2-Thiouracil- 13 C, 15 N 2 is the 13 C, 15 N labeled 2-Thiouracil. 2-Thiouracil (Thiouracil) is an antithyroid compound. 2-Thiouracil can function as a highly specific melanoma seeker. 2-Thiouracil is a selective inhibitor of neuronal nitric oxide synthase ( nNOS ) with a Ki of 20 μM.