SAR exploration of the non-imidazole histamine H3 receptor ligand ZEL-H16 reveals potent inverse agonism.

Histamine H3 receptor (H3 R) agonists without an imidazole moiety remain very scarce. Of these, ZEL-H16 (1) has been reported previously as a high-affinity non-imidazole H3 R (partial) agonist. Our structure-activity relationship analysis using derivatives of 1 identified both basic moieties as key interaction motifs and the distance of these from the central core as a determinant for H3 R affinity. However, in spite of the reported H3 R (partial) agonism, in our hands, 1 acts as an inverse agonist for Gαi signaling in a CRE-luciferase reporter gene assay and using an H3 R conformational sensor. Inverse agonism was also observed for all of the synthesized derivatives of 1. Docking studies and molecular dynamics simulations suggest ionic interactions/hydrogen bonds to H3 R residues D1143.32 and E2065.46 as essential interaction points.

Green Drug Discovery: Novel Fragment Space from the Biomass-Derived Molecule Dihydrolevoglucosenone (CyreneTM).

Biomass-derived molecules can provide a basis for sustainable drug discovery. However, their full exploration is hampered by the dominance of millions of old-fashioned screening compounds in classical high-throughput screening (HTS) libraries frequently utilized. We propose a fragment-based drug discovery (FBDD) approach as an efficient method to navigate biomass-derived drug space. Here, we perform a proof-of-concept study with dihydrolevoglucosenone (CyreneTM), a pyrolysis product of cellulose. Diverse synthetic routes afforded a 100-membered fragment library with a diversity in functional groups appended. The library overall performs well in terms of novelty, physicochemical properties, aqueous solubility, stability, and three-dimensionality. Our study suggests that Cyrene-based fragments are a valuable green addition to the drug discovery toolbox. Our findings can help in paving the way for new hit drug candidates that are based on renewable resources.

Covalent Inhibition of the Histamine H3 Receptor.

Covalent binding of G protein-coupled receptors by small molecules is a useful approach for better understanding of the structure and function of these proteins. We designed, synthesized and characterized a series of 6 potential covalent ligands for the histamine H3 receptor (H3R). Starting from a 2-amino-pyrimidine scaffold, optimization of anchor moiety and warhead followed by fine-tuning of the required reactivity via scaffold hopping resulted in the isothiocyanate H3R ligand 44. It shows high reactivity toward glutathione combined with appropriate stability in water and reacts selectively with the cysteine sidechain in a model nonapeptide equipped with nucleophilic residues. The covalent interaction of 44 with H3R was validated with washout experiments and leads to inverse agonism on H3R. Irreversible binder 44 (VUF15662) may serve as a useful tool compound to stabilize the inactive H3R conformation and to study the consequences of prolonged inhibition of the H3R.

Charting the chemical space around the (iso)indoline scaffold, a comprehensive approach towards multitarget directed ligands.

Within the framework of orthosteric G protein coupled receptor (GPCR) polypharmacology herein we report the systematic elaboration and thorough evaluation of a data matrix generated by sampling the chemical space around a common 5,6-fused bicyclic heteroaromatic template applying characteristic pharmacophore elements of central nervous system (CNS) relevant aminergic GPCR ligands.

4-Aryl-3-arylsulfonyl-quinolines as negative allosteric modulators of metabotropic GluR5 receptors: From HTS hit to development candidate.

High throughput screening of our corporate compound library followed by hit-to-lead development resulted in a 4-aryl-3-arylsulfonyl-quinoline derivative lead (2) with mGluR5 negative allosteric modulator activity. During the lead optimization process, our objective was to improve affinity and metabolic stability. Modifications at the three targeted regions of the lead structure resulted in compounds with nanomolar affinity and acceptable metabolic stability. One of the most promising compounds (3), showing excellent in vivo efficacy, was selected for preclinical development and subsequent phase I clinical studies.

Thieno[2,3-b]pyridines as negative allosteric modulators of metabotropic GluR5 receptors: Lead optimization.

