New hexadentate ligands composed of 1-hydroxy-2(1H)-pyrimidinone, α,ω-diamine and 1,1,1-tris(carboxyethoxymethyl)ethane or tri(carboxybutyl)isocyanurate. Synthesis and characterization of their iron(III) complexes

The successive coupling of 1-benzyloxy-2(1H)-pyrimidinone with α,ω-diamines, 1,1,1-tris(carboxyethoxymethyl)ethane or tri(carboxybutyl)isocyanurate, and final removal of the benzyl protecting group afforded new hexadentate ligands (TEPOHn or TCPOH). The UV/VIS spectroscopic analysis in aqueous solution indicated 1∶1 stoichiometric complexation of the hexadentate ligand with iron(III). The relative stability constants of iron(III) complexes of the hexadentate ligands were estimated to be log K 24.4–26.3 by the competitive reaction with EDTA, suggesting that the stability was affected by the methylene chain length. The standard redox potential E1/2 of Fe(TEPO2) was measured to be –493 mV at apparent pH 8.0 in 50% aqueous DMF solution. This value was approximately 300 mV higher than that of the iron(III) complex of natural desferrioxamine B (DFB). Further, all synthetic hexadentate ligands effectively removed 3–6 times as much iron(III) from human transferrin as DFB even though the ratio of the synthetic ligand to transferrin was one-fifth that of DFB.