Potential anxiolytic properties of R-(+)-8-OSO2CF3-PAT, a 5-HT 1A receptor agonist

The anxiolytic property of R-(+)-8-OSO2CF3-PAT(R-(+)-8- [[(trifluoromethyl)sulfonyl]oxy]-2-(n-propyl-amino)tetralin), a 5-HT1A receptor agonist, was evaluated in Wistar rats by means of animal models of anxiety, the conditioned defensive burying model and the conditioned stress-induced freezing response followed by the elevated plus-maze test, respectively. In addition, the 5-HIAA/5-HT ratio (5-hydroxy-indole acetic acid/5-hydroxytryptamine) of rat brain homogenates was studied. Acute drug administration resulted in abolition of the burying behaviour (3 mg/kg i.p.), a dose-dependent decrease of rearing and induction of hyperphagia. R-(+)-8-OSO2CF3-PAT had no effect on conditioned footshock-induced freezing behaviour but increased open-arm activity in the rats on the plus-maze. The 5-HIAA/5-HT ratio was decreased in the lateral septum (1 and 3 mg/kg), dorsal hippocampus (3 mg/kg) and somatosensory cortex (3 mg/kg), implying that R-(+)-8-OSO2CF3-PAT affects particularly the limbic system in anxiety-inducing situations.

Characterization of binding of [3H]PD 128907, a selective dopamine D3 receptor agonist ligand, to CHO-K1 cells

PD 128907 [4a R, 10 b R-(+)-trans-3, 4, 4a, 10 b - tetrahydro - 4- n -propyl2 H,5H-[1]benzop-yrano[4,3-b]1,4-oxazin-9-ol.], a selective dopamine (DA) D3 receptor agonist ligand exhibits about a 1000-fold selectivity for human D3 receptors (Ki, 1 nM) versus human D2 receptors (Ki, 1183 nM) and a 10000-fold selectivity versus human D4 receptors (Ki, 7000 nM) using [3H]spiperone as the radioligand in CHO-K1-cells. Studies with [3H]PD 128907, showed saturable, high affinity binding to human D3 receptors expressed in CHO-K1 cells (CHO-K1-D3) with an equilibrium dissociation constant (Kd) of 0.99 nM and a binding density (Bmax) of 475 fmol/mg protein. Under the same conditions, there was no significant specific binding in CHO-K1-cells expressing human D2 receptors (CHO-K1-D2). The rank order of potency for inhibition of [3H]PD 128907 binding with reference DA agents was consistent with reported values for D3 receptors. These results indicate that [3H]PD 128907 is a new, highly selective D3 receptor ligand with high specific activity, high specific binding and low non-specific binding and therefore should be useful for further characterizing the DA D3 receptors.

Assessment of cocaine-like discriminative stimulus effects of dopamine D3 receptor ligands

The highly selective dopamine D3 receptor ligand, (+)-PD 128907 4aR10bR-(+)-trans-3,4,4a,10b-tetrahydro-4-n-propyl-2H5H[4,3- b]-1,4- oxazin-9-ol), and other dopamine D3 receptor ligands, (+/-)-7-hydroxy-2-(N,N-di-n-propylamino)tetralin and (+)-7-hydroxy-2-(N,N-di-n-propylamino)tetralin, substituted for the discriminative stimulus effects of cocaine in rats, an animal model of subjective effects in humans. Substitution only occurred at doses that markedly decreased responding. These results suggest that dopamine D3 receptors may be involved in the subjective effects of cocaine, and therefore may be a target for the discovery of treatments for cocaine dependence.

Structure-activity relationships in the 8-amino-6,7,8,9-tetrahydro-3H-benz[e]indole ring system. 1. Effects of substituents in the aromatic system on serotonin and dopamine receptor subtypes

A series of 1-, 3-, and 4-substituted analogs to the potent 5-HT1A against 8-(dipropylamino)-6,7,8,9-tetrahydro-3H-benz[e]indole-1-carbaldehyde (5) were prepared and tested in vitro at 5-HT1A, 5-HT1D alpha, 5-HT1D beta, D2, and D3 receptors and in vivo for agonist activity in the 5-HTP and DOPA accumulation assays in reserpine-pretreated rats. Some of the compounds were resolved. The substituents used in the 1-position were chosen from a principal component analysis (PCA) plot constructed from both tabulated variables and variables calculated by semiempirical methods (PM3) and molecular mechanics software (MMX). Among the analogs prepared, some, e.g., compound 21, were equipotent to compound 5 with respect to 5-HT1A effects. All compounds were more or less selective for the 5-HT1A receptor, but many of the compounds displayed higher affinities for 5-HT1D alpha than for 5-HT1D beta receptors.

