Methylation of the thiophene ring using Carbon‐11‐labelled methyl iodide: formation of 3‐[ 11 C]methylthiophene

This paper describes the radiosynthesis of 3‐[ 11 C]methylthiophene, chosen as a model reaction for the preparation of heteroaromatic methylthienyl compounds. Labelling was performed from the corresponding lithiothiophene derivative and [ 11 C]methyl iodide as the alkylating agent in THF at −78°C. The conditions used were the following: (1) trapping for 2–3 min at −78°C of the [ 11 C]methyl iodide in the THF solution containing the freshly prepared 3‐lithiothiophene; (2) Hydrolysis of the reaction mixture by adding 0.5 ml of the HPLC mobile phase and (3) HPLC purification. 3‐[ 11 C]Methylthiophene ([ 11 C]‐ 1 ) was collected in high yield as the unique peak of the HPLC radiochromatogram. Non‐reacted [ 11 C]methyl iodide was not present. Typically, 50–60 mCi (1.85–2.22 GBq) of 3‐[ 11 C]methylthiophene ([ 11 C]‐ 1 ) were obtained within 20 min of radiosynthesis (including HPLC purification) with specific radioactivities ranging from 0.6 to 1.0 Ci/μmol (22.2–37.0 GBq/μmol) starting from 180 to 200 mCi (6.66–7.40 GBq) of [ 11 C]CO 2 (10 μA, 10 min (6000 μC) irradiation). Copyright © 2002 John Wiley & Sons, Ltd.