New nemadectin congeners with acaricidal and nematocidal activity from Streptomyces microflavus neau3 Y-3

Two nemadectin congeners 1 and 2 were isolated from the fermentation broth of a mutant strain (Y-3) of Streptomyces microflavus neau3. Their structures were determined on the basis of extensive spectroscopic analysis and comparison with data from the literature. Compound 2 possessed a 5-membered ring lactone that is unprecedented among known milbemycins and avermectins. Both compounds 1 and 2 exhibited potent acaricidal activity and nematocidal activity. Especially, compound 2 demonstrated impressive acaricidal activity against adult mites with an IC50 of 2.3 ± 0.9 μg/mL and mite eggs with an IC50 of 17.5 ± 2.1 μg/mL and nematocidal activity against Caenorhabditis elegans with an IC50 of 0.7 ± 0.2 μg/mL, which are higher than those of nemadectin and the known commercial acaricide and nematocide milbemycin A3/A4.