Preparation of no carrier added fluorine-18 labeled 16-fluorohexadecanoic and fluoroacetic acids from highly reactive tetraethylammonium [18F]fluoride

No carrier added tetraethylammonium [18F]fluoride prepared via synthesis and hydrolysis of fluorotrimethylsilane was reacted with methyl 16-iodohexadecanoate in acetonitrile. At 800C, yields of up to 80% were found with reaction time of 20-30 min. As would be expected for fluoride-for-iodide exchange, reactions were slower than previously-reported cyclic sulfate and triflate displacements. TLC and reverse-phase HPLC indicated that a single pure radioactive product was formed, which was hydrolyzed with alkali to the free acid. NMR spectroscopy of a carrier added preparation was consistent with assignment as 16-fluorohexadecanoic acid and no rearrangement to the 15-fluoro compound. [18F]Fluoroacetic acid was prepared analogously in high yield from ethyl iodoacetate. The results are discussed in terms of guidelines for syntheses of other 18F compounds and of the properties of near anhydrous tetraethylammonium fluoride in acetonitrile. (author)