Abstract

The hypnotic zaleplon displays novel receptor selectivity different from other benzodiazepine receptor ligands in clinical use. Zaleplon was successfully labeled with iodine-125 via electrophilic substitution reaction producing 125I-Zaleplon tracer. This reaction proceeds well in acidic pH of value equal to 4, due to the solubility of the Zaleplon in this acidic pH value. Chloramine-T (CAT) was used as oxidizing agent, at low amount of (CAT) (25–50 ug) the radiochemical yield of the labeled compound was low (80%) while at 200 ug, an optimum yield (97%) was obtained.Heating the reaction mixture to 40 oC for 15 min was recommended to get a yield more than 97%, but heating for longer time causes a decomposition of the labeled Zaleplon. The in-vitro stability of 125I-Zaleplon was determined along 24 hours; the data confirms that 125I-Zaleplon tracer was stable along eight hours without the detection of any by-products in the reaction mixture. The biodistribution data of the labeled Zaleplon shows rapid blood clearance passes through the blood brain barrier (BBB) and the activity detected in the brain exceeds 4.4% at 1 h post injection.

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