Abstract
N-(3-Phenylisoxazol-5-yl)benzamides (5-benzoylamino-3-phenylisoxazoles: IOXs) with various substituents at two benzene rings were synthesized, and the chitin synthesis inhibition was measured in the cultured integumentary system of Chilo suppressalis. Larvicidal effects against C. suppressalis and Spodoptera litura were also examined, and the larvicidal activity in terms of the 50% lethal dose (LD(50)) was determined for some compounds. Among IOXs with various substituents at the benzoyl moiety, 2,6-difluoro-substituted (2,6-F(2)) benzoyl analogs showed the highest chitin synthesis activity. The larvicidal activities against C. suppressalis and S. litura were 1/138 and 1/35 that of diflubenzuron, a representative benzoylphenylurea-type insecticide, respectively. In a further study, 2,6-F(2) benzoyl analogs with various substituents at the phenyl moiety, such as Br, CF(3), CN, OEt, Ph, and alkyls (CH(3), Et, i-Pr, n-Bu, and t-Bu), were synthesized, and their chitin synthesis inhibition in the Chilo integument and their larvicidal activity against S. litura were quantitatively measured. The introduction of bulky CF(3) and t-Bu at the phenyl moiety of 2,6-F(2) benzoyl analog favorably enhanced the larvicidal activity against S. litura.