An HTS campaign of our corporate compound library, and hit-to lead development resulted in thieno[2,3-b]pyridine derivative leads with mGluR5 negative allosteric modulator effects. During the lead optimization process, our objective was to improve affinity and metabolic stability. Modification of the first two targeted regions resulted in compounds with nanomolar affinity, then optimal substitution of the third region improved metabolic stability. One of the most promising compounds showed excellent in vivo efficacy and is a potential development candidate.

Thieno[2,3-b]pyridines as negative allosteric modulators of metabotropic GluR5 receptors: hit-to-lead optimization.

An HTS campaign of our corporate compound library resulted in thieno[2,3-b]pyridines derivative hits with mGluR5 negative allosteric modulator effects. During the hit-to-lead development our objective was to improve affinity, and to keep the ligand efficiency values at an acceptable level. After different modifications of the linker resulted in a 2-sulfonyl-thieno[2,3-b]pyridines derivative, which fulfilled the lead criteria.

New Chemical Biology Tools for the Histamine Receptor Family.

The histamine research community has in the last decade been very active and generated a number of exciting new chemical biology tools for the study of histamine receptors, their ligands, and their pharmacology. In this paper we describe the development of histamine receptor structural biology, the use of receptor conformational biosensors, and the development of new ligands for covalent or fluorescent labeling or for photopharmacological approaches (photocaging and photoswitching). These new tools allow new approaches to study histamine receptors and hopefully will lead to better insights in the molecular aspects of histamine receptors and their ligands.

Carbamoyloximes as novel non-competitive mGlu5 receptor antagonists.

Hit-to-lead optimization of a HTS hit led to new carbamoyloxime derivatives. After identification of an advanced hit (8d) the CYP enzyme inhibitory activity of this class of compounds was successfully eliminated. Systematic exploration of different parts of the advanced hit led us to some promising lead compounds with mGluR5 affinities comparable to that of MPEP.

Hit-to-lead optimization of disubstituted oxadiazoles and tetrazoles as mGluR5 NAMs.

Here we report the discovery and early SAR of a series of mGluR5 negative allosteric modulators (NAMs). Starting from a moderately active HTS hit we synthesized 3,5-disubstituted-oxadiazoles and tetrazoles as mGluR5 NAMs. Based on the analysis of ligand efficiency and lipophilic efficiency metrics we identified a promising lead candidate as a starting point for further optimization.

4-(3-Aminoazetidin-1-yl)pyrimidin-2-amines as High-Affinity Non-imidazole Histamine H3 Receptor Agonists with in Vivo Central Nervous System Activity.

Despite the high diversity of histamine H3 receptor (H3R) antagonist/inverse agonist structures, partial or full H3R agonists have typically been imidazole derivatives. An in-house screening campaign intriguingly afforded the non-imidazole 4-(3-azetidin-1-yl)pyrimidin-2-amine 11b as a partial H3R agonist. Here, the design, synthesis, and structure-activity relationships of 11b analogues are described. This series yields several non-imidazole full agonists with potencies varying with the alkyl substitution pattern on the basic amine following the in vitro evaluation of H3R agonism using a cyclic adenosine monophosphate response element-luciferase reporter gene assay. The key compound VUF16839 (14d) combines nanomolar on-target activity (pKi = 8.5, pEC50 = 9.5) with weak activity on cytochrome P450 enzymes and good metabolic stability. The proposed H3R binding mode of 14d indicates key interactions similar to those attained by histamine. In vivo evaluation of 14d in a social recognition test in mice revealed an amnesic effect at 5 mg/kg intraperitoneally. The excellent in vitro and in vivo pharmacological profiles and the non-imidazole structure of 14d make it a promising tool compound in H3R research.

Discovery and Preclinical Characterization of 3-((4-(4-Chlorophenyl)-7-fluoroquinoline-3-yl)sulfonyl)benzonitrile, a Novel Non-acetylenic Metabotropic Glutamate Receptor 5 (mGluR5) Negative Allosteric Modulator for Psychiatric Indications.

