Synthesis of 24a-Substituted Milbemycin A 4 Derivatives and Their Acaricidal Activity against Tetranychus uvticae

A series of 24a-substituted milbemycin A derivatives were synthesized from 24a-hydroxymilbemycin A , which had been obtained by the microbial oxidation of milbemycin A . The acaricidal activity of each synthesized derivative against Tetranychus urticae was tested and some of the derivatives showed higher activity than parent milbemycin A . Among them, 24a-methylmilbemycin A (22) was the most active derivative, with 100% mortality of the mite at a concentration of 1 ppm and 50% mortality at a concentration of 0.1 ppm.