[Chemical Design of Radiohalogenated Agents Using Neopentyl Structure]

Many useful radionuclides exist among the halogen elements. Fluorine-18 (¹⁸F) is used for positron emission tomography (PET) diagnosis, iodine-123 and iodine-131 (¹³¹I) for single photon emission computed tomography (SPECT) diagnosis, ¹³¹I for nuclear medicine therapy, and iodine-125 (¹²⁵I) for research. Astatine-211 (²¹¹At), which can be produced by a cyclotron and is attracting attention as a versatile α-ray emitting radionuclide, also belongs to the halogen family. Therefore, if a labeling agent that can stably hold radio-halogens can be developed, it would be useful for the development of radiotheranostic agents that can be expanded from nuclear medicine diagnosis using PET and SPECT to nuclear medicine therapy using β^--rays and even α-rays. Currently, benzoic acid derivatives are widely used as labeling agents for radio-halogens. The compounds labeled with ¹⁸F or radioiodine using this structure retain the radionuclide stably in vivo, but when ²¹¹At is labeled using this structure, ²¹¹At is rapidly released from the structure in vivo. Therefore, it is desirable to develop labeling agents that can stably hold ¹⁸F to ²¹¹At. Under these circumstances, we have found that a neopentyl structure with diol can stably retain ²¹¹At and ¹²⁵I in vivo. Furthermore, this structure can also stably retain ¹⁸F in vivo. In this review, I would like to introduce the characteristics of neopentyl diol as a radio-halogens labeling agent and the development of radiotheranositc agents using neopentyl diol.