Synthesis of Novel 25-Substituted Milbemycin A₄ Derivatives and Their Acaricidal Activity against Tetranychus urticae

Abstract

Novel 25-substituted milbemycin A₄ derivatives were synthesized from 25a-hydroxymilbemycin A₄ and 25b-hydroxymilbemycin A₄, which had been obtained by the microbial oxidation of milbemycin A₄. The acaricidal activity of each synthesized derivative was tested against Tetranychus urticae, and all of the synthesized derivatives showed higher activity than parent milbemycin A₄. Some of the derivatives had higher acaricidal activity than milbemycin D, which had higher acaricidal activity than milbemycin A₄. Among them, 25b-methylmilbemycin A₄ was the most active derivative, with 100% mortality of the mite at a concentration of 1 ppm, and 63% mortality at 0.1 ppm.