Synthesis of [75Se]5-ethoxycarbonyl-4-methyl-1,2,3-selenadiazole

Selenium-75 (t1/2=120.4 d; 100% EC) was prepared in no-carrier-added form by 22 MeV proton-bombardment of natural arsenic(III) oxide powder held in a copper–aluminum drawer target (highest yield, 35 μCi/μAh; maximum current, 6 μA), followed by oxidation to [75Se]selenium(IV) oxide. No-carrier-added [75Se]5-ethoxycarbonyl-4-methyl-1,2,3-selenadiazole was prepared in one step from ethylacetoacetate semicarbazone with [75Se]selenium(IV) oxide in glacial acetic acid at 50°C. Column chromatography of the final solution afforded the desired labeled compound in 30% yield and greater than 98% radiochemical purity.