electron microscopy, microscale thermophoresis (MST) determination, RT-qPCR, and Western blot analysis. The results showed that compound 7d blocked the assembly of TMV by binding with coat protein (Kd = 0.7 μM) and suppressed TMV coat protein gene expression and biosynthesis process. Computational simulations indicated that 7d displayed strong H-bonds and pi interactions with TMV coat protein, affording a lower binding energy (ΔGbind = -17.8 kcal/mol) compared with Ribavirin (ΔGbind = -10.7 kcal/mol). Overall, current results present a valuable perception of bisamide decorated benzotriazole derivatives with appreciably virustatic competence and should be profoundly developed as virucidal candidates in agrochemical.

Antimicrobial activity of natural and semi-synthetic carbazole alkaloids

Since the first natural carbazole alkaloid, murrayanine, was isolated from Mwraya Spreng, carbazole alkaloid derivatives have been widely concerned for their anti-tumor, anti-viral and anti-bacterial activities. In recent decades, a growing body of data suggest that carbazole alkaloids and their derivatives have different biological activities. This is the first comprehensive description of the antifungal and antibacterial activities of carbazole alkaloids in the past decade (2012-2022), including natural and partially synthesized carbazole alkaloids in the past decade. Finally, the challenges and problems faced by this kind of alkaloids are summarized. This paper will be helpful for further exploration of this kind of alkaloids.

Nortopsentins as Leads from Marine Organisms for Anticancer and Anti-Inflammatory Agent Development

The marine environment is an excellent source of molecules that have a wide structural diversity and a variety of biological activities. Many marine natural products (MNPs) have been established as leads for anticancer drug discovery. Most of these compounds are alkaloids, including several chemical subclasses. In this review, we focus on the bis-indolyl alkaloid Nortopsentins and their derivatives with antiproliferative properties. Nortopsentins A-C were found to exhibit in vitro cytotoxicity against the P388 murine leukaemia cell line. Their structural manipulation provided a wide range of derivatives with significant anti-tumour activity against human cell lines derived from different cancer types (bladder, colon, gastric, CNS, liver, lung, breast, melanoma, ovarian, pancreatic, prostate, pleural mesothelioma, renal, sarcoma, and uterus). In vivo assays on animal models also proved that Nortopsentins and related bis-indolyl compounds have potent anti-inflammatory activity. These remarks set the foundation for future investigations into the development of new Nortopsentin derivatives as new anticancer and anti-inflammatory agents.

Discovery of Chiral Diamine Derivatives Containing 1,2-Diphenylethylenediamine as Novel Antiviral and Fungicidal Agents

Severe plant virus diseases lead to poor harvests and poor crop quality, and the lack of effective suppressive drugs makes plant disease control a huge challenge. Natural product-based structural simplification is an important strategy for finding novel pesticide candidates. According to our previous research on the antiviral activities of harmine and tetrahydroharmine derivatives, a series of chiral diamine compounds were designed and synthesized by means of structural simplification using diamines in natural products as the core structure in this work, and the antiviral and fungicidal activities were investigated. Most of these compounds displayed higher antiviral activities than those of ribavirin. Compounds 1a and 4g displayed higher antiviral activities than ningnanmycin at 500 μg/mL. The antiviral mechanism research revealed that compounds 1a and 4g could inhibit virus assembly by binding to tobacco mosaic virus (TMV) CP and interfere with the assembly process of TMV CP and RNA via transmission electron microscopy and molecular docking. Further fungicidal activity tests showed that these compounds displayed broad-spectrum fungicidal activities. Compounds 3a, 3i, 5c, and 5d with excellent fungicidal activities against Fusarium oxysporum f.sp. cucumerinum can be considered as new fungicidal candidates for further research. The current work provides a reference to the development of agricultural active ingredients in crop protection.

Recent Achievements in Antiviral Agent Development for Plant Protection

Plant virus disease is the second most prevalent plant diseases and can cause extensive loss in global agricultural economy. Extensive work has been carried out on the development of novel antiplant virus agents for preventing and treating plant virus diseases. In this review, we summarize the achievements of the research and development of new antiviral agents in the recent five years and provide our own perspective on the future development in this highly active research field.

