Abstract
Three ^11^C‐labelled tracers for the serotonin reuptake site, S‐[N‐methyl‐^11^C]citalopram ([^11^C]‐4), S‐[N‐methyl‐d~3~‐^11^C]citalopram ([^11^C]‐12), and S‐[N‐methyl‐^11^C]citalopram‐α,α‐d~2~ ([^11^C]‐13) were synthesized and the distribution of radioactivity after injection of radioligand was examined ex vivo in rats. The deuterated analogue of (S)‐desmethylcitalopram, (S)‐1‐(4‐fluorophenyl)‐1‐(3‐methylamino‐[3‐d~2~]‐propyl)‐1,3‐di‐hydro‐isobenzofuran‐5‐carbonitrile (11), was synthesized in a multi‐step synthesis from escitalopram (4) and used as precursor in the synthesis of [^11^C]‐13. In analogy with the reported gas phase synthesis of [^11^C]methyl iodide the first gas phase synthesis of [^11^C]Methyl iodide‐d~3~ is reported. The ^1^H/^2^H kinetic isotope effect related to the synthesized compounds were investigated in ex vivo rat studies, where the brain regions of interest to cerebellum ratios of the tracers [^11^C]‐4, [^11^C]‐12 and [^11^C]‐13 were compared. The ex vivo data indicated no significant differences in binding in any of the investigated brain regions after injection of the three tracers. Copyright © 2004 John Wiley & Sons, Ltd.