Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter: Part 3. A potential 5-HT transporter imaging agent, 3-(3-[18F]fluoropropyl)-6-nitroquipazine

Fluorine-18 Radiolabeled PET Tracers for Imaging Monoamine Transporters: Dopamine, Serotonin, and Norepinephrine

This review focuses on the development of fluorine-18 radiolabeled PET tracers for imaging the dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET). All successful DAT PET tracers reported to date are members of the 3β-phenyl tropane class and are synthesized from cocaine. Currently available carbon-11 SERT PET tracers come from both the diphenylsulfide and 3β-phenyl nortropane class, but so far only the nortropanes have found success with fluorine-18 derivatives. NET imaging has so far employed carbon-11 and fluorine-18 derivatives of reboxetine but due to defluorination of the fluorine-18 derivatives further research is still necessary.

High efficiency synthesis of F-18 fluoromethyl ethers: an attractive alternative for C-11 methyl groups in positron emission tomography radiopharmaceuticals

A rapid and efficient method for the synthesis of O-fluoromethyl aliphatic and aromatic ethers is presented. This method is so mild that it can be used for the preparation of positron emission tomography (PET) radiopharmaceuticals bearing O-[(18)F]fluoromethyl groups.

Synthesis, antidepressant evaluation and docking studies of long-chain alkylnitroquipazines as serotonin transporter inhibitors

Twelve alkyl analogues (1-12) of the high-affinity serotonin transporter (SERT) inhibitor 6-nitroquipazine (6-NQ) were synthesized and studied using in vitro radioligand competition binding assays to determine their binding affinity (Ki ). The putative antidepressant activity of five of the binders with the highest SERT binding affinities was studied by the forced swim and locomotor activity mouse tests. The three-dimensional (3D) structures of 8 and 9 were determined using NOE NMR technique. Flexible docking of the compounds was undertaken to illustrate the binding of the compounds in the SERT model. Our results showed that several of the 6-NQ analogues are high-affinity SERT inhibitors and indicated that the octyl (8), decyl (10) and dodecyl (12) 6-NQ analogues exhibit moderate antidepressant activity.

Synthesis and biological evaluation of one novel technetium-99m-labeled nitroquipazine derivative as an imaging agent for serotonin transporter

Imaging of serotonin transporter (SERT) by positron emission tomography (PET) or single-photon emission-computed tomography (SPECT) in humans would provide useful information in diagnosis and therapy of several neurodegenerative and neuropsychiatric disorders. 6-Nitroquipazine is a highly potent and selective inhibitor of the SERT. For the development of new (99m)Tc-labeled 6-nitroquipazine derivatives as SERT imaging agents, novel [N-[2-((3-(4-(6-nitroquinolin-2-yl)piperazin-1-yl)propyl)(2-mercaptoethyl)amino]-acetyl-2-aminoethanethiolato] [(99m)Tc]technetium (V) oxide ((99m)Tc-MAMA-3-PQ) and its rhenium analog were synthesized and characterized. (99m)Tc-MAMA-3-PQ displayed high initial brain uptake (0.52% ID/organ at 2 min post-injection (pi)) and relatively fast washout in mice (0.09% ID/organ at 60 min pi). The regional brain distribution studies in rats showed high-specific binding ratios at 60 min pi. Maximum regional contrast ratio observed for thalamus/cerebellum was 2.94, followed by 2.62 for hypothalamus/cerebellum. These encouraging results lead us to further explore its derivatives as new imaging agents for the SERT in the brain.

Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter. Part 5: 2'-Substituted 6-nitroquipazines

Five C2'-substituted 6-nitroquipazine (6-NQ) derivatives were prepared and evaluated in terms of their biological abilities (K(i)) to displace [(3)H]citalopram binding to serotonin transporter. The relationship between their structure and biological activities revealed that shorter alkyl groups tend to possess higher binding affinity. Both compounds 12a and 12c were found to have the equally highest binding affinity (K(i)=0.43+/-0.02 nM).

Structure-affinity relationship studies on arylpiperazine derivatives related to quipazine as serotonin transporter ligands. Molecular basis of the selectivity SERT/5HT3 receptor

A series of quipazine derivatives, previously synthesized to probe the 5-HT(3) receptor, was evaluated for its potential interaction with serotonin transporter (SERT). Some of them show nanomolar affinity for the rodent SERT comparable to or slightly higher than quipazine or N-methylquipazine. Subsequently a candidate was selected on the basis of its SERT affinity and submitted to a molecular manipulation of the basic moiety. The structure-affinity relationships obtained provided information on the role of the fused benzene ring of quipazine in the interaction with the SERT binding site and on the stereoelectronic requirements for the interaction of both the heteroaromatic component and the basic moiety. Moreover, the comparison of the structure-affinity relationships obtained in the present work with those concerning the interaction of these heteroarylpiperazine derivatives with 5-HT3 receptor suggested some molecular determinants of the selectivity SERT/5HT3 receptor.

Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter. Part 4: 3-Alkyl-4-halo-6-nitroquipazines

On the basis of the structure-activity relationship (SAR) of 4-chloro-6-nitroquipazine (Ki = 0.03 nM) and 3-fluoropropyl-6-nitroquipazine (Ki = 0.32 nM), 3-alkyl-4-halo-6-nitroquipazines were synthesized and tested for their potential abilities in vitro to displace [3H]citalopram binding to the rat cortical membranes. Binding affinities of 3b and 4d were Ki = 2.70+/-0.32 and 2.23+/-0.46 nM, respectively. The syntheses of 3-alkyl-4-halo-6-nitroquipazine, their in vitro binding affinities, and the SAR of C3, C4 position in 6-nitroquipazine are described.