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

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