Selective synthesis of [2-11C]2-iodopropane and [1-11C]iodoethane using the loop method by reacting methylmagnesium bromide with [11C]carbon dioxide

[2-C-11]2-iodopropane ([2-C-11]i-PrI) and [1-C-11]iodoethane ([I-C-11]EtI) were selectively synthesized using the loop method by reacting methylmagnesium bromide (MeMgBr) with [C-11]carbon oxide ([C-11]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-C-11]i-PrI and [1-C-11]EtI. By examining the reaction temperature and time of MeMgBr with [C-11]CO2 in the loop, we determined the optimal respective conditions of forming [2-C-11]i-PrI and [1-C-11]EtI. Moreover, [2-C-11]i-PrI and [1-C-11]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 [C-11]CO2 to the purification of [C-11]RI were automated. When we started from about 37 GBq Of [C-11]CO2, 3.9-5.3 GBq of [1-C-11]EtI or 3.7-4.4 GBq of [2-C-11]i-PrI was obtained with a specific activity of 37-99 GBq/mu mol at FOS (n = 3). This amount of radioactivity is sufficient for the synthesis of [C-11]radioligands. (c) 2005 Elsevier Ltd. All rights reserved.