Cryogenic Memory Architecture Integrating Spin Hall Effect based Magnetic Memory and Superconductive Cryotron Devices.

One of the most challenging obstacles to realizing exascale computing is minimizing the energy consumption of L2 cache, main memory, and interconnects to that memory. For promising cryogenic computing schemes utilizing Josephson junction superconducting logic, this obstacle is exacerbated by the cryogenic system requirements that expose the technology's lack of high-density, high-speed and power-efficient memory. Here we demonstrate an array of cryogenic memory cells consisting of a non-volatile three-terminal magnetic tunnel junction element driven by the spin Hall effect, combined with a superconducting heater-cryotron bit-select element. The write energy of these memory elements is roughly 8 pJ with a bit-select element, designed to achieve a minimum overhead power consumption of about 30%. Individual magnetic memory cells measured at 4 K show reliable switching with write error rates below 10-6, and a 4 × 4 array can be fully addressed with bit select error rates of 10-6. This demonstration is a first step towards a full cryogenic memory architecture targeting energy and performance specifications appropriate for applications in superconducting high performance and quantum computing control systems, which require significant memory resources operating at 4 K.

TC299423, a Novel Agonist for Nicotinic Acetylcholine Receptors.

(E)-5-(Pyrimidin-5-yl)-1,2,3,4,7,8-hexahydroazocine (TC299423) is a novel agonist for nicotinic acetylcholine receptors (nAChRs). We examined its efficacy, affinity, and potency for α6ß2∗ (α6ß2-containing), α4ß2∗, and α3ß4∗ nAChRs, using [125I]-epibatidine binding, whole-cell patch-clamp recordings, synaptosomal 86Rb+ efflux, [3H]-dopamine release, and [3H]-acetylcholine release. TC299423 displayed an EC50 of 30-60 nM for α6ß2∗ nAChRs in patch-clamp recordings and [3H]-dopamine release assays. Its potency for α6ß2∗ in these assays was 2.5-fold greater than that for α4ß2∗, and much greater than that for α3ß4∗-mediated [3H]-acetylcholine release. We observed no major off-target binding on 70 diverse molecular targets. TC299423 was bioavailable after intraperitoneal or oral administration. Locomotor assays, measured with gain-of-function, mutant α6 (α6L9'S) nAChR mice, show that TC299423 elicits α6ß2∗ nAChR-mediated responses at low doses. Conditioned place preference assays show that low-dose TC299423 also produces significant reward in α6L9'S mice, and modest reward in WT mice, through a mechanism that probably involves α6(non-α4)ß2∗ nAChRs. However, TC299423 did not suppress nicotine self-administration in rats, indicating that it did not block nicotine reinforcement in the dosage range that was tested. In a hot-plate test, TC299423 evoked antinociceptive responses in mice similar to those of nicotine. TC299423 and nicotine similarly inhibited mouse marble burying as a measure of anxiolytic effects. Taken together, our data suggest that TC299423 will be a useful small-molecule agonist for future in vitro and in vivo studies of nAChR function and physiology.

Anticholinergic therapy for overactive bladder: a nicotinic modality?

Until recently the treatment of Overactive Bladder (OAB) has primarily been aimed at mitigating hypercholinergic activity in the bladder via antagonism of muscarinic acetylcholine receptors. However, antimuscarinic therapies have limited efficacy and significant side effects. It is now known that nicotinic acetylcholine receptor (nAChR) subtypes are expressed in the urothelium and on afferent nerve fibers in the bladder, and it is believed that these receptors serve to communicate urgency and facilitate voiding function. This presents the opportunity for an alternative to the antimuscarinic approach, one which involves inhibition of nAChRs in the bladder that are chronically overstimulated by acetylcholine. Specifically, we hypothesize that an orally administered nAChR-selective inhibitor with extensive renal elimination will result in higher local concentrations in the bladder and lower systemic exposure than current therapies, representing a novel targeted approach to the treatment of OAB with a more favorable side effect profile.

Novel nicotinic acetylcholine receptor agonists containing carbonyl moiety as a hydrogen bond acceptor.

