Characterization and preliminary evaluation of ester-modified technetium-99m SNS/S mixed ligand complexes as potential brain perfusion agents.

Two novel [99mTc](SNS/S) mixed ligand complexes carrying a pendant ester function on the monothiolate coligand were synthesized. The corresponding oxorhenium and [99gTc]oxotechnetium complexes prepared at the macroscopic level and chemically characterized were used for structure assignment of [99mTc](SNS/S) complexes prepared at the nanomolar level. Enzymatic hydrolysis of the pendant ester group of [99mTc](SNS/S) mixed ligand complexes by esterase was investigated in vitro and compared with that of the ethyl cysteinate dimer, [99mTc]ECD. Preliminary biodistribution data in mice shows that the complexes are lipophilic and exhibit significant initial uptake in rodent brain.