Valerjans Kauss

Positive and Negative Modulation of Group I Metabotropic Glutamate Receptors

A discriminating pharmacophore model for noncompetitive metabotropic glutamate receptor antagonists of subtype 1 (mGluR1) was developed that facilitated the discovery of moderately active mGluR1 antagonists. One scaffold was selected for the design of several focused libraries where different substitution patterns were introduced. This approach facilitated the discovery of potent mGluR1 antagonists, as well as positive and negative mGluR5 modulators, because both receptor subtypes share similar binding pockets. For mGluR1 antagonists, a homology model of the mGlu1 receptor was established, and a putative binding mode within the receptors transmembrane domain was visualized.

Virtual screening for selective allosteric mGluR1 antagonists and structure-activity relationship investigations for coumarine derivatives.

A virtual screening study towards novel noncompetitive antagonists of the metabotropic glutamate receptor 1 (mGluR1) is described. Alignment‐free topological pharmacophore descriptors (CATS) were used to encode the screening compounds. All virtual hits were characterized with respect to their allosteric antagonistic effect on mGluR1 in both functional and binding assays. Exceptionally high hit rates of up to 26 % were achieved, confirming the applicability of this virtual screening concept. Most of the compounds were found to be moderately active, however, one potent and subtype selective mGluR1 antagonist, 13 (IC50: 0.362 μM, SEM ±0.031; Ki: 0.753 μM, SEM ±0.048), based on a coumarine scaffold was discovered. In a following activity optimization program a series of coumarine derivatives was synthesized. This led to the discovery of potent (60, IC50: 0.058 μM, SEM ±0.008; Ki: 0.293 μM, SEM ±0.022) and subtype selective (rmGluR5 IC50: 28.6 μM) mGluR1 antagonists. From our homology model of mGluR1 we derived a potential binding mode within the allosteric transmembrane region. Potential interacting patterns are proposed considering the difference of the binding pockets between rat and human receptors. The study demonstrates the applicability of ligand‐based virtual screening for noncompetitive antagonists of a G‐protein coupled receptor, resulting in novel, potent, and selective agents.

Synergism of virtual screening and medicinal chemistry: identification and optimization of allosteric antagonists of metabotropic glutamate receptor 1.

We report the identification of novel potent and selective metabotropic glutamate receptor 1 (mGluR1) antagonists by virtual screening and subsequent hit optimization. For ligand-based virtual screening, molecules were represented by a topological pharmacophore descriptor (CATS-2D) and clustered by a self-organizing map (SOM). The most promising compounds were tested in mGluR1 functional and binding assays. We identified a potent chemotype exhibiting selective antagonistic activity at mGluR1 (functional IC(50)=0.74+/-0.29 microM). Hit optimization yielded lead structure 16 with an affinity of K(i)=0.024+/-0.001 microM and greater than 1000-fold selectivity for mGluR1 versus mGluR5. Homology-based receptor modelling suggests a binding site compatible with previously reported mutation studies. Our study demonstrates the usefulness of ligand-based virtual screening for scaffold-hopping and rapid lead structure identification in early drug discovery projects.

Synthesis and structure–affinity relationships of 1,3,5-alkylsubstituted cyclohexylamines binding at NMDA receptor PCP site

A series of 1,3,5-alkylsubstituted cyclohexylamines 2 were synthesized as ligands for the N-methyl-D-aspartate (NMDA) receptor phencyclidine (PCP) binding site. Pure diastereomers with defined configuration of amino group 2-ax and 2-eq were obtained. The optimal size of 1,3,5-substituents was determined for cyclohexylamines 2 with an equatorial amino group in the lowest energy conformation using Hansch analysis. According to the data, the lipophilic part of cyclohexylamines 2 does not discriminate between hydrophobic regions of the PCP binding site but rather recognizes this site as a whole lipophilic pocket.

Discovery, synthesis, and structure-activity relationships of 2-aminoquinazoline derivatives as a novel class of metabotropic glutamate receptor 5 negative allosteric modulators.

A virtual screening approach using various in silico methodologies led to the discovery of 2-(m-tolylamino)-7,8-dihydroquinazolin-5(6H)-one (1) as a moderately active negative allosteric modulator (NAM) of the metabotropic glutamate receptor subtype 5 (mGluR5) showing high selectivity against the subtype mGluR1. Modifications of the parent compound by rational design yielded a series of highly potent derivatives which will serve as valuable starting points for further hit-to-lead optimization efforts toward a suitable drug candidate for the treatment of L-DOPA induced dyskinesia.