A novel series of α4ß2 nAChR agonists lacking common pyridine or its bioisosteric heterocycle have been disclosed. Essential pharmacophoric elements of the series are exocyclic carbonyl moiety as a hydrogen bond acceptor and secondary amino group within diaza- or azabicyclic scaffold. Computer modeling studies suggested that molecular shape of the ligand also contributes to promotion of agonism. Proof of concept for improving working memory performance in a novel object recognition task has been demonstrated on a representative of the series, 3-propionyl-3,7-diazabicyclo[3.3.0]octane (34).

Discovery of (2S,3R)-N-[2-(pyridin-3-ylmethyl)-1-azabicyclo[2.2.2]oct-3-yl]benzo[b]furan-2-carboxamide (TC-5619), a selective α7 nicotinic acetylcholine receptor agonist, for the treatment of cognitive disorders.

(2S,3R)-N-[2-(Pyridin-3-ylmethyl)-1-azabicyclo[2.2.2]oct-3-yl]benzo[b]furan-2-carboxamide (7a, TC-5619), a novel selective agonist of the α7 neuronal nicotinic acetylcholine receptor, has been identified as a promising drug candidate for the treatment of cognitive impairment associated with neurological disorders. 7a demonstrated more than a thousand-fold separation between the affinities for the α7 and α4ß2 receptor subtypes and had no detectable effects on muscle or ganglionic nicotinic receptor subtypes, indicating a marked selectivity for the central nervous system over the peripheral nervous system. Results obtained from homology modeling and docking explain the observed selectivity. 7a had positive effects across cognitive, positive, and negative symptoms of schizophrenia in animal models and was additive or synergistic with the antipsychotic clozapine. Compound 7a, as an augmentation therapy to the standard treatment with antipsychotics, demonstrated encouraging results on measures of negative symptoms and cognitive dysfunction in schizophrenia and was well tolerated in a phase II clinical proof of concept trial in patients with schizophrenia.

Structure-activity studies of 7-heteroaryl-3-azabicyclo[3.3.1]non-6-enes: a novel class of highly potent nicotinic receptor ligands.

The potential for nicotinic ligands with affinity for the α4ß2 or α7 subtypes to treat such diverse diseases as nicotine addiction, neuropathic pain, and neurodegenerative and cognitive disorders has been exhibited clinically for several compounds while preclinical activity in relevant in vivo models has been demonstrated for many more. For several therapeutic programs, we sought nicotinic ligands with various combinations of affinity and function across both subtypes, with an emphasis on dual α4ß2-α7 ligands, to explore the possibility of synergistic effects. We report here the structure-activity relationships (SAR) for a novel series of 7-heteroaryl-3-azabicyclo[3.3.1]non-6-enes and characterize many of the analogues for activity at multiple nicotinic subtypes.

Multiple interaction regions in the orthosteric ligand binding domain of the α7 neuronal nicotinic acetylcholine receptor.

Neuronal nicotinic receptors (nAChRs) belong to the Cys-loop family of ligand-gated ion channels and are formed from five subunits either as homologous or heterologous, oligomeric receptors, and are of interest as targets for treatment of a variety of central and peripheral nervous system disorders. Using a model of the homopentameric α7 nAChR extracellular region derived from the homologous acetylcholine binding protein (AChBP) from Aplysia California, binding modes of structurally diverse, high affinity α7 ligands were examined by docking to the orthosteric ligand binding domain. While all α7 ligands show similar interactions between the essential positively charged cationic center of the ligand and αTRP147 of the receptor (i.e., hydrogen bond to the tryptophan backbone carbonyl and cation-π interaction), docked poses of various ligands show the potential to interact with three additional regions within the binding domain, identified as regions 1, 2, and 3. Region 1 is located in the vicinity of Loop-E, involves ligand-protein interactions via a network of water-mediated hydrogen bonds, and is analogous to the region where pyridinyl groups are located in many of the AChBP-nicotinic ligand cocrystal structures. Ligands interacting with region 2 probe an area that spans from Loop-E to Loops-D and -F and may contribute to α7-selectivity over other nAChR subtypes. Several high affinity α7 ligands show strong interactions in this region. Region 3 is located near Loop-F of the protein and is analogous to an area involved in binding of an active metabolite derived from DMXBA, in an AChBP cocrystal structure. It appears that π-π interactions contribute to binding affinities of α7 nAChR ligands in this latter region, and further, this region may also contribute to α7-selectivity over other nAChR subtypes. Analysis of the resulting poses suggests that compounds with high α7 binding affinity do not require interactions across all regions simultaneously, but that interactions in multiple regions may enhance ligand binding and increase selectivity. Our results provide insight for further development of selective α7 nAChR ligands and may prove useful for the design of novel scaffolds for specific nicotinic therapeutic agents.

