Recent advances in the design and synthesis of carbon-14 labelled pharmaceuticals from small molecule precursors

Over the past decade, the increased chemical complexity of new drug candidates has resulted in a parallel need to develop innovative syntheses of carbon-14 labelled pharmaceuticals. Faced with short time-lines and a limited number of labelled precursors, radiochemists have addressed this challenge by developing new reagents and adapting existing technology to labelled syntheses. Selected examples from the recent radiochemical literature illustrate some of the creative strategies used to rapidly solve these synthetic challenges. Examples describing the handling and use of common small molecule reagents, such as carbon-14 labelled carbon dioxide, methyl iodide, cyanide, acetic acids, sulfur and phosphorous stabilized ylides for the synthesis of labelled steroids, prostanoids, nucleosides, pyridines, quinolines, benzazepines and other heterocycles are presented. Several general strategies for radiolabelling are also discussed including the degradation strategy for accessing necessary intermediates and precursors, the radiolabelling of aromatic substrates, transition metal mediated cross-couplings, and the use of chiral auxiliaries for the enantioselective syntheses of radiolabelled pharmaceuticals.