The present invention relates to derivatives of known active pharmaceutical compounds. These derivatives are differentiated from the parent active compound by virtue of being redox derivatives of the active compound. This means that one or more of the functional groups in the active compound has been converted to another group in one or more reactions which may be considered to represent a change of oxidation state. We refer to these compounds generally as redox derivatives. The derivatives of the invention may be related to the original parent active pharmaceutical compound by only a single step transformation, or may be related via several synthetic steps including one or more changes of oxidation state. Exemplary derivatives have the formula