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Updated: Aug 15, 2026

Enhancing Efficiency and Radiolabeling Yields of Carbon-11 Radioligands for Clinical Research Using the Loop Method
Published on: December 20, 2024
Selective synthesis of [2-(11)C]2-iodopropane and [1-(11)C]iodoethane using the loop method by reacting
Ming-Rong Zhang1, Masanao Ogawa, Yuichiro Yoshida
1Department of Medical Imaging, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
Abstract:
[2-(11)C]2-iodopropane ([2-(11)C]i-PrI) and [1-(11)C]iodoethane ([1-(11)C]EtI) were selectively synthesized using the loop method by reacting methylmagnesium bromide (MeMgBr) with [11C]carbon oxide ([11C]CO2), followed by treatment with LiAlH4 and then HI. The loop method, in which a low amount of MeMgBr was used for the Grignard reaction, diminished the formation of non-radioactive iodomethane (MeI) and improved the specific activity of [2-(11)C]i-PrI and [1-(11)C]EtI. By examining the reaction temperature and time of MeMgBr with [11C]CO2 in the loop, we determined the optimal respective conditions of forming [2-(11)C]i-PrI and [1-(11)C]EtI. Moreover, [2-(11)C]i-PrI and [1-(11)C]EtI could be simultaneously synthesized at a designated ratio in one production run. These substances were obtained by gas chromatographic purification as two radiochemically pure products. All the processes from the production of [11C]CO2 to the purification of [11C]RI were automated. When we started from about 37 GBq of [11C]CO2, 3.9-5.3 GBq of [1-(11)C]EtI or 3.7-4.4 GBq of [2-(11)C]i-PrI was obtained with a specific activity of 37-99 GBq/micromol at EOS (n=3). This amount of radioactivity is sufficient for the synthesis of [11C]radioligands.
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