(1) wherein the Ca-Nß, C5-C6" and C6-C7 bonds a re each single or double bonds, except that both C5-C6 and C6-C7 are double bonds Rl is selected from hydrogen, alkyl, aryl, and heterocycle R2-R15 are independently selected from hydrogen and other substituents and pharmaceutically-acceptable forms thereof. The subject invention also involves pharmaceutical compositions containing such compounds, and methods for treating . or preventing diseases and disorders using such compounds.