Fradiamine A, a new siderophore from the deep-sea actinomycete Streptomyces fradiae MM456M-mF7.

New bioactive substances were identified from several marine actinomycetes strains by LC-HRESI-MS based non-targeted metabolomics. A new siderophore and its derivative, named fradiamines A and B, were isolated from the extract of the deep-sea actinomycetes Streptomyces fradiae MM456M-mF7 by Diaion CHP-20P, Sephadex LH-20 column chromatography and HPLC. Fradiamine A was a new compound, but fradiamine B was previously patented as a sweetness enhancer. Their structures were determined by NMR and LC-HRESI-MS/MS analysis. Fradiamines A and B contained two alkyl amines asymmetrically bonded to citrate, a type of structure derived from actinomycetes and other bacteria and rarely observed in siderophores. Fradiamines A and B showed moderate antibiotic activity against Clostridium difficile with IC50 values of 32 and 8 μg ml(-1), respectively.