Synthesis, Antifungal, and Antibacterial Activities of Novel Benzoylurea Derivatives Containing a Pyrimidine Moiety

To explore more efficient and less toxic antibacterial and antifungal pesticides, we utilized 2,6-difluorobenzamide as a starting material and ultimately synthesized 23 novel benzoylurea derivatives containing a pyrimidine moiety. Their structures were characterized and confirmed by 1H NMR, 13C NMR, 19F NMR, and HRMS. The bioassay results demonstrated that some of the title compounds exhibited moderate to good in vitro antifungal activities against Botrytis cinerea in cucumber, Botrytis cinerea in tobacco, Botrytis cinerea in blueberry, Phomopsis sp., and Rhizoctonia solani. Notably, compounds 4j and 4l displayed EC50 values of 6.72 and 5.21 μg/mL against Rhizoctonia solani, respectively, which were comparable to that of hymexazol (6.11 μg/mL). Meanwhile, at 200 and 100 concentrations, the target compounds 4a-4w exhibited lower in vitro antibacterial activities against Xanthomonas oryzae pv. oryzicola and Xanthomonas citri subsp. citri, respectively, compared to those of thiodiazole copper. Furthermore, the molecular docking simulation demonstrated that compound 4l formed hydrogen bonds with SER-17 and SER-39 of succinate dehydrogenase (SDH), providing a possible explanation for the mechanism of action between the target compounds and SDH. This study represents the first report on the antifungal and antibacterial activities of novel benzoylurea derivatives containing a pyrimidine moiety.

Association of growth-regulating insecticides and limonoid-based formulations: physicochemical compatibility and toxicity against Spodoptera frugiperda (Lepidoptera: Noctuidae)

The objective of this study was to evaluate the physicochemical compatibility of mixtures of synthetic and botanical limonoid-based insecticides, as well as the toxicity of these associations, in the management of Spodoptera frugiperda (J.E. Smith) under laboratory and field conditions. For this, the associations of 4 commercial botanical insecticides based on neem registered in Brazil (Azamax, Agroneem, Azact CE, and Fitoneem) were tested with synthetic insecticides from the group of growth regulators (IGRs [triflumuron, lufenuron, methoxyfenozide and tebufenozide]). When mixed, all combinations caused a significant reduction in the pH of the mixture and a significant increase in electrical conductivity. However, all tested combinations showed similar stability behavior to the negative control (distilled water), which demonstrated their physicochemical compatibility. Furthermore, in laboratory and field bioassays, mixtures of IRGs with limonoid-based formulations provided satisfactory effects in the management of S. frugiperda. However, binary mixtures of insecticide Intrepid 240 SC with Azamax or Azact CE (at LC25 previously estimated) showed the highest toxicities on S. frugiperda larvae in laboratory bioassays and damage reduction caused by S. frugiperda in a 2-yr field experiments. Therefore, mixtures of IGRs with limonoid-based botanical insecticides are promising alternatives for the management of S. frugiperda and important component of integrated pest management and insect resistance management programs.

Design, synthesis, fungicidal property and QSAR studies of novel β-carbolines containing urea, benzoylthiourea and benzoylurea for the control of rice sheath blight

BACKGROUND

Rice sheath blight is a globally important rice disease. Unfortunately, this critical disease has not been effectively controlled, and the intensive and continuous use of the same fungicide might increase the risk of resistance development in the pathogen. To discover new active agents against rice sheath blight, in this study, three series of β-carboline urea, benzoylurea and benzoylthiourea derivatives were designed, synthesized and evaluated for in vitro and in vivo fungicidal activity against Rhizoctonia solani.

RESULTS

All these compounds (EC₅₀ : 0.131-1.227 mmol L^-1 ) exhibited better fungicidal activity than harmine itself (EC₅₀ : 2.453 mmol L^-1 ). Significantly, compound 17c (EC₅₀ : 0.131 mmol L^-1 ) displayed the best efficacy in vitro and superior fungicidal activity compared with validamycin A (EC₅₀ : 0.397 mmol L^-1 ). Moreover, the in vivo bioassay also indicated that compound 17c could be effective for the control of rice sheath blight.

