New conformationally restricted 99mTc N2S2 complexes as myocardial perfusion imaging agents

In developing 99mTc complexes as potential myocardial imaging agents, a new series of ligands based on a conformationally restricted N2S2 system were investigated. Using piperazine or homopiperazine as the starting material, two N2S2 ligands (4a and 4b) with additional conformation restriction between the two nitrogen donor atoms were synthesized. The 99mTc complexes were prepared by a direct labeling method with tin(II) tartrate as the reducing agent for [99mTc]pertechnetate. The resulting 99mTc complexes were purified through a sulfonpropyl Sephadex column and further purified by HPLC with a reverse-phase column eluting with a solvent system of acetonitrile/buffer. Biodistribution studies in rats showed initial uptake in the heart (0.21%, 0.42% dose/order for [99mTc]4a and 4b at 2 min postinjection). Carrier-added preparation of [99mTc]4b was successful. NMR, IR, UV, crystallographic, and elemental analysis of the [99Tc]4b complex suggest that it contains a TcVO3+ center core and is 1+ charged. The results suggest that this series of 1+ charged 99mTc complexes may have potential as myocardial imaging agents, and further study of the complexes is warranted.