Synthesis of [75Se]trimethylselenonium iodide from [75Se]selenocystine

The synthesis of [75Se]trimethylselenonium iodide from [75Se]selenocystine is described. The starting compound is reduced to [75Se]selenocysteine with borohydride and reacted with methyl iodide to form [75Se]Se-methyl-selenocysteine, then treated with methyl iodide in formic acid solution to form Se-dimethyl-selenocysteine selenonium iodide. Over a period of days, the selenonium intermediate undergoes spontaneous elimination to form alanine and dimethyl selenide, which reacts with methyl iodide to give the trimethylselenonium product in over 90% yield.