Synthesis and evaluation of novel radioligands for positron emission tomography imaging of the orexin-2 receptor.
08 Aug 2013-Journal of Medicinal Chemistry (American Chemical Society)-Vol. 56, Iss: 16, pp 6371-6385
TL;DR: The design, synthesis, and evaluation of OXR ligands related to (1R,2S)-2-(((2-methyl-4-methoxymethylpyrimidin-5-yl)oxy)methyl)-N-(5-fluoropyridIn-2-yl)-2-(3- fluorophenyl)cyclopropanecarboxamide) applicable to positron emission tomography (PET) imaging are described.
Abstract: Orexin receptors (OXRs) in the brain have been implicated in diverse physiological and neuropsychiatric conditions. Here we describe the design, synthesis, and evaluation of OXR ligands related to (1R,2S)-2-(((2-methyl-4-methoxymethylpyrimidin-5-yl)oxy)methyl)-N-(5-fluoropyridin-2-yl)-2-(3-fluorophenyl)cyclopropanecarboxamide (9a) applicable to positron emission tomography (PET) imaging. Structural features were incorporated to increase binding affinity for OXRs, to enable carbon-11 radiolabeling, and to adjust lipophilicity considered optimal for brain penetration and low nonspecific binding. 9a displayed nanomolar affinity for OXRs, and autoradiography using rat brain sections showed that specific binding of [11C]9a was distributed primarily to neocortical layer VI and hypothalamus, consistent with reported localizations of orexin-2 receptors (OX2Rs). In vivo PET study of [11C]9a demonstrated moderate uptake of radioactivity into rat and monkey brains under deficiency or blockade of P-glycoprotein, and ...
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TL;DR: The Orexin system, consisting of the two orexin-neuropeptides and two G-protein-coupled receptors, is as well involved in reward and addictive behaviors.
63 citations
TL;DR: Novel approaches to generate [11C]CO using CO‐releasing molecules (CO‐RMs), such as silacarboxylic acids and disilanes, applied to radiochemistry are described and compared with standard [11 C]CO production methods.
Abstract: [11 C]Carbon dioxide ([11 C]CO2 ) and [11 C]carbon monoxide ([11 C]CO) are 2 attractive precursors for labelling the carbonyl position (C═O) in a vast range of functionalised molecules (eg, ureas, amides, and carboxylic acids). The development of radiosynthetic methods to produce functionalised 11 C-labelled compounds is required to enhance the radiotracers available for positron emission tomography, molecular, and medical imaging applications. Following a brief summary of secondary 11 C-precursor production and uses, the review focuses on recent progress with direct 11 C-carboxylation routes with [11 C]CO2 and 11 C-carbonylation with [11 C]CO. Novel approaches to generate [11 C]CO using CO-releasing molecules (CO-RMs), such as silacarboxylic acids and disilanes, applied to radiochemistry are described and compared with standard [11 C]CO production methods. These innovative [11 C]CO synthesis strategies represent efficient and reliable [11 C]CO production processes, enabling the widespread use of [11 C]CO chemistry within the wider radiochemistry community.
49 citations
TL;DR: The reference standard MK-1064 was synthesized from methyl 2-chloro-5-iodonicotinate and 5-(chloropyridin-3-yl)boronic acid in 4 steps with 33% overall chemical yield and the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 185-555GBq/μmol.
22 citations
TL;DR: The current approach has facilitated the discovery of a PET probe potentially suitable for translational research and development focused on AMPA receptors that was shown by autoradiography to specifically bind to the neocortex and hippocampus, consistent with AMPA receptor localization.
Abstract: We document the development of PET probes for central AMPA receptors and their application to in vivo animal imaging. An initial screening of perampanel derivatives was performed to identify probe candidates. Despite the high autoradiographic contrast yielded by several radioligands, rat PET scans did not support their in vivo suitability. Further focused derivatization and a second screening by ex vivo LC-MS measurements led to the selection of 2-[1-(3-methylaminophenyl)-2-oxo-5-(pyrimidin-2-yl)-1,2-dihydropyridin-3-yl]benzonitrile, 21a, and its analogues as candidates. [(11)C]21a was shown by autoradiography to specifically bind to the neocortex and hippocampus, consistent with AMPA receptor localization. PET imaging with [(11)C]21a demonstrated moderate uptake of radioactivity in rat and monkey brains, with the retention of radiosignals being consistent with that from the autoradiogram data, and the uptake was blocked by pretreatment with unlabeled 21a in a dose-dependent manner. The current approach has facilitated the discovery of a PET probe potentially suitable for translational research and development focused on AMPA receptors.
