Production and transport of gaseous ¹⁸F-synthons: ¹⁸F-acyl fluorides

Fluorine-18 (¹⁸F, T_1/2 = 109.7 min) is a positron-emitting isotope that has found extensive application as a radiolabel for positron emission tomography (PET). Although gaseous ¹¹C-CO₂ and ¹¹C-CH₄ are practically transported from cyclotron to radiochemistry processes, ¹⁸F-fluoride is routinely transported in aqueous solution because it is commonly produced by proton irradiation of ¹⁸O-enriched water. In most cases, subsequent dry-down steps are necessary to prepare reactive ¹⁸F-fluoride for radiofluorination. In this work, a simple module was designed to generate gaseous ¹⁸F-acyl fluorides from aqueous ¹⁸F-fluoride solution by solid phase ¹⁸F-radiofluorination of acyl anhydride. The gaseous ¹⁸F-acyl fluorides were purified through a column containing Porapak Q/Na₂SO₄, resulting in high yields (>86%), purities (>99%) and specific activities (>1200 GBq/μmol). Prototypic ¹⁸F-acetyl fluoride (¹⁸F-AcF) was readily transported through 15 m of 0.8 mm ID polypropylene tubing with low (0.64 ± 0.12%) adsorption to the tubing. Following dissolution of ¹⁸F-AcF in solvent containing base, highly reactive ¹⁸F-flouride was generated immediately and used directly for ¹⁸F-labeling reactions. These data indicate that ¹⁸F-acyl fluorides represent a new paradigm for preparation and transport of anhydrous, reactive ¹⁸F-fluoride for radiofluorinations.