In one aspect, the invention provides compounds of Formula I: (I) and pharmaceutically acceptable salts and solvates thereof, wherein R1, R2, R3, R4, R5, Y, Za are defined as set forth in the disclosure. The invention also provides compounds of any one of Formulae II to VII, IA to IC, and IIA to IIC, and pharmaceutically acceptable salts and solvates thereof. Other aspects of the invention include the use of compounds of Formulae I to VII, IA to IC, and IIA to IIC, and pharmaceutically acceptable salts and solvates thereof for the treatment of disorders responsive to modulation of one or more opioid receptors. In certain embodiments, the Compounds of the Invention are useful for treating pain.
