Synthesis and σ₁ Receptor Binding of Halogenated N,N'-Diphenethylethylenediamines

Eight halogenated N,N'-diphenethylethylenediamines were synthesized, characterized and evaluated for σ₁ receptor binding affinity in vitro. Measurements of lipophilicity also were obtained. The substitution pattern on one of the aromatic rings remained constant as 3,4-dichloro, while the substituents on the other aromatic ring were varied to include fluorine, bromine or iodine in either the 2-, 3- or 4- positions. Two main structure activity relationships were observed. First, halogen substitution on the 3- or 4-positions of the aromatic ring conferred higher binding affinities (K_i values 6.35 - 15.82 nM) than the corresponding substitutions at the 2-position (K_i values 12.08 - 43.15 nM). Second, derivatives containing either a bromo or fluoro substituent at a given position showed higher σ₁ receptor binding affinities than derivatives with a corresponding iodo substituent. The data indicate that σ₁ receptor affinity for this structural series is sensitive to steric bulk at the 2-position. Log k'_w measurements for the halogenated N,N'-diphenethylethylenediamines were determined by high performance liquid chromatography, and varied from 2.54 - 3.71. In particular, the 3-fluoro analog exhibited a log k'_w = 2.54 accompanied by a σ₁ receptor K_i = 7.8 nM. These novel N,N'-diphenethylethylenediamines warrant further investigation in behavioral assays, and radiolabeled versions may prove suitable for in vivo studies of σ₁ receptors.