Molecular Modeling, Structure–Activity Relationships and Functional Antagonism Studies of 4-Hydroxy-1-methyl-4-(4-methylphenyl)-3-piperidyl 4-Methylphenyl Ketones as a Novel Class of Dopamine Transporter Inhibitors Original Research Article

We previously disclosed the discovery of 4-hydroxy-1-methyl-4-(4-methylphenyl)-3-piperidyl 4-methylphenyl ketone (3) as a novel class of dopamine transporter (DAT) inhibitors and showed that (±)-3 has a significant functional antagonism against cocaine in vitro. Our previous preliminary structure–activity relationship study led to identification of a more potent DAT inhibitor [(±)-4] but this compound failed to show any significant functional antagonism. To search for more potent analogues than 3 but still displaying significant functional antagonism, further SARs, molecular modeling studies and in vitro pharmacological evaluation of this novel class of DAT inhibitors were performed. Sixteen new analogues were synthesized in racemic form and evaluated as DAT inhibitors. It was found that seven new analogues are reasonably potent DAT inhibitors with Ki values of 0.041–0.30 and 0.052–0.16 μM in [3H]mazindol binding and inhibition of DA reuptake. Chiral isomers of several potent DAT inhibitors were obtained through chiral HPLC separation and evaluated as inhibitors at all the three monoamine transporter sites. In general, the (−)-isomer is more active than the (+)-isomer in inhibition of DA reuptake and all the (−)-isomers are selective inhibitors at the DAT site. Evaluation of cocaineʹs effect on dopamine uptake in the presence and absence of (+)-3 and (−)-3 showed that (−)-3 is responsible for the functional antagonism obtained with the original lead (±)-3. Out of the new compounds synthesized, analogue (±)-20, which is 8- and 3-fold more potent than (±)-3 in binding and inhibition of DA reuptake, appeared to have improved functional antagonism as compared to (±)-3.