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

Abstract

5′-N-(2-[18F]Fluoroethyl)-carboxamidoadenosine ([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%, means±sd, n=7, decay corrected). In the second, 2-[18F]fluoro-ethylamine 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. Copyright © 2000 John Wiley & Sons, Ltd.