Reactions of Organoselenenyl Iodides with Thiouracil Drugs: An Enzyme Mimetic Study on the Inhibition of Iodothyronine Deiodinase

The proposed mechanism of iodothyronine deiodinase inhibition by the thiourea‐derived drugs 6‐n‐propylthiouracil (PTU) and 6‐methylthiouracil is supported by experimental evidence. Model reactions with sterically or coordinatively stabilized organoselenyl iodides as enzyme‐mimetic substrates (E‐SeI; see scheme) support the proposal that PTU reacts not with the enzyme but with the enzyme–SeI intermediate containing a covalent Se−I bond, and suggest that the Se−I bond is kinetically activated by basic amino acid groups such as histidine.