Synthesis of [ 18 F]FETO, a novel potential 11‐ β hydroxylase inhibitor

Recent publications reported high uptake of the carbon‐11 labelled 11β‐hydroxylase inhibitors (R)–[ O –methyl‐ 11 C]metomidate ([ 11 C]MTO) and (R)–[ O –ethyl‐ 11 C]etomidate ([ 11 C]ETO) in adrenocortical incidentalomas with excellent selectivity for positron emission tomography (PET). In our studies [ 18 F]FETO, (the [ 18 F]fluoroethyl ester of etomidate, (R)‐1‐(1‐phenylethyl)‐1 H ‐imidazole‐5‐carboxylic acid, 2′‐[ 18 F]fluoroethyl ester), an analogue of [ 11 C]MTO and [ 11 C]ETO was chosen due to the suspected similarity of the pharmacokinetic and pharmacodynamic properties, and was prepared in the following two step procedure: First, [ 18 F]fluoride was reacted with 2‐bromoethyl triflate using the kryptofix/acetonitrile method to yield 2–bromo‐[ 18 F]fluoroethane ([ 18 F]BFE). In the second step, [ 18 F]BFE was reacted with the tetrabutylammonium salt of (R)‐1‐(1‐phenylethyl)‐1 H ‐imidazole‐5‐carboxylic acid to yield [ 18 F]FETO, a novel inhibitor of the 11β‐hydroxylase. The proposed synthesis of [ 18 F]FETO allows the production of sufficient amounts of this new PET‐tracer to serve 1–2 patients with an overall synthesis time of less than 80 min. Copyright © 2003 John Wiley & Sons, Ltd.