Steroids labeled with 18F for imaging tumors by positron emission tomography

The chemistry to label radiopharmaceuticals for imaging with positron emission tomography (PET) with the 2 h half life positron-emitting radionuclide fluorine-18 (18F) requires ease, efficiency, and speed. Furthermore, when high specific activities are needed, as in imaging high affinity, low capacity receptors, reactions need to work well at the tracer level scale. This review covers 18F synthetic methods and their application to the preparation of [18F]-labeled steroids for imaging hormone-responsive cancers. The methods exemplified are fluoride ion displacement of sulfonates and opening of cyclic sulfates, nucleophilic aromatic substitution, and halogen fluoride addition to alkenes.