Studies on Novel 3(2H)-pyridazinone Derivatives with Juvenile Hormone-Like Activity

Abstract

In the course of studies on 3(2H)-pyridazinone derivatives, the authors found that some compounds substituted with phenyl group at 2-position showed distinct JH-like activity (metamorphosis-inhibiting activity) on the green rice leafhopper, Nephotettix cincticeps. Following elaborate investigations of structure-activity relationships among the related compounds, NC-170 [4-chloro-5-(6-chloro-3-pyridylmethoxy)-2-(3, 4-dichlorophenyl)-pyridazin-3(2H)-one] was discovered as the most potent candidate, which strongly inhibited the metamorphosis in leafhoppers and planthoppers, but not in any other insects at all. Further studies showed that the substituent at the 2-position on the pyridazinone ring played an important role on this strict selectivity and that the introduction of halogenated alkyl groups into the position drastically expanded the biological spectrum. NC-184 [4-chloro-2-(2-chloro-2-methylpropyl)-5-{(6-iodo-3-pyridyl)methoxy}-pyridazin-3(2H)-one], one of the most potent compounds among 2-halogenated alkyl derivatives, exhibited JH-like activity not only in hoppers but in various species over 11 orders. In the field trials against the brown planthopper, Nilaparvata lugens, a single treatment of NC-184 in late-July suppressed the population growth during summer and prevented the ‘hopper-burn’ in autumn. The results suggested that these novel JH mimics are promising agents for future hopper-control programs in paddy fields.