Purine Nucleoside Derivatives Containing a Sulfa Ethylamine Moiety: Design, Synthesis, Antiviral Activity, and Mechanism

Discovery of highly effective antiviral agents based on flavonoid-benzothiazole against TMV

A series of flavonol derivatives containing benzothiazole were designed and synthesized. The structures of all the compounds were characterized by NMR and HRMS. The results of the activity assay showed that some of the target compounds possessed outstanding in vivo antiviral activity against the tobacco mosaic virus (TMV). Among them, the median effective concentration (EC50) of L20 was 90.5 and 202.2 μg/mL for curative and protective activity against TMV, respectively, which was better than that of ningnanmycin (NNM: 252.0 and 204.2 μg/mL). The results of microcalorimetric thermophoresis (MST) and molecular docking experiments indicate that L20 binds TMV-CP more strongly than NNM; density functional theory (DFT) calculation the indicating that L20 is more chemical reactivity than NNM. In addition, malondialdehyde (MDA) and superoxide dismutase assay (SOD) activity measurements also fully confirmed that L20 stimulated the plant immune system and strengthened the plant's resistance to diseases by lowering the MDA content and increasing the SOD activity. Furthermore, the chlorophyll content test experiment found that L20 could reduce the destructive effect of viruses on chloroplasts, increase the content of chlorophyll, and promote photosynthesis. In conclusion, above experimental results suggested that flavonol derivatives containing benzothiazole could be further investigated as new plant virus antiviral drugs.

Discovery of Crinasiadine, Trisphaeridine, Bicolorine, and Their Derivatives as Anti-Tobacco Mosaic Virus (TMV) Agents

Plant viral diseases cause great harm to crops in terms of yield and quality. Natural products have been providing an excellent source of novel chemistry, inspiring the development of novel synthetic pesticides. The Amaryllidaceae alkaloids crinasiadine (3a), trisphaeridine (4a), and bicolorine (5a) were selected as parent structures, and a series of their derivatives were designed, synthesized, and investigated for their anti-plant virus effects for the first time. Compounds 13b and 18 exhibited comparable inhibitory activities to ningnanmycin against tobacco mosaic virus (TMV). Preliminary research into the mechanism, involving transmission electron microscopy and molecular docking studies, suggests that compound 18 may interfere with the elongation phase of the TMV assembly process. This study provides some important information for the research and development of agrochemicals with phenanthridine structures.

Microwave-assisted synthesis of base-modified fluorescent 1,4-dihydropyridine nucleosides: photophysical characterization and insights

A synthesis of a small library of fluorescent 1,4-dihydropyridine nucleoside analogues has been successfully carried out under solvent-free conditions via a one-pot three-component Hantzsch condensation reaction. The process involved a Ba(NO3)2 catalyzed solvent-free reaction between 3',5'-di-O-acetyl-5-formyl-2'-deoxyuridine, differently substituted β-keto ester and ammonium acetate under microwave irradiation. This facile methodology yielded the desired products with very high yields (86-96%) under solvent-free reaction conditions in a short reaction time, which was followed by a simple workup. Yields obtained under microwave and conventional heating were compared, with the microwave irradiation condition displaying superior results. The synthesized compounds were characterized by IR, 1H-NMR, 13C-NMR, 1H-1H COSY, 1H-13C HETCOR, 2D NOESY NMR and HRMS analysis. These nucleoside analogues exhibited significant fluorescence, with a prominent emission band around 460 nm (excitation at 235 nm). Photophysical studies revealed strong fluorescence intensity, excellent Stokes shifts (70-162 nm), and high quantum yields (0.022-0.579), outperforming other pyrimidine-based fluorescent nucleosides. Notably, 5-(diethyl 2'',6''-propyl-1'',4''-dihydropyridine-3'',5''-dicarboxylate)-4''-yl-2'-deoxyuridine demonstrated a quantum yield as high as 0.579 in DMSO during solvatochromic studies, highlighting their potential for probing local nucleic acid structure and dynamics. Additionally, we demonstrated the scalability of the synthesis protocol by producing one of the compounds on a gram scale, confirming its practical viability for large-scale production. This study underscores the potential of these fluorescent nucleoside analogues for various biochemical applications.

