Synthesis of selenocysteine-containing dipeptides modeling the active site of thioredoxin reductase

Four cyclic dipeptides modeling the active site of thioredoxin reductase (TrxR), UU, CU, UC, and CC, where U and C represent selenocystine and cystine, respectively, were synthesized and their glutathione peroxidase (GPx)-like catalytic activity was evaluated by the reaction of hydrogen peroxide (H2O2) with glutathione (GSH) in the presence of glutathione reductase (GR). Among these, only UC exhibited the significant antioxidant capacity, suggesting that an atomic environment around the Se–S bond is relevant to the reactivity toward a thiol substrate.