Synthesis of [19‐ 11 C]arachidonic acid

The preparation of (all Z)‐1,17‐dichloro‐4,7,10,13‐heptadecatetraene is reported. The synthesis was performed in five steps with a total yield of 22 %, starting from 5‐chloro‐1‐pentyne. The corresponding bis Grignard reagent was used in a copper‐mediated coupling reaction with [1‐ 11 C]ethyl iodide followed by a carbonation with CO 2 to afford [19‐ 11 C]arachidonic acid in 23 % decay corrected radiochemical yield within 52 min. The radiochemical purity of the final product was 98 %. In a typical run starting with 20 GBq [ 11 C]O 2 , 760 MBq of [19‐ 11 C]arachidonic acid was obtained, with a specific activity of 1.6 GBq/μmol.