Synthesis, Characterization, and Functionality of Quinol-Based Superoxide Dismutase Mimics

Abstract

There is great interest in developing biopharmaceuticals that can slow or halt the effects of the primary and secondary oxidative stressors that are responsible for aging, chronic diseases, and other health disorders. A number of enzymes are capable of degrading reactive oxygen species (ROS) into less toxic H2O and O2. One such enzyme is superoxide dismutase (SOD), which catalyzes the conversion of superoxide (O2-·) to H2O2 and O2. Catalase is another antioxidant enzyme that instead targets H2O2, converting it to O2 and H2O. In many health conditions, the concentrations of ROS rise to levels that can overwhelm the defense system provided by SOD and other antioxidant enzymes, making the body more susceptible to oxidative stress. A therapeutic strategy to combat disorders resulting from oxidative stress would be to administer a pharmaceutical capable of catalytically degrading ROS. Consequently, small molecule mimics of SOD have been explored heavily. Most SOD and catalase mimics derive activity from a redox-active metal cation. Unfortunately, the ligands of the most active mimetics are difficult to modify and prepare in high quantities. In this dissertation, I complex a series of highly modifiable redox-active quinol-containing organic ligands to either redox-active or redox-inactive metal ions to yield a variety of potent antioxidants that mimic either SOD or catalase. With respect to the SOD mimics, the activity can be enhanced by i) altering the coordination sphere of the metal complexes to improve the accessibility of superoxide, ii) making the overall charge more positive, iii) and stabilizing key mechanistic intermediates. Surprisingly, the complexes instead target H2O2 when the metal center is more positively charged; the selection of metal therefore determines whether the complex is a mimic of SOD or catalase. The ability of these ligands to allow redox-inactive metals to catalyze ROS degradation is novel, and the work in this dissertation has outlined key structure-function trends.