We designed and synthesized of 1,3,5-trioxazatriquinanes with o- or p-hydroxyphenyl rings as analogs of the κ opioid receptor agonist SYK-146 with m-hydroxyphenyl groups. Although almost all tested compounds did not bind to the opioid receptors, only 17b (SYK-524) with two o-hydroxyphenyl rings showed moderate or potent binding affinities and exhibited agonistic activities for the three opioid receptor types. Because the basicity of the nitrogen atom in the 1,3,5-trioxazatriquinane structure was predicted to be very low due to the electron withdrawing effect of the three oxygen atoms, SYK-524 was a novel non-morphinan and nonpeptidic opioid universal agonist lacking a basic nitrogen atom.