**4. Conclusions**

In conclusion, a series of ebselen, diaryl selenides and spirodiazaselenuranes and its glutathione peroxidase (GPx) activity were discussed. A detailed mechanistic study suggests that the spirocyclization occurs *via* the formation of selenoxide intermediates. The glutathione peroxidase (GPx) mimetic activity of the selenides and the spirodiazaselenuranes indicates that the substituents attached to nitrogen atom have significant effect on the activity. Therefore, the selenoxide intermediates involved in the cyclization process could be isolated at the room temperature when it reacts with methyl halide. The comparison of the GPx-like activity showed that the antioxidant activity of diaryl selenids shows significant antioxidant activity due to oxidation of selenium and followed by the addition of H2O2 leads to spiro-compounds. Therefore, these compounds can provide a better protection against reactive oxygen species like H2O2 and peroxynitrite.
