Production of selenium-75 and radiosynthesis of [75 Se]-4-ethoxycarbonyl-5-methyl-1,2,3-selenadiazole

75 Se-Selenium is a potential radioisotope used in gamma camera calibration and preparation of adrenal imaging agents. It has been prepared in no-carrier-added (n.c.a) form, by 22 MeV proton-bombardment of a compressed disc of high purity natural arsenous oxide, using a newly designed copper-aluminum drawer target in a 30 MeV cyclotron at NRCAM. As a model compound, [75 Se]-4-ethoxycarbonyl 5-methyl 1,2,3-selenadiazole (2b) was prepared from ethylacetoacetate semicarbazone (1) in one step using [75 Se]-selenium dioxide in glacial acetic acid as the solvent at 50 deg C. Column chromatography by silica and C18 short columns afforded the desired labeled compound in 25-30 % yield with a specific activity about 3 Ci/mmol and radiochemical purity more than 95% at a high purity. Chemical and radiochemical analysis by TLC and RTLC showed that the radiosynthesis had been successful. The final solution was then purified for biological studies on test animals. (author)