Structure-activity relationships in the 8-amino-6,7,8,9-tetrahydro-3H-benz[e]indole ring system. 2. Effects of 8-amino nitrogen substitution on serotonin receptor binding and pharmacology

A series of analogs of the potent and selective 5-HT1A agonist 8-(di-n-propylamino)-6,7,8,9-tetrahydro-3H-benz[e]indole-1-carbaldehyde (2b) (OSU191) was prepared in which the dipropylamino group was modified to bear a variety of substituents. These compounds were evaluated for both in vitro and in vivo effects, including the establishment of a receptor binding profile for these analogs at the 5-HT1A, dopamine D-2, dopamine D-3, 5-HT1D alpha, and 5-HT1D beta sites. Several of the analogs were evaluated for their biochemical effects in reserpinized rats, specifically with regard to in vivo changes in brain levels of 5-HTP and DOPA. Nearly all of the compounds prepared for this study were exceedingly potent at the 5-HT1A receptor, although most also displayed significant affinity for the dopamine D-2 receptor. A strong preference for the 5-HT1D alpha over the 5-HT1D beta receptor was also apparent. An analog bearing a butylglutarimide side chain, S-7k, was extremely selective for the 5-HT1A receptor. Although this compound possessed a Ki of 0.6 nM, it elicited only modest changes in 5-HTP brain levels. However, this compound did not appear as an antagonist when tested in a cyclic-AMP-based intrinsic activity assay.

6,7,8,9-Tetrahydro-N,N-di-n-propyl-3H-benzindol-8-amines. Derivatives as potent and orally active serotonin 5-HT1A receptor agonists

Derivatives and isosteric derivatives of the potent 5-HT1A agonist 8-(di-n-propylamino)-6,7,8,9- tetrahydro-3H-benz[e]indole-1-carbaldehyde (5) were prepared and evaluated in vivo and in vitro for serotonergic and dopaminergic activity. The 1-cyano analog 8 was found to be almost equipotent to 5 and the previously described 2-cyano derivative 6, while a 1-chloro and 1-(1,1,1-trifluoroethyl) substituent (9 and 10, respectively) formed less potent derivatives. The isosteric 6,7,8,9-tetrahydro-1H-benz[g]indoles 4 and 12-15 showed surprisingly low affinity or activity at both serotonergic and dopaminergic systems. The interpretations of these results by means of drug-receptor interactions at the 5-HT1A subtype are discussed. Compounds 6 and 8 were found to have high oral bioavailability in the rat (63% and 54%, respectively).

Substituted (S)-phenylpiperidines and rigid congeners as preferential dopamine autoreceptor antagonists: synthesis and structure-activity relationships

A series of (S)-phenylpiperidines in which the substituents on the aromatic ring and nitrogen have been varied has been prepared. They have been evaluated pharmacologically to explore the importance of these substituents for the interaction with central dopamine (DA) receptors. On the basis of biochemical and behavioral data in rats, several of these compounds are characterized as centrally acting DA autoreceptor antagonists. (S)-Phenylpiperidines having an aromatic substituent with a high group dipole moment in the 3-position, i.e., meta with respect to the piperidine ring, and being N-substituted with a propyl group were found to be highly active in vivo on the synthesis and turnover of dopamine. However, they do not induce strong hypoactivity or catalepsy. Interestingly, the most active compounds in vivo were found to display only low affinity for DA D2 and D3 receptors in vitro. In addition, 7-triflate-substituted octahydrobenzo[f]quinolines and 6-triflate-substituted hexahydro-1H-benz[e]indoles have been prepared and pharmacologically evaluated. The trans isomers of these rigid structures were found to display a pharmacological profile similar to that of the flexible phenylpiperidines. The corresponding cis isomers were found to be inactive in vivo.