CONCLUSION

Based on the bioassay result and quantitative structure-activity relationship (QSAR) information, structure modification in β-carboline warrants further investigation and its benzoylurea derivative 17c, which showed the best fungicidal activities, could emerge as a potential fungicide against rice sheath blight. © 2018 Society of Chemical Industry.

Benzoylurea resistance in western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae): the presence of a point mutation in chitin synthase 1

We examined the susceptibility of field strains (BO-1, BO-2, TO-1, and YH-1) and one laboratory strain (H-1) of the western flower thrip, Frankliniella occidentalis, to benzoylureas. LC₅₀ values of novaluron were determined as 0.64 ppm against laboratory strain and 2.1-130 ppm against field strains. In the presence of piperonyl butoxide, a cytochrome P450 inhibitor, the insecticidal activity of novaluron tended to be enhanced. To examine whether point mutations in chitin synthase 1 (CHS1) discovered in an etoxazole-resistant strain of Tetranychus urticae and a benzoylurea-resistant strain of Plutella xylostella exist in F. occidentalis, the nucleotide sequence of CHS1 was analyzed. We found a nonsynonymous substitution that corresponded to the location of the mutations found in T. urticae and P. xylostella in the field strains of F. occidentalis but not in the laboratory strain, indicating that this point mutation might be associated with the benzoylurea resistance exhibited by the field strains.

Review of the existing maximum residue levels for lufenuron according to Article 12 of Regulation (EC) No 396/2005

According to Article 12 of Regulation (EC) No 396/2005, EFSA has reviewed the maximum residue levels (MRLs) currently established at the European level for the pesticide active substance lufenuron. To assess the occurrence of lufenuron residues in plants, processed commodities, rotational crops and livestock, EFSA considered the conclusions derived in the framework of Directive 91/414/EEC, the MRLs established by the Codex Alimentarius Commission as well as the authorisations reported by the Member States (including the supporting residues data) and import tolerances. Based on the assessment of the available data, MRL proposals were derived and a consumer risk assessment was carried out. Although no apparent risk to consumers was identified, some information required by the regulatory framework was missing. Hence, the consumer risk assessment is considered indicative only and some MRL proposals derived by EFSA still require further consideration by risk managers.

Benzoylurea Chitin Synthesis Inhibitors

Benzoylurea chitin synthesis inhibitors are widely used in integrated pest management (IPM) and insecticide resistance management (IRM) programs due to their low toxicity to mammals and predatory insects. In the past decades, a large number of benzoylurea derivatives have been synthesized, and 15 benzoylurea chitin synthesis inhibitors have been commercialized. This review focuses on the history of commercial benzolyphenylureas (BPUs), synthetic methods, structure-activity relationships (SAR), action mechanism research, environmental behaviors, and ecotoxicology. Furthermore, their disadvantages of high risk to aquatic invertebrates and crustaceans are pointed out. Finally, we propose that the para-substituents at anilide of benzoylphenylureas should be the functional groups, and bipartite model BPU analogues are discussed in an attempt to provide new insight for future development of BPUs.

Chitin synthesis inhibitors: old molecules and new developments

Abstract  Chitin is the most abundant natural aminopolysaccharide and serves as a structural component of extracellular matrices. It is found in fungal septa, spores, and cell walls, and in arthropod cuticles and peritrophic matrices, squid pens, mollusk shells, nematode egg shells, and some protozoan cyst walls. As prokaryotes, plants and vertebrates including humans do not produce chitin, its synthesis is considered as an attractive target site for fungicides, insecticides, and acaricides. Although no chitin synthesis inhibitor has been developed into a therapeutic drug to treat fungal infections in humans, a larger number of compounds have been successfully launched worldwide to combat arthropod pests in agriculture and forestry. This review summarizes the latest advances on the mode of action of chitin synthesis inhibitors with a special focus on those molecules that act on a postcatalytic step of chitin synthesis.