Astatine

This educational review describes and summarizes the historic discovery of element 85, the experiments leading to its physical and chemical characterization and comparison with its lighter homologue iodine. The half-lives of its longest living isotopes ²¹⁰ At and ²¹¹ At with 8.3 and 7.22 hours respectively together with their alpha decay characteristics made these isotopes interesting for radiation biological research. However, the lack of stable isotopes of astatine presents a strong challenge for all characterizations. Nevertheless, the decay characteristics especially of ²¹¹ At stimulated several research groups to develop labelling strategies for the preparation of astatinated radiopharmaceuticals for targeted alpha radiation therapy. Because of the distinct differences in the chemical behaviour of astatine, when compared with iodine, these approaches are quite challenging. Accordingly, quite different labelling strategies have been tested, namely nucleophilic and electrophilic substitution reactions as well as complex forming strategies. Classic and new developments for the preparation of these compounds are reviewed.