Pharmacological aspects of R-(+)-7-OH-DPAT, a putative dopamine D3 receptor ligand

The R-(+)-isomer of 7-hydroxy-2-(N,N-di-n-propylamino)tetralin (7-OH-DPAT) bound with a more than 200-fold higher affinity to cloned human dopamine D3 receptors (Ki = 0.57 nM) than to dopamine D2 receptors; the corresponding S-(-)-enantiomer had considerably less affinity for both dopamine receptor subtypes, indicating that the known enantiomer selectivity of 7-OH-DPAT for the 'classical' dopamine D2 receptor subtype extends to the recently discovered dopamine D3 receptor subtype. In rats R-(+)-7-OH-DPAT dose dependently (10-1000 nmol/kg) decreased dopamine release and induced yawning, while sniffing behaviour occurred at the highest dose tested (1000 nmol/kg). The possibility that the inhibition of dopamine release and the elicitation of yawning are mediated by dopamine D3 receptors is considered.

Orally active central dopamine and serotonin receptor ligands: 5-, 6-, 7-, and 8-[[trifluoromethyl)sulfonyl]oxy]-2-(di-n-propylamino)tetralins and the formation of active metabolites in vivo

The racemic triflate derivatives 5-8 of the 5-, 6-, 7-, and 8-hydroxylated 2-(di-n-propylamino)-teralins 1-4 were shown to possess similar pharmacological profiles to their phenolic counterparts in in vitro binding and in vivo biochemical and behavioral assays in rats. Consequently, subcutaneous administration of the 5-, 6-, and 7-triflates displayed essentially dopaminergic agonist properties, while the 8-triflate was shown to be a selective 5-HT1A receptor agonist. With respect to their agonist activities, the triflates were less potent than their phenolic analogs. The absolute oral bioavailability of compound 8 (8-triflate) was 4-5 times greater than the corresponding hydroxylated compound. Interestingly, in the in vivo biochemical assay compound 8 was found to be more potent after oral than after subcutaneous administration, indicating formation of one or more active metabolites. Following a study of the metabolism of compound 8 in rat hepatocytes, the monopropyl analog 9 was identified as the major metabolite and was surprisingly found to be more potent than compound 8. Oral administration of compound 5 (5-triflate) resulted in behavioral and biochemical effects indicative of mixed DA/5-HT1A agonist properties not seen after subcutaneous administration. These results may also be indicative of the formation of active metabolites.

Substituted 3-phenylpiperidines: new centrally acting dopamine autoreceptor antagonists

The (+)-and (-)-enantiomer of compounds 4 and 5 were synthesized and tested for central dopamine (DA) receptor stimulating activity, using biochemical and behavioral tests in rats. Based on the available data the (-)-enantiomers of 4 and 5 are characterized as centrally acting DA autoreceptor antagonists with oral activity. They display a similar pharmacological profile as the prototype DA autoreceptor antagonists (+)-1 and (+)-2 and show a certain preference for the D3 DA receptor antagonist binding site.

(S)- and (R)-8-(di-n-propylamino)-6,7,8,9-tetrahydro-3H-benz[e]indole-1- carbaldehyde: a new class of orally active 5-HT1A-receptor agonists

The enantiomers of 6,7,8,9-tetrahydro-N,N-di-n-propyl-3H-benz[e]indol-8- amine (S-(-)-2b and R-(+)-2b) and their corresponding 1-formyl analogs (S-(-)-6 and R-(+)-6) were prepared and evaluated pharmacologically for serotonergic and dopaminergic activity. The introduction of a formyl group in the 1-position shifted the pharmacological profile of 2b from a mixed D2/5-HT1A agonists to a selective 5-HT1A agonist (6). The enantiomers of 6 were agonists with full intrinsic activity and had an affinity comparable to that of 8-hydroxy-2-(di-n-propylamino)tetrahydronaphthalene (8-OH-DPAT). In contrast to 8-OH-DPAT, the enantiomers of compound 6 were found to have good oral availability.

6-Hydroxy-3-n-propyl-2,3,4,5-tetrahydro-1H-3-benzazepine and analogs: new centrally acting 5-HT1A receptor agonists

The ring-closed phenylethylamine analogue 6-hydroxy-3-n-propyl-2,3,4,5-tetrahydro-1H-3-benzazepine (1) is a 5-HT1A receptor agonist of moderate potency, according to both in vivo biochemical data and in vitro binding data. The active compounds of this series also induce the 5-HT behavioral syndrome. Molecular modeling studies were performed with molecular mechanics calculations, and a tentative explanation for the relatively low potency of these serotonergic benzazepines is provided.

