2-(3,4-Di-chloro-phen-yl)-N-methyl-N-[2-(pyrrolidin-1-yl)cyclo-hex-yl]acetamide hydro-chloride: (±)-U50,488H.

The crystal structure of the methanol-solvated hydro-chloride salt of the selective κ-opioid receptor agonist (±)-U50,488, namely, 1-{2-[2-(3,4-di-chloro-phen-yl)-N-methyl-acetamido]-cyclo-hex-yl}pyrrolidin-1-ium chloride methanol monosolvate, C19H27Cl2N2O+·Cl-·CH3OH, is reported. The compound crystallized as a racemate of the (S,S) and (R,R) enanti-omers, consistent with the anti-selective nucleophilic substitution used in its synthesis. The cyclo-hexane ring adopts a chair conformation with an equatorial-equatorial conformation of its 1,2-substituents. Protonation occurs exclusively at the pyrrolidine nitro-gen atom, and the pyrrolidine ring displays a half-chair conformation twisted on the bond opposite the nitro-gen. In the crystal, the chloride anion forms a hydrogen-bonding network with the protonated pyrrolidine unit, the methanol solvent mol-ecule, and adjacent C-H groups. The crystal packing is further consolidated by C-H⋯O inter-actions involving the amide oxygen atom that form centrosymmetric dimers, alongside inter-molecular π-stacking and Cl⋯O halogen-bonding inter-actions. This study provides the first structural characterization of the hydro-chloride salt form of this widely used pharmacological compound.