Design, synthesis, and insecticidal/acaricidal evaluation of novel pyrimidinamine derivatives containing phenyloxazole moiety

1,2,4-Oxadiazole as a potential scaffold in agrochemistry: a review

N,O-containing heterocycles have been incorporated into various approved pesticides and pesticide candidates. The persistent challenge in contemporary crop protection lies in the continuous pursuit of novel N,O-heterocycle-containing compounds with pesticidal properties. Among them, the 1,2,4-oxadiazole scaffold is one of the most extensively explored heterocycles in new pesticide discovery and development. This review focuses on elucidating the molecular design strategy employed along with highlighting the bioactivity of 1,2,4-oxadiazole derivatives since 2012. Throughout this time frame, tioxazafen and flufenoxadiazam have emerged as prominent examples in which 1,2,4-oxadiazole derivatives were utilized as the core active structure within numerous applications. Additionally, the preparation methods for substituted 1,2,4-oxadiazole derivatives are elaborated upon, and their potential value within agrochemistry is discussed.

Discovery of HNPC-A9229: A Novel Pyridin-2-yloxy-Based Pyrimidin-4-amine Fungicide

To search for novel pesticides, the synthesis around commercialized insecticide tebufenpyrad accidentally led us to the discovery of the fungicidal lead compound, 3-ethyl-1-methyl-N-((2-phenylthiazol-4-yl)methyl)-1H-pyrazole-5-carboxamide (1a) and its pyrimidin-4-amine-based optimization derivative 5-chloro-2,6-dimethyl-N-(1-(2-(p-tolyl)thiazol-4-yl)ethyl)pyrimidin-4-amine (2a). Compound 2a not only demonstrates fungicidal activity superior to commercial fungicides such as diflumetorim but also exhibits the good features that come with pyrimidin-4-amines, such as unique modes of action and no cross-resistance to other pesticide classes. However, 2a is highly toxic to rats. Further optimization of 2a by introducing pyridin-2-yloxy substructure finally led to the discovery of 5b5-6 (HNPC-A9229) (5-chloro-N-(1-((3-chloropyridin-2-yl)oxy)propan-2-yl)-6-(difluoromethyl)pyrimidin-4-amine). HNPC-A9229 exhibits excellent fungicidal activities with EC₅₀ values of 0.16 mg/L against Puccinia sorghi and 1.14 mg/L against Erysiphe graminis, respectively. Not only that its fungicidal potency is significantly superior to or comparable to commercial fungicides including diflumetorim, tebuconazole, flusilazole, and isopyrazam, HNPC-A9229 possesses low toxicity to rats.

Room-Temperature Dialkylamination of Chloroheteroarenes Using a Cu(II)/PTABS Catalytic System

The dimethylamino functionality has significant importance in industrially relevant molecules and methodologies to install these efficiently are highly desirable. We report herein a highly efficient, room-temperature dimethylamination of chloroheteroarenes performed via the in-situ generation of dimethylamine using N,N-dimethylformamide (DMF) as precursor wiith a large substrate scope that includes various heteroarenes, purines as well as commercially relevant drugs such as altretamine, ampyzine and puromycin precursor.

Design, Synthesis, and Bioactivities of Novel Trifluoromethyl Pyrimidine Derivatives Bearing an Amide Moiety

Twenty-three novel trifluoromethyl pyrimidine derivatives containing an amide moiety were designed and synthesized through four-step reactions and evaluated for their antifungal, insecticidal, and anticancer properties. Bioassay results indicated that some of the title compounds exhibited good in vitro antifungal activities against Botryosphaeria dothidea (B. dothidea), Phompsis sp., Botrytis cinereal (B. cinerea), Colletotrichum gloeosporioides (C. gloeosporioides), Pyricutaria oryzae (P. oryzae), and Sclerotinia sclerotiorum (S. sclerotiorum) at 50 μg/ml. Meanwhile, the synthesized compounds showed moderate insecticidal activities against Mythimna separata (M. separata) and Spdoptera frugiperda (S. frugiperda) at 500 μg/ml, which were lower than those of chlorantraniliprole. In addition, the synthesized compounds indicated certain anticancer activities against PC3, K562, Hela, and A549 at 5 μg/ml, which were lower than those of doxorubicin. Notably, this work is the first report on the antifungal, insecticidal, and anticancer activities of trifluoromethyl pyrimidine derivatives bearing an amide moiety.