5 Centrally Acting Dopamine D2 Receptor Ligands: Agonists

The collected amount of research on D2 agonists is immense. The D2 research field has been, and still is, very dynamic. Despite this fact, only a few compounds have reached the clinic so far. At present there are clinical trials ongoing with partial D2 agonists possessing a range of intrinsic efficacies. Some of these agonists are tested for their potential effects in Parkinson's disease (high intrinsic efficacy), while others are tested for potential anti-psychotic effects (low intrinsic efficacy). An interesting possibility has arisen through the research on the synergism between D1 and D2 receptors. This could possibly be utilized in the alleviation of Parkinsonian symptomatology. The near future will show whether the compounds under evaluation hold promise for being new, valuable medicines for treating major diseases like Parkinson's disease and schizophrenia.

Sigma-receptors: implication for the control of neuronal activity of nigral dopamine-containing neurons

Using extracellular single unit recording techniques, we analyzed the significance of sigma-receptors in the neuronal control of dopamine (DA) neurons in the zona compacta of the substantia nigra. Administration of racemic trans-9-methoxy-4-benzyl-1,2,3,4,4a,5,6,10b-octahydrobenzo[f]quinoline (HW 173), a drug displaying high and specific affinity for sigma-receptors, was not associated with any change in the firing rate of DA neurons. Furthermore, pretreatment with the drug did not affect the dose-response curve for the inhibitory effects of the DA receptor agonist apomorphine or the mixed DA agonist/sigma-receptor ligand (+)-3-(3-hydroxyphenyl)-N-1-propyl)piperidine ((+)-3-PPP). In contrast to the effects of HW 173 on the DA cell firing rate, the firing pattern of the DA cells was significantly changed by the drug. The data suggest that sigma-receptors do not play a pivotal role in the control of the firing rate of DA neurons in the substantia nigra. Rather, they may have a function in the regulation of the firing pattern of these neurons.

Synthesis of 3-dialkylaminochromans via thallium(III)-induced cyclization of allyl aryl ethers

The sulfur-containing 3-alkylaminochromans, 5-methoxy-3-[N-(2- methylthioethyl)-propylamino]chroman (15), 5-hydroxy-3-[N-(2-methylthioethyl)propylamino]chroman (5) and 5-methoxy-8-methylthio-3-(dipropylamino)chroman (6), have been prepared from 8-bromo-5-methoxy-3-chromanol (11). This precursor was synthesized from 3-allyloxy-4-bromoanisole (8), by a thallium(III)-mediated ring-closure reaction. Compound 11 also served as starting material for the synthesis of 8-bromo-3-(dipropylamino)-5-methoxychroman (7).

Pre- and postsynaptic dopaminergic activities of indolizidine and quinolizidine derivatives of 3-(3-hydroxyphenyl)-N-(n-propyl)piperidine (3-PPP). Further developments of a dopamine receptor model

Pre- and postsynaptic dopaminergic activities of a series of indolizidine and quinolizidine analogues of 3-(3-hydroxyphenyl)-N-(n-propyl)piperidine (3-PPP) have been studied. The pharmacological data have been interpreted in terms of a previously reported model for interactions with dopamine pre- and postsynaptic D2-receptors and molecular mechanics (MM2(85] calculated geometries and conformational energies. The model has been further developed with respect to the receptor topography in the vicinity of the nitrogen binding site. In particular, a novel spatial orientation of the important "propyl cleft" has been proposed. This cleft is suggested to be located mainly above a plane through the receptor-bound substrate. The biologically active agonist and antagonist conformations of the enantiomers of 3-PPP have been reinvestigated.

Resolved 6,7,8,9-tetrahydro-N,N-dimethyl-3H-benz[e]indol-8-amine: central dopamine and serotonin receptor stimulating properties

The enantiomers of 6,7,8,9-tetrahydro-N,N-dimethyl-3H-benz[e]indol-8- amine (1a) were prepared and tested for their actions on central dopamine and serotonin (5-HT) receptors. The dopaminergic effects were shown to reside in the (1)-R enantiomer. It was shown that compound 1a and its (+)-R enantiomer possess potent central 5-HT1A receptor stimulating properties.

