Dufulin Intervenes the Viroplasmic Proteins as the Mechanism of Action against Southern Rice Black-Streaked Dwarf Virus

Effects of charged polystyrene microplastics on the bioavailability of dufulin in tomato plant

Microplastics (MPs) and pesticides commonly exist in the environment, yet the interactions between them and their subsequent impacts on plants remain poorly understood. Thus, this study aimed to investigate the impacts of differently charged polystyrene (PS) MPs, including PS-COO-, PS and PS-NH3+ MPs, on the fate of 14C-labelled new antiviral pesticide Dufulin (DFL) in a hydroponic tomato system. The results showed that MPs greatly reduced the growth of tomato plants, with suppression of 18.4-30.2%. Compared to the control group, PS-COO-, PS and PS-NH3+ MPs also reduced the bioaccumulation of DFL in whole tomato plants by 40.3%, 34.5%, and 26.1%, respectively. Furthermore, MPs influenced the translocation of DFL in plant tissues, and the values decreased at the rates of 38.7%, 26.5% and 15.7% for PS-COO-, PS and PS-NH3+, respectively. Interestingly, compared to the control group, PS-COO- exhibited a profound inhibitory effect on DFL concentrations in tomatoes, potentially resulting in a lower dietary risk in the hydroponic tomato system. This may be due to the strong adsorption between PS-COO- and DFL, and PS-COO- may also inhibit the growth of tomato plants. Overall, our study could provide valuable insights into the risk assessment of DFL in the presence of MPs in plant systems.

Discovery of phosphonate derivatives containing different substituted 1,2,3-triazole motif as promising tobacco mosaic virus (TMV) helicase inhibitors for controlling plant viral diseases

BACKGROUND

The discovery and identification of targets is of far-reaching significance for developing novel pesticide candidates and increasing the probability of success. To explore and identify highly effective tobacco mosaic virus (TMV) helicase-targeted lead structures, a series of novel phosphonate derivatives containing a 1,2,3-triazole motif were rationally engineered and their antiviral activity was assessed.

RESULTS

Bioassay results showed that the optimized B17 exhibited more potent curative activity (EC50  = 271.5 μg mL-1 ) against TMV in vivo, which was superior to that of commercial Ribavirin (EC50  = 689.3 μg mL-1 ). B17 presented a stronger binding capacity through binding analysis with helicase, affording a corresponding value of 12.7 μM. Enzyme activity assay showed B17 exhibited excellent inhibitory activity on TMV helicase (39.2% at 300 μM). Furthermore, molecular docking simulations demonstrated that B17 displayed strong hydrogen-bond interactions (2.1, 2.1, 2.2, and 3.2 Å) with Ala-33, Gly-10, Gly-8, and Glu-217 of TMV helicase. Encouragingly, transmission electron microscopy analysis revealed that B17 could remarkably disrupt surface morphology and inhibit TMV proliferation. Additionally, these compounds also displayed potential anti-CMV (cucumber mosaic virus) and antipathogens (Xanthomonas oryzae pv. oryzae and Xanthomonas axonopodis pv. citri) by expanding their applications in agriculture.

CONCLUSION

Current research demonstrated that B17 could be considered as a potential antiviral agent alternative though targeting TMV helicase. © 2023 Society of Chemical Industry.

A systematic review of southern rice black-streaked dwarf virus in the age of omics

Southern rice black-streaked dwarf virus (SRBSDV) is one of the most damaging rice viruses. The virus decreases rice quality and yield, and poses a serious threat to food security. From this perspective, this review performed a survey of published studies in recent years to understand the current status of SRBSDV and white-backed planthopper (WBPH, Sogatella furcifera) transmission processes in rice. Recent studies have shown that the interactions between viral virulence proteins and rice susceptibility factors shape the transmission of SRBSDV. Moreover, the transmission of SRBSDV is influenced by the interactions between viral virulence proteins and S. furcifera susceptibility factors. This review focused on the molecular mechanisms of key genes or proteins associated with SRBSDV infection in rice via the S. furcifera vector, and the host defense response mechanisms against viral infection. A sustainable control strategy using RNAi was summarized to address this pest. Finally, we also present a model for screening anti-SRBSDV inhibitors using viral proteins as targets. © 2023 Society of Chemical Industry.

