Synthesis of novel 1,3-diphenylurea derivatives and their molluscicidal activity against Pomacea canaliculata

Pomacea canaliculata is a typical invasive alien species in southern China. Due to its strong adaptability and fecundity, it causes crop yield reduction and threatens food security. Therefore, the development of environmentally friendly molluscicides against P. canaliculata and the exploration of their action mechanisms are urgent needs for the prevention and control of invasive alien species at present. In this study, aniline and isocyanate derivatives were used as starting materials, and 10 novel 1,3-diphenylurea compounds (N-F-3a to N-F-3e and N-L-6a to N-L-6e) were synthesized via directed nucleophilic addition reaction between aniline and isocyanate derivatives. Their molluscicidal activity was evaluated by laboratory immersion toxicity tests; the changes in tissue morphology were observed by hematoxylin-eosin staining (H&E); and the action mechanisms were explored by multiple methods including enzyme activity assay and ligand-protein molecular docking. The results showed that compounds N-F-3a, N-F-3b, and N-L-6a to N-L-6c exhibited excellent molluscicidal activity against P. canaliculata, with a mortality rate > 79.2% at 10 mg/L. Among them, compound N-F-3a showed the best activity: the mortality rate of P. canaliculata reached 100% within 72 h at 5 mg/L; the survival rate of carp larvae was 83.3% after 72 h of exposure at 20 mg/L, indicating a safer profile than the commercial molluscicide niclosamide. The results of hematoxylin-eosin staining (H&E) indicated that compound N-F-3a could cause significant hepatopancreas damage to P. canaliculata, which was an important factor leading to the death of P. canaliculata. Molecular docking calculations revealed that compound N-F-3a bound to phosphofructokinase through multiple interactions including hydrogen bonds, hydrophobic interactions, and π-π stacking, with a binding energy of -8.40 kcal/mol, which was lower than that of N-F-3d (-8.04 kcal/mol). This result was consistent with the molluscicidal activity data, which assisted in verifying the molluscicidal mechanism of compound N-F-3a against P. canaliculata. In conclusion, compound N-F-3a exhibits excellent molluscicidal efficacy against P. canaliculata and good biosafety, and is thus represents a promising candidate for developing novel molluscicide for P. canaliculata control.