Design, Synthesis and Bioassay of 2-Phenylglycine Derivatives as Potential Pesticide Candidates

Plant diseases can seriously affect the growth of food crops and economic crops. To date, pesticides are still among the most effective methods to prevent and control plant diseases worldwide. Consequently, to develop potential pesticide molecules, a series of novel 2-phenylglycine derivatives containing 1,3,4-oxadiazole-2-thioethers were designed and synthesized. The bioassay results revealed that G₁₉ exhibited great in vitro antifungal activity against Thanatephorus cucumeris with an EC₅₀ value of 32.4 μg/mL, and in vivo antifungal activity against T. cucumeris on rice leaves at a concentration of 200.0 μg/mL (66.9 %) which was close that of azoxystrobin (73.2 %). Compounds G₂₄ (80.2 %), G₂₅ (89.4 %), and G₂₇ (83.3 %) exhibited impressive in vivo inactivation activity against tobacco mosaic virus (TMV) at a concentration of 500.0 μg/mL, which was comparable to that of ningnanmycin (96.3 %) and markedly higher than that of ribavirin (55.6 %). The antibacterial activity of G₁₆ (63.1 %), G₂₆ (89.9 %), G₂₇ (78.0 %), and G₂₈ (68.0 %) against Xoo at a concentration of 50.0 μg/mL was higher than that of thiadiazole copper (18.0 %) and bismerthiazol (38.9 %). Preliminary mechanism studies on the antifungal activity against T. cucumeris demonstrated that G₁₉ can affect the growth of mycelia by disrupting the integrity of the cell membrane and altering the permeability of the cell. These studies revealed that the amino acid derivatives containing a 1,3,4-oxadiazole moiety exhibited certain antifungal, antibacterial, and anti-TMV activities, and these derivatives can be further modified and developed as potential pesticide molecules.

Discovery of Aldisine and Its Derivatives as Novel Antiviral, Larvicidal, and Antiphytopathogenic-Fungus Agents

Based on the widespread use of hydrogen bonds in drug design, a series of aldisine derivatives containing oxime, oxime ether, and hydrazone moieties were designed and synthesized, and their antiviral, larvicidal, and fungicidal activities were evaluated for the first time. The bioassay results showed that most of these derivatives were active against tobacco mosaic virus (TMV). Hydrazone derivative 12 showed in vivo inactivation, curative, and protection activities of 52 ± 4, 49 ± 1, and 52 ± 3% at 500 mg/L, which are comparable to that of the commercial antiviral drug ningnanmycin (57 ± 3, 56 ± 2, and 59 ± 1%, respectively) at the same dose. The antiviral mechanism study showed that compound 12 could cause 20S CP (coating protein) disk fusion and disintegration, thus affecting the assembly of virus particles. The result of molecular docking indicated that there were obvious hydrogen bonds between compound 12 and TMV CP. Most derivatives were active against larvae of lepidopteran pests, such as Mythimna separata, Pyrausta nubilalis, and Plutella xylostella. Some compounds also exhibited larvicidal activities against Culex pipiens; among them compounds 9 and 13 exhibited larvicidal activities of 0.81 and 1.54 mg/L (LC₅₀), respectively. Moreover, most of the derivatives showed broad-spectrum fungicidal activities against 14 kinds of phytopathogenic fungi at 50 mg/L.

Design, Synthesis and in Vitro Antifungal Mechanism of Novel Phenylalanine Derivatives

To explore novel molecules with unique mechanisms against plant pathogenic fungi, a series of phenylalanine derivatives containing a 1,3,4-oxadiazothioether moiety were designed and synthesized. Bioassays revealed that some target compounds at 100 μg/mL exhibited excellent antifungal activities against Thanatephorus cucumeris, such as G₆ (92.1 %), G₁₀ (94.3 %), G₁₈ (99.1 %), and G₁₉ (98.7 %), better than that of the commercial fungicide azoxystrobin (90.6 %), and the EC₅₀ value of G₁₀ against T. cucumeris was 31.9 μg/mL. Further mechanism studies of T. cucumeris treated with G₁₀ demonstrated that this compound can affect the growth of mycelia by disrupting the integrity of the membrane, and the higher the concentration of the compound is, the greater the degree of membrane integrity damage, similar to the commercial fungicide azoxystrobin. These conclusions provide important information for further mechanism studies of this series of phenylalanine derivatives.

