Inorganic Chemistry of the Tripodal Picolinate Ligand with Gallium(III) and Radiolabeling with Gallium-68.

We report here the improved synthesis of the tripodal picolinate chelator , with an overall yield of 41% over five steps, in comparison to the previously reported 6% yield. was investigated for its coordination chemistry with Ga(III) and radiolabeling properties with gallium-68 (Ga). The obtained crystal structure for [Ga()] shows that the three picolinate arms coordinate to the Ga(III) ion, fully occupying the octahedral coordination geometry. This is supported by H NMR which shows that the three arms are symmetrical when coordinated to Ga(III). Assessment of the thermodynamic stability through potentiometry gives log = 21.32, with a single species being produced across the range of pH 3.5-7.5. achieved >99% radiochemical conversion with Ga under mild conditions ([] = 6.6 μM, pH 7.4, 37 °C) with a molar activity of 3.1 GBq μmol. The resulting complex, [Ga][Ga()], showed improved stability over the previously reported [Ga][Ga()(HO)] in a serum challenge, with 32% of [Ga][Ga()] remaining intact after 30 min of incubation with fetal bovine serum.