A series of 2-amino-1,2,3,4-tetrahydronaphthalene compounds bearing substituents on the nitrogen and in the aromatic ring was synthesized from beta-tetralone intermediates. Compounds were screened in vivo for dopaminergic activity using tests in which apomorphine was especially active. It was found that apparent dopaminergic activity is inherent in 2-dialkylaminotetralins, the dipropylamine substitution being the most consistently productive amine group studies. Activity was greatly enhanced by proper substitution in the aromatic ring. The 5,6-dihydroxy group was the best potentiating group found. These data support the idea that the extended conformation for the phenylethylamine moiety of ampmorphine and dopamine is favorable for dopaminergic agonist activity. They also suggest that an unetherified catechol group may not be essential for such activity.

In an effort to identify further the structural requirements for central dopamine receptor agonists, some monohydroxyl analogs of the known agonist 5,6-dihydroxy-2-dipropylamino-1,2,3,4-tetrahydronaphthalene were synthesized. They were examined for production of emesis in dogs and stereotyped behavior in rats. The most potent was 5-hydroxy-2-dipropylamino-1,2,3,4-tetrahydronaphthalene, which was more potent than apomorphine but less so than the dihydroxyl analog. The two enantiomers of the monohydroxyl analog were synthesized by conventional methods from an optically active intermediate, 2-benzylamino-5-methoxy-1,2,3,4-tetrahydronaphthalene. The resolution of this amine was performed with the aid of mandelic acid. Dopaminergic activity was found to be confined to the levo enantiomer. Requirements for both substitution and chirality in the tetralines were found to correspond closely to those known for the dopaminergic aporphines.

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