Siderophores with 2-Oxoglutaric Acid Units

N-Alkylated 2-oxoglutaric acid derivatives cyclize at neutral pH values to two epimeric 5-carboxy-5-hydroxy-2-oxopyrolidine structures (Chart 4). In this way, ot-hydroxycarboxylic acid groupings are formed that can act as ligand sites for Fe .  

Staphyloferrin B (59, Fig. 17) is produced together with staphyloferrin A (see below Sect. 4.4) by Staphylococcus hyicus and other staphylococci 94, 131), by Ralstonia eutropha 250) (= Cupriavidus metallidurans 90a)). Comparison of its CD spectrum with those of model compounds suggests the (S)-configuration of the central citric acid C-atom. Mass spectral investigations show a 1 1 Fe V to-ligand ratio, and NMR studies of the Ga complex confirm the participation of the two ot-hydroxy- and of the a-amino acid functions in complex formation. Uptake studies with Fe showed that staphyloferrin B acts as a siderophore, but it is less efficient than staphyloferrin A. 

Achromobactin (60, Fig. 18) is produced by Erwinia chrysanthemi in addition to chrysobactin (see above under the catecholate siderophores, Sect. 2.7). It has two chiral centers, a L-Dab unit and the central citric acid C-atom (not determined) (249). Recently, achromobactin was also found to be produced by Pseudomonas syringae (30b), a very versatile bacterial species (see pyoverdin, Sect. 2.1, and yersiniabactin. Sect. 5). 

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