Rational design of 2H-chromene-based antiphytovirals that inhibit virion assembly by outcompeting virus capsid-RNA interactions

Although the determination of the structural basis of potato virus Y (PVY) coat protein (CP) provides the possibility for CP-based antiviral drug design, the role of many specific residues on CP in regulating virion pathogenicity is largely unknown, and fewer small-molecular drugs have been discovered to act on these potential sites. In this study, a series of derivatives of 2,2-dimethyl-2H-chromene are rationally designed by employing a molecular hybridization strategy. We screen a case of phytovirucide C50 that could form a stable H-bond with Ser125 of PVY CP to exert antiviral properties. Ser125 is further identified to be crucial for CP-viral RNA (vRNA) interaction, enabling PVY virion assembly. This interaction can be significantly inhibited through competitive binding with compound C50. The study enhances our understanding of anti-PVY drug mechanisms and provides a basis for developing new CP-targeting virus particle assembly inhibitors.

Synthesis, Anti-TMV Activities, and Action Mechanisms of a Novel Cytidine Peptide Compound

Cytidine has a broad range of applications in the pharmaceutical field as an intermediate of antitumor or antiviral agent. Here, a series of new cytidine peptide compounds were synthesized using cytidine and Boc group-protected amino acids and analyzed for their antiviral activities against tobacco mosaic virus (TMV). Among these compounds, the structure of an effective antiviral cytidine peptide SN11 was characterized by 1H NMR, 13C NMR, and high-resolution mass spectrometer. The compound SN11 has a molecular formula of C15H22N6O8 and is named 2-amino-N-(2- ((1- (3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl) -2-oxo-1,2-dihydropyrimidin-4-yl) amino) -2-oxyethyl) amino). The protection, inactivation, and curation activities of SN11 at a concentration of 500 μg/mL against TMV in Nicotiana glutinosa were 82.6%, 84.2%, and 72.8%, respectively. SN11 also effectively suppressed the systemic transportation of a recombinant TMV carrying GFP reporter gene (p35S-30B:GFP) in Nicotiana benthamiana by reducing viral accumulation to 71.3% in the upper uninoculated leaves and inhibited the systemic infection of TMV in Nicotiana tabacum plants. Furthermore, the results of RNA-seq showed that compound SN11 induced differential expression of genes involved in the biogenesis and function of ribosome, plant hormone signal transduction, plant pathogen interaction, and chromatin. These results validate the antiviral mechanisms of the cytidine peptide compound and provide a theoretical basis for their potential application in the management of plant virus diseases.

Ferulic Acid Dimers as Potential Antiviral Agents by Inhibiting TMV Self-Assembly

A series of ferulic acid dimers were designed, synthesized, and evaluated for anti-TMV activity. Biological assays demonstrated that compounds A6, E3, and E5 displayed excellent inactivating against tobacco mosaic virus (TMV) with EC50 values of 62.8, 94.4, and 85.2 μg mL-1, respectively, which were superior to that of ningnanmycin (108.1 μg mL-1). Microscale thermophoresis indicated that compounds A6, E3, and E5 showed strong binding capacity to TMV coat protein with binding affinity values of 1.862, 3.439, and 2.926 μM, respectively. Molecular docking and molecular dynamics simulation revealed that compound A6 could firmly bind to the TMV coat protein through hydrogen and hydrophobic bonds. Transmission electron microscopy and self-assembly experiments indicated that compound A6 obviously destroyed the integrity of the TMV particles and blocked the virus from infecting the host. This study revealed that A6 can be used as a promising leading structure for the development of antiviral agents by inhibiting TMV self-assembly.

