Synthesis of [¹⁸F] SR144385: A selective radioligand for positron emission tomographic studies of brain cannabinoid receptors

A cannabinoid receptor antagonist, SR144385, has been labeled with fluorine-18. [¹⁸F] SR144385 was synthesized in a multi-step reaction in which fluorine-18 was introduced by nucleophilic halogen displacement on a bromo precursor. The fluorine-18 labeled intermediate was deprotected and coupled with 1-aminopiperidine to give [¹⁸F] SR144385. The time for radiosynthesis, HPLC purification, and formulation was 2 hours from end-of-bombardment. [¹⁸F] SR144385 of high radiochemical purity was obtained at end-of-synthesis with an average (n = 11) specific radioactivity of 1852 mCi/μmol and an average isolated, non-decay corrected radiochemical yield of 4% from potassium [¹⁸F] fluoride.