22 citations
Patent•
12 Mar 2014TL;DR: In this article, the present invention is directed to compounds of Formula (I): Methods of making the compounds of formula I are also described, and the invention also relates to pharmaceutical compositions comprising compounds of the formula (I).
Abstract: The present invention is directed to compounds of Formula (I): Methods of making the compounds of Formula I are also described. The invention also relates to pharmaceutical compositions comprising compounds of Formula (I). Methods of using the compounds of the invention are also within the scope of the invention.
20 citations
References
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TL;DR: Two novel neuropeptides are identified, both derived from the same precursor by proteolytic processing, that bind and activate two closely related (previously) orphan G protein-coupled receptors in the hypothalamus of rats.
5,162 citations
TL;DR: A hypothalamus-specific mRNA is described that encodes preprohypocretin, the putative precursor of a pair of peptides that share substantial amino acid identities with the gut hormone secretin, suggesting that the hypocretins function within the CNS as neurotransmitters.
Abstract: We describe a hypothalamus-specific mRNA that encodes preprohypocretin, the putative precursor of a pair of peptides that share substantial amino acid identities with the gut hormone secretin. The hypocretin (Hcrt) protein products are restricted to neuronal cell bodies of the dorsal and lateral hypothalamic areas. The fibers of these neurons are widespread throughout the posterior hypothalamus and project to multiple targets in other areas, including brainstem and thalamus. Hcrt immunoreactivity is associated with large granular vesicles at synapses. One of the Hcrt peptides was excitatory when applied to cultured, synaptically coupled hypothalamic neurons, but not hippocampal neurons. These observations suggest that the hypocretins function within the CNS as neurotransmitters.
3,558 citations
TL;DR: The results of this immunohistochemical study suggest that hypocretins are likely to have a role in physiological functions in addition to food intake such as regulation of blood pressure, the neuroendocrine system, body temperature, and the sleep–waking cycle.
Abstract: The novel neuropeptides called hypocretins (orexins) have recently been identified as being localized exclusively in cell bodies in a subregion of the tuberal part of the hypothalamus. The structure of the hypocretins, their accumulation in vesicles of axon terminals, and their excitatory effect on cultured hypothalamic neurons suggest that the hypocretins function in intercellular communication. To characterize these peptides further and to help understand what physiological functions they may serve, we undertook an immunohistochemical study to examine the distribution of preprohypocretin-immunoreactive neurons and fibers in the rat brain. Preprohypocretin-positive neurons were found in the perifornical nucleus and in the dorsal and lateral hypothalamic areas. These cells were distinct from those that express melanin-concentrating hormone. Although they represent a restricted group of cells, their projections were widely distributed in the brain. We observed labeled fibers throughout the hypothalamus. The densest extrahypothalamic projection was found in the locus coeruleus. Fibers were also seen in the septal nuclei, the bed nucleus of the stria terminalis, the paraventricular and reuniens nuclei of the thalamus, the zona incerta, the subthalamic nucleus, the central gray, the substantia nigra, the raphe nuclei, the parabrachial area, the medullary reticular formation, and the nucleus of the solitary tract. Less prominent projections were found in cortical regions, central and anterior amygdaloid nuclei, and the olfactory bulb. These results suggest that hypocretins are likely to have a role in physiological functions in addition to food intake such as regulation of blood pressure, the neuroendocrine system, body temperature, and the sleep–waking cycle.
3,255 citations
TL;DR: It is proposed that orexin regulates sleep/wakefulness states, and that Orexin knockout mice are a model of human narcolepsy, a disorder characterized primarily by rapid eye movement (REM) sleep dysregulation.
2,935 citations
TL;DR: It is determined that canine narcolepsy is caused by disruption of the hypocretin (orexin) receptor 2 gene (Hcrtr2) and this result identifies hypocretins as major sleep-modulating neurotransmitters and opens novel potential therapeutic approaches for Narcoleptic patients.
2,450 citations