Practical experiences with the synthesis of [11C]CH3I through gas phase iodination reaction using a TRACERlabFXC...

The results of [(11)C]CH(3)I synthesis through hydrogen gas reduction of [(11)C]CO(2) on different nickel catalysts (HARSHAW-nickel, SHIMALITE-nickel, nickel on silica/alumina, nickel nanosize 99.99%) followed by gas phase iodination using a TRACERlab FX(C) synthesis unit are reported. Further reaction parameters such as furnace temperatures, flow rate of hydrogen gas and reduction time were optimized. It was found that reduction of [(11)C]CO(2) proceeded in 28-83% yield depending on the nickel catalyst and temperature. The gas phase iodination (methane conversion) gave 31-62% of [(11)C]CH(3)I depending on temperature and amount of iodine in the iodine furnace. [(11)C]CH(3)I was used for heteroatom methylation reactions exemplified by a piperazine and a phenol (1 and 3). The specific activity of the (11)C-labelled products 2 and 4 was determined after HPLC purification and solid-phase extraction. Compounds 2 and 4 were obtained in 8-14% radiochemical yield (decay-corrected, based upon trapped [(11)C]CH(4)) within 30 min. The specific activity was determined to be in the range of 20-30 GBq/mumol at the end-of-synthesis. Nickel catalyst nanosize was found to be superior compared with other Ni catalysts tested. The relatively low specific activity may be mainly due to carbon contaminations originating from the long copper tubing (500 m) between the cyclotron and the radiochemistry facility.