3-HYDROXY-4-PIRIDINONE DERIVATIVES: SYNTHESIS, ACID-BASE PROPERTIES AND INTERACTIONS WITH Al3+

The 3-hydroxy-4-piridinones (3,4-hydroxypiridinones) are a family of ligand derivatives of 1,2-dimethyl-3-hydroxy-4-pyridinone (commercially known as Deferriprone), which have been recently developed in view of applications in metalchelation therapy and metal detoxication, because they are effective in all biological conditions and do not involve relevant undesired effects. [1,2] This contribution describes the synthetic procedures used in the preparation of a set of extrafunctionalized 3,4- hydroxypiridinones and the results of investigation of their acid-base properties and binding ability towards the metal cation Al3+ in aqueous solution. They can be synthesized from the 3,4-hydroxypyranone (maltol) through a reaction of protection of the –OH group with a benzyl group, followed by a double Michael-type addition with opening and closure of the aromatoid ring. These compounds can be further derivatized via the formation of amide bonds and final deprotection of the hydroxyl group with a hydrogenation catalyzed by 10% Pd/C. [3] The study of speciation of the 3,4-hydroxypiridinones in aqueous solution started from the investigation of their acid-base behavior, by performing spectrophotometric (200 ≤λ/nm ≤ 400) and spectrofluorimetric measurements at I = 0.15 mol L-1 in NaCl(aq) and T = 298.15 K and at T = 310.15 K (physiological conditions). The analysis of experimental data allowed to refine the protonation constants of all these ligands, with values quite in accordance either between the two analytical techniques or with the literature data [4,5]. The binding ability of the 3,4-hydroxypiridinones towards the Al3+ was studied through potentiometric and spectrophotometric experiments carried out at T = 298.15 K and I = 0.15 mol L-1 in NaCl(aq). The speciation models are characterized by species (AlpLqHr) with different stoichiometry. Finally, the sequestering ability of the ligands towards the chosen metal cation was investigated with the calculation of the pL0.5, an empirical parameter already proposed by the research group [6], which represents the total concentration of ligand necessary to sequester the 50% of a given ion present in trace in solution.