Discovery of Pyrido[1,2-α] Pyrimidinone Mesoionic Compounds as Potential Control Agents Against Potato Virus Y

Potato virus Y (PVY) relies on aphids and tubers to spread in the field and causes serious economic losses in the potato industry. Here, we found that pyrido[1,2-α] pyrimidinone mesoionic compounds with insecticidal activity against aphids possessed a good inhibitory effect on PVY. Among them, compound 35 had the best inhibitory activity against PVY (EC50 = 104 μg/mL), even superior to that of ningnanmycin (125 μg/mL). The fluorescence and qPCR results confirmed that compound 35 could inhibit the proliferation of PVY in Nicotiana benthamiana. Preliminary experiments on the mechanism of action indicated that compound 35 had good binding affinity with the coat protein (CP), which plays an essential role in aphid-PVY interactions. Molecular docking revealed that compound 35 could bind to the pocket of CP formed by Ser52, Glu204, and Arg208. Compound 35 had substantially lower binding affinity (Kd) values with CPS52A (219 μM), CPE204A (231 μM), and CPR208A (189 μM) than those with CPWT (5.80 μM). A luciferase assay confirmed that mutating Ser52, Glu204, and Arg208 significantly affected the expression level of CP and further reduced virus proliferation. Therefore, the broad-spectrum activity of compound 35 provides a unique strategy for the prevention and treatment of PVY.

Recent Advances and Outlook of Benzopyran Derivatives in the Discovery of Agricultural Chemicals

Scaffold structures, new mechanisms of action, and targets present enormous challenges in the discovery of novel pesticides. The discovery of new scaffolds is the basis for the continuous development of modern agrochemicals. Identification of a good scaffold such as triazole, carbamate, methoxy acrylate, pyrazolamide, pyrido-pyrimidinone mesoionic, and bisamide often leads to the development of a new series of pesticides. In addition, pesticides with the same target, including the inhibitors of succinate dehydrogenase (SDH), oxysterol-binding-protein, and p-hydroxyphenyl pyruvate dioxygenase (HPPD), may have the same or similar scaffold structure. Recent years have witnessed significant progress in the discovery of new pesticides using natural products as scaffolds or bridges. In recent years, there have been increasing reports on the application of natural benzopyran compounds in the discovery of new pesticides, especially osthole and coumarin. A systematic and comprehensive review of benzopyran active compounds in the discovery of new agricultural chemicals is helpful to promote the discussion and development of benzopyran active compounds. Therefore, this work systematically reviewed the research and application of benzopyran derivatives in the discovery of agricultural chemicals, summarized the antiviral, herbicidal, antibacterial, fungicidal, insecticidal, nematicidal and acaricidal activities of benzopyran active compounds, and discussed the structural-activity relationship and mechanism of action. In addition, some active fragments were recommended to further optimize the chemical structure of benzopyran active compounds based on reference information.

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.

Tryptanthrin Derivative B1 Binds Viral Genome-Linked Protein (VPg) of Potato Virus Y

Potato virus Y (PVY) is a plant virus that is known to be responsible for substantial economic losses in agriculture. Within the PVY genome, viral genome-linked protein (VPg) plays a pivotal role in the viral translation process. In this study, VPg was used as a potential target for analyzing the antiviral activity of tryptanthrin derivatives. In vitro, the dissociation constants of B1 with PVY VPg were 0.69 μmol/L (measured by microscale thermophoresis) and 4.01 μmol/L (measured via isothermal titration calorimetry). B1 also strongly bound to VPg proteins from three other Potyviruses. Moreover, in vivo experiments demonstrated that B1 effectively suppressed the expression of the PVY gene. Molecular docking experiments revealed that B1 formed a hydrogen bond with N121 and that no specific binding occurred between B1 and the PVY VPgN121A mutant. Therefore, N121 is a key amino acid residue in PVY VPg involved in B1 binding. These results highlight the potential of PVY VPg as a potential target for the development of antiviral agents.

