The present invention is directed to Buprenorphine Analog compounds of the Formula (I), Formula (IA) or Formula (IB) shown below, wherein R1, R2, R8, R 3a, R 3b, G, X, Z and Y are as defined herein. Compounds of the Invention are useful for treating pain, constipation, and other conditions modulated by activity of opioid and ORL-1 receptors.