Siderophores catecholate units

The effective molarity measured for [Phen2]PAAcPEI may be compared with that for enterobactin, the strongest microbial siderophore, containing three catechol units connected by a spacer. The effective molarity of a catechol unit towards a Fe(m) ion bound to another catechol unit contained in enterobactin is estimated to be 3 x 104 m [37]. Enterobactin contains three catechol units, whereas the Cu(ii) binding site of [Phen2]-paAcPEI consists of only two phenanthrolines. Nevertheless, the effective molarity observed for [Phen2]PAAcPEI is extraordinary for a synthetic system. 

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). 

In this chapter, we wiU concentrate mainly on hydroxamate-based siderophores. However, the most representative example of the catechol-based siderophore family is entero-bactin , a highly Cs-symmetric molecule based on a trilactone ring system derived from three L-serine amino acids. The serine amino groups are extended with three catecholic acid units. Enterobactin binds iron(III) in an octahedral coordination of preferred A-cis configuration (see Figure 1 in Section n.C). 

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