Two new milbemycin metabolites, 13α-hydroxymilbemycin β13 (1) and 26-methyl-13α-hydroxymilbemycin β13 (2), were isolated from the fermentation broth of a genetically engineered strain Streptomyces avermitilis AVE-H39. Their structures were determined by the comprehensive spectroscopic data, including 1 D, 2 D NMR, MS spectral analysis and the comparison with data from the literature. Compounds 1 and 2 not only exhibited potent acaricidal activities against Tetranychus cinnabarinus, but also had nematocidal activity against Bursaphelenchus xylophilus.
Keywords: Genetically engineered strain; acaricidal activity; nematocidal activity; new milbemycins; structure elucidation.