Negative allosteric modulators (NAM) of metabotropic glutamate receptor 5 (mGluR5) have been implicated as a potential pharmacotherapy for a number of psychiatric diseases, including anxiety and depression. Most of the mGluR5 NAM clinical candidates can be characterized by the central acetylenic moiety that connects the terminal pharmacophores. Identification of a sulfoquinoline hit via high throughput screening (HTS) followed by optimization provided a 4-phenyl-3-aryl-sulfoquinoline lead compound with the minimal pharmacophore. Optimization of the core and aryl appendages was performed by scanning and matrix libraries synthesized by the multiple parallel synthesis approach. Biological evaluation of matrix libraries provided a number of potent, metabolically stable, and in vivo active compounds. One of these compounds, 25 showed high efficacy and safety in preclinical in vivo models; this allowed its nomination as a novel, nonacetylenic mGluR5 NAM clinical candidate. Compound 25 was advanced to first-in-man trials for the treatment of psychiatric conditions.

Discovery of 4-amino-3-arylsulfoquinolines, a novel non-acetylenic chemotype of metabotropic glutamate 5 (mGlu5) receptor negative allosteric modulators.

Negative allosteric modulators of metabotropic glutamate receptor 5 (mGlu5) showed efficacy in a number of animal models of different CNS diseases including anxiety and depression. Virtually all of the compounds which reached the clinic belong to the same chemotype having an acetylenic linker that connects (hetero)cyclic moieties. Searching for new chemotypes we identified a morpholino-sulfoquinoline derivative (1) by screening our corporate compound deck. The HTS hit showed reasonable affinity and selectivity towards mGlu5 receptors, however, its inferior metabolic stability prevented its testing in vivo. In a chemical program we aimed to improve the affinity, physicochemical properties and metabolic stability exploring three regions of the hit. Systematic variation of different amines at position 4 (region I) led to the identification of 4-methyl-piperidinyl analogues. Substituents of the quinoline core (region II) and the phenylsulfonyl moiety (region III) were mapped by parallel synthesis. Evaluation of both morpholino- and 4-methyl-piperidinyl-sulfoquinoline libraries of about 270 derivatives revealed beneficial substituent combinations in regions II and III. Blood levels of optimized 4-methyl-piperidinyl-sulfoquinolines, however, were still insufficient for robust in vivo efficacy. Finally, introducing 4-hydoxymethyl-piperidinyl substituent to region I resulted in new sulfoquinolines with greatly improved solubility and reasonable affinity coupled with affordable metabolic stability. The most promising analogues (24 and 25) showed high blood levels and demonstrated significant efficacy in the experimental model of anxiety.

Glucose conversion by multiple pathways in brain extract: theoretical and experimental analysis.

Experimental and model studies were performed to characterize the flux of glucose metabolism and the sharing of glucose-6-phosphate (Glu6P) by the upper parts of glycolytic and pentosephosphate pathways in the brain extract. A mathematical model based upon the kinetic equations of the individual enzymes was evaluated to fit the experimental data. Glucose is converted to glucose-6-phosphate by hexokinase that controls almost exclusively the glucose metabolism. Experiments showed that this crossroad-metabolite was shared between glycolysis and pentosephosphate pathway in the brain extract in a ratio of 1.5:1. This ratio was favorable to the pentosephosphate pathway by the addition of high excess of exogenous glucose-6-phosphate dehydrogenase, standardly used for the activity assay of hexokinase, but still a significant part (17+/-3%) of the common intermediate was converted into the direction of glycolysis. Stimulation of glucose-6-phosphate formation via moderate (30-50%) increase of hexokinase activity by adding exogenous hexokinase or tubulin resulted in the slight increase of the relative flux into direction of glycolysis. The model correctly described all of these observations. However, when the activity of hexokinase was doubled with exogenous enzyme, significantly less glucose-6-phosphate was converted into direction of glycolysis than predicted. This discrepancy shows that the system did not behave in this case as an ideal one, which could be due to the formation of distinct pools for the intermediate.