Synthesis of 4H-Pyrazolo[3,4-d]pyrimidin-4-one Hydrazine Derivatives as a Potential Inhibitor for the Self-Assembly of TMV Particles

Tobacco mosaic virus coat protein (TMV-CP), as a potential target for the development of antiviral agents, can assist in the long-distance movement of viruses and plays an extremely important role in virus replication and propagation. This work focuses on the synthesis and the action mechanism of novel 4H-pyrazolo[3,4-d] pyrimidin-4-one hydrazine derivatives. The synthesized compounds exhibited promising antiviral activity on TMV. Specifically, compound G2 exhibited high inactivating activity (93%) toward TMV, slightly better than commercial reagent NNM (90%). The action of mechanism was further explored by employed molecular docking, molecular dynamics simulation, microscale thermophoresis, qRT-PCR, and transmission electron microscopy. Results indicated that G2 had the capability to interact with amino acid residues such as Trp352, Tyr139, and Asn73 in the active pocket of TMV-CP, creating strong hydrophobic interactions and thus obstructing the virus's self-assembly.

Flavonol Derivatives Containing a Quinazolinone Moiety: Design, Synthesis, and Antiviral Activity

A series of flavonol derivatives containing quinazolinone were designed and synthesized, and their antiviral activities against tobacco mosaic virus (TMV) were evaluated. The results of the half maximal effective concentration (EC50 ) test against TMV showed that the EC50 value of curative activity of K5 was 139.6 μg/mL, which was better than that of the commercial drug ningnanmycin (NNM) 296.0 μg/mL, and the EC50 value of protective activity of K5 was 120.6 μg/mL, which was superior to that of NNM 207.0 μg/mL. The interaction of K5 with TMV coat protein (TMV-CP) was investigated using microscale thermophoresis (MST) and molecular docking and the results showed that K5 can combine with TMV-CP more strongly to TMV-CP than that NNM can. Furthermore, the assay measuring malondialdehyde (MDA) content indicated that K5 had the ability to improve the disease resistance of tobacco. Hence, this study offers strong evidence that flavonol derivatives have potential as novel antiviral agents.

Antiviral Activity of Ailanthone from Ailanthus altissima on the Rice Stripe Virus

Rice stripe disease caused by the rice stripe virus (RSV), which infects many Poaceae species in nature, is one of the most devastating plant viruses in rice that causes enormous losses in production. Ailanthone is one of the typical C20 quassinoids synthesized by the secondary metabolism of Ailanthus altissima, which has been proven to be a biologically active natural product with promising prospects and great potential for use as a lead structure for pesticide development. Based on the achievement of the systemic infection and replication of RSV in Nicotiana benthamiana plants and rice protoplasts, the antiviral properties of Ailanthone were investigated by determining its effects on viral-coding RNA gene expression using reverse transcription polymerase chain reaction, and Western blot analysis. Ailanthone exhibited a dose-dependent inhibitory effect on RSV NSvc3 expression in the assay in both virus-infected tobacco plants and rice protoplasts. Further efforts revealed a potent inhibitory effect of Ailanthone on the expression of seven RSV protein-encoding genes, among which NS3, NSvc3, NS4, and NSvc4 are the most affected genes. These facts promoted an extended and greater depth of understanding of the antiviral nature of Ailanthone against plant viruses, in addition to the limited knowledge of its anti-tobacco mosaic virus properties. Moreover, the leaf disc method introduced and developed in the study for the detection of the antiviral activity of Ailanthone facilitates an available and convenient screening method for anti-RSV natural products or synthetic chemicals.

Research Progress of Benzothiazole and Benzoxazole Derivatives in the Discovery of Agricultural Chemicals

Benzoxazole and benzothiazole have a broad spectrum of agricultural biological activities, such as antibacterial, antiviral, and herbicidal activities, which are important fused heterocyclic scaffold structures in agrochemical discovery. In recent years, great progress has been made in the research of benzoxazoles and benzothiazoles, especially in the development of herbicides and insecticides. With the widespread use of benzoxazoles and benzothiazoles, there may be more new products containing benzoxazoles and benzothiazoles in the future. We systematically reviewed the application of benzoxazoles and benzothiazoles in discovering new agrochemicals in the past two decades and summarized the antibacterial, fungicidal, antiviral, herbicidal, and insecticidal activities of the active compounds. We also discussed the structural-activity relationship and mechanism of the active compounds. This work aims to provide inspiration and ideas for the discovery of new agrochemicals based on benzoxazole and benzothiazole.

