Microbial conversion of milbemycins: oxidation of milbemycin A4 and related compounds at the C-25 ethyl group by Circinella umbellata and Absidia cylindrospora.

Microbial oxidation of milbemycin A4 at the C-25 ethyl group was performed. Milbemycin A4 was converted to 31- and 32-hydroxy derivatives by Circinella umbellata SANK 44272 along with 24- and 30-hydroxy derivatives. Related compounds, 5-ketomilbemycin A4 5-oxime and 13 beta-fluoromilbemycin A4 were similarly converted to the hydroxylated compounds by this microorganism. Absidia cylindrospora SANK 31472 converted milbemycin A4 to the corresponding 32-oic acid, 24-hydroxy derivative and a few oxygenated compounds including at the C-25 ethyl group.