Chemical synthesis and pharmacology of 6- and 7-hydroxylated 2-carbomethoxy-3-(p-tolyl)tropanes: Antagonism of cocaine's locomotor stimulant effects

In our efforts to identify molecules that might act as cocaine antagonists or cocaine partial agonists, efforts were made to further capitalize on our earlier finding regarding the ability of a 7-methoxylated pseudococaine analogue to act as a weak cocaine functional antagonist. Herein, a series of the 6- and 7-hydroxylated WIN analogues possessing a boat or chair conformation of the tropane ring were prepared and tested for their ability to displace [³H]mazindol binding and to inhibit high-affinity monoamine uptake into rat brain nerve endings. These 6- and 7-hydroxylated WIN analogues were readily prepared by use of a classical Willstatter synthesis to construct an appropriately functionalized tropane ring followed by use of a Suzuki coupling reaction to introduce the aryl group at position 3. Reduction of the resulting tropene by use of SmI₂ or by catalytic hydrogenation followed by deprotection delivered the final target compounds. Some of these compounds were found to retain considerable affinity as inhibitors of the dopamine transporter (DAT) and the norepinephrine transporter (NET), but they were less potent inhibitors of the serotonin transporter (SERT). None of the compounds of the present series revealed any substantial potency difference in [³H]mazindol binding versus [³H]DA uptake, and failed to show 'cocaine antagonism' when tested for their ability to prevent cocaine's inhibition of DA transport. However, one of these hydroxylated WIN analogues, namely 12b, which possesses nanomolar potency at the DAT and NET and micromolar potency at the SERT, when tested in vivo, was found capable of attenuating cocaine's locomotor activity (AD₅₀ = 94 mg/kg). Taken together, this work provides further support for our hypothesis that drugs that lack the ability to inhibit transport by all three monoaminergic transporters may exhibit 'partial' cocaine-like properties, but act as cocaine antagonists. Consequently, it may prove valuable to examine the behavioral activity of other 6- and 7-substituted tropanes in animal behavioral paradigms in the search for a cocaine medication.