N'-3-(Trifluoromethyl)phenyl Derivatives of N-Aryl-N'-methylguanidines as Prospective PET Radioligands for the Open Channel of the N-Methyl-d-aspartate (NMDA) Receptor: Synthesis and Structure-Affinity Relationships

Application and assessment of deep learning for the generation of potential NMDA receptor antagonists

Uncompetitive antagonists of the N-methyl d-aspartate receptor (NMDAR) have demonstrated therapeutic benefit in the treatment of neurological diseases such as Parkinson's and Alzheimer's, but some also cause dissociative effects that have led to the synthesis of illicit drugs. The ability to generate NMDAR antagonists in silico is therefore desirable for both new medication development and preempting and identifying new designer drugs. Recently, generative deep learning models have been applied to de novo drug design as a means to expand the amount of chemical space that can be explored for potential drug-like compounds. In this study, we assess the application of a generative model to the NMDAR to achieve two primary objectives: (i) the creation and release of a comprehensive library of experimentally validated NMDAR phencyclidine (PCP) site antagonists to assist the drug discovery community and (ii) an analysis of both the advantages conferred by applying such generative artificial intelligence models to drug design and the current limitations of the approach. We apply, and provide source code for, a variety of ligand- and structure-based assessment techniques used in standard drug discovery analyses to the deep learning-generated compounds. We present twelve candidate antagonists that are not available in existing chemical databases to provide an example of what this type of workflow can achieve, though synthesis and experimental validation of these compounds are still required.

A Review of Molecular Imaging of Glutamate Receptors

Molecular imaging with positron emission tomography (PET) and single photon emission computed tomography (SPECT) is a well-established and important in vivo technique to evaluate fundamental biological processes and unravel the role of neurotransmitter receptors in various neuropsychiatric disorders. Specific ligands are available for PET/SPECT studies of dopamine, serotonin, and opiate receptors, but corresponding development of radiotracers for receptors of glutamate, the main excitatory neurotransmitter in mammalian brain, has lagged behind. This state of affairs has persisted despite the central importance of glutamate neurotransmission in brain physiology and in disorders such as stroke, epilepsy, schizophrenia, and neurodegenerative diseases. Recent years have seen extensive efforts to develop useful ligands for molecular imaging of subtypes of the ionotropic (N-methyl-D-aspartate (NMDA), kainate, and AMPA/quisqualate receptors) and metabotropic glutamate receptors (types I, II, and III mGluRs). We now review the state of development of radioligands for glutamate receptor imaging, placing main emphasis on the suitability of available ligands for reliable in vivo applications. We give a brief account of the radiosynthetic approach for selected molecules. In general, with the exception of ligands for the GluN2B subunit of NMDA receptors, there has been little success in developing radiotracers for imaging ionotropic glutamate receptors; failure of ligands for the PCP/MK801 binding site in vivo doubtless relates their dependence on the open, unblocked state of the ion channel. Many AMPA and kainite receptor ligands with good binding properties in vitro have failed to give measurable specific binding in the living brain. This may reflect the challenge of developing brain-penetrating ligands for amino acid receptors, compounded by conformational differences in vivo. The situation is better with respect to mGluR imaging, particularly for the mGluR5 subtype. Several successful PET ligands serve for investigations of mGluRs in conditions such as schizophrenia, depression, substance abuse and aging. Considering the centrality and diversity of glutamatergic signaling in brain function, we have relatively few selective and sensitive tools for molecular imaging of ionotropic and metabotropic glutamate receptors. Further radiopharmaceutical research targeting specific subtypes and subunits of the glutamate receptors may yet open up new investigational vistas with broad applications in basic and clinical research.

Palladium-Catalyzed Cascade Decarboxylative Amination/6-endo-dig Benzannulation of o-Alkynylarylketones with N-Hydroxyamides To Access Diverse 1-Naphthylamine Derivatives

An efficient and practical one-pot strategy to produce highly substituted 1-naphthylamines via sequential palladium-catalyzed decarboxylative amination/intramolecular 6-endo-dig benzannulation reactions has been described. In this reaction, a broad range of electron-rich, electron-neutral, and electron-deficient o-alkynylarylketones react well with N-hydroxyl aryl/alkylamides to give a diversity of 1-naphthylamines in good to excellent yields under mild reaction conditions. The gram-scale synthesis, with benefits such as undiminished product yield and easy transformation, illustrated the practicality of this method.

Aza-Henry Reaction: Synthesis of Nitronaphthylamines from 2-(Alkynyl)benzonitriles

A transition-metal-free approach for construction of nitronaphthylamines has been developed for the first time through aza-henry, chemoselective, and regioselective annulation of 2-alkynylbenzonitriles with nitromethane. In addition, the strategy provides an elegant, operationally simple and atom-economical route for the synthesis of nitroamino substituted heterocyclic scaffolds, featuring a range of sensitive functional groups. The reaction could also devise acetonitrile and acetophenone as nucleophile. The protocol has been successfully implemented for late-stage modification of bioactive molecules.

Saccharin guanidination via facile three-component “two saccharins-one dialkylcyanamide” integration

Novel three-component “two saccharins-one dialkylcyanamide” integration.

Copper-Catalyzed Borylative Cyclization of in Situ Generated o-Allenylaryl Nitriles with Bis(pinacolato)diboron

A Cu-catalyzed cascade borylcupration/cyclization of in situ generated allene-nitriles with B₂pin₂ has been developed, which provides highly substituted 3-boryl-1-naphthylamines with excellent regioselectivity and wide functional group compatibility. It has been shown that, for the first time, the catalytically generated allylcopper species can be captured by a cyano group from a normal nitrile to furnish a carbocycle.

The chemistry and biology of guanidine natural products

The chemistry and biology of natural guanidines isolated from microbial culture media, from marine invertebrates, as well as from terrestrial plants and animals, are reviewed.

Development of Radiolabeled Ligands Targeting the Glutamate Binding Site of the N-Methyl-d-aspartate Receptor as Potential Imaging Agents for Brain

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 [^124/125I]4d and [¹¹C]4e (i.e., [^124/125I]11d and [¹¹C]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 [¹²⁵I]11d and [¹¹C]11e through autoradiography and biodistribution studies, imaging of neither [¹²⁴I]11d nor [¹¹C]11e could demonstrate brain penetration sufficient for detection by PET.