New microwave assisted radiolabelling method and rat brain biodistribution study of two new 99mTc-tricarbonyl complexes as potential brain imaging agents

Two new cyclopentadienyl piperidine derivatives, namely ferrocene carboxylic acid 1-ethyl-3-hydroxypiperidinyl ester and ferrocene carboxylic acid 4-hydroxypiperidinyl ester, were synthesized. The ligands were then radiolabelled with 99mTc using two different approaches. The first method consisted of reacting the ligand precursor with Mn(CO)5Br in pertechnetate 99mTcO4 - in normal saline and dimethyl formamide (DMF) at 150°C for 1 h. The yields were 70% and 90%, respectively. For the second method, the reactions mixtures were placed in a microwave oven for 2 min at 650 watt. The yields were higher than 90% for both 99mTc complexes. Biodistribution studies showed that tricarbonyl{eta5- [carboxy-3-hydroxy(N-ethyl)piperidine]cyclopentadienyl}technetium(I) had the highest brain uptake. The regional distribution in the brain also demonstrated relatively higher uptake of tricarbonyl{eta5-[carboxy-3-hydroxy(N-ethyl) piperidine]cyclopentadienyl}technetium(I) in the colliculus (1.97% ID/g tissue,) with the colliculus to cerebellum ratio of 1.99. We conclude that the radiolabelling can be achieved by microwave activation, and tricarbonyl{eta5-[carboxy-3- hydroxy(N-ethyl)piperidine]cyclopentadienyl}technetium(I) has the potential for use as central nervous system (CNS) imaging agent.