Eukaryotic splicing machinery in the plant-virus battleground

Plant virual infections are mainly caused by plant-virus parasitism which affects ecological communities. Some viruses are highly pathogen specific that can infect only specific plants, while some can cause widespread harm, such as tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV). After a virus infects the host, undergoes a series of harmful effects, including the destruction of host cell membrane receptors, changes in cell membrane components, cell fusion, and the production of neoantigens on the cell surface. Therefore, competition between the host and the virus arises. The virus starts gaining control of critical cellular functions of the host cells and ultimately affects the fate of the targeted host plants. Among these critical cellular processes, alternative splicing (AS) is an essential posttranscriptional regulation process in RNA maturation, which amplify host protein diversity and manipulates transcript abundance in response to plant pathogens. AS is widespread in nearly all human genes and critical in regulating animal-virus interactions. In particular, an animal virus can hijack the host splicing machinery to re-organize its compartments for propagation. Changes in AS are known to cause human disease, and various AS events have been reported to regulate tissue specificity, development, tumour proliferation, and multi-functionality. However, the mechanisms underlying plant-virus interactions are poorly understood. Here, we summarize the current understanding of how viruses interact with their plant hosts compared with humans, analyze currently used and putative candidate agrochemicals to treat plant-viral infections, and finally discussed the potential research hotspots in the future. This article is categorized under: RNA Processing > Splicing Mechanisms RNA Processing > Splicing Regulation/Alternative Splicing.

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.

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.

Plant Protection against Viruses: An Integrated Review of Plant Immunity Agents

Plant viruses are an important class of pathogens that seriously affect plant growth and harm crop production. Viruses are simple in structure but complex in mutation and have thus always posed a continuous threat to agricultural development. Low resistance and eco-friendliness are important features of green pesticides. Plant immunity agents can enhance the resilience of the immune system by activating plants to regulate their metabolism. Therefore, plant immune agents are of great importance in pesticide science. In this paper, we review plant immunity agents, such as ningnanmycin, vanisulfane, dufulin, cytosinpeptidemycin, and oligosaccharins, and their antiviral molecular mechanisms and discuss the antiviral applications and development of plant immunity agents. Plant immunity agents can trigger defense responses and confer disease resistance to plants, and the development trends and application prospects of plant immunity agents in plant protection are analyzed in depth.

Myricetin Derivative Targets Cucumber Mosaic Virus 2b Protein to Achieve In Vivo Antiviral Activity in Plants

Cucumber mosaic virus (CMV) 2b protein plays a key role in the process of CMV infecting plants and symptom formation and is a potential molecular target for the control of this important plant virus. The exploitation of antiviral compounds is one of the strategies with the highest input: output ratio in plant protection. In this study, the CMV 2b recombinant protein was cloned, purified, and identified as the target protein by mass spectrometry. Subsequently, we carried out preliminary functional screening of the LP series of myricetin derivatives designed and synthesized in our laboratory and commercial antiviral compounds by microscale thermophoresis (MST), which showed that LP compounds LP4, LP11, LP13, and LP20 interacted well with CMV 2b, with dissociation constant (K_d) values of 1.39, 0.88, 1.52, and 1.77 μM, respectively. Among the commercially available antiviral compounds, ningnanmycin (NNM) was the most active, with a K_d value of 4.09 μM. Then, the strongest binding force to CMV 2b was identified to be from LP11 by isothermal titration calorimetry (ITC) experiments, with a K_d of 1.19 μM. Among the commercial compounds, NNM had the strongest binding force with CMV 2b, with a K_d of 4.62 μM. Through the screening of commercial compounds and LP series compounds by MST and ITC, LP11, NNM (positive control), LP16 (negative control), and the blank control group were selected to test the in vivo impact of LP11 on CMV. Specifically, the screened compounds were sprayed onto CMV-inoculated Nicotiana benthamiana plants to determine their impact on the regulation of CMV pathogenic gene expression, symptoms, and virus titer. The results showed that LP11 had a strong ability to inhibit CMV infection of tobacco at the transcriptional and translational levels. By mutating the CMV 2b protein, the 15th amino acid leucine and the 18th amino acid methionine at the N-terminal region were shown to be potential sites for binding to compound LP11. This finding provided a theoretical basis for screening and developing anti-CMV agents.