Discovery of 3-(5-chloro-2-furoyl)-3,7-diazabicyclo[3.3.0]octane (TC-6683, AZD1446), a novel highly selective α4ß2 nicotinic acetylcholine receptor agonist for the treatment of cognitive disorders.

Diversification of essential nicotinic cholinergic pharmacophoric elements, i.e., cationic center and hydrogen bond acceptor, resulted in the discovery of novel potent α4ß2 nAChR selective agonists comprising a series of N-acyldiazabicycles. Core characteristics of the series are an exocyclic carbonyl moiety as a hydrogen bond acceptor and endocyclic secondary amino group. These features are positioned at optimal distance and with optimal relative spatial orientation to provide near optimal interactions with the receptor. A novel potent and highly selective α4ß2 nAChR agonist 3-(5-chloro-2-furoyl)-3,7-diazabicyclo[3.3.0]octane (56, TC-6683, AZD1446) with favorable pharmaceutical properties and in vivo efficacy in animal models has been identified as a potential treatment for cognitive deficits associated with psychiatric or neurological conditions and is currently being progressed to phase 2 clinical trials as a treatment for Alzheimer's disease.

Comparison of acetylcholine receptor interactions of the marine toxins, 13-desmethylspirolide C and gymnodimine.

The interaction of 13-desmethylspirolide C (SPX-desMe-C) and gymnodimine with several nicotinic and muscarinic acetylcholine receptors was investigated. Interaction at the muscarinic receptors was minimal. At nicotinic receptors, both SPX-desMe-C and gymnodimine displayed greatest affinity for the α7 receptor. The rank order for binding affinity (Ki) for SPX-desMe-C was α7 > α6ß3ß4α5 >> rat α3ß4, α1ßγδ > α4ß4, human α3ß4 > human α4ß2 > rat α4ß2 and for gymnodimine was α7, α6ß3ß4α5 > rat α3ß4 > human α3ß4, α4ß4 > rat α4ß2, human α4ß2 > α1ßγδ. Both molecules antagonized agonist-induced nicotinic responses. The antagonism rank order of potency (IC(50)) for SPX-desMe-C was α7 > low sensitivity (LS) α4ß2 > human α3ß4 > high sensitivity (HS) α4ß2, α1ßγδ > α4ß4 > rat α3ß4 and for gymnodimine was LS α4ß2 > human α3ß4 > α7 > HS α4ß2 > α4ß4 > rat α3ß4 > α1ßγδ. Neither gymnodimine nor SPX-desMe-C antagonism could be surmounted by increasing concentrations of nicotine. To elucidate the nature of this insurmountable blockade, we carried out homology modelling and molecular docking studies of both ligands with α7 nAChR. Their very high binding affinity results from very tight hydrophobic enclosures, in addition to previously reported hydrogen-bond and cation-π interactions. Also, the higher the hydrophilic surface area of the binding site of nAChRs, the weaker the binding affinity of both ligands. Together these results show the targets of action are nicotinic and define these marine toxins as additional tools to advance our understanding regarding interactions between antagonists and the nAChR ligand binding domain.

Discovery of novel α7 nicotinic acetylcholine receptor ligands via pharmacophoric and docking studies of benzylidene anabaseine analogs.

