Synthesis, characterization and X-ray crystal structure of [Re(L4)(CO) 3]Br · 2CH 3OH (L4 = N, N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine): A model compound for novel cationic 99mTc(I)-tricarbonyl radiotracers useful for heart imaging

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This report describes synthesis and evaluation of cationic complexes, [ 99mTc(CO) 3(L)] + (L = N-methoxyethyl- N, N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L1), N-[(15-crown-5)-2-yl]- N, N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L2) and N-[(18-crown-6)-2-yl]- N, N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L3)) as potential radiotracers for heart imaging. Preliminary results from biodistribution studies in female adult BALB-c mice indicated that the cationic 99mTc(I)-tricarbonyl complex, [ 99mTc(CO) 3(L2)] +, has a significant localization in the heart at 60 min post-injection. To understand the coordination chemistry of these bisphosphine ligands with the 99mTc(I)-tricarbonyl core, we prepared [Re(CO) 3(L4)]Br (L4: N, N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine) as a model compound. [Re(CO) 3(L4)]Br has been characterized by elemental analysis, IR, ESI-MS, NMR ( 1H, 13C, 1H– 1H COSY, and 1H– 13C HMQC) methods, and X-ray crystallography. In solid state, [Re(CO) 3(L4)] + has a distorted octahedron coordination geometry with PNP occupying one facial plane. The chelator backbone adopts a “chair” conformation with phosphine-P atoms at equatorial positions and the amine-N at the apical site. In solution, [Re(CO) 3(L4)] + is able to maintain its cationic nature with no dissociation of carbonyl ligands or any of the three PNP donors.