Structural Modification of the Designer Stimulant α-Pyrrolidinovalerophenone (α-PVP) Influences Potency at Dopamine Transporters.

α-Pyrrolidinovalerophenone (α-PVP, 7) is an illegal synthetic stimulant that is being sold on the clandestine market as "flakka" and "gravel". The potent pharmacological effects of α-PVP are presumably mediated by inhibition of dopamine uptake at the dopamine transporter (DAT). However, little is known about how structural modification of α-PVP influences activity at DAT. Eleven analogs of α-PVP were synthesized and examined for their ability to inhibit uptake of [(3)H]dopamine and [(3)H]serotonin in rat brain synaptosomes. None of the analogs significantly inhibited [(3)H]serotonin uptake when tested at 10 µM at the serotonin transporter (SERT). All of the analogs behaved as DAT reuptake inhibitors, but potencies varied over a >1500-fold range. Potency was primarily associated with the nature of the α-substituent, with the more bulky substituents imparting the highest potency. Expansion of the pyrrolidine ring to a piperidine reduced potency up to 10-fold, whereas conformational constraint in the form of an aminotetralone resulted in the least potent compound. Our study provides the first systematic and comparative structure-activity investigation on the ability of α-PVP analogs to act as inhibitors of DAT.

Quantitative structure-activity relationship analysis of the pharmacology of para-substituted methcathinone analogues.

BACKGROUND AND PURPOSE: Methcathinone (MCAT) is a potent monoamine releaser and parent compound to emerging drugs of abuse including mephedrone (4-CH3 MCAT), the para-methyl analogue of MCAT. This study examined quantitative structure-activity relationships (QSAR) for MCAT and six para-substituted MCAT analogues on (a) in vitro potency to promote monoamine release via dopamine and serotonin transporters (DAT and SERT, respectively), and (b) in vivo modulation of intracranial self-stimulation (ICSS), a behavioural procedure used to evaluate abuse potential. Neurochemical and behavioural effects were correlated with steric (Es ), electronic (σp ) and lipophilic (πp ) parameters of the para substituents. EXPERIMENTAL APPROACH: For neurochemical studies, drug effects on monoamine release through DAT and SERT were evaluated in rat brain synaptosomes. For behavioural studies, drug effects were tested in male Sprague-Dawley rats implanted with electrodes targeting the medial forebrain bundle and trained to lever-press for electrical brain stimulation. KEY RESULTS: MCAT and all six para-substituted analogues increased monoamine release via DAT and SERT and dose- and time-dependently modulated ICSS. In vitro selectivity for DAT versus SERT correlated with in vivo efficacy to produce abuse-related ICSS facilitation. In addition, the Es values of the para substituents correlated with both selectivity for DAT versus SERT and magnitude of ICSS facilitation. CONCLUSIONS AND IMPLICATIONS: Selectivity for DAT versus SERT in vitro is a key determinant of abuse-related ICSS facilitation by these MCAT analogues, and steric aspects of the para substituent of the MCAT scaffold (indicated by Es ) are key determinants of this selectivity.

Steric parameters, molecular modeling and hydropathic interaction analysis of the pharmacology of para-substituted methcathinone analogues.

BACKGROUND AND PURPOSE: There is growing concern over the abuse of certain psychostimulant methcathinone (MCAT) analogues. This study extends an initial quantitative structure-activity relationship (QSAR) investigation that demonstrated important steric considerations of seven 4- (or para-)substituted analogues of MCAT. Specifically, the steric character (Taft's steric ES ) of the 4-position substituent affected in vitro potency to induce monoamine release via dopamine and 5-HT transporters (DAT and SERT) and in vivo modulation of intracranial self-stimulation (ICSS). Here, we have assessed the effects of other steric properties of the 4-position substituents. EXPERIMENTAL APPROACH: Definitive steric parameters that more explicitly focus on the volume, width and length of the MCAT 4-position substituents were assessed. In addition, homology models of human DAT and human SERT based upon the crystallized Drosophila DAT were constructed and docking studies were performed, followed by hydropathic interaction (HINT) analysis of the docking results. KEY RESULTS: The potency of seven MCAT analogues at DAT was negatively correlated with the volume and maximal width of their 4-position substituents, whereas potency at SERT increased as substituent volume and length increased. SERT/DAT selectivity, as well as abuse-related drug effects in the ICSS procedure, also correlated with the same parameters. Docking solutions offered a means of visualizing these findings. CONCLUSIONS AND IMPLICATIONS: These results suggest that steric aspects of the 4-position substituents of MCAT analogues are key determinants of their action and selectivity, and that the hydrophobic nature of these substituents is involved in their potency at SERT.