New N-aryl-N′-(3-(substituted)phenyl)-N′-methylguanidines as leads to potential PET radioligands for imaging the open NMDA receptor (original) (raw)
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Journal of Medicinal Chemistry, 2015
N-Methyl-D-aspartate (NMDA) receptor dysfunction has been linked to several neuropsychiatric disorders, including Alzheimer's disease, epilepsy, drug addiction, and schizophrenia. A radioligand that could be used with PET to image and quantify human brain NMDA receptors in the activated "open channel" state would be useful for research on such disorders and for the development of novel therapies. To date, no radioligands have shown well-validated efficacy for imaging NMDA receptors in human subjects. In order to discover improved radioligands for PET imaging, we explored structure-affinity relationships in N′-3-(trifluoromethyl)phenyl derivatives of N-aryl-N′-methylguanidines, seeking high affinity and moderate lipophilicity, plus necessary amenability for labeling with a positron-emitter, either carbon-11 or fluorine-18. Among a diverse set of 80 prepared N′-3-(trifluoromethyl)phenyl derivatives, four of these compounds (13, 19, 20, and 36) displayed desirable low nanomolar affinity for inhibition of [ 3 H](+)-MK801 at the PCP binding site and are of interest for candidate PET radioligand development.
Journal of Medicinal Chemistry, 2015
N-Methyl-D-aspartate (NMDA) receptor dysfunction has been linked to several neuropsychiatric disorders, including Alzheimer's disease, epilepsy, drug addiction, and schizophrenia. A radioligand that could be used with PET to image and quantify human brain NMDA receptors in the activated "open channel" state would be useful for research on such disorders and for the development of novel therapies. To date, no radioligands have shown well-validated efficacy for imaging NMDA receptors in human subjects. In order to discover improved radioligands for PET imaging, we explored structure-affinity relationships in N′-3-(trifluoromethyl)phenyl derivatives of N-aryl-N′-methylguanidines, seeking high affinity and moderate lipophilicity, plus necessary amenability for labeling with a positron-emitter, either carbon-11 or fluorine-18. Among a diverse set of 80 prepared N′-3-(trifluoromethyl)phenyl derivatives, four of these compounds (13, 19, 20, and 36) displayed desirable low nanomolar affinity for inhibition of [ 3 H](+)-MK801 at the PCP binding site and are of interest for candidate PET radioligand development.
Nuclear medicine and biology, 2014
The N-methyl-D-Aspartate (NMDA) receptor plays an important role in learning and memory. Overactivation is thought to play an important role in neurodegenerative disorders such as Alzheimer's disease. Currently, it is not possible to assess N-methyl-D-aspartate receptor (NMDAr) bio-availability in vivo. The purpose of this study was to develop a positron emission tomography (PET) ligand for the NR2B binding site of the NMDA receptor. N-((5-(4-fluoro-2-methoxyphenyl)pyridin-3-yl)methyl)cyclopentanamine was radiolabelled with carbon-11 in the phenyl moiety. Biodistribution and blocking studies were carried out in anaesthetized mice and in non-anaesthetized rats. N-((5-(4-fluoro-2-[(11)C]methoxyphenyl)pyridin-3-yl)methyl)cyclopentanamine was prepared in 49±3% (decay-corrected) yield, affording 4.1±0.3 GBq of formulated product at the end of synthesis with a radiochemical purity of >99% and with a specific activity of 78±10 GBq/μmol. A new NR2B PET ligand was developed in high yi...
