Radioiodinated compounds

The in vitro stabilities of the radioiodinated compound were evaluated by incubating the radiolabelled protein in PBS and in human serum. The radiochemical purities were evaluated at 12, 24, 48 and 72 h post-labelling. The stability of the labelled compound with low specific activity was compared with that of the labelled compound with high specific activity. The results showed complete retention of the radiochemical purity of the low specific activity preparation for up to 48 h in both media. However, in the case of the high specific activity preparation, rapid degradation of the radiolabelled protein was observed (Fig. 4.1), with a loss of 54% of the radioiodine in PBS and even higher losses in human serum. These results show a dependence of the stability on the specific activity and/or the radioactive concentration resulting from... 

Ideally, the best approach for preparing a radiotracer is to replace one atom of the target molecule with one of its radioactive isotopes. When this is not possible, labefing it with radioiodine, and particularly is generally a suitable alternative. Indeed, some radioiodinated compounds have already found applications in clinical settings. 

After hydroboration, oxidation of radioiodide is performed with Chloramine-T, forming HO-I, which then adds to the C-B bond. The reactivity of the C-B bonds depends on the position of boron, which can either be formed from a terminal double bond or from an internal alkene. While the former case produces two radioiodinated compounds, the latter forms only one. Therefore, dicyclohexylborane is used for the hydroboration step. Both reactions, hydroboration of the alkene and radioiodination can be performed in one sequence without isolating the intermediately formed trialkylborane. 

The orientation of the substitution reaction is sometimes not predictable (O Fig. 44.6). The formation of [ I]IBZM may result in two isomers but only the (S)-(—)-3-[ I]iodo-2-hydroxy derivative is formed. The position of the radioiodine can be investigated by NMR of the stable iodo derivative. Comparison of the stable and radioiodinated compounds with HPLC is proving the substituent position. 

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