Design, synthesis and characterization of new iron and aluminium chelating agents

Chelation therapy is widely used for metal-unbalance related diseases, namely those due to disorders on metal metabolism, such as beta-thalassemia, hemochromatosis (Fe), and neurodegenerative diseases (Cu, Fe, Zn and Al). The study of metal chelators for clinical applications, either as chelating therapeutics able to target specific metal ions in the body, or as metal-carriers for therapeutic or imaging purposes, is a topical research area which faces up to urgent medical problems. Metal-chelating drugs are used in many ways for the prevention, diagnosis and treatment of cancer, since cancer cells, like normal cells, require essential metal ions such as iron, copper and zinc for growth and proliferation. Chelators can target the metabolic pathways of cancer cells through the control of proteins involved in the regulation of these metals and also of other molecules involved in cell cycle control, angiogenesis and metastatic suppression. The thermodynamic aspects regarding the complexation of metal ions of medical interest are of primary importance for a correct understanding of the role of metals in human diseases in order to rationalize the design of new molecules for diagnostic and therapeutic purposes. A typical case is the treatment of metal overload diseases where the highest thermodynamic stability and largest selectivity of the complexes are crucial factors in the ligand design. This thesis is focused on the development and study of new compounds which, as a result of their strong interaction with specific metal ions, can be potentially used as pharmaceutical drugs for diagnosis or therapy. The work was performed with a multidisciplinary approach regarding mostly chemistry, but including also biochemistry and biology. The work presented in this thesis is devoted to reach the following aims: Design and synthesis of new multivalent ligands in order to enhance the efficiency and selectivity of both metal-interaction and biomolecular recognition of available ligands (or metal complexes), as well as the targeting for drug delivery; Assessment of the most important physical and chemical properties of metal related compounds, namely metal-chelating efficacy and selectivity (thermodynamic and kinetic) with respect to other biometals or biological molecules, mostly in solution but also in silico; Bioevoluation, in vitro and in vivo, for the most promising compounds. This thesis is divided in two chapters. Chapter I is dedicated to a description of Chelation Therapy for treating metal intoxication in humans. The importance of chelating agents in neurodegenerative diseases like Alzheimer disease, is introduced. The main aspects of Fe, Al, and Cu metabolism in humans are presented. The papers I, II, III and IV relative to this chapter has been appended. Chapter II describes the synthesis of the new studied ligands, and the experimental methods and techniques that were used for the investigation of the ligands and of their complexes with a number of metal ions. Important features of the used techniques are briefly described including basic principles, advantages and limitations. The papers V, VI, and VII explain in detail the developed work. The main conclusions of this work are: A new family of hydroxypyrone ligands (L4, L5, L6, L7, L8, and L9) has been synthesized and fully characterized. These ligands are easy and cheap to produce; Complex formation equilibria showed good efficiency and selectivity for iron and aluminium. With Fe3+ various protonated 2:3 Fe:L species have been detected (with exception for L7). Experimental data give evidence of a strong chelating ability for L8 and, in order of decreasing ability, for ligands L5 > L4 > L9 = L6 > L7. Al3+ also forms 2:3 Al:L complexes with the ligands L4, L5, L6, and L9. The ligand with a shorter linker, L8, forms the most stable complexes of stoichiometry 2:2 (Al:L). Also Al3+ forms with L8 the strongest complexes, and in order of decreasing stabilities with the ligands L6 > L5 > L4 > L9 > L7. Studies in mice confirmed the high in vivo metal scavenging ability of the tetradentate ligands (L4, L5, L6, L8, and L9) in comparison with the corresponding bidentate (L7). The excellent chelating properties recommend further toxicological and pharmacological research on these new promising ligands.