Synthesis and evaluation of novel tropane derivatives as potential PET imaging agents for the dopamine transporter

A facile synthesis of precursor for the σ-1 receptor PET radioligand [18 F]FTC-146 and its radiofluorination

The σ-1 receptor is a non-opioid transmembrane protein involved in various human pathologies including neurodegenerative diseases, inflammation, and cancer. The previously published ligand [18 F]FTC-146 is among the most promising tools for σ-1 molecular imaging by positron emission tomography (PET), with a potential for application in clinical diagnostics and research. However, the published six- or four-step synthesis of the tosyl ester precursor for its radiosynthesis is complicated and time-consuming. Herein, we present a simple one-step precursor synthesis followed by a one-step fluorine-18 labeling procedure that streamlines the preparation of [18 F]FTC-146. Instead of a tosyl-based precursor, we developed a one-step synthesis of the precursor analog AM-16 containing a chloride leaving group for the SN 2 reaction with 18 F-fluoride. 18 F-fluorination of AM-16 led to a moderate decay-corrected radiochemical yield (RCY = 7.5%) with molar activity (Am ) of 45.9 GBq/μmol. Further optimization of this procedure should enable routine radiopharmaceutical production of this promising PET tracer.

Cocaine: from a controlled drug by the DEA to an approved drug by the FDA

Abstract:

NumbrinoTM, a nasal anesthetic solution based on cocaine hydrochloride, was recently approved by the FDA for diagnostic procedures and surgery – now, what will be the role of the controlling agencies and the legislation of producing countries to face the imminent medicinal use of cocaine? Would chemistry be the protagonist in proposing alternative approaches to help and overcome this issue? The debate is open with this commentary

Structure Modeling of the Norepinephrine Transporter

The norepinephrine transporter (NET) is one of the monoamine transporters. Its X-ray crystal structure has not been obtained yet. Inhibitors of human NET (hNET) play a major role in the treatment of many central and peripheral nervous system diseases. In this study, we focused on the spatial structure of a NET constructed by homology modeling on Drosophila melanogaster dopamine transporter templates. We further examined molecular construction of primary binding pocket (S1) together with secondary binding site (S2) and extracellular loop 4 (EL4). The next stage involved docking of transporter inhibitors: Reboxetine, duloxetine, desipramine, and other commonly used drugs. The procedure revealed the molecular orientation of residues and disclosed ones that are the most important for ligand binding: Phenylalanine F72, aspartic acid D75, tyrosine Y152, and phenylalanine F317. Aspartic acid D75 plays a key role in recognition of the basic amino group present in monoamine transporter inhibitors and substrates. The study also presents a comparison of hNET models with other related proteins, which could provide new insights into their interaction with therapeutics and aid future development of novel bioactive compounds.

Ventral striatal dopamine transporter availability is associated with lower trait motor impulsivity in healthy adults

Impulsivity is a transdiagnostic feature of a range of externalizing psychiatric disorders. Preclinical work links reduced ventral striatal dopamine transporter (DAT) availability with heightened impulsivity and novelty seeking. However, there is a lack of human data investigating the relationship between DAT availability, particularly in subregions of the striatum, and the personality traits of impulsivity and novelty seeking. Here we collected PET measures of DAT availability (BP_ND) using the tracer ¹⁸F-FE-PE2I in 47 healthy adult subjects and examined relations between BP_ND in striatum, including its subregions: caudate, putamen, and ventral striatum (VS), and trait impulsivity (Barratt Impulsiveness Scale: BIS-11) and novelty seeking (Tridimensional Personality Questionnaire: TPQ-NS), controlling for age and sex. DAT BP_ND in each striatal subregion showed nominal negative associations with total BIS-11 but not TPQ-NS. At the subscale level, VS DAT BP_ND was significantly associated with BIS-11 motor impulsivity (e.g., taking actions without thinking) after correction for multiple comparisons. VS DAT BP_ND explained 13.2% of the variance in motor impulsivity. Our data demonstrate that DAT availability in VS is negatively related to impulsivity and suggest a particular influence of DAT regulation of dopamine signaling in VS on acting without deliberation (BIS motor impulsivity). While needing replication, these data converge with models of ventral striatal functions that emphasize its role as a key interface linking motivation to action.

Synthesis of novel halo and tosyloxy nortropane derivatives as efficient precursors for the one-step synthesis of the dopamine transporter PET ligand [(18)F]FECNT

The fluorine-18 labeled nortropane derivative 2β-carbomethoxy-3β-(4-chlorophenyl)-8-(2-fluoroethyl)-nortropane (FECNT) is a dopamine transporter (DAT) ligand. Currently, it is considered as reference for positron emission tomography imaging. Herein, the synthesis of novel precursors (N-tosyloxy-, chloro-, and bromo- analogues) for one-step radiosynthesis of [(18)F]FECNT is reported. Using the N-mesyloxy- precursor in a one-step radiosynthesis, the crude [(18)F]FECNT was obtained with the radiolabeling yield of 45 ± 10%, confirming the practical efficiency of this approach in the design of novel precursors for labeling.