Dufulin enhances salt resistance of rice

Dufulin is a newly developed plant antiviral agent, which is widely used in the control of many viral crop diseases. Existing research mainly focuses on its antiviral effect, but research in relation to resistance to abiotic stress is unclear. This study was based on the treatment of rice with salt (NaCl), and exogenous application of Dufulin as a stress-resistant agent. The effect of Dufulin on salt stress of rice was revealed. There were 1997 differential genes detected, including 1449 up-regulated and 548 down-regulated. After the application of Dufulin to rice, when salt stress was applied, peroxidase activity was increased and superoxide dismutase activity was reduced; GO and KEGG analyses indicated that the stimulated genes are related to the stress resistance pathway, thus improving the ability of rice to resist salt stress. Quantitative real-time PCR analysis was used to verify the dynamic changes of growth- and stress-resistance-related genes, among which integral membrane protein DUF6 containing protein, OsHKT1;4 (Na⁺ transporter) and zinc-finger protein were verified to increase by more than three times, and OsIAA1 and OsIAA9 were verified as down-regulated. Measuring the length of root, stem and leaf, and OsIAA1 and OsIAA9 expression showed that Dufulin promoted rice growth. After that, Dufulin could enhance the salt resistance of rice by regulating the expression of integral membrane protein DUF6 containing protein, OsHKT1;4, zinc-finger protein and other related genes under salt stress. The results elucidated the mechanism of Dufulin action during salt stress in rice at the transcriptional level.

Discovery of Novel α-Methylene-γ-Butyrolactone Derivatives Containing Vanillin Moieties as Antiviral and Antifungal Agents

On the basis of the structure of nicotlactone A (L1), a series of novel α-methylene-γ-butyrolactone derivatives B1-B43 were designed and synthesized by structure simplification and active fragment replacement strategies, and their antiviral and antifungal activities were evaluated. The bioassay studies indicated that many target compounds possessed good to excellent antiviral activity against tobacco mosaic virus (TMV) and some of these compounds exhibited specific antifungal activities against Valsa mali and Fusarium graminearum. Compound B32 exhibited the best anti-TMV activity (inactivation effect, 88.9%; protection effect, 65.8%; curative effect, 52.8%) in vivo at 500 mg/L, which is significantly higher than that of commercial virucides ribavirin and ningnanmycin. The inhibition effect of compound B32 was also visualized by the inoculation test using green fluorescent protein (GFP)-labeled TMV. The preliminary antiviral mechanism of compound B32 was investigated. Transmission electron microscopy (TEM) showed that compound B32 could destroy the integrity of virus particles. Then, molecular docking and isothermal titration calorimetry (ITC) analysis further demonstrated that compound B32 exhibited a strong binding affinity to the TMV coat protein with a dissociation constant (K_d) of 3.06 μM, superior to ribavirin. Thus, we deduced that compound B32 may interfere with the self-assembly of TMV particles by binding TMV coat protein (CP). In addition, compound B28 showed good in vitro activity against F. graminearum with an inhibition rate of 90.9% at 50 mg/L, which was greater than that of fluxapyroxad (59.1%) but lower than that of the commercial fungicide carbendazim (96.8%). The present study provides support for the application of these α-methylene-γ-butyrolactone derivatives as novel antiviral and antifungal agents in crop protection.

