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: ##STR00001## including all prodrugs, pharmaceutically acceptable salts and stereoisomers, R.sup.1, R.sup.2, R.sup.3, R.sup.3a, R.sup.4, A, B, b, n, W, X, Y and Z are described herein.