Two New Aromatic Milbemycin Metabolites With Unusual Epoxide Moiety From Mutant Streptomyces bingchenggensis HU176.

Two new aromatic milbemycin metabolites with unusual epoxide moiety, milbemycin A5 (1) and 9-O-methylmilbemycin A5 (2), were isolated from the fermentation broth of mutant Streptomyces bingchenggensis HU176. Their structures were established by extensive spectroscopic analysis including 1D and 2D NMR, HRESIMS data, literature data comparison and NMR calculations. Bioassay test showed that these two new milbemycin metabolites exhibited moderate cytotoxic activity against tumor cell lines HepG2 and HCT116.