Structural Optimization of the Natural Product: Discovery of Almazoles C-D and Their Derivatives as Novel Antiviral and Anti-phytopathogenic Fungus Agents

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.

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

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

Design, Synthesis, Structure-Activity Relationship, and Three-Dimensional Quantitative Structure-Activity Relationship of Fusarium Acid Derivatives and Analogues as Potential Fungicides

In research related to fungicides, the development of compounds from natural products with high antifungal activity has attracted considerable attention. Fusaric acid (FA), an alkaloid isolated from the metabolites of Fusarium oxysporum, is an important precursor for developing pharmacologically active herbicides. In our previous work, we reported that FA has a wide range of inhibitory activities against 14 plant pathogenic fungi. In particular, it exhibited excellent antifugal effects on Colletotrichum higginsianum (EC50 = 31.7 μg/mL). Herein, to explore the practical application in the agricultural field, the design and synthesis of three series of FA derivatives and their inhibitory activities against plant pathogenic fungi were examined. Results demonstrated that the optimized FA derivatives had excellent inhibitory activities against C. higginsianum, Helminthosporium (Harpophora maydis), and Pyricularia grisea. In particular, the inhibitory activities were considerably improved when the 5-butyl groups of FA were substituted. The EC50 of C. higginsianum and P. grisea was only 1.2 and 12.0 μg/mL when 5-butylalkyl groups were substituted with 5-([1,1'-biphenyl]-4-yl) and 5-phenyl, respectively. Moreover, the safety index of target compounds, which was obtained from the treatment index of medicines, on rice seeds was evaluated. Finally, 16 leading compounds (H4, H22-H24, H27, H29, H30-H34, H37, H45, H50, H52, and H53) were obtained; they had considerable potential for additional modification and optimization as agricultural fungicides. Moreover, three-dimensional quantitative structure-activity relationship models were developed for obtaining a systematic structure-activity relationship profile to explore the possibility of more potent FA derivatives as novel fungicides.

Sequential annulation and isomerisation reaction of 3-acylmethylidene oxindoles with Huisgen zwitterions and synthesis of 5-(3-oxindolyl)oxazoles

Herein, we report a facile synthesis of 5-(3-oxindolyl)oxazole derivatives via a sequential annulation and isomerisation reaction of 3-acylmethylidene oxindoles with in situ generated Huisgen zwitterions (HZs) from PPh3 and azodicarboxylates. This reaction exhibits good functional group tolerance with 30 examples of structurally diverse products prepared with moderate to good efficiencies (up to 88% yield), thus providing a generally applicable route to the biologically important 5-(3-indolyl)oxazole structural motifs. Key to the success of this sequential one-pot strategy is the utilization of DBU as a base to promote the isomerisation process of the corresponding intermediate annulation products.