Novel Benzothiazole Derivatives as Potential Anti-Quorum Sensing Agents for Managing Plant Bacterial Diseases: Synthesis, Antibacterial Activity Assessment, and SAR Study.

As quorum sensing (QS) regulates bacterial pathogenicity, antiquorum sensing agents have powerful application potential for controlling bacterial infections and overcoming pesticide/drug resistance. Identifying anti-QS agents thus represents a promising approach in agrochemical development. In this study, the anti-QS potency of 53 newly prepared benzothiazole derivatives containing an isopropanolamine moiety was analyzed, and structure-activity relationships were examined. Compound D3 exhibited the strongest antibacterial activity, with an in vitro EC50 of 1.54 µg mL-1 against Xanthomonas oryzae pv oryzae (Xoo). Compound D3 suppressed QS-regulated virulence factors (e.g., biofilm, extracellular polysaccharides, extracellular enzymes, and flagella) to inhibit bacterial infection. In vivo anti-Xoo assays indicated good control efficiency (curative activity, 47.8%; protective activity, 48.7%) at 200 µg mL-1. Greater control efficiency was achieved with addition of 0.1% organic silicone or orange peel essential oil. The remarkable anti-QS potency of these benzothiazole derivatives could facilitate further novel bactericidal compound development.

Exploiting Natural Maltol for Synthesis of Novel Hydroxypyridone Derivatives as Promising Anti-Virulence Agents in Bactericides Discovery.

Anti-infection strategies based on suppression of bacterial virulence factors represent a crucial direction for the development of new antibacterial agents to address the resistance triggered by traditional drugs'/pesticides' bactericidal activity. To identify and obtain more effective and diverse molecules targeting virulence, we prepared a series of 3-hydroxy-2-methyl-1-pyridin-4-(1H)-one derivatives and evaluated their antibacterial behaviors. Compound B6 exhibited the highest bioactivity, with half-maximal effective concentration (EC50) values ranging fro9m 10.03 to 30.16 µg mL-1 against three plant pathogenic bacteria. The antibacterial mechanism showed that it could considerably reduce various virulence factors (such as extracellular enzymes, biofilm, and T3SS effectors) and inhibit the expression of virulence factor-related genes. In addition, the control efficiency of compound B6 against rice bacterial leaf blight at 200 µg mL-1 was 46.15-49.15%, and their control efficiency was improved by approximately 12% after the addition of pesticide additives. Thus, a new class of bactericidal candidates targeting bacterial virulence factors was developed for controlling plant bacterial diseases.

1,3,4-Oxadiazole Derivatives as Plant Activators for Controlling Plant Viral Diseases: Preparation and Assessment of the Effect of Auxiliaries.

Plant viral diseases cause the loss of millions of dollars to agriculture around the world annually. Therefore, the development of highly efficient, ultra-low-dosage agrochemicals is desirable for protecting the health of crops and ensuring food security. Herein, a series of 1,3,4-oxadiazole derivatives bearing an isopropanol amine moiety was prepared, and the inhibitory activity against tobacco mosaic virus (TMV) was assessed. Notably, compound A14 exhibited excellent anti-TMV protective activity with an EC50 value of 137.7 mg L-1, which was superior to that of ribavirin (590.0 mg L-1) and ningnanmycin (248.2 mg L-1). Moreover, the anti-TMV activity of some compounds could be further enhanced (by up to 5-30%) through supplementation with 0.1% auxiliaries. Biochemical assays suggested that compound A14 could suppress the biosynthesis of TMV and induce the plant's defense response. Given these merits, designed compounds had outstanding bioactivities and unusual action mechanisms and were promising candidates for controlling plant viral diseases.