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Excitotoxicity driven by overactivation of NMDA receptors represents a major mechanism of acute and chronic neurological and neurodegenerative disorders. Negative allosteric modulators interacting with the ifenprodil binding site of the NMDA receptor are able to interrupt this ongoing neurodamaging process. Starting from the potent 3-benzazepine-1,7-diol 4a novel NMDA receptor antagonists were designed by modification of the N-(4-phenylbutyl) side chain. With respect to developing novel fluorinated PET tracers, regioisomeric fluoroethoxy derivatives 11 , 12, 14 , and 15 were synthesized. Analogs 19 and 20 with various heteroaryl moieties at the end of the N-side chain were prepared by Sonogashira reaction and nucleophilic substitution. The fluoroethyl triazole 37 was obtained by 1,3-dipolar cycloaddition. In several new ligands, the flexibility of the (hetero)arylbutyl side chain was restricted by incorporation of a triple bond. The affinity towards the ifenprodil binding site was tested in an established competition assay using [3H]ifenprodil as radioligand. Introduction of a fluoroethoxy moiety at the terminal phenyl ring, replacement of the terminal phenyl ring by a heteroaryl ring and incorporation of a triple bond into the butyl spacer led to considerable reduction of GluN2B affinity. The phenol 15 (K i = 193 nM) bearing a p -fluoroethoxy moiety at the terminal phenyl ring represents the most promising GluN2B ligand of this series of compounds. With exception of 15 showing moderate σ 2 affinity (K i = 79 nM), the interaction of synthesized 3-benzazepines towards the PCP binding site of the NMDA receptor, σ 1 and σ 2 receptors was rather low (K i > 100 nM). [ABSTRACT FROM AUTHOR]

The title compounds, C22H29NO2 (3) and C22H29NO2 (4) [systematic names: (1S*,2R*)-7-methoxy-2-methyl-3-(4-phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepin-1-ol and (1R*,2R*)-7-methoxy-2-methyl-3-(4-phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepin-1-ol, are diastereomers with the relative configuration of the adjacent hydroxyl and methyl groups at the seven-membered azepine ring being trans in (3) and cis in (4). In the crystals the orientation of these groups is −anti-periplanar (3) and +syn-clinal (4). In both cases, the crystals studied proved to be of a racemic mixture, with relative configurations (R*,S*)-3 and (R*,R*)-4. In both compounds, the seven-membered azepine ring has a chair-like conformation, and the 4-phenylbutyl side chain adopts a extended conformation in (R*,S*)-3, but a twisted conformation in (R*,R*)-4. In the crystal of (S*,R*)-3, molecules are linked via C—H...O hydrogen bonds, forming slabs parallel to the ac plane. In the crystal of (R*,R*)-4, molecules are linked via O—H...N hydrogen bonds, forming chains propagating along the c-axis direction. The chains are linked by C—H...O hydrogen bonds, forming slabs parallel to the ac plane.

In the title compound, C25H27NO4S, which crystallized as a racemate, the relative configuration of the adjacent OH and CH3 groups on the azepine ring is trans. The seven-membered azepin ring has a chair-like conformation. The planar aromatic rings of the benzyl and tosylate moiety are inclined to the planar 3-benzazepine ring by 78.39 (15) and 77.03 (14)°, respectively, and to each another by 13.82 (15)°. In the crystal, molecules are linked via O—H...O and C—H...O hydrogen bonds, forming double-stranded chains along the a-axis direction. The chains are linked via C—H...π interactions, forming a three-dimensional architecture.

Abstract It has been reported that benzo [7]annulen-7-amines bearing electron withdrawing substituents such as 3d with a 2-Cl or 3e with a 2-NO 2 moiety show very high affinity towards the ifenprodil binding site of GluN2B subunit containing NMDA receptors. Therefore, bioisosteres of 3 with an electron deficient pyridine ring instead of the chloro- or nitrobenzene ring were envisaged. Starting from pyridine-2,3-dicarboxylic acid (5) a five-step synthesis of the key intermediate, the ketone 10 , was developed. Reductive amination with various primary amines and NaBH(OAc) 3 led to the homologous secondary amines 11a - c. Subsequent methylation yielded the tertiary amines 12b and 12c. Receptor binding studies with [3H]ifenprodil revealed K i -values above 100 nM for the most active phenylpropyl- and phenylbutylamines 11b and 11c. The >100-fold reduced GluN2B affinity of pyridines 11b and 11c compared to the GluN2B affinity of the corresponding chloro- and nitrobenzene derivatives 3d and 3e indicates that the pyridine ring is not tolerated as bioisosteric replacement of the chloro- or nitrobenzene ring in this type of compounds. Graphical abstract Image 1 Highlights • A series of [7]annulene [b]pyridin-7-amines was prepared. • Bioisosteric replacement of nitrobenzene by pyridine. • Pyridine bioisosteres show reduced GluN2B affinity. • Interaction with the ifenprodil binding site. [ABSTRACT FROM AUTHOR]

