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

A cannabinoid receptor antagonist, SR144385, has been labeled with fluorine -18. [F-18] SR144385 was synthesized in a multi-step reaction in which fluo rine-18 was introduced by nucleophilic halogen displacement on a bromo prec ursor. The fluorine-18 labeled intermediate was deprotected and coupled wit h 1-aminopiperidine to give [F-18] SR144385. The time for radiosynthesis, H PLC purification, and formulation was 2 hours from end-of-bombardment. [F-1 8] SR144385 of high radiochemical purity was obtained at end-of-synthesis w ith an average (n = 11) specific radioactivity of 1852 mCi/mu mol and an av erage isolated, non-decay corrected radiochemical yield of 4% from potassiu m [F-18] fluoride.