Synthesis and pharmacology of site-specific cocaine abuse treatment agents: 2-(aminomethyl)-3-phenylbicyclo[2.2.2]- and -[2.2.1]alkane dopamine uptake inhibitors

As part of a program to develop site-specific medications for cocaine abuse, a series of 2-(aminomethyl)-3-phenylbicyclo2.2.2]- and -2.2.1]alkane derivatives was synthesized and tested for inhibitory potency in 3H]WIN 35,428 binding and 3H]dopamine uptake assays using rat striatal tissue. Selected compounds were tested for their ability to substitute for cocaine in rat drug discrimination tests. Synthesis was accomplished by a series of Diels-Alder reactions, using cis- and trans-cinnamic acid derivatives (nitrile, acid, acid chloride) with cyclohexadiene and cyclopentadiene. Standard manipulations produced the aminomethyl side chain. Many of the compounds bound with high affinity (median IC50 = 223 nM) to the cocaine binding site as marked by 3H]WIN 35,428. Potency in the binding assay was strongly enhanced by chlorine atoms in the 3- and/or 4-position on the aromatic ring and was little affected by corresponding methoxy groups. In the 2.2.2] series there was little difference in potency between cis and trans compounds or between N, N-dimethylamines and primary amines. In the 2.2.1] series the trans exo compounds tended to be least potent against binding, whereas the cis exo compounds were the most potent (4-Cl cis exo: IC50 = 7.7 nM, 27-fold more potent than 4-Cl trans-exo). Although the potencies of the bicyclic derivatives in the binding and uptake assays were highly correlated, some of the compounds were 5-7-fold less potent at inhibiting 3H]dopamine uptake than 3H]WIN 35,428 binding (for comparison, cocaine has a lower discrimination ratio (DR) of 2.5). The DR values were higher for almost all primary amines and for the trans-2.2.2] series as compared to the cis-2.2.2]. Most of the compounds had Hill coefficients approaching unity, except for the 2. 2.2] 3,4-dichloro derivatives, which all had nH values of about 2.0. Two of the compounds were shown to fully substitute for cocaine in drug discrimination tests in rats, and one had a very long duration of action.