Based on pharmacophore elucidation and docking studies on interactions of benzylidene anabaseine analogs with AChBPs and α7 nAChR, novel spirodiazepine and spiroimidazoline quinuclidine series have been designed. Binding studies revealed that some of hydrogen-bond donor containing compounds exhibit improved affinity and selectivity for the α7 nAChR subtype in comparison with most potent metabolite of GTS-21, 3-(4-hydroxy-2-methoxybenzylidene)-anabaseine. Hydrophobicity and rigidity of the ligand also contribute into its binding affinity. We also describe alternative pharmacophoric features equidistant from the carbonyl oxygen atom of the conserved Trp-148 of the principal face, which may be exploited to further design diverse focused libraries targeting the α7 nAChR.

Docking studies of benzylidene anabaseine interactions with α7 nicotinic acetylcholine receptor (nAChR) and acetylcholine binding proteins (AChBPs): application to the design of related α7 selective ligands.

AChBPs isolated from Lymnaea stagnalis (Ls), Aplysia californica (Ac) and Bulinus truncatus (Bt) have been extensively used as structural prototypes to understand the molecular mechanisms that underlie ligand-interactions with nAChRs [1]. Here, we describe docking studies on interactions of benzylidene anabaseine analogs with AChBPs and α7 nAChR. Results reveal that docking of these compounds using Glide software accurately reproduces experimentally-observed binding modes of DMXBA and of its active metabolite, in the binding pocket of Ac. In addition to the well-known nicotinic pharmacophore (positive charge, hydrogen-bond acceptor, and hydrophobic aromatic groups), a hydrogen-bond donor feature contributes to binding of these compounds to Ac, Bt, and the α7 nAChR. This is consistent with benzylidene anabaseine analogs with OH and NH(2) functional groups showing the highest binding affinity of these congeners, and the position of the ligand shown in previous X-ray crystallographic studies of ligand-Ac complexes. In the predicted ligand-Ls complex, by contrast, the ligand OH group acts as hydrogen-bond acceptor. We have applied our structural findings to optimizing the design of novel spirodiazepine and spiroimidazoline quinuclidine series. Binding and functional studies revealed that these hydrogen-bond donor containing compounds exhibit improved affinity and selectivity for the α7 nAChR subtype and demonstrate partial agonism. The gain in affinity is also due to conformational restriction, tighter hydrophobic enclosures, and stronger cation-π interactions. The use of AChBPs structure as a surrogate to predict binding affinity to α7 nAChR has also been investigated. On the whole, we found that molecular docking into Ls binding site generally scores better than when a α7 homology model, Bt or Ac crystal structure is used.

Structural differences determine the relative selectivity of nicotinic compounds for native alpha 4 beta 2*-, alpha 6 beta 2*-, alpha 3 beta 4*- and alpha 7-nicotine acetylcholine receptors.

Mammalian brain expresses multiple nicotinic acetylcholine receptor (nAChR) subtypes that differ in subunit composition, sites of expression and pharmacological and functional properties. Among known subtypes of receptors, alpha 4 beta 2* and alpha 6 beta 2*-nAChR have the highest affinity for nicotine (where * indicates possibility of other subunits). The alpha 4 beta 2*-nAChRs are widely distributed, while alpha 6 beta 2*-nAChR are restricted to a few regions. Both subtypes modulate release of dopamine from the dopaminergic neurons of the mesoaccumbens pathway thought to be essential for reward and addiction. alpha 4 beta 2*-nAChR also modulate GABA release in these areas. Identification of selective compounds would facilitate study of nAChR subtypes. An improved understanding of the role of nAChR subtypes may help in developing more effective smoking cessation aids with fewer side effects than current therapeutics. We have screened a series of nicotinic compounds that vary in the distance between the pyridine and the cationic center, in steric bulk, and in flexibility of the molecule. These compounds were screened using membrane binding and synaptosomal function assays, or recordings from GH4C1 cells expressing h alpha 7, to determine affinity, potency and efficacy at four subtypes of nAChRs found in brain, alpha 4 beta 2*, alpha 6 beta 2*, alpha 7 and alpha 3 beta 4*. In addition, physiological assays in gain-of-function mutant mice were used to assess in vivo activity at alpha 4 beta 2* and alpha 6 beta 2*-nAChRs. This approach has identified several compounds with agonist or partial agonist activity that display improved selectivity for alpha 6 beta 2*-nAChR.

