Employing a rat fundus model, the serotonin (5-HT) receptor affinities of 45 phenalkylamine analogues were determined. Phenethylamine and phenylisopropylamine possess relatively low receptor affinities; in general, mono-, di-, and trimethoxylation enhance affinity. Of the disubstituted compounds, methoxyl groups at the 2 and 5 positions are optimal for imparting a high affinity. 4-Methylation, 4-ethylation and 4-bromination also enhance receptor affinity, while N,N-dimethylation of the terminal amine decreases affinity. alpha-Methylation of phenethylamines has little effect on affinity when racemates are examined. Introduction of a benzylic keto group can either increase or decrease affinity, depending upon the presence of other aromatic substituents. The most behaviorally active compounds were found to possess the highest 5-HT receptor affinities, while less active compounds were found to possess lower affinities.

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A series of cathinone (alpha-aminopropiophenone) analogues was examined using the isolated rat fundus preparation. (S)-(-)-Cathinone possesses twice the serotonin receptor affinity of (+/-)-cathinone and four times the affinity of racemic amphetamine. Several derivatives of cathinone were found to either possess a lower affinity than the parent compound or did not interact with the receptors in a competitive manner. Several novel analogues, 1-(aminomethyl)-3,4-dihydronaphthalene hydrochloride (3), 4-(aminomethyl)-3-chromene hydrochloride (4b), as well as its 6-methoxy derivative, a, interact with serotonin receptors but in a fashion which is, most likely, dissimilar to the interaction of the substituted cathinone analogues.

Hallucinogenic phenylalkylamine and N,N-dimethyltryptamine analogues are known to affect serotonergic systems both in vivo and in vitro. Using a rat stomach fundus model, the 5-HT receptor binding affinities of several of these analogues were determined and compared. The most behaviorally potent analogues examined, DOB, DOM, and 5-methoxy-N,N-dimethyltryptamine, were found to possess rather high affirmities (pA2 = 7.35, 7.12, and 7.08, respectively) for the 5-HT receptors of the model system.

Mono-O-demethylation of several 2,5-dimethoxyphenalkylamines increases their affinity for the serotonin receptors of the isolated rat fundus preparation. In several instances, demethylation of methoxyphenalkylamines results in compounds which produce an antagonism which is not of a competitive nature. With respect to 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), demethylation of the 2-methoxy group alters affinity in a manner which parallels that observed upon demethylation of 5-methoxy-N,N-dimethyltryptamine. Using a discriminative stimulus paradigm, behavioral studies with rats reveal that the 2-hydroxy analogue, but not the 5-hydroxy analogue, of DOM produces effects (interoceptive cues) similar to those produced by 5-methoxy-N,N-dimethyltryptamine.