| Abstract: | The present study reports the syntheses of half‐sandwich complexes of the type M(η5‐C5H4CONH‐R)(CO)3] (M═Re,99mTc;R═cyclic RGD peptide (cRGDyK) for potential imaging of αvβ3 integrin expression. The 99mTc complex was prepared directly from the reaction of 99mTc(OH2)3(CO)3]+ with cRGDyK, doubly conjugated to Thiele's acid (C5H5COOH)2] in water. This approach extends the viability of metal‐mediated retro Diels‐Alder reactions for the preparation of small molecules such as linear tripeptides to a more complex cyclic peptide carrying a (η5‐C5H4)99mTc(CO)3] tag. The Diels‐Alder product (C5H5CONH‐cRGDyK)2] was prepared from Thiele's acid via double peptide coupling. The Re‐complex Re(η5‐C5H4CONH‐cRGDyK)(CO)3] was obtained by attaching Re(η5‐C5H4COOH)(CO)3] directly to the N‐terminus of cRGDyK. The identity of the 99mTc‐complex is confirmed by chromatographic comparison with the corresponding rhenium complex, fully characterized by spectroscopic techniques. |
