New Chelating Ligands with Potential for Pharmaceutical Applications

2-hydroxybenzylaminomethylphosphonic acid (HBAMPA) has been synthesized from commercially available chemicals and its aqueous coordination chemistry involving Al 3 + , Ga 3 + and Fe 3 + is described. At 25°C and 0.1 M ionic strength KNO3, both Al 3 + and Ga 3 + formed dinuclear complexes while Fe 3 + formed the simple 1:1 complex (FeL) along with a mono-protonated complex (FeLH). HBAMPA formed neutral complexes with these trivalent metal ions, which lead to an early precipitation. The solution mixtures precipitated at ∼ pH 6.0 for Al 3 + , ∼ pH 4.0 for Fe 3 + , and ∼ pH 3.0 for the Ga 3 + ion. The carboxylic acid analogue of HBAMPA, 2-hydroxybenzylalanine (HBA) also has been tested with Al 3 + and Fe 3 + . It appeared that HBA solubilized the Al 3 + ion at pH 7.4. However, the Fe 3 + -HBA solution mixture formed a complex of a very minimum solubility and an early pH precipitation prevailed. HBA and HBAMPA are multi-dentate, phenol-containing ligands capable of binding a variety of metal ions with very high stability constants. These stability constants are discussed.