Compounds, compositions and methods treating arthritic disorders such as osteoarthritis or rheumatoid arthritis, and for treating other diseases associated with altered mitochondrial function, such as cancer, psoriasis, stroke, Alzheimer's Disease and diabetes. The compounds of this invention have the following structure (I): including stereoisomers, prodrugs and pharmaceutically acceptable salts thereof, wherein R.sub.1-5 are as defined herein. The methods of this invention are directed to administering to a warm-blooded animal in need thereof an effective amount of a compound of structure (I), typically in the form of a pharmaceutical composition.