Nematicidal activity of pyrazine compounds against Meloidogyne incongnita, Burshaphelenchus xylophilus, and Aphelenchoides besseyi

Design, Synthesis, and Nematicidal Activity of Novel Amide Derivatives Containing an 1,2,4/1,3,4-Oxadiazole Moiety against Bursaphelenchus xylophilus

To discover novel structural nematicides, 79 amide compounds containing 1,2,4/1,3,4-oxadiazole moiety were designed, synthesized, and evaluated for nematicidal efficacy against second-stage juveniles of Bursaphelenchus xylophilus (B. xylophilus). Notably, some compounds exhibited superior nematicidal efficacy, for example, the LC50 values of compounds 11, 39, 40, 48, 49, 51, 52, and 54 were 7.4, 31.0, 35.3, 10.3, 12.7, 6.9, 21.5, and 52.2 mg/L, respectively, with nematicidal activities significantly surpassing that of tioxazafen (79.3 mg/L). Compound 51 exhibited multifaceted nematicidal activity through suppression of motility, feeding, and reproduction, combined with induction of oxidative stress. Compound 51 significantly reduced nematode protein content and impaired antioxidant capacity. Meanwhile, compound 51 demonstrates superior binding energy and interaction mode with succinate dehydrogenase (SDH), showing potent SDH inhibition (IC50 = 15.0 μmol/L). Therefore, compound 51, which may become a potential SDH inhibitor, interferes with nematode energy metabolism by inhibiting SDH activity, resulting in nematode death.

Discovery of Novel Amide Derivatives Containing an Oxazole/Isoxazole Moiety as Potential SDH Inhibitors: Design, Synthesis, and Nematicidal Activity

To develop new nematicides, amide derivatives with oxazole/isoxazole were synthesized via scaffold-hopping as succinate dehydrogenase (SDH) inhibitors. The nematicidal activities of these target compounds were tested against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus destructor. Some of the compounds showed excellent nematicidal activities. Compound B21 had LC50 values of 3.2 mg/L for B. xylophilus, 11.5 mg/L for A. besseyi, and 10.5 mg/L for D. destructor. Compound B21 exerted a pronounced inhibitory effect on feeding, reproduction, and embryonic development capabilities of B. xylophilus, while concurrently triggering deleterious oxidative stress responses within the nematodes. These reactions led to intestinal damage and eventually death of the nematodes. Compound B21 exhibited strong hydrophobic interactions with the residues Arg-76, Val-103, Pro-193, and Ile-242 of SDH. Additionally, B21 significantly inhibited the SDH of B. xylophilus, with an IC50 value of 6.5 μmol/L.