SYNTHESIS AND EVALUATION OF 5-HT3 RECEPTOR ANTAGONIST [C-11] KF17643

For imaging CNS 5-HT3 receptors by PET, a high affinity 5 HT3 receptor ligand, endo-8-methyl-8-azabicyclo[3.2.1]oct-3-yl 2-(n-propyloxy)-4-q uinolinecarboxylate (KF17643), have been labeled with C-11. N Methylat ion of the desmethyl compound with [C-11]methyl iodide followed by HPL C separation produced [C-11]KF1764 3 with the decay corrected radioche mical yield of 19-28%, the specific activity of 7.5-4 9 GBq/mu mol and the radiochemical purity of >99% at 35-40 min from EOB. After i.v. in jection of [C-11]KF17643 into mice, it was taken by the brain at a hig h level and was stable for metabolism, but no sign for the 5-HT3 recep tor selectivity was found in the brain tissues by the tissue sampling and autoradiography, probably because of large non-specific binding. T he [C-11]KF17643 was not suitable as a PET ligand for mapping the CNS 5-HT3 receptors.