Novel extracellular mycobactins, the carboxymycobactins from Mycobacterium avium

A series of novel extracellular siderophores, termed carboxymycobactins, have been isolated from M. avium as iron complexes and their structures determined. They are the first extracellular siderophores to be characterised from pathogenic mycobacteria and are analogous to their intracellular mycobactin counterparts, except that their R 1 alkyl sidechain is shorter and terminates in a carboxylic acid, resulting in much greater hydrophilicity and explaining their occurrence in the aqueous extracellular medium.