Synthesis of no-carrier-added N-([18F]fluoroalkyl)spiperone derivatives

3-N-([18F]fluoroalkyl)spiperone derivatives (2,3) can be prepared by N-alkylation of spiperone (1) with fluoroalkyl halides. The fluoroalkylating species 2-[18F]fluoroethyl bromide (7), 3-[18F]fluoropropyl bromide (8) and 4-[18F]fluorobutyl bromide (9) were prepared by [18F]fluoride ion displacement of the corresponding trifluoromethanesulfonates (triflates 4,5,6). By this method, the 2-[18F]fluoroethyl-, 3-[18F]fluoropropyl-, and 4-[18F]fluorobutyl spiperone derivatives (2a-c) can be prepared and purified rapidly and conveniently, within 40 min, in yields of 30-40% (end of synthesis, EOS). An alternative approach, suitable for the preparation of 2-[18F]fluoroalkyl (ethyl, propyl, butyl, pentyl and hexyl) spiperone derivatives (3a-d), involves iodo[18F]fluorination of terminal olefins, followed by N-alkylation of spiperone. This sequence is less convenient and proceeds in lower overall yields (less than 5%).