Antagonists addressing selectively NMDA receptors containing the GluN2B subunit are of particular interest for the treatment of various neurological disorders including neurodegenerative diseases. With the aim to bioisosterically replace the metabolically labile phenol of 7-amino-6,7,8,9-tetrahydro-5 H -benzo[7]annulen-2-ols, several analogs were docked into the ifenprodil binding site leading to the hydroxymethyl derivatives 4 as promising candidates. They display the same binding pose as Ro 25-6981 and the same H-bond interactions with Gln110 and Glu236 within the GluN2B subunit. The phenylalkyl moieties occupy the hydrophobic pocket formed predominantly by Pro78 (GluN2B), Phe114 (GluN2B), and Tyr109 (GluN1b). Starting from o -phthalaldehyde, the hydroxymethyl derivatives 4 were prepared in a 7-step synthesis with a haloform reaction of trichloroacetophenone 7 as key step. In receptor binding studies, the phenylpropyl derivative 4a shows promising GluN2B affinity ( K i  = 101 nM) and high selectivity over the PCP binding site and both σ receptor subtypes. 4a was able to inhibit the glutamate/glycine induced cytotoxicity at mouse fibroblasts with an IC 50 value of 5.2 μM. It is assumed that the hydroxymethyl moiety of 4a stabilizes the closed channel conformation by an H-bond with Glu236 as does the phenolic OH moiety of 3 , Ro 25-6981 and ifenprodil. [ABSTRACT FROM AUTHOR]

Benzo[7]annulen-7-amines 7 without further polar substituents have been reported as conformationally restricted Ro 25-6981 analogs and show unexpectedly high GluN2B affinity. Herein the corresponding 2-NO 2 derivatives 8 were synthesized and pharmacologically evaluated. NO 2 derivatives 8 show 5- to 10-fold higher GluN2B affinity than the unsubstituted ligands 7 . Docking studies of ligands 7c and 8c reveal an important contribution of the 2-NO 2 -substituent in determining the binding pose and modulating the GluN2B affinity. [ABSTRACT FROM AUTHOR]

Due to their beneficial side effect profile, NMDA receptor antagonists interacting selectively with the allosteric ifenprodil binding site of the GluN2B subunit are of major interest for the treatment of neurological and neurodegenerative disorders. A series of benzo[7]annulen-7-amines 6 was designed by conformational restriction of ifenprodil ( 1 ). At first the benzo[7]annulen-7-one 11 was prepared in a three-step synthesis comprising of a double Knoevenagel condensation of phthalaldehyde ( 7 ) with dimethyl 3-oxoglutarate ( 8 ), hydrogenation of 9 and saponification/decarboxylation of 10 . Reductive amination of the ketone 11 with primary amines and NaBH(OAc) 3 led to the secondary amines 6a – d , cis - 6h and trans - 6i . The tertiary amines 6e – g were obtained by S N 2-substitution of the nosylate 13 . Although H-bond forming substituents in 2- and 5-position are missing, the amines 6 exhibit high affinity towards GluN2B containing NMDA receptors. A distance of four to five bond lengths between the basic amino moiety and the phenyl ring in the side chain appears to be optimal for high GluN2B affinity. The phenylcyclohexylamine cis - 6h and the 4-benzylpiperidine 6g show the highest GluN2B affinities ( K i = 2.3 nM and 2.9 nM, respectively). With respect to selectivity against the PCP binding site, σ 1 and σ 2 receptors the phenylpiperazine 6f is the most promising GluN2B antagonist. [ABSTRACT FROM AUTHOR]

l -glutamate is an excitatory neurotransmitter in the central nervous system (CNS), which can activate ionotropic receptors (iGluRs) and metabotropic (mGluRs) receptors. N-methyl-D-aspartate (NMDA) receptor is a ligand-gated ion channel belonging to the iGluRs family. Among NMDA receptor subtypes, GluN2B subtype plays a crucial role in CNS diseases. In this review, we summarize, classify and discuss the reports on GluN2B antagonists, published from the 1990s to 2020, to provide the therapeutic potential of GluN2B antagonists on various disorders. The GluN2B antagonists are broadly classified into two categories, which are prototypical antagonists and atypical antagonists. And the latter are further divided into amidine derivatives, 4-aminoquinolines, indole derivatives, benzimidazole derivatives, oxamide derivatives, carbamate derivatives, EVT-101 analogues, 1 H -pyrrolo[3,2-b]pyridine derivatives, benzazepin derivatives, other heterocyles and radiotracers. This review will provide a comprehensive description including structure, structure-activity relationship (SAR), and pharmacology of novel GluN2B-subtype selective NMDA antagonists to the medicinal chemists, which would be helpful in rational designing effective drugs aimed toward related CNS disease. Image 1 • Antagonizing GluN2B-selective NMDA receptors is thought to be an important target for various CNS disease. • The different chemical series of GluN2B-selective NMDA receptor antagonists are reviewed. • SAR and pharmacology are described in detail for each class. • Limitations and perspectives of GluN2B-selective NMDA receptor antagonists are discussed. [ABSTRACT FROM AUTHOR]