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.

Crystal Structure of the Disease-Specific Protein of Rice Stripe Virus

The rice stripe virus (RSV) is responsible for devastating effects in East Asian rice-producing areas. The disease-specific protein (SP) level in rice plants determines the severity of RSV symptoms. Isothermal titration calorimetry (ITC) and bimolecular fluorescence complementation (BiFC) assays confirmed the interaction between an R3H domain-containing host factor, OsR3H3, and RSV SP in vitro and in vivo. This study determined the crystal structure of SP at 1.71 Å. It is a monomer with a clear shallow groove to accommodate host factors. Docking OsR3H3 into the groove generates an SP/OsR3H3 complex, which provides insights into the protein-binding mechanism of SP. Furthermore, SP's protein-binding properties and model-defined recognition residues were assessed using mutagenesis, ITC, and BiFC assays. This study revealed the structure and preliminary protein interaction mechanisms of RSV SP, shedding light on the molecular mechanism underlying the development of RSV infection symptoms.

Design, Synthesis, and Bioactivities of Phthalide and Coumarin Derivatives Based on the Biosynthesis and Structure Simplification of Gossypol

Because gossypol and hemigossypol show antiviral activity but are structurally complex, we designed and synthesized a series of structurally simpler phthalide and coumarin derivatives. The phthalide derivatives were synthesized by opening the naphthalene ring of hemigossypol, and the coumarin derivatives were synthesized by ring-opening reactions of the phthalide derivatives with the goal of investigating the effect of the lactone ring size on bioactivity. The bioassay results showed that the two series of target compounds possessed moderate to good activities against tobacco mosaic virus, One of the compounds showed in vivo inactivation, curative, and protection activities of 50 ± 1, 53 ± 3, and 48 ± 2% at 500 mg/L, values which are higher than those of gossypol (32 ± 1, 35 ± 1, 29 ± 1%, respectively) and comparable to those of hemigossypol (55 ± 1, 49 ± 1, and 48 ± 1%, respectively) and the commercial antiviral agent ningnanmycin (56 ± 2, 54 ± 1, 58 ± 1%) at the same dose. Thus, this compound is a promising candidate for the development of new anti-plant-virus agents. In addition, most of the synthesized compounds showed broad-spectrum activity when tested against 14 kinds of phytopathogenic fungi and showed selectivity against Sclerotinia sclerotiorum, Physalospora piricola, and Rhizoctonia cerealis. Moreover, some of the compounds exhibited activity against Plutella xylostella larvae; the two most active compounds exhibited larvicidal activities (LC₅₀) of 4.10 and 5.47 mg/L, respectively. Further studies showed that these compounds also exhibited insecticidal activities against Mythimna separata, Helicoverpa armigera, and Pyrausta nubilalis larvae.

Saponin Stabilization via Progressive Freeze Concentration and Sterilization Treatment

Saponin is a biopesticide used to suppress the growth of the golden apple snail population. This study aims to determine the stabilized conditions for saponin storage. The maceration process was used for saponin extraction, and for saponin concentration, progressive freeze concentration (PFC) was used. Afterwards, stability analysis was performed by storing the sample for 21 days in two conditions: Room temperature (26 °C) and cold room (10 °C). The samples kept in a cold room were sterilized samples that undergo thermal treatment by placing the sample in the water bath. The non-sterilized samples were kept in room temperature condition for 21 days. The results showed that saponin stored in the cold room (sterilized sample) has low degradation with higher concentration than those stored at room temperature in stability analysis with the highest saponin concentration (0.730 mg/mL) at a concentration temperature of −6 °C and concentration time of 15 min. The lowest saponin concentration obtained by saponin stored at room temperature (non-sterilized sample) is 0.025 mg/mL at a concentration temperature of −6 °C and concentration time of 10 min. Thus, the finding concluded that saponin is sensitive to temperature. Hence, the best storage condition to store saponin after thermal treatment is to keep it in a cold room at 10 °C.

