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.