Evaluation of structurally diverse neuronal nicotinic receptor ligands for selectivity at the alpha6( *) subtype.

Direct comparison of pyridine versus pyrimidine substituents on a small but diverse set of ligands indicates that the pyrimidine substitution has the potential to enhance affinity and/or functional activity at alpha6 subunit-containing neuronal nicotinic receptors (NNRs) and decrease activation of ganglionic nicotinic receptors, depending on the scaffold. The ramifications of this structure-activity relationship are discussed in the context of the design of small molecules targeting smoking cessation.

Diversity-oriented synthesis of a cytisine-inspired pyridone library leading to the discovery of novel inhibitors of Bcl-2.

Four enantiopure cytisine-inspired scaffolds can be accessed via a versatile pyrrolidine template derived from a stereocontrolled [3+2] azomethine ylide-alkene cycloaddition. Differential ester protection allows for the selective formation of either a bridged bicyclic or tricyclic scaffold via pyridone cyclization. Solid-phase diversification of the pyridone scaffolds yielded a diverse library of 15,000 compounds enabling the discovery of a novel class of Bcl-2 inhibitors.

First total synthesis of (+/-)-3-hydroxy-11-norcytisine: structure confirmation and biological characterization.

The first total synthesis of the natural product 3-hydroxy-11-norcytisine (1), structurally related to cytisine (2), a benchmark ligand at neuronal nicotinic acetylcholine receptors (NNRs), has been achieved. The synthesis permits the unambiguous confirmation of the structure originally proposed for 1 and has enabled initial biological characterization of 1 and its related compounds against NNRs.

Deconstructing cytisine: The syntheses of (+/-)-cyfusine and (+/-)-cyclopropylcyfusine, fused ring analogs of cytisine.

A novel fused tricyclic analog (11) of cytisine has been prepared (coined 'cyfusine') and determined to have high affinity at neuronal nicotinic acetylcholine receptors. A [3+2] cycloaddition protocol permitted entry into a 3,4-differentially difunctionalized dihydropyrrole (7). The penultimate cyclization was accomplished using the modified Van Tamelen conditions developed in our earlier synthesis of (+/-)-cytisine. Sequential ring-forming reactions ([3+2] cycloaddition/cyclopropanation/pyridone cyclization) gives a unique cyclopropyl analog (16) possessing a skeleton isoatomic with that of cytisine.

Novel and expeditious microwave-assisted three-component reactions for the synthesis of spiroimidazolin-4-ones.

Highly efficient methods for the syntheses of spiroimidazolinones via microwave-assisted three-component one-pot sequential reactions or one-pot domino reactions are described. The efficiency and utility of the methods have been demonstrated by quickly accessing the antihypertensive drug irbesartan (2).

Identification of a small molecule that induces mitotic arrest using a simplified high-content screening assay and data analysis method.

High-content screening has emerged as a new and powerful technique for identifying small-molecule modulators of mammalian cell biology. The authors describe the development and execution of a high-content screen to identify small molecules that induce mitotic arrest in mammalian cancer cells. Many widely used chemotherapeutics, such as Taxol and vinblastine, induce mitotic arrest, and the creation of new drugs that also induce mitotic arrest may have tremendous therapeutic value. In their screen, the authors employed a simple DNA stain (DAPI) and a sensitive nonparametric statistical test to identify compounds from an internal collection of approximately 13,000 high-quality lead-like small molecules. Subsequent analysis of 1 active compound indicated that it induces mitotic arrest, assessed using a high-content phosphohistone H3 detection assay, and caused cell proliferation defects in multiple cancer cell lines. The active compound, a quinazolinone originating from a natural product-like subset of the screened compounds, is active in cells at approximately 500 nM and appears to act by inhibiting the polymerization of tubulin.