Structure-activity relationships of N-n-propyl-2-(4-fluoro-3-hydroxyphenyl)ethylamine derivatives as dopamine receptor ligands

A series of N-n-propyl-2-(4-fluoro-3-hydroxyphenyl)ethylamine derivatives obtained by introducing on nitrogen atom a 2-phenylethyl moiety (with aromatic nucleus substituted at 3 or 4 position with fluorine, chlorine or hydroxy and methyl groups), as well as a 2-cyclohexylethyl or 3-phenylpropyl groups were synthesized. These substituents can interact with the D2 accessory binding site pi 3. The affinities of new compounds for D1 and D2 subtypes of dopamine (DA) receptor were measured in a test involving displacement of [3H]SCH 23390 and [3H]spiperone, respectively, from homogenates of rat striatum. The new derivatives are selective for D2 sites, and are more potent than the parent compound N-n-propyl-N-(2-phenylethyl)-2-(4-fluoro-3-hydroxyphenyl)ethylamine 2a. The N-n-propyl-N-[2-(4-hydroxyphenyl)ethyl]-2-(4-fluoro-3-hydroxyphenyl) ethylamine (11f) is the most potent and selective member in the series. Other derivatives are less effective but are as potent as the D2 agonist RU 24213. The results indicate that the pi 3 site is a rather large lipophilic pocket which can accommodate not only aromatic nuclei, but also the cyclohexyl group.