Effects of Dufulin on Oxidative Stress and Metabolomic Profile of Tubifex

Dufulin is a highly effective antiviral pesticide used in plants. In this study, a seven-day experiment was conducted to evaluate the effects of Dufulin at five different concentrations (1 × 10⁻⁴, 1 × 10⁻³, 1 × 10⁻², 0.1, and 1 mg/L) on Tubifex. LC-MS-based metabolome analysis detected a total of 5356 features in positive and 9110 features in negative, of which 41 showed significant changes and were identified as differential metabolites. Four metabolic pathways were selected for further study. Detailed analysis revealed that Dufulin exposure affected the urea cycle of Tubifex, probably via argininosuccinate lyase (ASL) inhibition. It also affected the fatty acid metabolism, leading to changes in the concentration of free fatty acids in Tubifex. Furthermore, the changes in metabolites after exposure to Dufulin at 1 × 10⁻² mg/L were different from those at the other concentrations.

Research on the Interaction Mechanism Between α Mino-Phosphonate Derivative Q-R and Harpin-Binding Protein 1 in Tobacco (Nicotiana tabacum) Plants

Amino-phosphonate derivative R-diphenyl-1-(4-methylbenzothiazole-2-amino)-1-(thiphene-2-yl)-methylphosphonate (Q-R) has a high protective anti-tobacco mosaic virus (TMV) activity. However, the mechanism responsible for Q-R's effect on TMV infection is largely unknown. Here, we studied the expression levels of harpin-binding protein 1 (HrBP1) and pathogenesis-related protein-1a (PR-1a) in TMV-infected tobacco plants by using reverse transcription quantitative real-time PCR. Then, we verified the interactions between Q-R and the HrBP1 protein from Escherichia coli using isothermal titration calorimetry and studied the Q-R-associated assembly of HrBP1 using size-exclusion chromatography. The results showed that the expression levels of HrBP1 and PR-1a genes were significantly increased by Q-R at the transcriptional level in TMV-infected tobacco plants, and the E. coli-expressed HrBP1 protein was assembled into oligomers by Q-R via binding to HrBP1 with a dissociation constant of 1.19 μM. We, therefore, concluded that Q-R activated the HrBP1 and PR-1a genes and enhanced the ability of HrBP1 to assemble in tobacco plants.

Detection of Southern Rice Black-Streaked Dwarf Virus Using Western Blotting With P6

The southern rice black-streaked dwarf virus (SRBSDV) is a severe threat to the yield and quality of rice products worldwide. Traditional detection methods for diagnosing SRBSDV infection show several false positives and thus provide inaccurate findings. However, Western blotting (WB) can precisely solve this problem. In this study, P6—a viral RNA-silencing suppressor—was expressed and purified in vitro. Two polyclonal P6 antibodies were obtained and quantified by enzyme-linked immunosorbent assay and WB. Subsequently, WB was performed using the P6 antibodies to identify SRBSDV antigens derived from the suspected rice samples collected from nine districts in Guizhou, China. The assay results showed that Libo, Pingtang, Huishui, Dushan, and Anshun districts had experienced an SRBSDV outbreak. The virus content in the sampled rice tissues was quantified by WB. Our results revealed that SRBSDV mainly accumulated in rice stems rather than rice leaves. Thus, the findings of our study show that the SRBSDV P6 antibody can be used in WB for detecting and monitoring SRBSDV infection in infected rice plants.

