A COMPARISON OF THE INCORPORATION OF I-123 AND F-18 INTO 1-[1-(3-HYDROXYPHENYL) CYCLOHEXYL]-4-(METHANESULFONYLOXY)PIPERIDINE BY NUCLEOPHILIC DISPLACEMENT WITH I-123 AND F-18

Unlabelled and labelled 4-fluoro- and -iodo-1-[1-(3-hydroxyphenyl)cycl ohexyl]piperidines (3 and 4, respectively), derivatives of phencyclidi ne, were synthesized in 3-steps via nucleophilic displacement reaction of 1-[1-(3-hydroxyphenyl) cyclohexyl]-4-(methanesulfonyloxy)piperidin e (8). The displacement reaction with 3 molar equivalents of Bu4N+I- g ave 58% of 4 with no detectable methanesulfonate elimination. Reaction of a large excess of 8 with (NaI)-I-123- under similar conditions gav e up to 40% yield of (I-123]8. In contrast reaction of 8 with 3 molar equivalents of unlabelled Bu4N+F- in refluxing acetonitrile yielded on ly 3.1% of 3 and 97% of elimination product. Similarly, reaction of a large excess of 8 with (Bu4N+F-)-F-18- at 80-degrees-C in acetonitrile failed to yield detectable quantities of [F-18]3. However, low (0-4%) yields of [F-18]3 were obtained using F-18- in the presence of varyin g proportions of inorganic base and Krytofix in acetonitrile.