Studies towards the development of lipophilic bifunctional N3S3 chelators for 68Ga

Summary. The present study is concerned with a concept of charge-neutral, lipophilic, macrocyclic bifunctional chelators, suitable for the introduction of a gallium-68 label into small molecules. The synthesis of a novel bifunctional N3S3type chelator, derived from 1,4,7-triazacyclononane, initial 68 Ga-radiolabelling and the determination of stability and calculated lipophilicity of the compound are described. The 68 Ga-labelled chelate was obtained in a maximum radiochemical yield of 93 ± 5% after a reaction time of 2 min. It remained intact over 3 h in a DTPA-challenge and a transferrin challenge experiment, indicating sufficient stability for PET studies.