In this review the recent progress in the development of suitable precursors for 11C‐labelling is discussed. Especially the last few years' advancement of the use of [11C] carbon monoxide as a versatile and useful precursor in labelling chemistry is presented. The development is set in perspective of its potential in applying molecular imaging tools in drug and tracer development.The possibility of exploring small tracer libraries utilizing the microdosing concept is explored. Copyright © 2007 John Wiley & Sons, Ltd.

Photoinitiated radical carbonylation with [(11)C]carbon monoxide at low concentration was employed in syntheses of carbonyl-(11)C-labeled amides using alkyl iodides and amines as precursors. Eleven (11)C-amides were synthesized in up to 74% decay-corrected radiochemical yields with reaction times of 400 s and with up to 95% conversion of carbon monoxide. Starting with 26.3 GBq of [(11)C]carbon monoxide, 10.6 GBq of 1-cyclohexane [(11)C]carbonyl-4-phenyl-piperazine (15) was obtained within 35 min from the end of bombardment (33 microA) and with a specific radioactivity of 192 GBq/micromol at the same time point. The influence of solvents was investigated. The described procedure extends the range of accessible labeling methods. The method may also be useful for preparation of (13)C- and (14)C-substituted compounds.

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[(11)C]Carbon monoxide ((11)CO) is a versatile building block for the synthesis of Positron Emission Tomography (PET) radioligands. However, the difficulty of trapping (11)CO in a small solvent volume has limited its utility. We here report an evaluation of a simple, fully automated high-pressure synthesizer prototype for the use in (11)C-carbonylation reactions. [(11)C]Carbon monoxide was easily prepared by online reduction of [(11)C]carbon dioxide using either Mo(s) or Zn(s) as the reducing agent. The conversion yield of (11)CO was >99% when zinc was used as the reducing agent, and the corresponding value for Mo was approximately 71%. When the Zn or Mo column was constantly kept under inert atmosphere, no significant decrease in reducing properties was observed for more than 100 (11)CO productions. However, in our hands, Mo reductant was much easier to service. A total of nine functional groups were successfully radiolabeled using the (11)CO synthesizer prototype. All measured radiochemical yields exceeded 37%, and the (11)CO trapping efficiency was generally above 90%, except for the Suzuki coupling where the trapping efficiency was 80%. This high-pressure synthesizer using [(11)C]carbon monoxide as the labeling precursor is easy to operate allowing for (11)C-carbonylation reactions to be performed in a high yield and in a routinely fashion.

Aliphatic esters were labelled with a short-lived radionuclide, 11C with t ½ = 20.3 min, at the carbonyl position using [ 11 C]carbon monoxide via rapid (6 min) photoinduced radical-mediated carbonylation reactions. The esters were prepared from primary, secondary, and tertiary alkyl iodides, and various alcohols, including tert-butyl alcohol and phenol. The use of strong bases was necessary to achieve good radiochemical yields in short reaction times. Isolated decay-corrected radiochemical yields were in the range of 40-68 %.