Capoamycin

A new antibiotic, dioxamycin (1) was isolated from the culture broth of the strain MH406-SF1, which was closely related to Streptomyces xantholiticus. This antibiotic was purified by countercurrent chromatography, column chromatography and preparative HPLC. The molecular formula of 1 was determined to be C38H40O15 by HRFAB-MS. The structure was determined by spectral analysis of 2D NMR; 1H-1H COSY, 13C-1H COSY, long range 13C-1H COSY (HMBC) and NOESY. The antibiotic is active in vitro against Gram-positive bacteria and some tumor cells. Dioxamycin is a benz[a]anthraquinone antibiotic related to capoamycin.

Capoamycin-type antibiotics (2-5) and polyene acids (6, 7) were isolated from marine Streptomyces fradiae strain PTZ0025. Their structures were established by extensive nuclear magnetic resonance (NMR) and high resolution electron spray ionization mass spectroscopy (HRESIMS) analyses and chemical degradation. Compounds 3, 4, 6, 7 were found to be new and named as fradimycins A (3) and B (4), and fradic acids A (6) and B (7). Compounds 3-5 showed in vitro antimicrobial activity against Staphylococcus aureus with a minimal inhibitory concentration (MIC) of 2.0 to 6.0 μg/mL. Interestingly, Compounds 3-5 also significantly inhibited cell growth of colon cancer and glioma with IC₅₀ values ranging from 0.13 to 6.46 μM. Fradimycin B (4), the most active compound, was further determined to arrest cell cycle and induce apoptosis in tumor cells. The results indicated that fradimycin B (4) arrested the cell cycle at the G₀/G₁ phase and induced apoptosis and necrosis in colon cancer and glioma cells. Taken together, the results demonstrated that the marine natural products 3-5, particularly fradimycin B (4), possessed potent antimicrobial and antitumor activities.