Novel 6-ketolevorphanol analogs with diverse substitution patterns at ring C were synthesized and their binding affinities at the μ,δ and κ opioid receptors were investigated. The in vitro activity of the new analogs was then evaluated in the functional assay based on the electrically-stimulated contractions of the mouse ileum. It was shown that analogs with Δ7,8 bond had no significant potency at any of the opioid receptor types. In contrast, analogs with the saturated ring C were either potent κ agonist or antagonist depending on the absence or presence of the hydroxyl group in position 14.