Recent Research Progress: Discovery of Anti-Plant Virus Agents Based on Natural Scaffold

Plant virus diseases, also known as “plant cancers”, cause serious harm to the agriculture of the world and huge economic losses every year. Antiviral agents are one of the most effective ways to control plant virus diseases. Ningnanmycin is currently the most successful anti-plant virus agent, but its field control effect is not ideal due to its instability. In recent years, great progress has been made in the research and development of antiviral agents, the mainstream research direction is to obtain antiviral agents or lead compounds based on structural modification of natural products. However, no antiviral agent has been able to completely inhibit plant viruses. Therefore, the development of highly effective antiviral agents still faces enormous challenges. Therefore, we reviewed the recent research progress of anti-plant virus agents based on natural products in the past decade, and discussed their structure-activity relationship (SAR) and mechanism of action. It is hoped that this review can provide new inspiration for the discovery and mechanism of action of novel antiviral agents.

Bioactivity-Guided Synthesis Accelerates the Discovery of Evodiamine Derivatives as Potent Insecticide Candidates

Pests threaten worldwide food security by decreasing crop yields and damaging their quality. Natural product-based molecular design and structural optimization have been one of the most effective ways to innovate pesticides for integrated insect management. To continue our previous studies on the discovery of insecticidal lead, a series of evodiamine derivatives were designed, synthesized, and evaluated for their insecticidal activities. The bioassay results demonstrated that compounds Ian and Iao exhibited 90 and 80% insecticidal activities against Mythimna separata at 2.5 mg/L, respectively, which were superior to evodiamine (10% at 10 mg/L), matrine (45% at 600 mg/L), and rotenone (30% at 200 mg/L). Compounds Ian-Iap showed 90% insecticidal activities against Plutella xylostella at 1.0 mg/L, far more potent than those of evodiamine, matrine, and rotenone. Compound Ian displayed 60% insecticidal activity against Helicoverpa armigera at 5.0 mg/L, while evodiamine, matrine, and rotenone showed very poor activities. The study on the insecticidal mechanism of action by a calcium imaging experiment indicated that the insect ryanodine receptors (RyRs) could be the potential target of Ian. Furthermore, the molecular docking indicated that Ian anchored in the binding site of the RyR of P. xylostella. The above results manifested the potential of evodiamine derivatives as potent insecticide candidates.

Discovery of Phytoalexin Camalexin and Its Derivatives as Novel Antiviral and Antiphytopathogenic-Fungus Agents

In response to the invasion of plant viruses and pathogenic fungi, higher plants produce defensive allelochemicals. Finding candidate varieties of botanical pesticides based on allelochemicals is one of the important ways to create efficient and green pesticides. Here, a series of camalexin derivatives based on a phytoalexin camalexin scaffold were designed, synthesized, and assessed for their antiviral and fungicidal activities systematically. Most of these camalexin derivatives exhibited better antiviral activities against tobacco mosaic virus (TMV) than the control antiviral agent ribavirin. Under the same test conditions, the anti-TMV activities of compounds 3d, 5a, 5d, and 10f-10h were found to be equivalent to or better than that of ningnanmycin, an agricultural cytosine nucleoside antibiotic with excellent protective effect. The antiviral mechanism research showed that compound 5a could cause 20S CP disk fusion and disintegration, thus affecting the assembly of virus particles. The results of molecular docking indicate that there were obvious hydrogen bonds between compounds 3d, 5a, and 10f and TMV CP. The binding constants of compounds 5a and 10f to TMV CP were also calculated using fluorescence titration. These camalexin derivatives also presented broad spectrum fungicidal activities, especially for Rhizoctonia solani and Physalospora piricola. In this work, the design, synthesis, structure optimization, and mode of action of camalexin derivatives were carried out progressively. This work provides a reference for using defensive chemical compounds as novel pesticide lead compounds.

