Chalcomycin B, a new macrolide antibiotic from the marine isolate Streptomyces sp B7064

In our screening of marine streptomycete isolates for bioactive components, a new macrolide antibiotic designated as chalcomycin B (1b) was isolated from the culture broth of a marine Streptomycete isolate B7064 together with chalcomycin (1a) as the active principles. The structure of the new antibiotic was determined by EI and ESI MS, H-1, C-13 and 2D NMR spectroscopy and by comparison of the NMR data with those of chalcomycin.