Piperazine Derivatives Containing the α-Ketoamide Moiety Discovered as Potential Anti-Tomato Spotted Wilt Virus Agents

A total of 35 piperazine derivatives were designed and synthesized, and their activities against tomato spotted wilt virus (TSWV) were evaluated systematically. Compounds 34 and 35 with significant anti-TSWV activity were obtained. Their EC₅₀ values were 62.4 and 59.9 μg/mL, prominently better than the control agents ningnanmycin (113.7 μg/mL) and ribavirin (591.1 μg/mL). To explore the mechanism of the interaction between these compounds and the virus, we demonstrated by agrobacterium-mediated, molecular docking, and microscale thermophoresis (MST) experimental methods that compounds 34 and 35 could inhibit the infection of TSWV by binding with the N protein to prevent the assembly of the virus core structure ribonucleoprotein (RNP), and it also meant that the arginine at 94 of the N protein was the key site of interaction between the compounds and the TSWV N target. Therefore, this study demonstrated the potential for forming antiviral agents from piperazine derivatives containing α-ketoamide moieties.

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 Bioactivity of Chalcone Derivatives Containing Indanone

A series of chalcone derivatives containing indanone were designed and synthesized by aldehyde-ketone condensation and etherification. The activity test demonstrated that the majority of the compounds had good therapeutic and protective activities against tobacco mosaic virus (TMV) at a concentration of 500 μg/mL when being tested. Among them, the target compounds N2 and N7 showed good therapeutic activities against TMV with EC₅₀ values of 70.7 and 89.9 μg/mL, respectively, which were better than that of ningnanmycin (158.3 μg/mL). N2 and N10 showed better protective activities against TMV with EC₅₀ values of 60.8 and 120.3 μg/mL, which were superior to that of ningnanmycin (175.6 μg/mL). A hydrogen bond interaction was observed between N2 and ARG-341 with a bond length of 3.08 Å and a hydrogen bond was observed between ningnanmycin and ASP-66 with a bond length of 3.72 Å. In contrast, the hydrogen bond length of compound N2 was shorter and its binding was closer. Meanwhile, when the heartleaf tobacco was being treated with N2, its increasing rate of malondialdehyde slowed and its content of defense enzymes significantly increased, again reflecting the good activity of N2 against TMV.

3-Hydroxy-2-oxindole Derivatives Containing Sulfonamide Motif: Synthesis, Antiviral Activity, and Modes of Action

3-Hydroxy-2-oxindole motif constitutes a core structure in numerous natural products and imparts notable biological activities. Here, we describe the design and synthesis of four series of novel 3-substituted-3-hydroxy-2-oxindole derivatives containing sulfonamide moiety along with their antiviral activities against potato virus Y (PVY). Compound 10b displayed optimal antiviral activity and superior anti-PVY activity compared with the lead compound and commercial Ningnanmycin in terms of curative and protective effects. Additionally, 10b considerably inhibited PVY systemic infection in Nicotiana benthamiana. Physiological and biochemical analyses revealed that the activities of the four crucial defense-related enzymes increased in the tobacco plant following treatment with 10b. RNA-sequencing analysis revealed that 10b substantially induced the upregulation of 38 differentially expressed genes, which were enriched in the photosynthesis pathway. These findings suggest that 10b is a promising antiviral agrochemical that can effectively control PVY infection and trigger plant host immunity to develop virus resistance. This study provides novel molecular entities and ideas for developing new pesticides.

