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The N-n-propyl homologues of the title compounds were prepared for further assessment of the ability of the "p-dimethoxy" moiety to confer dopaminergic agonism upon a variety of ring systems. Both the angularly and the linearly annulated trans-benzoquinoline ring derivatives displayed prominent DA2 dopaminergic effects on the peripheral sympathetic nerve terminal and displayed postjunctional dopamine receptor agonist properties in the striatum. It is speculated that the angular octahydrobenzo[f]quinoline derivative (but not the linear octahydrobenzo[g]quinoline derivative) may owe its dopamine-like effects to metabolic activation phenomena. In contrast, the cis-fused isomer of the angularly annulated benzoquinoline was inactive, as was the simple benzene derivative N,N-di-n-propyl-beta-(2,6-dimethoxyphenyl)ethylamine.

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p-Dimethoxyaryl analogs of certain potent catechol-derived dopaminergic agonists show dopaminergic properties for which no structure-activity relationship has yet been defined. (S)-3-(3-Hydroxyphenyl)-N-n-propylpiperidine (1, S-"3-PPP") is a dopaminergic autoreceptor agonist, and at high doses it also exhibits postsynaptic antagonism. (R)-1 is a postsynaptic agonist. In a continuation of studies of effects of the p-dimethoxy moiety at dopamine receptors, synthesis and resolution of the 2,5-dimethoxy analog 3 of 3-PPP was undertaken. The two enantiomers and the racemic modification showed cardiovascular effects consistent with actions at DA-2 receptors. The potency of all three compounds was much lower than that of 3-PPP, although they displayed approximately the same duration of action. Absolute configuration does not seem to be a major determinant of these compounds' ability to interact with DA-2 receptors.