Nuclear Medicine and Biology, 2004
The development of imaging methods to measure changes in NMDA ion channel activation would provide a powerful means to probe the mechanisms of drugs and device based treatments (e.g., ECT) thought to alter glutamate neurotransmission. To provide a potential NMDA/PCP receptor PET tracer, we synthesized the radioligand [ 11 C]GMOM (K i ϭ 5.2 Ϯ0.3 nM; log P ϭ 2.34) and evaluated this ligand in vivo in awake male rats and isoflurane anesthetized baboons. In rats, the regional brain uptake of [ 11 C]GMOM ranged from 0.75Ϯ0.13% ID/g in the medulla and pons to 1.15Ϯ0.17% ID/g in the occipital cortex. MK801 (1 mg/kg i.v.) significantly reduced (24-28%) [ 11 C]GMOM uptake in all regions. D-serine (10 mg/kg i.v.) increased [ 11 C]GMOM %ID/g values in all regions (10-24%) reaching significance in the frontal cortex and cerebellum only. The NR2B ligand RO 25-6981 (10 mg/kg i.v.) reduced [ 11 C]GMOM uptake significantly (24-38%) in all regions except for the cerebellum and striatum. Blood activity was 0.11Ϯ0.03 %ID/g in the controls group and did not vary significantly across groups. PET imaging in isoflurane-anesthetized baboons with high specific activity [ 11 C]GMOM provided fairly uniform regional brain distribution volume (V T ) values (12.8 -17.1 ml g Ϫ1 ). MK801 (0.5 mg/kg, i.v., n ϭ 1, and 1.0 mg/kg, i.v., n ϭ 1) did not significantly alter regional V T values, indicating a lack of saturable binding. However, the potential confounding effects associated with ketamine induction of anesthesia along with isoflurane maintenance must be considered because both agents are known to reduce NMDA ion channel activation. Future and carefully designed studies, presumably utilizing an optimized NMDA/PCP site tracer, will be carried out to further explore these hypotheses. We conclude that, even though [ 11 C]GMOM is not an optimized PCP site radiotracer, its binding is altered in vivo in awake rats as expected by modulation of NMDA ion channel activity by MK801, D-serine or RO 25-6981. The development of higher affinity NMDA/PCP site radioligands is in progress.
Journal of Labelled Compounds and Radiopharmaceuticals, 2002
To provide effective PET or SPECT ligands for the glycine binding site of the NMDA ion channel, we have synthesized and characterized in vitro four substituted derivatives of the potent glycine site antagonist 3-[2-[(phenylamino)carbonyl]ethenyl]-4,6-dichloroindole-2-carboxylic acid (Ki=3.0 nM). These new ligands contain groups amenable to labeling with C-11 for PET, or I-123 for SPECT. In vitro analysis of these compounds revealed that placement of a methoxy group at either the ortho or para position of the phenylaminocarbonyl group significantly reduced receptor affinity (Ki=74.0 AE 8.1 and 26.5 AE 4.9 nM, respectively), as did placement of an iodine at the para position (Ki=60.4 AE 8.2 nM). However, the meta-methoxy derivative (4b) maintained high affinity (Ki=4.8 AE 0.9 nM) for the glycine site and was therefore labeled with carbon-11 by reacting the corresponding desmethyl derivative with [ 11 C]methyl iodide. Radiochemical yields of 14 AE 10% (EOS), and high specific activity (1.2 AE 0.5 Ci/mmol (EOS, n=7)) were realized, and the product was
Nuclear medicine and biology, 2015
The present study was designed to assess whether [(18)F]PK-209 (3-(2-chloro-5-(methylthio)phenyl)-1-(3-([(18)F]fluoromethoxy)phenyl)-1-methylguanidine) is a suitable ligand for imaging the ion-channel site of N-methyl-D-aspartate receptors (NMDArs) using positron emission tomography (PET). Dynamic PET scans were acquired from male rhesus monkeys over 120min, at baseline and after the acute administration of dizocilpine (MK-801, 0.3mg/kg; n=3/condition). Continuous and discrete arterial blood samples were manually obtained, to generate metabolite-corrected input functions. Parametric volume-of-distribution (VT) images were obtained using Logan analysis. The selectivity profile of PK-209 was assessed in vitro, on a broad screen of 79 targets. PK-209 was at least 50-fold more selective for NMDArs over all other targets examined. At baseline, prolonged retention of radioactivity was observed in NMDAr-rich cortical regions relative to the cerebellum. Pretreatment with MK-801 reduced the ...
Journal of Medicinal Chemistry, 2016
Abnormal activity of various N-methyl-D-aspartate receptor (NMDAR) subtypes has been implicated in a wide variety of neurological disorders such as Alzheimer's disease, schizophrenia, and epilepsy. Imaging agents for PET and SPECT that target NMDARs in a subtype-selective fashion may enable better characterization of those disorders and enhance drug development. On the basis of a pyrazoline derivative that demonstrated neuroprotective effects in vivo, we synthesized a series of para-substituted analogues and measured their affinities to various NMDAR subtypes. Compounds 4a-c and 4e showed greater, nanomolar affinity for the GluN1/2A subtype versus GluN1/2B. Dicarbomethoxy (pro-drug) analogues of [ 124/125 I]4d and [ 11 C] 4e (i.e., [ 124/125 I]11d and [ 11 C]11e) were generated and tested for NMDAR binding specificity in ex vivo autoradiography and brain biodistribution studies. Although NMDAR-specific binding could be demonstrated for [ 125 I]11d and [ 11 C]11e through autoradiography and biodistribution studies, *