L-Selenocysteine which is the 21st proteinogenic amino acid containing selenium exists in 25 mammalian selenoproteins. Therefore, the target of our laboratory is to design and synthesize novel organoselenium and organotellurium compounds as the "Multifunctional Regenerable Antioxidants" which could be expected to mimic the actions of such selenoenzymes as preventive, peroxide-decomposing and radical-trapping antioxidants. The next agenda of our research is the development of "Mitochondria-directed Novel Fluorogenic Antioxidant Probes". We conduct a number of kinetic, analytical and biological methods to evaluate the antioxidant capacities of catalysts. Into a more biologically setting, the ROS-scavenging capacity and cytotoxicity effects of catalysts in human cell lines will be studied. We support our synthetic mechanisms and biological evaluations of antioxidants based on computational chemistry. We feel that these synthetic antioxidants would be considered for future life in treatment of several diseases where the natural antioxidant defenses are overwhelmed (cardiovascular diseases, neurodegenerative diseases, Alzhiemer’s and Parkinson’s diseases etc.