The Radiopharmaceutical Chemistry of Carbon-11: Tracers and Applications

Abstract

In this chapter, several different aspects of carbon-11 radiochemistry are discussed, including general and technical considerations surrounding the setup for 11C-radiosyntheses and specific radiolabeling routes for the preparation of 11C-labeled radiotracers. Both equipment and procedures have to be thoroughly optimized for the radiosynthesis and quality control testing of radiopharmaceuticals labeled with the short-lived radionuclide carbon-11. In particular, special attention has to be paid to time reduction in all processes while concomitantly maintaining accuracy and reproducibility. The synthetic possibilities for 11C-labeled radiotracers resemble a multicolored bouquet of flowers, with methods ranging from gas-phase reactions to in-loop syntheses and from rather simple 11C-methylations to more complex 11C-carbonylations or even tricky multistep Grignard reactions. A variety of synthons—including [11C]CH3I, [11C]HCN, [11C]CS2, and [11C]CO—can be used to prepare a plethora of radiotracers containing 11C-labels at desired positions in the target molecule without altering its physicochemical and biological properties. This may seem to be a heaven for radiochemists where only the sky is the limit. However, the reality is unfortunately quite different, as several critical limitations are placed upon 11C-radiochemists, including time constraints as well as the need for sufficient yields and molar activities. Nevertheless, you will find plenty of examples within this chapter in which scientists have overcome these obstacles and were able to set up feasible synthetic routes that demonstrate the beauty of 11C-radiochemistry.