Specific in vivo binding to the norepinephrine transporter demonstrated with the PET radioligand, (S,S)-[11C]MeNER.

(S,S)-2-(alpha-(2-Methoxyphenoxy)benzyl)morpholine (MeNER), an O-methyl analog of the selective and potent norepinephrine transporter (NET) inhibitor, (S,S)-reboxetine, and its less active enantiomer, (R,R)-MeNER, have each been radiolabeled by O-methylation of their corresponding phenolic precursors in good yields from [(11)C]methyl iodide or [(11)C]methyl triflate. Radiochemical purities were >99% and specific radioactivity at time of injection was about 74 GBq/micromol. Autoradiographic examination of (S,S)-[(11)C]MeNER binding to human brain slices post mortem indicated specific binding in a brain region including the locus coeruleus. PET examination of both [(11)C]MeNER enantiomers in a cynomolgus monkey demonstrated a higher specific binding of the (S,S)-enantiomer with ratios of 1.4-1.6 in the lower brainstem, mesencephalon and thalamus to striatum. Pretreatment with the NET ligand, desipramine, decreased the specific binding of (S,S)-[(11)C]MeNER. Labeled metabolites of [(11)C]MeNER were all more polar. (S,S)-[(11)C]MeNER is a good lead compound in the search for a selective radioligand for quantitation of NET in the human brain in vivo.