Cyclopentadienyl tricarbonyl complexes of 99mTc for the in vivo imaging of the serotonin 5-HT1A receptor in the brain

Technetium and rhenium tricarbonyl complexes with derivatized cyclopentadienyl ligands were prepared starting from pertechnetate and an appropriate ferrocene ligand. Furthermore, the complexes (M(CO)3cp-COOC5H9N-R, M = Tc, Re; R = Me, isopropyl) could be obtained starting from the precursor complexes [99mTc(CO)3(H2O)3]+ and [Re(CO)3Br3]2−. Their chemical identity was confirmed by chromatographic methods and electron spray mass spectrometry. The biodistribution of the 99mTc complexes (cytectrene I and cytectrene II) in Wistar rats was studied. Both compounds show high uptake in the brain and fast blood clearance. The pattern of regional distribution in the brain demonstrated in autoradiographic studies indicates binding to the 5-HT1A and α1 adrenergic receptors.