Hydrazone modification of non-food natural product sclareolide as potential agents for plant disease

Plant diseases and their drug resistance pose a serious threat to agricultural production. One way to solve this problem is to discover new and efficient botanical pesticides. Herein, a series of novel hydrazide-hydrazone-containing sesquiterpenoid derivatives were synthesized by simply modifying the structure of the non-food natural product sclareolide. The biological activity results illustrated that compared to ningnanmycin (39.2 μg/mL), compound Z28 had the highest antiviral activity against tobacco mosaic virus (TMV), and the concentration for 50% of maximal effect (EC₅₀) of its inactivation activity was 38.7 μg/mL, followed by compound Z14 (40.6 μg/mL). Transmission electron microscopy (TEM) demonstrated that TMVs treated with compounds Z14 and Z28 were broken into rods of different lengths, and their external morphology was fragmented or even severely fragmented. Autodocking and molecular dynamics (MD) simulations indicated that compound Z28 had a strong affinity for tobacco mosaic virus coat protein (TMV-CP), with a higher binding energy of -8.25 kcal/mol compared to ningnanmycin (-6.79 kcal/mol). The preliminary mechanism revealed that compound Z28 can achieve an antiviral effect by targeting TMV-CP, rendering TMV unable to self-assemble and replicate, and might be a candidate for a novel plant antiviral agent. Furthermore, the curative and protective activities of compound Z22 (EC₅₀ = 16.1 μg/mL) against rice bacterial blight were 51.3% and 50.8%, respectively. Its control effect was better than that of bismerthiazol (BT) and thiadiazole copper (TC), compound Z22 that can be optimized as an active molecule.

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.

Antibacterial Activity of Aureonuclemycin Produced by Streptomyces aureus Strain SPRI-371

Actinomycetes play a vital role as one of the most important natural resources for both pharmaceutical and agricultural applications. The actinomycete strain SPRI-371, isolated from soil collected in Jiangsu province, China, was classified as Streptomyces aureus based on its morphological, physiological, biochemical and molecular biological characteristics. Its bacterial activity metabolites were identified as aureonuclemycin (ANM), belonging to adenosine derivatives with the molecular formula C16H19N5O9 for ANM A and C10H13N5O3 for ANM B. Simultaneously, the industrial fermentation process of a mutated S. aureus strain SPRI-371 was optimized in a 20 m3 fermentation tank, featuring a rotation speed of 170 rpm, a pressure of 0.05 MPa, an inoculum age of 36−40 h and a dissolved oxygen level maintained at 1−30% within 40−80 h and at >60% in the later period, resulting in an ANM yield of >3700 mg/L. In the industrial separation of fermentation broth, the sulfuric acid solution was selected to adjust pH and 4# resin was used for adsorption. Then, it was resolved with 20% ethanol solution and concentrated in a vacuum (60−65 °C), with excellent results. Antibacterial experiments showed that ANM was less active or inactive against Xanthomonas oryzae pv. oryzae, Xanthomonas citri subsp. citri and Xanthomonas oryzae pv. oryzicola and most bacteria, yeast and fungi in vitro. However, in vivo experiments showed that ANM exhibited extremely significant protective and therapeutic activity against diseases caused by X. oryzae pv. oryzae and X. oryzae pv. oryzicola in rice and X. citri in oranges and lemons. In field trials, ANM A 150 gai/ha + ANM B 75 gai/ha exhibited excellent therapeutic activity against rice bacterial leaf blight, citrus canker and rice bacterial leaf streak. Furthermore, as the dosage and production cost of ANM are lower than those of commercial drugs, it has good application prospects.

Plant Viral Coat Proteins as Biochemical Targets for Antiviral Compounds

Coat proteins (CPs) of RNA plant viruses play a pivotal role in virus particle assembly, vector transmission, host identification, RNA replication, and intracellular and intercellular movement. Numerous compounds targeting CPs have been designed, synthesized, and screened for their antiviral activities. This review is intended to fill a knowledge gap where a comprehensive summary is needed for antiviral agent discovery based on plant viral CPs. In this review, major achievements are summarized with emphasis on plant viral CPs as biochemical targets and action mechanisms of antiviral agents. This review hopefully provides new insights and references for the further development of new safe and effective antiviral pesticides.

