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 125 I-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g) the radiochemical yield of the labeled compound was low (80%) while at 200 g, an optimum yield (97%) was obtained.Heating the reaction mixture to 40 C 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 125 I-Zaleplon was determined along 24 hours; the data confirms that 125 I-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.

This paper addresses the development of a new radiopharmaceutical for cancer imaging and therapy. The optimization of the labeling conditions of thymidine analogue, melphalan, with 125 I is described. High radiochemical yield 96.8% was obtained by reacting 0.2 mg melphalan with 125 I in the presence of choloramin-T as oxidizing agent in 0.5 M phosphate buffer, pH 7, at 701C for 15 min. Preliminary in vivo study was done in non-tumor bearing mice. The results revealed that this new tracer, 125 I-melphalan, has a high affinity to be localized in the tumor site for a long period, which indicates the specificity of this tracer to the tumor cells. The labeled compound was cleared quickly from most of the body organs. These findings suggest that 125 I-melphalan allows imaging and treatment of cancer. 125 I-melphalan meets most of the requirements necessary to be used as a successful diagnostic and therapeutic agent: it is a low-molecular-weight molecule that diffuses readily in the tissues, and dose not induce an antibody response.

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