Synthesis and Structure-Affinity Relationships of Spirocyclic Benzopyrans with Exocyclic Amino Moiety

σ₁ and/or σ₂ receptors play a crucial role in pathological conditions such as pain, neurodegenerative disorders, and cancer. A set of spirocyclic cyclohexanes with diverse O-heterocycles and amino moieties (general structure III) was prepared and pharmacologically evaluated. In structure-activity relationships studies, the σ₁ receptor affinity and σ₁:σ₂ selectivity were correlated with the stereochemistry, the kind and substitution pattern of the O-heterocycle, and the substituents at the exocyclic amino moiety. cis-configured 2-benzopyran cis-11b bearing a methoxy group and a tertiary cyclohexylmethylamino moiety showed the highest σ₁ affinity ( K_i = 1.9 nM) of this series of compounds. In a Ca²⁺ influx assay, cis-11b behaved as a σ₁ antagonist. cis-11b reveals high selectivity over σ₂ and opioid receptors. The interactions of the novel σ₁ ligands were analyzed on the molecular level using the recently reported X-ray crystal structure of the σ₁ receptor protein. The protonated amino moiety forms a persistent salt bridge with E172. The spiro[benzopyran-1,1'-cyclohexane] scaffold and the cyclohexylmethyl moiety occupy two hydrophobic pockets. Exchange of the N-cyclohexylmethyl moiety by a benzyl group led unexpectedly to potent and selective μ-opioid receptor ligands.