NSD 1034: an amino acid decarboxylase inhibitor with a stimulatory action on dopamine synthesis not mediated by classical dopamine receptors

The accumulation rates of 3,4'-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) after inhibition of aromatic amino acid decarboxylase (AADC) by 3-hydroxybenzylhydrazine (NSD 1015) or 1-(DL-seryl)-2- (2,3,4-trihydroxybenzyl)hydrazine (Ro 4-4602) have widely been used as measurements of the in vivo synthesis rates of monoamines. However, the values of dopamine (DA) turnover in rat striatum obtained using these drugs are much lower than values obtained by other methods. This discrepancy prompted us to further investigate the AADC inhibitor 1-(3-hydroxybenzyl)-1-methylhydrazine (NSD 1034) which earlier has been shown to give a DOPA accumulation rate in the striatum of the same magnitude as other measures of DA turnover. NSD 1034 was found to give a more than twofold higher DOPA accumulation rate than NSD 1015, NSD 1024, NSD 1039, NSD 1055 and Ro 4-4602 in the striatum. Also, in the limbic region and the hemispheres, but not in the substantia nigra, the DOPA accumulation was higher after NSD 1034 than after NSD 1015, but the difference was less pronounced. There was, however, no difference in 5-HTP accumulation between the drugs in any of the brain parts investigated. Although the DOPA accumulation rates are higher after NSD 1034 than after NSD 1015, the NSD 1015-induced DOPA accumulation seems to be more sensitive to changes in dopamine receptor occupancy. The different DOPA accumulation rates obtained with NSD 1015 and NSD 1034 are not due to differences in MAO inhibition, to interference with classical DA receptors, or to different degrees of AADC inhibition, but to an ability of NSD 1034 to stimulate DA synthesis. In addition, under certain conditions NSD 1034 also has a DA releasing action, like amphetamine. It is proposed that NSD 1034 and amphetamine stimulate DA synthesis and release by a common mechanism. The low value of DA synthesis rate, obtained when measured as DOPA accumulation after NSD 1015, is due to a substantial efflux of DOPA from the brain. The efflux of DOPA is equally large after NSD 1034 but the loss is compensated for by an increase in DOPA synthesis.

Occurrence and pharmacological significance of metabolic ortho-hydroxylation of 5- and 8-hydroxy-2-(di-n-propylamino)tetralin

Aromatic ortho-hydroxylation in the liver might be one of several possible reasons for the low bioavailabilities of the potent, centrally acting dopaminergic and serotoninergic agonists 5- and 8-hydroxy-2-(di-n-propylamino)tetralin, respectively. In vitro and in vivo experiments showed that such an oxidative metabolism did indeed take place. However, the amount of hydroxylated metabolites found in the brain was estimated to represent only 0.3% of the total amount of drug administered. The O-methylation rates of these catechols were also measured in vitro and showed that 5,6-dihydroxy-2-(di-n-propylamino)tetralin is a poor substrate for catechol O-methyltransferase (COMT) and that its 7,8-dihydroxy isomer is virtually devoid of substrate activity. No O-methylated metabolites were detected in the in vivo samples analyzed. A new synthetic strategy was applied to achieve the isomeric catechols studied. 5-Methoxy- or 8-methoxy-2-(di-n-propylamino)tetralin was lithiated in the ortho position and the metalated species was subsequently quenched in nitrobenzene, yielding the methoxy hydroxy isomers, which were heated in 48% aqueous HBr to achieve the corresponding catechols.

Quantitative structure-activity relationships and eudismic analyses of the presynaptic dopaminergic activity and dopamine D2 and sigma receptor affinities of 3-(3-hydroxyphenyl)piperidines and octahydrobenzo[f]quinolines

Data from the preceding paper were examined by QSAR and eudismic analyses. A fair parabolic relationship was found between the lipophilicity (measured by a RP-HPLC method) and the sigma-receptor affinity of 3-(3-hydroxyphenyl)piperidines (3HPP derivatives) and octahydrobenzo[f]quinolines (OHBQ derivatives). As far as the dopamine D2 receptor is concerned, the trans-7-hydroxy-OHBQ derivatives show a 10-fold higher affinity than the eutomeric S enantiomers of 3HPP derivatives, once lipophilicity has been accounted for. This difference in affinity is suggested to correspond to the energy necessary for the 3HPP derivatives to adopt the receptor-bound conformation. The R enantiomers of 3HPP derivatives display no apparent increase in D2 affinity with increasing lipophilicity, and indeed the eudismic index in this series increases with affinity (eudismic affinity quotient = 0.70), in agreement with a recent model of the binding of N-propyl-3HPP (3PPP) enantiomers to the D2 receptor. The selectivity in sigma/D2 affinities was found to depend on both lipophilicity and configuration of the ligands; thus, the selectivity is maximal for log kw values of ca. 1.7-2.1 and is much larger for the R than for the S enantiomers of 3HPP derivatives.

