Desferrioxamine-B

Iron uptake by bacteria at sites of lateral root emergence has been further confirmed using another technique employing 7-nitrobenz-2-oxa-l,3-diazole-desferrioxamine B, which is a derivitized siderophore that becomes fluorescent after it is deferrated (78). In this case, iron uptake from the siderophore ferrox-amine B was a.ssociated primarily with microbially colonized roots, but both plant and iron uptake from this chelate occurred in the regions just behind the root tips. 

V. Solinas, S. Deiana, C. Gessa, C. Pistidda, and R. Rausa, Reduction of the Felll-desferrioxamine-B complexes by caffeic acid a reduction mechanism of biochemical significance. Soil. Biol. Biochem. 275 649 (1996). 

Figure 11.1 Representative secondary metabolites produced by Streptomyces ceolicolor and other microorganisms, including aromatic polyketides actinorhodin and tetrohydroxynaphthalene (a), side-rophore desferrioxamines (b), polyunsaturated fatty acid eicosapentaenoic acid (c) and terpenoids beta-...

Another factor that relates complex stability and siderophore architecture is the chelate effect. The chelate effect is represented by an increase in complex stability for a multidentate ligand when compared to complexes with homologous donor atoms of lower denticity. The effect can be observed when comparing the stability of complexes of mono-hydroxamate ligands to their tris-hydroxamate analogs, such as ferrichrome (6) or desferrioxamine B (4). However, the increase in stability alone is not sufficient to explain the preponderance of hexadentate siderophores over tetradentate or bidentate siderophores in nature, and the chelate effect is not observed to a great extent in some siderophore structures (10,22,50,51). 

Matsumoto et al. demonstrated that the removal of iron from diferric transferrin by the tris-hydroxamate siderophore mimic TAGE occurs in two discreet steps (90). The slower step corresponds to iron removal from the more stable C-lobe site on transferrin and the faster step to removal from the N-lobe. The rates of removal are similar to the rates of removal of iron from diferric transferrin by desferrioxamine B (4), signifying similar mechanisms of removal between the two systems (90). 

The exchange of iron from transferrin to desferrioxamine B (4), some catecholate siderophores, and some hydroxypyridinone-based siderophore mimics has been investigated (139,189,190). Turcot et al. found that at concentrations similar to those that would be observed in biological settings or clinical treatments,... 

Figure 5.7. Example of a chelate (EDTA) and a siderosphore (desferrioxamine B).

Unlike desferrioxamine analogs designed for specific therapeutic purposes described above, chiral DFO analogs that form conformationally unique complexes with iron(lll) were designed to serve as chemical probes of microbial iron(lll) uptake processes. As mentioned above, ferrioxamine B can form a total of five isomers when binding trivalent metal ions, each as a racemic mixture. Muller and Raymond studied three separate, kinetically inert chromium complexes of desferrioxamine B (N-cis,cis, C-cis,cis and trans isomers), which showed the same inhibition of Fe-ferrioxamine B uptake by Streptomyces pilosus. This result may indicate either that (i) ferrioxamine B receptor in this microorganism does not discriminate between geometrical isomers, or that (ii) ferrioxamine B complexes are conformationally poorly defined and are not optimal to serve as probes. 

The high efficiency and selectivity of the natural siderophores in binding iron(lll) inspired attempts to develop siderophore analogs with improved iron-scavenging properties amenable for chelation therapy. A most pertinent example is desferrioxamine B (DFO), where low patient compliance generates the need for developing oral means of administration for... 

There is a considerable difference in the antimalarial action of desferrioxamine B (DFO) and the hydrophobic chelators based on ferrichrome analogs. While the former is limited to mature forms in the life cycle of P. falciparum (trophozoites and schizonts), the latter effects to a greater extent early developing stages (ring). Therefore, studies explored... 

Cerpa, A. Garcia-Gonzalez, M.T. Tartaj, P. Re-quena, J. Garcell, L. Serna, C.J. (1999) Mineral-content and particle-size effects on the colloidal properties of concentrated lateri-tic suspensions. Clays Clay Min. 47 515-521 Cervini-Silva, J. Sposito, G. (2002) Steady-state dissolution kinetics of aluminum-goethite in the presence of desferrioxamine-B and oxalate. Environ. Sci. Technol. 36 337-342 Cesco, S. Rdmheld.V. Varanini, Z. Pinton,... 

Chromium(III) complexes of a number of polyhydroxamic acids, microbial iron sequestering and transport agents (siderochromes) have been reported.797,798 The kinetic inertness of the chromium(III) complexes allows the facile separation of isomers for the model complex tris(iV-methyl-( - )-methoxyacetylhydroxamato)chromium(III), D-cis, L-cis and the l/d-trans isomers have been separated.798 The chromium complexes of desferrioxamine B (191) have been investigated the possible isomers are illustrated below (192-196). The cis isomer was isolated in relatively pure form.799 Thiohydroxamate800 and dihydroxamate (rhodotorulic acid) complexes have also been studied.801... 

To enhance iron excretion, intensive chelation therapy is used. The most successful drug is desferrioxamine B, a powerful Fe3+-chelator produced by the microbe Streptomyces pilosus,6 The formation constant for the Fe(III) complex, called ferrioxamine B, is 103afi. Used in conjunction with ascorbic acid—vitamin C, a reducing agent that reduces Fe3+ to the more soluble Fe2+— desferrioxamine clears several grams of iron per year from an overloaded patient. The ferrioxamine complex is excreted in the urine. 

A. G3 This problem can be worked with Equations 19-6 on a calculator or with the spreadsheet in Figure 19-5. Transferrin is the iron-transport protein found in blood. It has a molecular mass of 81 000 and carries two FeJ+ ions. Desferrioxamine B is a chelator... 

As we have seen, the body has essentially no means of eliminating iron, so an excessive intake of iron causes various problems known as siderosis. Chelating agents are used to treat the excessive buildup of iron. In many cases (he chelates resemble or are identical to the analogous compounds used by bacteria to chelate iron. Thus desferrioxamine B is the drug of choice for African siderosis.1)7 The ideal chelating... 

Desferrioxamine B (Desferal), a chelating agent that occurs naturally in certain microorganisms, has a very high affinity for ferric ion but only a relatively weak affinity for most other cations. Under physiological conditions it can complex free iron and competitively remove iron from ferritin and haemosiderin. It also binds,... 

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