The chemistry of labeling heterocycles with carbon-11 or fluorine-18 for biomedical imaging

Abstract Over the last half-century, the molecular imaging technique of positron emission tomography (PET) has emerged as an important tool for biomedical research, drug development and medical diagnosis. The power of PET derives from its utilization of radiotracers that can report specific information on pharmacology, biochemistry, and physiology. Many of these radiotracers are heterocycles that have been labeled with a short-lived cyclotron-produced radioisotope, either carbon-11 (t1/2 = 20.4 min) or fluorine-18 (t1/2 = 109.8 min). This review addresses the chemical challenges to be met in producing PET radiotracers with these radioisotope labels at heterocyclic moieties and the methods now available for doing so.