Synthesis and in vivo evaluation of both (2R,3R)-[123I]- and (2S,3S)- -[123I]-trans-2-hydroxy-5-((E)-3-(iodo) allyloxy)-3-(4-phenyl-1-piperazinyl) tetralin as SPECT radiotracer

We report the synthesis of enantiopure benzovesamicol derivatives: (2R,3R)-[123I]-trans-2-hydroxy-5-((E)-3- -(iodo)allyloxy)-3-(4-phenyl-1-piperazinyl) tetralin and (2S,3S)-[123I]-trans-2-hydroxy-5-((E)-3-(iodo)allyloxy)-3-(4- phenyl-1-piperazinyl) tetralin; [(2R,3R)-[123I]-1 and (2S,3S)-[123I]-1]. Both compounds were obtained with radiochemical and optical purities greater than 97% and with radiochemical yields in the range of 50–60%. To determine whether these compounds could have potential advantage compared to [125I]-iodo benzovesamicol (IBVM), IBVM was also labelled and used as the reference compound in all in vivo experiments. Both (2R,3R)-[123I]-1 and (-)-[125I]-IBVM showed similar time activity curves (TACs) with the highest accumulations in the striatum region followed by the cortex, hippocampus and then cerebellum. While (2S,3S)-[123I]-1 showed an overall homogeneous brain distribution. However, time activity curves of (2R,3R)-[123I]-1 confirmed that this compound could be used to visualize the vesicular acetylcholine transporter (VAChT) in vivo, at each point of the kinetic study. Also (2R,3R)-[123I]-1 showed lower specific bindings compared to [125I]-IBVM. These results suggested that (2R,3R)-[123I]-1 is inferior in comparison with [125I]-IBVM for in vivo VAChT exploration.