Siderophores with Two Citric Acid Units

Staphyloferrin A (Fig. 20, 65) is a second siderophore of Staphylococcus spp. (226). D-Omithine coimects the two citric acid parts. Due to the unsymmetrical link the central C-atoms of the citric acid units are chiral, but their stereochemistry has not been determined. Another consequence of the asymmetric structure is that two mono- and one di-dehydration products are observed. Staphyloferrin A forms a 1 1 Fe -to-ligand complex, which is preferentially A-configured. For steric considerations only cis-(SR ) or cis-(RS ) arrangements can be considered. Uptake experiments with Fe showed that it is a true siderophore (193). 

Legionella pneumophila produces a siderophore named legiobactin, which shows no catecholate or hydroxamate reactions (206). Enzymatic studies suggest a citrate structure in agreement with the data obtained by mass spectrometry (molecular mass ca. 350 Da) and NMR (three carbonyl and ten aliphatic C atoms). It is not clear yet as to whether legiobactin is essential for the iron acquisition in the aqueous habitat of the bacterium or during lung infection (2, 65). 

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