Inhibition of chitin synthesis by 5-benzoylamino-3-phenylisoxazoles with various substituents at two benzene rings and their larvicidal activity

<i>N</i>-(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 <i>Chilo suppressalis</i>. Larvicidal effects against <i>C. suppressalis</i> and <i>Spodoptera litura</i> were also examined, and the larvicidal activity in terms of the 50% lethal dose (LD₅₀) was determined for some compounds. Among IOXs with various substituents at the benzoyl moiety, 2,6-difluoro-substituted (2,6-F₂) benzoyl analogs showed the highest chitin synthesis activity. The larvicidal activities against <i>C. suppressalis</i> and <i>S. litura</i> were 1/138 and 1/35 that of diflubenzuron, a representative benzoylphenylurea-type insecticide, respectively. In a further study, 2,6-F₂ benzoyl analogs with various substituents at the phenyl moiety, such as Br, CF₃, CN, OEt, Ph, and alkyls (CH₃, Et, <i>i</i>-Pr, <i>n</i>-Bu, and <i>t</i>-Bu), were synthesized, and their chitin synthesis inhibition in the <i>Chilo</i> integument and their larvicidal activity against <i>S. litura</i> were quantitatively measured. The introduction of bulky CF₃ and <i>t</i>-Bu at the phenyl moiety of 2,6-F₂ benzoyl analog favorably enhanced the larvicidal activity against <i>S. litura.</i>