Glycogen synthase kinase 3 (GSK-3) is a serine/threonine protein kinase. Development of GSK3 inhibitor Alsterpaullone as a therapeutic agent for mood disorders, such as Alzheimer's disease and bipolar disorder, required the synthesis of a suitably labeled drug product for use in human metabolism and pharmacokinetic studies. Owing to the potential metabolic degradation of the molecule, a multi-labeled approach utilizing (14)C was adopted. The synthesis of [(14)C]Alsterpaullone was accomplished in separate routes from methyl-[1, 2-(14)C]-2-bromoacetate and [1, 2-(14)C]-2-bromoethanol, respectively. Labeled versions were combined on the basis of molar radioactivity giving a final product with a radiochemical purity of 99.0% and a specific activity of 54.0 mCi/mmol.