Synthesis and nematicidal activity of natural nematicidal lead compound Waltherione A analogues

To find out the key pharmacores of Waltherione A which is a natural nematicidal lead alkaloid and simplify its structure, twelve Waltherione A analogues were synthesized from 2,3-dimethoxybenzaldehyde and 3,4-dimethoxybenzaldehyde through intramolecular Friedel-Crafts alkylation reaction, and connected with the bridge ring with different substituents. Among them, eight compounds have not been reported in the literature. The structures of all target compounds were confirmed by ¹H NMR,¹³C NMR and HRMS. The nematicidal activity of the target compounds against Meloidogyne incognita was determined by the immersion method. The results showed that the nematicidal activity of all the target compounds was lower than that of Waltherione A. The 72-h mortality of compound A-12 against the 2^nd instar larvae of M. incognita was 69.7% at 200 μg/mL, and the nematicidal activity of compound A-12 was higher in comparation with other compounds. The results showed that the aromatic substituents connected with bridge ring had a positive effect on the activity of the compound, which provides a direction for further structural optimization.