Synthesis and biological evaluation of a novel 99mTc‐cyclopentadienyltricarbonyl technetium complex as a new potential brain perfusion imaging agent

A new cytectrene prototype of general formula RCpTc(CO)3 (R = C6H5NHCO, Cp = cyclopentadienyl moiety) has been synthesized from N‐phenylferrocenecarboxamide 2, characterized and evaluated as a potential brain perfusion imaging agent. An improved procedure has been developed to obtain both the ligand 2, characterized by its solid‐state structure (orthorhombic, Pccn, a = 10.4443(2) Å, b = 26.1467(6) Å, c = 9.9977(3) Å), and the corresponding metallic Tc‐ and Re‐complexes in good yield. These latter complexes possessed similar HPLC retention times, thereby indicating identity of their molecular structures. The Tc‐complex 99mTc‐2 is lipophilic enough to cross the blood‐brain barrier. This complex exhibits good brain uptake (1.41% injected dose per gram tissue at 5 min) combined with a fairly good retention of radioactivity in brain (0.48% injected dose per gram tissue after 1 h). Then, the distribution of the activity at 5 min post‐injection in various rat brain regions showed a higher accumulation in the hippocampus area. The new 99mTc‐cyclopentadienyltricarbonyl technetium complex reported here showed promising biological results, making it an interesting base for the development of a new generation of cytectrene as brain perfusion imaging agent.