First Discovery of Imidazo[1,2-a]pyridine Mesoionic Compounds Incorporating a Sulfonamide Moiety as Antiviral Agents

The applications of mesoionic compounds and their analogues as agents against plant viruses remain unexplored. This was the first evaluation of the antiviral activities of mesoionic compounds on this issue. Our study involved the design and synthesis of a series of novel imidazo[1,2-a]pyridine mesoionic compounds containing a sulfonamide moiety and the assessment of their antiviral activities against potato virus Y (PVY). Compound A33 was assessed on the basis of three-dimensional quantitative structure-activity relationship (3D-QSAR) model analysis and displayed good curative, protective, and inactivating activity effects against PVY at 500 mg/L, up to 51.0, 62.0, and 82.1%, respectively, which were higher than those of commercial ningnanmycin (NNM, at 47.2, 50.1, and 81.4%). Significantly, defensive enzyme activities and proteomics results showed that compound A33 could enhance the defense response by activating the activity of defense enzymes, inducing the glycolysis/gluconeogenesis pathway of tobacco to resist PVY infection. Therefore, our study indicates that compound A33 could be applied as a potential viral inhibitor.

Synthesis and Bioactivity of Novel Sulfonate Scaffold-Containing Pyrazolecarbamide Derivatives as Antifungal and Antiviral Agents

Novel pyrazolecarbamide derivatives bearing a sulfonate fragment were synthesized to identify potential antifungal and antiviral agents. All the structures of the key intermediates and target compounds were confirmed by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). The single-crystal X-ray diffraction of the compound T22 showed that pyrazole carbamide is a sulfonate. The in vitro antifungal activities of the target compounds against Colletotrichum camelliae, Pestalotiopsis theae, Gibberella zeae, and Rhizoctonia solani were evaluated at 50 μg/ml. Among the four pathogens, the target compounds exhibited the highest antifungal activity against Rhizoctonia solani. The compound T24 (EC₅₀ = 0.45 mg/L) had higher antifungal activity than the commercial fungicide hymexazol (EC₅₀ = 10.49 mg/L) against R. solani, almost similar to bixafen (EC₅₀ = 0.25 mg/L). Additionally, the target compounds exhibited protective effects in vivo against TMV. Thus, this study reveals that pyrazolecarbamide derivatives bearing a sulfonate fragment exhibit potential antifungal and antiviral activities.

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.

Discovery of Novel α-Aminophosphonates with Hydrazone as Potential Antiviral Agents Combined With Active Fragment and Molecular Docking

A series of novel α-aminophosphonate derivatives containing hydrazone were designed and synthesized based on active fragments. Bioassay results demonstrated that title compounds possessed good activities against tobacco mosaic virus. Among them, compounds 6a, 6g, 6i, and 6j were equivalent to the commercial antiviral agents like dufulin. On structure optimization-based molecular docking, compound 6k was synthesized and displayed excellent activity with values of 65.1% curative activity, 74.3% protective activity, and 94.3% inactivation activity, which were significantly superior to the commercial antiviral agents dufulin and ningnanmycin. Therefore, this study indicated that new lead compounds could be developed by adopting a joint strategy with active fragments and molecular docking.

Ferulic acid derivatives with piperazine moiety as potential antiviral agents

BACKGROUND

Plant virus diseases are difficult to control and severely threaten the productivity of crops, which leads to huge financial losses. To discover the new antiviral drugs, 34 novel ferulic acid derivatives with piperazine moiety were synthesized, and the antiviral activities were systematically screened as well.

RESULTS

Bioassay results indicated that most of the target compounds had outstanding antiviral activities against tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV) in vivo. In particular, compound E2 exhibited remarkable curative activities to TMV and CMV with EC₅₀ values of 189.0 and 401.7 μg/mL compared to those for ningnanmycin (387.0, 519.3 μg/mL) and ribavirin (542.1, 721.5 μg/mL). And then the mechanisms of compound E2 were studied by chlorophyll content, differentially expressed proteins and genes tests.

CONCLUSION

The excellent antiviral activity of compound E2 was closely associated with the increase in host photosynthesis, which was confirmed by chlorophyll content, differentially expressed proteins and genes assays. Compound E2 can be considered as a lead structure for the discovery of new antiviral agents. © 2022 Society of Chemical Industry.

