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Summary. So far, [carbonyl- 11 C]WAY-100635 is the PET-tracer of choice for 5HT 1A -receptor-imaging. Since thepreparation is still a challenge, we aimed at (1) the eval-uation of various essential parameters for the successfulpreparation, (2) the simplification of the radiosynthesis and(3) the establishment of a safe and fully automated system.The preparation is based on a commercial synthesizer andall chemicals are used without further processing. We founda low failure rate (7 . 7%), high average yield (4 . 0±1 . 0GBq)and a specific radioactivity of 292 ±168 GBq / µmol (both atthe end of synthesis, EOS). Introduction Carbon-11 labelled WAY-100635 ( N -(2-(1-(4-(2-methoxy-phenyl)-1-piperazinyl)ethyl))- N -(2-pyridyl)-cyclohexane-carboxamide; WAY) was introduced into positron emis-sion tomography (PET) as a highly potent and selectiveantagonist at the 5HT 1A receptors more than a decade ago.Since 5HT 1A receptors are implicated in the pathogenesisof anxiety, depression, eating disorders and motion sick-ness, they are an important target for drug therapy [1,2].The visualisation and quantification of this receptor is a ba-sis for further exploration of molecular pathologies causingpsychiatric conspicuousness. The most extensively studiedtracers are two carbon-11 labelled WAY-100635 derivatives,[O-methyl

PET imaging of the μ-opioid receptor (OR) is still restricted to [11C]carfentanil ([11C]CFN) but its use is limited due to its short half-life and high agonistic potency. Recently, the radiosynthesis of [18F]fluoroalkyl esters of CFN was proposed, unfortunately yielding products not suitable for human PET due to their low specific activities. Therefore, our rationale was to develop a reliable radiosynthesis of a [18F]fluoroethylated CFN derivative overcoming these drawbacks. The [18F]fluoroethyl ester of carfentanil, [18F]FE@CFN (2-[18F]fluoroethyl 4-[N-(1-oxopropyl)-N-phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate), and its corresponding inactive standard compound were prepared. Purification of [18F]FE@CFN was achieved via a simple solid phase extraction method. [18F]FE@CFN was prepared with excellent purity (> 98%) and sufficient yields. Specific activity surpassed the level required for safe administration. We therefore conclude that our simplified synthesis of [18F]FE@CFN, for the first time, overcomes the shortcomings of [11C]CFN and the previously suggested alternatives, namely, (1) longer half-life; (2) easy production and (3) adequate specific activity, should make a wider application possible. Hence, [18F]FE@CFN may become a valuable PET tracer for the imaging of the μ-OR in human brain and heart.

In vivo labelling of serotonergic receptors (5HT) could be a useful tool for understanding the physiological and pathophysiological role of neurodegenerative disorders. 1-[2,5-Dimethoxy-4-iodophenyl]-2-aminopropane (DOI), a well known agonist with high affinity to 5HT2 receptors, was labelled with C-11 for PET. Here we report the evaluation of the mono-methylated and dimethylated analogs of DOI for PET. The syntheses of [N-11C-methyl]-DOI ([11C]MDOI) and [N-11C-dimethyl]-DOI ([11C]DMDOI) were optimized resulting in radiochemical yields of up to 43%, allowing efficient production for clinical use. High affinities for the 5HT2A and 5HT2C receptors with a slight preference for 5HT2A were found for MDOI, similar to the highly potent hallucinogen DOI.