The present study reports a convenient method for 68Ga-labelling under anhydrous conditions using solid-phase derived gallium-68-acetylacetonate ([ 68Ga]Ga(acac)3) in a microwave-enhanced radiosynthesis. Commercial 68Ge/68Ga-radionuclide generators utilizing TiO2 to adsorb 68Ge(IV) (Obninsk-generators) were used. The initial aqueous generator eluate was transferred online onto a cation exchange resin and 68Ga was absorbed quantitatively. From this resin, 68Ga was eluted with different acetone-based, non-aqueous solvent systems. More than 95% of the generator-eluted 68Ga was obtained from the cation exchange resin with 600 μL of a 98% acetone/2% acetylacetone mixture providing n.c.a. [ 68Ga]Ga(acac)3 as labelling agent. Water-insoluble macrocyclic polypyrrole derivatives were chosen as model compounds for a proof-of-principle labelling of lipophilic compounds with 68Ga. Labelling of two different porphyrin derivatives, meso -tetraphenyl-porphyrin (Tpp) and (3-(1-hydroxyheptyl)deuteroporphyrin dimethylester (HHDPD) was performed in chloroform in a focused microwave synthesis system in yields of up to 90% within 5 min using phenol as co-ligand. Moreover, new co-ligands were investigated to be more effective and significantly less toxic than phenol. Among the phenol alternatives, gentisic acid (2,5-dihydroxy benzoic acid, DHB, 5 mg) emerged as the most useful, non-toxic phenol substitute. It facilitates reducing the load of co-ligand by 95%, while providing an increased labeling yield of 97%. 68Ga-labelled porphyrins may facilitate the medical application for molecular imaging via positron emission tomography.
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