With [3H]ketanserin as the radioligand, structure-affinity relationships (SAFIRs) for binding at central 5-HT2 serotonin receptors (rat frontal cortex) were examined for a series of 27 4-substituted 1-(2,5-dimethoxyphenyl)-2-aminopropane derivatives (2,5-DMAs). The affinity (Ki values) ranged over a span of several orders of magnitude. It appears that the lipophilic character of the 4-position substituent plays a major role in determining the affinity of these agents for 5-HT2 receptors, 2,5-DMAs with polar 4-substituents (e.g. OH, NH2, COOH) display a very low affinity (Ki greater than 25,000 nM) for these receptors, whereas those with lipophilic functions display a significantly higher affinity. The results of these studies prompted us to synthesize and evaluate examples of newer lipophilic derivatives and several of these (e.g. n-hexyl, n-octyl) bind with very high (Ki values = 2.5 and 3 nM, respectively) affinities at central 5-HT2 sites. Although, 2,5-DMAs are generally considered to be 5-HT2 agonists, preliminary studies with isolated rat thoracic aorta suggest that some of the more lipophilic derivatives (e.g. the n-hexyl and n-octyl derivatives) are 5-HT2 antagonists.

No abstract

No abstract

No abstract

1-(4-Bromo-2,5-dimethoxyphenyl)-2-aminopropane (DOB) is a serotonin (5-HT) agonist that displays a high affinity and selectivity for a certain population of central 5-HT binding sites (i.e., 5-HT2 sites). In the present study, (a) an enantiomeric potency comparison was made for the optical isomers of DOB and (b) the activity of N-monomethyl-,N,N-dimethyl-, and N,N,N-trimethyl-DOB was examined. (R)-(-)-DOB (Ki = 0.39 nM) was found to have 6 times greater affinity than its S-(+) enantiomer at [3H]DOB-labeled (rat cortical homogenates) 5-HT2 sites; N-methylation of racemic DOB resulted in a decrease in affinity that was at least 1 order of magnitude per methyl group. Similar results were obtained in an in vivo drug discrimination paradigm with rats as subjects and (R)-(-)-DOB (0.2 mg/kg) as the training drug. Thus, the R-(-) isomer of DOB is more active than its S-(+) enantiomer and than any of the possible N-methyl derivatives of DOB, both with respect to affinity at central 5-HT2 binding sites and with respect to potency in the behavioral (i.e., stimulus generalization) studies.