Synthesis of 3 beta-aryl-8-azabicyclo[3.2.1]octanes with high binding affinities and selectivities for the serotonin transporter site.

A novel entry to tropane analogs of cocaine was developed based on the reaction of rhodium-stabilized vinylcarbenoids with pyrroles. These analogs were tested in binding to dopamine, serotonin (5-HT), and norepinephrine transporters in membranes from rat striatum and frontal cortex. In all the analogs, the aryl group at the 3 position was directly bound to the tropane ring and an ethyl ketone moiety was present at the 2 position. By appropriate modification of the aryl and nitrogen substituents, highly potent and 5-HT selective tropanes were prepared. The most potent and selective compound was 3 beta-[4-(1-methylethenyl)phenyl]-2 beta-propanoyl-8-azabicyclo[3.2.1]octane (13b) which had a Ki of 0.1 nM at 5-HT transporters and was 150 times more potent at 5-HT vs dopamine transporters and almost 1000 times more potent at 5-HT vs norepinephrine transporters.

Synthesis of 2 beta-acyl-3 beta-aryl-8-azabicyclo[3.2.1]octanes and their binding affinities at dopamine and serotonin transport sites in rat striatum and frontal cortex.

A novel entry to tropane analogs of cocaine was developed on the basis of the reaction of rhodium-stabilized vinylcarbenoids with pyrroles. These analogs were tested in binding to dopamine and serotonin (5-HT) transporters in membranes from rat striatum and frontal cortex. In all the analogs, the aryl group at the 3-position was directly bound to the tropane ring (as in WIN-35,428), and methyl or ethyl ketone moieties were present at the 2-position instead of the typical ester group. The series of analogs containing a 2-naphthyl group at the 3-position were most potent, with Ki values < 1 nM in binding to both dopamine and 5-HT transporters. Although the unsubstituted 2-naphthyl analog was nonselective at dopamine and 5-HT transport sites, other compounds were selective for either site. In general, compounds with relatively small substituents on the aromatic moiety (such as p-methyl or p-fluoro) were relatively selective for the dopamine transporters, while a p-isopropylphenyl derivative was selective for the 5-HT transport sites. This latter compound represents the first N-methyltropane derivative specific for 5-HT transporters. Resolution of two of the most significant analogs was achieved by HPLC on a chiral stationary phase; the active enantiomer of a 2-naphthyl analog exhibited Ki values of < 0.1 nM at both dopamine and 5-HT transporter sites.

Alterations in behavior and opioid gene expression induced by the novel tropane analog WF-31.

The effects of the acute administration of the serotonin-selective tropane analog, [2beta-propanoyl-3beta-(4-isopropylphenyl)-tropane, WF-31, on spontaneous locomotor activity were measured and compared to those of the highly selective serotonin uptake inhibitor, fluoxetine and cocaine, a non-selective re-uptake inhibitor of dopamine and serotonin. WF-31 (1, 10 and 30 mg/kg)-elicited increases in locomotor behaviors when compared to vehicle-treated rats. This increased activity was blocked by pre-treatment with the dopaminergic antagonist, flupenthixol, suggesting that these effects may be mediated by dopaminergic mechanisms. Cocaine, but not fluoxetine, also elicited increases in behaviors. In addition, the effects of these three compounds on opioid peptide gene expression were also assessed using in situ hybridization histochemistry in the same animals. The acute administration of both WF-31 and cocaine increased the expression of preprodynorphin mRNA in the dorsal striatum whereas fluoxetine had no effect. Expression of striatal preproenkephalin mRNA was augmented by all three compounds. Within the nucleus accumbens, PPD mRNA levels were affected only by treatment with WF-31, an effect that was blocked by pre-treatment with flupenthixol. In contrast, the acute administration of both WF-31 and fluoxetine, but not cocaine, increased the expression of preproenkephalin mRNA. These increases, however, were not reversed by pre-treatment with flupenthixol. Despite its profile in vitro as a relatively selective serotonin re-uptake inhibitor, some of the in vivo actions of WF-31 appear to be mediated by dopaminergic mechanisms. These data further suggest that the mechanisms underlying expression of the opioid peptides in the nucleus accumbens may vary from those in the dorsal striatum.

Local cerebral metabolic effects of the novel cocaine analog, WF-31: comparisons to fluoxetine.

The effects of the acute administration of the selective serotonin uptake inhibitor, fluoxetine, on rates of local cerebral glucose utilization in rats were compared to those of the novel cocaine analog, [2beta-propanoyl-3beta-(4-isopropylphenyl)-tropane, WF-31, which has greater affinity for serotonin than dopamine transporters, using the quantitative autoradiographic 2-[14C]deoxyglucose method. Locomotor activity was assessed simultaneously. Fluoxetine administration resulted in dose-dependent decreases in locomotor behavior, as well as widespread reductions in rates of metabolic activity in brain areas including raphe nuclei, dorsal and ventral striatum, amygdala, hippocampus, limbic cortex, and thalamus. These effects were largely concentrated in brain regions containing high densities of serotonin transporters as revealed by in vitro autoradiography. In contrast, the acute administration of WF-31 produced more discrete changes in metabolic activity that were localized within the raphe nuclei and in portions of the hippocampal formation. Blockade of WF-31's dopaminergic effects by pretreatment with the antagonist, alpha-flupenthixol, resulted in a pattern of metabolic changes that closely resembled that observed with fluoxetine. These data suggest that the alterations in functional activity produced by both fluoxetine and WF-31 are largely the result of actions on serotonergic systems.