Trifluoromethylpyridine thiourea derivatives: design, synthesis and inhibition of the self-assembly of tobacco mosaic virus particles

BACKGROUND

Devastating plant virus diseases leading to bad harvests and lower quality of crops have made feeding the beyond seven billion population a huge challenge. Nevertheless, growing resistance and cross resistance of crop protection agents have made this challenge harder. Therefore, an efficient crop protection agent with novel structure and mode of action showing higher efficiency and eco-friendly is urgently needed.

RESULTS

The coat protein (CP) of a virus is a potential target for the discovery of new antiviral agents. Antiviral molecules can inhibit infection by obstructing the assembly of virus particles. A series of novel phthalamide-like thiourea derivatives containing trifluoromethylpyridine was designed and synthesized. Most of the compounds exhibited good antiviral activity against tobacco mosaic virus (TMV). Compound 7b showed notable curative, protective and inactivation activities against TMV. Its inactivation half-maximal effective concentration (EC₅₀ ) value (20.5 μg mL^-1 ) was better even than commercial ningnanmycin (23.2 μg mL^-1 ). Compound 7b also had stronger TMV-CP binding ability than ningnanmycin and destroyed the external shape of TMV particles and hindered the self-assembly of TMV-CP and TMV-RNA.

CONCLUSION

These phthalamide-like thiourea derivatives especially compound 7b containing trifluoromethylpyridine are potential lead compounds and inhibitors of TMV particle self-assembly. © 2021 Society of Chemical Industry.

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.

Preparation and Anti-Tobacco Mosaic Virus Activities of Crocetin Diesters

The development of antiviral agents with an original structure and noticeable effect is always in great need. Natural products are important lead compounds in the development of new pesticides. Crocin-1 and crocin-2 were effectively isolated from Gardeniae fructus and found to have higher anti-tobacco mosaic virus (TMV) activity levels than ribavirin. A series of the crocetin diester derivatives were synthesized with separated crocetin-1 as material and evaluated for their anti-TMV activities. They could be dissolved in common organic solvents as dichloromethane, ethyl acetate, tetrahydrofuran, and methanol. Compounds 5, 9, 13, 14, and 15 displayed higher activities in vivo than ribavirin. Compound 14 with significantly higher antiviral activities than lead compounds (crocin-1 and crocin-2) emerged as a new antiviral candidate.

Design, Synthesis, Antibacterial Activity, Antiviral Activity, and Mechanism of Myricetin Derivatives Containing a Quinazolinone Moiety

Plant bacteria such as Xanthomonas axonopodis pv. citri (Xac), Pseudomonas syringae pv. actinidiae (Psa), Xanthomonas oryzae pv. oryzae (Xoo), and tobacco mosaic virus (TMV) have created huge obstacles to the global trade of food and economic crops. However, traditional chemical agents used to control these plant diseases have gradually become disadvantageous due to long-term irregular use. Therefore, finding new and efficient antibacterial and antiviral agents is becoming imperative. In this study, a series of myricetin derivatives containing a quinazolinone moiety were designed and synthesized, and the antibacterial and antiviral activities of these compounds were evaluated. The bioassay results showed that some target compounds exhibited good antibacterial activities in vitro and antiviral activities in vivo. Among them, the median effective concentration (EC50) value of compound L18 against Xac was 16.9 μg/mL, which was better than those of the control drugs bismerthiazol (BT) (62.2 μg/mL) and thiodiazole copper (TC) (97.5 μg/mL). Scanning electron microscopy (SEM) results confirmed that compound L18 inhibited the growth of Xac by affecting the morphology of cells. Microscale thermophoresis (MST) test results indicated that the dissociation constant (K d) value of compound L11 against TMV-CP was 0.012 μM, which was better than that of the control agent ningnanmycin (2.726 μM). This study reveals that myricetin derivatives containing a quinazolinone moiety are potential antibacterial and antiviral agents.