A set of GluN2B NMDA receptor antagonists with conformationally restricted phenylethylamine substructure was prepared and pharmacologically evaluated. The phenylethylamine substructure was embedded in ring expanded 3-benzazocines 4 as well as ring-contracted tetralinamines 6 and indanamines 7. The ligands 4 , 6 and 7 were synthesized by reductive alkylation of secondary amine 11 , reductive amination of ketones 12 and 16 and nucleophilic substitution of nosylates 14 and 17. The moderate GluN2B affinity of 3-benzazocine 4d (K i = 32 nM) translated into moderate cytoprotective activity (IC 50 = 890 nM) and moderate ion channel inhibition (60% at 10 μM) in two-electrode voltage clamp experiments with GluN1a/GluN2B expressing oocytes. Although some of the tetralinamines 6 and indanamines 7 showed very high GluN2B affinity (e.g. K i (7f) = 3.2 nM), they could not inhibit glutamate/glycine inducted cytotoxicity. The low cytoprotective activity of 3-benzazocines 4 , tetralinamines 6 and indanamines 7 was attributed to the missing OH moiety at the benzene ring and/or in benzylic position. Docking studies showed that the novel GluN2B ligands adopt similar binding poses as Ro 25–6981 with the central H-bond interaction between the protonated amino moiety of the ligands and the carbamoyl moiety of Gln110. However, due to the lack of a second H-bond forming group, the ligands can adopt two binding poses within the ifenprodil binding pocket. Image 1 • Conformational restriction was achieved by embedding the phenylethylamine substructure into various ring systems. • Moderate GluN2B affinity of 3-benzazcoines translated into cytoprotective activity. • High GluN2B affinity of indanamines did not result in cytoprotective potential. • Docking studies led to two different binding poses in the ifenprodil binding site. [ABSTRACT FROM AUTHOR]

N-methyl-d-aspartate receptors (NMDAR) are widely expressed in the brain. GluN2B subunit-containing NMDARs has recently attracted significant attention as potential pharmacological targets, with emphasis on the functional properties of allosteric antagonists. We used primary cultures from chicken embryo forebrain (E10), expressing native GluN2B-containing NMDA receptors as a novel model system. Comparing the inhibition of calcium influx by well-known GluN2B subunit-specific allosteric antagonists, the following rank order of potency was found: EVT-101 (EC 50 22 ± 8 nmol/L) > Ro 25-6981 (EC 50 60 ± 30 nmol/L) > ifenprodil (EC 50 100 ± 40 nmol/L) > eliprodil (EC 50 1300 ± 700 nmol/L), similar to previous observations in rat cortical cultures and cell lines overexpressing chimeric receptors. The less explored Ro 04-5595 had an EC 50 of 186 ± 32 nmol/L. Venturing to explain the differences in potency, binding properties were further studied by in silico docking and molecular dynamics simulations using x-ray crystal structures of GluN1/GluN2B amino terminal domain. We found that Ro 04-5595 was predicted to bind the recently discovered EVT-101 binding site, not the ifenprodil-binding site. The EVT-101 binding pocket appears to accommodate more structurally different ligands than the ifenprodil-binding site, and contains residues essential in ligand interactions necessary for calcium influx inhibition. For the ifenprodil site, the less effective antagonist (eliprodil) fails to interact with key residues, while in the EVT-101 pocket, difference in potency might be explained by differences in ligand-receptor interaction patterns.

Antagonists that selectively target GluN2B-subunit-containing N-methyl-d-aspartate (NMDA) receptors are of major interest for the treatment of various neurological disorders. In this study, relationships between variously substituted benzo[7]annulen-7-amines and their GluN2B affinity were investigated. 2-Nitro-5,6,8,9-tetrahydrobenzo[7]annulen-7-one (8) represents the central building block for the introduction of various substituents at the 2-position and various 7-amino moieties. N-(3-Phenylpropyl)-6,7,8,9-tetrahydro-5H-benzo[7]annulen-7-amines with a 2-NO 2 (7 c), 2-Cl (15 c), or 2-OBn group (22 c) show very high GluN2B affinity (K i =1.6-3.6 nm). Docking studies revealed the same binding poses for benzo[7]annulen-7-amines and ifenprodil at the interface of GluN1b and GluN2B subunits. The large 2-OBn moiety of 22 c occupies a previously unrecognized subpocket, which explains its high GluN2B affinity (K i =3.6 nm). In two-electrode voltage clamp experiments and cytoprotection assays, the high-affinity GluN2B ligands 7 c, 15 c, and 22 c could not inhibit the glutamate-/glycine-evoked current and cytotoxic effects. However, the analogous phenols 16 c ((3-phenylpropyl)amino moiety) and 16 d ((4-phenylbutyl)amino moiety) with 10-fold lower GluN2B affinity (K i =28 and 21 nm, respectively) showed promising inhibition of glutamate-/glycine-evoked effects in both assays. The presence of a phenolic hydroxy group seems to be essential for inducing conformational changes of the receptor protein, which finally results in closure of the ion conduction pathway., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)