The present application describes compounds according to Formula I, pharmaceutical compositions comprising at least one compound according to Formula I and optionally one or more additional therapeutic agents, and methods of treatment using the compounds according to Formula I both alone and in combination with one or more additional therapeutic agents. The compounds have the following general formula: including all prodrugs, solvates, pharmaceutically acceptable salts and stereoisomers, wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are described herein.