State of Art in 11C Labelled Radiotracers Synthesis

Positron Emission Tomography has become a powerful scientific and clinical tool probing biochemical processes in the human body. Their clinical applications have proven to be vital in the evaluation and diagnosis of diseases. This is due, in large part, to advances in instrumentation and synthetic chemistry. Carbon-11 is a valuable radionuclide in PET as it virtually permits the synthesis of radiolabelled versions of any compound of interest. The syntheses with carbon-11 present several features: limited number of labelled precursors, sub-micromolar amounts of the starting materials, and a need for the introduction of the radioisotope as late as possible in the synthesis. All of these reasons have restricted complex radiosyntheses. The short half-life of carbon-11 (20.4 min) requires the rapid preparation and purification of carbon-11 labelled molecules. Those have to be carried out immediately before use from cyclotron produced precursors ([11C]CO2, [11C]CO, [11C]CH4) or reagents rapidly prepared from them ([11C]CH3I, [11C]COCl2, [11C]HCN). As a consequence carbon-11 has been underused compared to fluorine-18. However, because of the increasing molecular complexity and diversity of biologically active compounds, there is a need for new methodologies giving access in short time and high yield to radioactive 11C-probes. The aim of this review is to emphasize the methodologies used in this field and to give a comprehensive overview of the numerous advances, which occurred over the past decade. In addition, for each labelling technique or reaction reported, a special attention has been brought to classify the applications in function of the targeted medical domain.