From dual norepinephrine-dopamine reuptake inhibition to selective dopamine reuptake inhibitors: a case of aromatically substituted N,2-cyclopentylamines

Abstract

Dopamine (DA) is essential for motor control, mood, motivation, and reward in the central nervous system. It functions through receptor activation and is regulated by the dopamine transporter (DAT, SLC6A3), which manages DA reuptake. DAT dysfunction can lead to abnormal DA levels, associated with conditions like depression, Parkinson's disease, and substance abuse. Current efforts to develop dopamine reuptake inhibitors (DRIs) have resulted in only one approved drug, emphasizing the need for new DRI chemotypes. To address this, we expanded the structure-activity relationship of our previously reported N,2-substituted cycloalkylamine scaffold. We synthesized and characterized two aliphatic (9a and 10b) and sixteen aromatic (11a-11p) N-substituted derivatives. Pharmacological evaluation with a fluorescent neurotransmitter uptake assay revealed that compounds 9a, 10b, and a previously reported compound (6) acted as dual norepinephrine-dopamine reuptake inhibitors. Contrarily, most aromatic compounds were selective for DAT, with meta-hydroxyl 11e and para-hydroxyl 11f as most potent DRIs with an inhibitory potency in the nanomolar range. Using molecular docking, key interactions with residues R85 and D476 were proposed to underlie potent inhibitory effects. The stabilization of residue F326 within the flexible loop region between TM6a and TM6b was predicted to contribute to DAT selectivity. In vivo characterization using hDAT-expressing Drosophila melanogaster showed increased locomotor activity and reduced sleep for para-hydroxyl compound 11f. This study introduces a new series of potent N,2-cyclopentylamine-based DRIs, providing insights into mechanisms of selectivity and offering potential directions for DAT-related drug discovery.