Synthesis and Antifungal and Insecticidal Activities of Novel N-Phenylbenzamide Derivatives Bearing a Trifluoromethylpyrimidine Moiety

Seventeen novel N-phenylbenzamide derivatives bearing a trifluoromethylpyrimidine moiety were synthesized via four-step reactions. Their antifungal and insecticidal properties were evaluated. Antifungal test results demonstrated that some of the synthesized compounds showed better in vitro bioactivities against Phomopsis sp., Botryosphaeria dothidea (B. dothidea), and Botrytis cinerea (B. cinerea) at 50 μg/mL than pyrimethanil. Unfortunately, the synthesized compounds revealed lower insecticidal activities against Spodoptera frugiperda (S. frugiperda) and Mythimna separata (M. separata) at 500 μg/mL than chlorantraniliprole.

Design, Synthesis, and Pesticidal Activities of Pyrimidin-4-amine Derivatives Bearing a 5-(Trifluoromethyl)-1,2,4-oxadiazole Moiety

It is important to discover new pesticides with new modes of action because of the increasing evolution of pesticide resistance. In this study, a series of novel pyrimidin-4-amine derivatives containing a 5-(trifluoromethyl)-1,2,4-oxadiazole moiety were designed and synthesized. Their structures were confirmed by ¹H NMR, ¹³C NMR, and HRMS. Bioassays indicated that the 29 compounds synthesized possessed excellent insecticidal activity against Mythimna separata, Aphis medicagini, and Tetranychus cinnabarinus and fungicidal activity against Pseudoperonospora cubensis. Among these pyrimidin-4-amine compounds, 5-chloro-N-(2-fluoro-4-(5-(trifluoromethyl)-1,2,4-oxadiazol-3-yl)benzyl)-6-(1-fluoroethyl)pyrimidin-4-amine (U7) and 5-bromo-N-(2-fluoro-4-(5-(trifluoromethyl)-1,2,4-oxadiazol-3-yl)benzyl)-6-(1-fluoroethyl) pyrimidin-4-amine(U8) had broad-spectrum insecticidal and fungicidal activity. The LC₅₀ values were 3.57 ± 0.42, 4.22 ± 0.47, and 3.14 ± 0.73 mg/L for U7, U8, and flufenerim against M. separata, respectively. The EC₅₀ values were 24.94 ± 2.13, 30.79 ± 2.21, and 3.18 ± 0.21 mg/L for U7, U8, and azoxystrobin against P. cubensis, respectively. The AChE enzymatic activity testing revealed that the enzyme activities of compounds U7, U8, and flufenerim are 0.215, 0.184, and 0.184 U/mg prot, respectively. The molecular docking results of compounds U7, U8, and flufenerim with the AChE model demonstrated the opposite docking mode between compound U7 or U8 and positive control flufenerim in the active site of AChE. The structure-activity relationships are also discussed. This work provided excellent pesticide for further optimization. Density functional theory analysis can potentially be used to design more active compounds.

Design, Synthesis, and Structure-Activity Relationship of Novel Spiropyrimidinamines as Fungicides against Pseudoperonospora cubensis

Harmful fungus and the developed resistance to available fungicides seriously threaten the yield and quality of crops; thus, the search for new, highly efficient, and resistance-overcoming fungicides remains a quite urgent goal of agricultural scientists. In this study, a series of novel spiropyrimidinamine derivatives were designed and synthesized by employing the intermediate derivatization method (IDM). Their structures were identified by ¹H NMR, elemental analyses, and MS spectra. The structure of compound 5 was further confirmed by X-ray diffraction. Bioassays indicated that a number of the title compounds exhibited some fungicidal activities against Pseudoperonospora cubensis. Especially, compound 5 displayed excellent activity (EC₅₀ = 0.422 mg/L), significantly higher than those of the commercialized fungicides cyazofamid, flumorph, and diflumetorim. The structure-activity relationship was also discussed. It was concluded that compound 5 with super fungicidal potency and a novel structure is a promising agrochemical fungicide candidate for further development.