Design, synthesis and biological activities of echinopsine derivatives containing acylhydrazone moiety

Based on the broad-spectrum biological activities of echinopsine and acylhydrazones, a series of echinopsine derivatives containing acylhydrazone moieties have been designed, synthesized and their biological activities were evaluated for the first time. The bioassay results indicated that most of the compounds showed moderate to good antiviral activities against tobacco mosaic virus (TMV), among which echinopsine (I) (inactivation activity, 49.5 ± 4.4%; curative activity, 46.1 ± 1.5%; protection activity, 42.6 ± 2.3%) and its derivatives 1 (inactivation activity, 44.9 ± 4.6%; curative activity, 39.8 ± 2.6%; protection activity, 47.3 ± 4.3%), 3 (inactivation activity, 47.9 ± 0.9%; curative activity, 43.7 ± 3.1%; protection activity, 44.6 ± 3.3%), 7 (inactivation activity, 46.2 ± 1.6%; curative activity, 45.0 ± 3.7%; protection activity, 41.7 ± 0.9%) showed higher anti-TMV activity in vivo at 500 mg/L than commercial ribavirin (inactivation activity, 38.9 ± 1.4%; curative activity, 39.2 ± 1.8%; protection activity, 36.4 ± 3.4%). Some compounds exhibited insecticidal activities against Plutella xylostella, Mythimna separate and Spodoptera frugiperda. Especially, compounds 7 and 27 displayed excellent insecticidal activities against Plutella xylostell (mortality 67 ± 6% and 53 ± 6%) even at 0.1 mg/L. Additionally, most echinopsine derivatives exhibited high fungicidal activities against Physalospora piricola and Sclerotinia sclerotiorum.

Design and synthesis of marine sesterterpene analogues as novel estrogen receptor α degraders for breast cancer treatment

Targeted protein degradation using small molecules is an intriguing strategy for drug development. The marine sesterterpene compound MHO7 had been reported to be a potential ERα degradation agent. In order to further improve its biological activity, two series of novel MHO7 derivatives with long side chains were designed and identified as novel selective estrogen receptor down-regulators (SERDs). The growth inhibition activity of the novel SERD compounds were significantly affected by the type and length of the side chain. Most of the derivatives were significantly more potent than MHO7 against both drug-sensitive and drug-resistant breast cancer cells. Among them, compound 16a, with IC₅₀ values of 0.41 μM against MCF-7 cell lines and 9.6-fold stronger than MHO7, was the most potential molecule. A whole-genome transcriptomic analysis of MCF-7 cells revealed that the mechanism of 16a against MCF-7 cell was similar with that of MHO7. The estrogen signaling pathway was the most affected among the disturbed genes, but the ERα degradation activity of 16a was observed higher than that of MHO7. Other effects of 16a were confirmed similar with MHO7, which means that the basic mechanisms of the derivatives are the same with the ophiobolin backbone, i.e. the degradation of ERα is mediated via proteasome-mediated process, the induction of apoptosis and the cell cycle arrest at the G1 phase. Meanwhile, a decrease of mitochondrial membrane potential and an increase of cellular ROS were also detected. Based on these results, as a novel modified ophiobolin derived compound, 16a may warrant further exploitation as a promising SERD candidate agent for the treatment of breast cancer.

Design, Semisynthesis, Insecticidal and Antibacterial Activities of a Series of Marine-Derived Geodin Derivatives and Their Preliminary Structure-Activity Relationships

To enhance the biological activity of the natural product geodin (1), isolated from the marine-derived fungus Aspergillus sp., a series of new ether derivatives (2-37) was designed and semisynthesized using a high-yielding one-step reaction. In addition, the insecticidal and antibacterial activities of all geodin congeners were evaluated systematically. Most of these derivatives showed better insecticidal activities against Helicoverpa armigera Hübner than 1. In particular, 15 showed potent insecticidal activity with an IC50 value of 89 μM, comparable to the positive control azadirachtin (IC50 = 70 μM). Additionally, 5, 12, 13, 16, 30 and 33 showed strong antibacterial activity against Staphylococcus aureus and Aeromonas salmonicida with MIC values in the range of 1.15-4.93 μM. The preliminary structure-activity relationships indicated that the introduction of halogenated benzyl especially fluorobenzyl, into 1 and substitution of 4-OH could be key factors in increasing the insecticidal and antibacterial activities of geodin.