Ribavirin targets sugar transporter 6 to suppress acquisition and transmission of rice stripe tenuivirus by its vector Laodelphax striatellus

BACKGROUND

Rice stripe tenuivirus (RSV) is one of the most destructive pathogens of rice and other cereal crops. The virus is transmitted by the small brown planthopper (SBPH, Laodelphax striatellus) in a circulative-propagative manner. Thus, blocking transmission by the insect vector would provide an effective strategy to prevent epidemic outbreaks of the disease.

RESULTS

In this study, we explored the effect of ribavirin on acquisition and transmission of the virus by specifically inhibiting the expression of sugar transporter 6 (LsSt-6), which was recently reported as a key vector component for RSV transmission. Ribavirin at the highest concentration tested (250 μmol L^-1 ) significantly reduced RSV acquisition and transmission efficiency by SBPHs through inhibiting LsSt-6 messenger RNA (mRNA) level. Survival of the model insect Spodoptera frugiperda cell line (Sf9) was 95.0 ± 2.2 and 85.6 ± 2.1% after exposure to 250 μmol L^-1 ribavirin or 8-azaguanine, respectively. Further study confirmed that 250 μmol L^-1 ribavirin also significantly reduced LsSt-6 mRNA and protein levels in Sf9 cells. However, 8-azaguanine did not significantly inhibit viral infectivity and LsSt-6 mRNA levels in SBPH or the Sf9 cell line.

CONCLUSION

This result provides evidence that ribavirin has the potential to disrupt LsSt-6 expression but not others like viral RNAs to prevent acquiring RSV, which leads to less viral accumulation in SBPH tissues and thereby lower transmission efficiency. © 2020 Society of Chemical Industry.

Review on Structures of Pesticide Targets

Molecular targets play important roles in agrochemical discovery. Numerous pesticides target the key proteins in pathogens, insect, or plants. Investigating ligand-binding pockets and/or active sites in the proteins' structures is usually the first step in designing new green pesticides. Thus, molecular target structures are extremely important for the discovery and development of such pesticides. In this manuscript, we present a review of the molecular target structures, including those of antiviral, fungicidal, bactericidal, insecticidal, herbicidal, and plant growth-regulator targets, currently used in agrochemical research. The data will be helpful in pesticide design and the discovery of new green pesticides.

Discovery of novel indole derivatives containing dithioacetal as potential antiviral agents for plants

Thirty unreported indole derivatives containing dithioacetal moiety were synthesized and evaluated for anti-plant viral activity. Bioassay results displayed that some of the target compounds showed better activities against tobacco mosaic virus (TMV) than the commercial Ribavirin in vivo. In particular, anti-TMV curative, protective and inactivating activity of 4p were 55.1, 57.2, and 80.3%, respectively, and EC₅₀ value for inactivating activity was 88.5 μg/mL. The observation of transmission electron microscope showed that 4p may have a certain destructive effect on TMV particles. To further study, microscale thermophoresis analysis result also demonstrated that 4p powerfully interacted with TMV coat protein in vitro. Hence, this study provides a strong evidence suporting that indole derivatives might be applied as new antiviral agents.

Synthesis of Four Optical Isomers of Antiviral Agent NK0209 and Determination of Their Configurations and Activities against a Plant Virus

Previously, we reported for the first time that harmala alkaloids harmine and tetrahydroharmine exhibit activity against plant viruses, and we developed an analogue, designated NK0209, that efficiently prevents and controls plant virus diseases. Here, to investigate the influence of the spatial configuration of NK0209 on its antiviral activities, we synthesized its four optical isomers, determined their configurations, and evaluated their activities against tobacco mosaic virus. All four isomers were significantly more active than ningnanmycin, which is one of the most successful commercial antiviral agents, with in vivo inactivation, cure, and protection rates of 57.3 ± 1.9, 54.2 ± 3.3, and 55.0 ± 4.1% at 500 μg/mL. Furthermore, analysis of structure-activity relationships demonstrated for the first time that the spatial conformation of NK0209 is an important determinant of its antiviral activity, and our results provide information about the possible optimum configuration for interaction of this molecule with its target protein.