A novel class of amino-alkylcyclohexanes as uncompetitive, fast, voltage-dependent, N-methyl-D-aspartate (NMDA) receptor antagonists – in vitro characterization

SummaryThe fact that potent NMDA receptor channel blockers produce phencyclidine-like psychotropic symptoms in man and rodents implies that uncompetitive antagonism of NMDA receptors may not be a promising therapeutic approach. However, recent data indicate that agents with moderate affinity such as memantine and neramexane (MRZ 2/579) are useful therapeutics due to their strong voltage-dependency and rapid unblocking kinetics. Merz has developed a series of novel uncompetitive NMDA receptor antagonists based on an amino-alkylcyclohexane structure. These compounds displaced [3H]-MK-801 binding to rat cortical membranes with Ki values between 1 and 100 µM and inward current responses of cultured hippocampal neurons to NMDA were antagonized in a strongly voltage-dependent manner with rapid blocking/unblocking kinetics. Three of these compounds, with similar biophysical properties to memantine, were chosen for development. MRZ 2/759 (1-ethenyl-3,3,5,5-tetramethyl-cyclohexylamine), 2/1010 (1,3,3,5-tetramethyl-6-azabicyclo[3.2.1]octane) and 2/1013 (8,8,10,10-tetramethyl-1-azaspiro[5.5] undecane) displaced [3H]-MK-801 binding with Ki values of 1.18, 2.59 and 3.64 µM, respectively. They were similarly potent against NMDA-induced currents in hippocampal neurons – IC50 values of 1.51, 3.06 and 2.20 µM, respectively. In line with their moderate affinity, all were voltage-dependent (δ = 0.86, 0.96 and 0.89, respectively) and fast, open-channel blockers (kon 7.90, 1.70 and 2.60 × 104 M−1 sec−1, koff 0.13, 0.12 and 0.24 sec−1, respectively). These compounds are also NMDA receptor antagonists in the CNS following systemic administration and have good therapeutic indices in a variety of in vivo behavioural models where glutamate is known to play a pivotal role. In view of their relatively low affinity and associated rapid kinetics, they should prove to be useful therapeutics in a wide range of CNS disorders.

A Convenient Reagent for N-hydroxyguanylation

Abstract 1-Benzyloxy-3-benzyloxycarbonylthiourea was prepared and demonstrated as a useful reagent for direct N-hydroxyguanylation of various amines.

Synthesis of 3,4-dihydro-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxides and their evaluation as ligands for NMDA receptor glycine binding site

Abstract A series of 2-substituted 3,4-dihydro-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxides were synthesized and evaluated for their affinity to the glycine binding site of the N-methyl-d-aspartate (NMDA) receptor. The binding affinity was determined by the displacement of radioligand [3H]MDL-105,519 from rat cortical membrane preparations. The most attractive structures in the search for prospective NMDA receptor ligands were identified to be 2-arylcarbonylmethyl substituted 3,4-dihydro-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxides. It has been demonstrated for the first time that the replacement of NH group in the ligand by sp3 CH2 is tolerated. This finding may pave the way for previously unexplored approaches for designing new ligands of the NMDA receptor.

Evaluation of an enantioselective synthesis of 6-chloro-3,4-dihydro-2 H -1,2-benzothiazine-3-carboxylic acid 1,1-dioxide and its derivatives

Step-by-step evaluation of an enantioselective synthesis of (S)- and (R)-ethyl 3,4-dihydro-2H-1,2-benzothiazine-3-carboxylates is described, starting from (S)- and (R)-methyl 2-acetamido-3-(3-chlorophenyl)propanoates as a source of chirality. A one-pot procedure for transesterification and cleavage of the N-acetyl group was developed to prevent racemization during the hydrolysis of the methyl ester group. It was demonstrated that the synthesized benzothiazines might serve as useful building blocks for enantioselective synthesis of pharmacologically active compounds.

The synthesis of 3-amino-3-methylbicyclo[3.3.1]nonanes: Endo-selectivity in the Ritter reaction of 1,3,5,7α-tetramethylbicyclo[3.3.1]nonan-3-ol

1,3,5,7α- and 1,3,5,7β-Tetramethylbicyclo[3.3.1]nonan-3-ols 3a and 3b were prepared from the corresponding ketones 2a and 2b. 7α-Methyl isomer 3a gave selectively endo-3α-N-formylaminobicyclononane 10 in the Ritter reaction with trimethylsilyl cyanide. 7β-Methyl epimer 3b suffered water elimination resulting in bicyclo[3.3.1]non-2-ene 12 under the same reaction conditions. The endo-amide structure was confirmed by X-ray analysis..