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 general Formula I ##STR1##

including all prodrugs, pharmaceutically acceptable salts and stereoisomers, R¹, R², R³, and R⁴ are described herein.