This invention relates to methods to screen for, identify, select and synthesise amphiphilic mitochondrially targeted antioxidant compounds, and compositions, dosage forms and methods reliant on said compounds. The exemplified compounds are all mitoquinone derivatives, being methoxyphenyl alkyl triphenylphosphonium or methoxy dioxocyclohexadiene alkyl triphenylphosphonium derivatives. The compounds, compositions, dosage forms and methods are useful in, for example, the treatment of diseases or conditions associated with oxidative stress.