N-substituted 1,2,3,4,4a,5,6,10b-octahydrobenzo[f]quinolines and 3-phenylpiperidines: effects on central dopamine and sigma receptors

N-Substituted analogues of trans-7- and trans-9-hydroxy-1,2,3,4,4a,5,6,10b-octahydrobenzo[f]quinoline (trans-7- and trans-9-OH-OHBQ) were tested for dopamine (DA) D2 receptor affinity by using in vitro [3H]spiperone and in vivo 5,6-di-n-Pr-ADTN binding assays. Potencies at central pre- (auto-) and postsynaptic DA receptors were determined by a biochemical and a behavioral method, respectively. Corresponding data were included for analogous, resolved 3-(3-hydroxyphenyl)piperidines and a few other substituted, racemic 3-phenylpiperidines. Beside the central dopaminergic effects of these compounds, previously reported sigma receptor affinity data [[3H]-(+)-3-(3-hydroxyphenyl)-N-n-propylpiperidine; [3H]-(+)-3-PPP] were also taken into account for a comparison of the structure-activity/affinity relationships of these compounds at these two receptor types. Larger N-substituents in both phenylpiperidines and OHBQs increase both pre- and postsynaptic dopaminergic activity. An n-propyl group gives high dopaminergic efficacy at both receptor sites (pre- and postsynaptic) in all series. However, even higher dopaminergic potency is observed for trans-7-OH-OHBQs and (S)-3-(3-hydroxyphenyl)piperidines with N-substituents larger than n-propyl. In contrast, trans-4-n-Bu-9-OH-OHBQ is inactive, and (R)-3-(3-hydroxyphenyl)-N-n-butylpiperidine is less active at central DA receptors than its corresponding n-propyl analogue. This implies interesting differences in N-substituent sensitivity for the different classes of compounds with respect to the direction of their respective N-substituents at the drug-receptor interaction. The stereochemical and steric demands for sigma receptor affinity are much less stringent. The general trend is that, up to a certain size, the more lipophilic the N-substituent, the higher the affinity for sigma receptor sites.

Structural determinants of sigma receptor affinity

The structural determinants of sigma receptor affinity have been evaluated by examining a wide range of compounds related to opioids, neuroleptics, and phenylpiperidine dopaminergic structures for affinity at sigma receptor-binding sites labeled with (+)-[3H]3-PPP. Among opioid compounds, requirements for sigma receptor affinity differ strikingly from the determinants of affinity for conventional opiate receptors. Sigma sites display reverse stereoselectivity to classical opiate receptors. Multi-ringed opiate-related compounds such as morphine and naloxone have negligible affinity for sigma sites, with the highest sigma receptor affinity apparent for benzomorphans which lack the C ring of opioids. Highest affinity among opioids and other compounds occurs with more lipophilic N-substituents. This feature is particularly striking among the 3-PPP derivatives as well as the opioids. The butyrophenone haloperidol is the most potent drug at sigma receptors we have detected. Among the series of butyrophenones, receptor affinity is primarily associated with the 4-phenylpiperidine moiety. Conformational calculations for various compounds indicate a fairly wide range of tolerance for distances between the aromatic ring and the amine nitrogen, which may account for the potency at sigma receptors of structures of considerable diversity. Among the wide range of structures that bind to sigma receptor-binding sites, the common pharmacophore associated with high receptor affinity is a phenylpiperidine with a lipophilic N-substituent.

(+)-cis-8-Hydroxy-1-methyl-2-(di-n-propylamino)tetralin: a potent and highly stereoselective 5-hydroxytryptamine receptor agonist

C1-Methylated derivatives of the potent 5-hydroxytryptamine (5-HT) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 1) were synthesized and tested for central 5-HT and dopamine receptor activity by use of a biochemical test method in rats. cis-8-Hydroxy-1-methyl-2-(di-n-propylamino)tetralin (8) was found to be a 5-HT receptor agonist. The (+)-enantiomer of 8 had a potency equal to that of 1, whereas (-)-8 and the trans isomer (+/-)-9 were inactive.