Thyroxine Methyl Ester- 13C6 is an intermediate in the synthesis of Thyroxine-13C6 4’-O-β-D-Glucuronide Disodium Salt, which is labelled Thyroxine 4’-O-β-D-Glucuronide (T425630), a major metabolite and glucuronide conjugate of Thyroxine (T425600) formed via the glucuronidation of the phenyl hydroxyl group.