Further new milbemycin antibiotics from Streptomyces bingchenggensis. Fermentation, isolation, structural elucidation and biological activities.

Three new alpha-class milbemycins from Streptomyces bingchenggensis, named milbemycins alpha28, alpha29 and alpha30, have been isolated and characterized. On the basis of detailed spectroscopic analysis and comparison with reported data, their structures were determined to be the 22alpha-hydroxy, 23beta-O-(2-methylbutanoyl) milbemycin alpha9, 22alpha-hydroxy, 23beta-O-(2,4-dimethylpentanoyl) milbemycin alpha9 and 22alpha-hydroxy, 23beta-O-(2-methylbutanoyl) milbemycin A4, respectively. Milbemycins alpha28 and alpha29 are the first reported milbemycins that possess both C-26 and C-23 substituents. These three new milbemycins possess potent acaricidal and nematocidal activity.