The [(Cp)M(CO)3] (M=Re, 99mTc) Building Block for Imaging Agents and Bioinorganic Probes: Perspectives and Limitations

Starting from asymmetric Thiele's acid derivatives, two different imaging probes [99mTc(CO)3(CpR)] (R=potential targeting vector) are generated simultaneously in one‐pot and from one substrate. This extends the previously introduced labeling strategy of metal‐mediated retro‐DielsAlder reaction with HCp‐R dimers. We demonstrate that chemically active functionalities such as hydroxamic acids are not following this labeling strategy. Adopting the principle of replacing phenyl rings by [Re(CO)3(Cp)] entities, potent histone deacetylase (HDAC)‐inhibiting Re analogs of suberoylanlilide hydroxamic acid (SAHA; N‐hydroxy‐N′‐phenyloctanediamide) were synthesized and characterized. Cytotoxic evaluation on different tumor cell lines revealed low IC50 values [μM] for these compounds, comparable to their purely organic congeners.