Synthesis of 5'-N-(2-[18F]Fluoroethyl)-carboxamidoadenosine: A promising tracer for investigation of adenosine receptor system by PET technique

Article abstract of DOI:10.1002/1099-1344(200007)43:8<807::AID-JLCR365>3.0.CO;2-K

5'-N-(2-[¹⁸F]Fluoroethyl)-carboxainidoadenosine ([¹⁸F]FNECA), a promising ¹⁸F-labelled adenosine agonist has been prepared by two different synthetic routes. In the first, [¹⁸F]fluoride was reacted with 5'-N,N-ethylene-2',3'-O-isopropylidenecarboxamido-adenosine and after removing the protective group [¹⁸F]FNECA was obtained in a low radiochemical yield (1 ± 1%, mean ± sd, n = 7, decay corrected). In the second, 2-[¹⁸F]fluoroethylamine was synthesised according to the literature and reacted with 2',3'-O-isopropylideneadenosine-5'-uronic acid in the presence of a coupling agent. The following hydrolysis step provided the [¹⁸F]FNECA with a modest radiochemical yield (24 ± 9%, n = 17, based on [¹⁸F]fluoride-activity). After purification by preparative reverse phase HPLC 18.9-166.5 MBq (0.51-4.5 mCi) [¹⁸F]FNECA was obtained with a specific activity of 2.35 ± 1.14 TBq/mmol (63.5 ± 30.9 Ci/mmol, n = 3). The total synthesis took 200 min and the decay corrected radiochemical yield based on [¹⁸F]F^- activity was 17 ± 9% (n = 5) with more than 99.9% radiochemical purity. This second route provides sufficient [¹⁸F]FNECA for the subsequent biological evaluation using PET-technique.