Morpholine ring facilitates antiviral potency of Pyrazoline Acylhydrazone against <scp>TMV</scp> : design, synthesis, and mechanistic study

BACKGROUND: Plant virus causes severe yield losses in cash crops such as pepper and tomatoes, and efficient antiviral agents remain an urgent demand in agricultural pest control. RESULTS: Two series of pyrazoline acylhydrazone derivatives (A-1 ~ A-18 and morpholine-containing T-1 ~ T-27) were synthesized and evaluated for their anti-tobacco mosaic virus (TMV) activity. Promisingly, the introduction of a morpholine ring in the T-series increased curative activity by 10-78%, and protective activity by 6-72%. DFT calculations indicated that compound T-8, which contains a morpholine structure, exhibited significant spatial separation between its HOMO and LUMO distributions compared to morpholine-free compound A-13. This spatial separation favors the establishment of an intramolecular charge-transfer channel, thus enhancing electron transfer efficiency during target binding. T-19 demonstrated significantly curative and inactivation activities of 80.9 and 90.5%, respectively, which is superior or similar to that of commercialized Ningnanmycin (67.2 and 89.6%, respectively). The results of molecular docking, dynamic simulation, qRT-PCR, microscale thermophoresis and transmission electron microscope revealed that T-19 showed a strong affinity with TMV coat protein, resulting in a direct disruption of viral particles and inhibiting viral replication and systematic movement in host plant. CONCLUSION: T-series with morpholine ring led to a substantial enhancement in antiviral potency compared to A-series, and the discovery of T-19 provides an innovative design strategy for antiviral candidate. © 2026 Society of Chemical Industry.