Chemoenzymatic synthesis and evaluation of 3-azabicyclo[3.2.0]heptane derivatives as dopaminergic ligands

Dopamine Receptor Ligand Selectivity-An In Silico/In Vitro Insight

Different dopamine receptor (DR) subtypes are involved in pathophysiological conditions such as Parkinson's Disease (PD), schizophrenia and depression. While many DR-targeting drugs have been approved by the U.S. Food and Drug Administration (FDA), only a very small number are truly selective for one of the DR subtypes. Additionally, most of them show promiscuous activity at related G-protein coupled receptors, thus suffering from diverse side-effect profiles. Multiple studies have shown that combined in silico/in vitro approaches are a valuable contribution to drug discovery processes. They can also be applied to divulge the mechanisms behind ligand selectivity. In this study, novel DR ligands were investigated in vitro to assess binding affinities at different DR subtypes. Thus, nine D2R/D3R-selective ligands (micro- to nanomolar binding affinities, D3R-selective profile) were successfully identified. The most promising ligand exerted nanomolar D3R activity (Ki = 2.3 nM) with 263.7-fold D2R/D3R selectivity. Subsequently, ligand selectivity was rationalized in silico based on ligand interaction with a secondary binding pocket, supporting the selectivity data determined in vitro. The developed workflow and identified ligands could aid in the further understanding of the structural motifs responsible for DR subtype selectivity, thus benefitting drug development in D2R/D3R-associated pathologies such as PD.

Fluorescence based HTS-compatible ligand binding assays for dopamine D3 receptors in baculovirus preparations and live cells

Dopamine receptors are G-protein-coupled receptors that are connected to severe neurological disorders. The development of new ligands targeting these receptors enables gaining a deeper insight into the receptor functioning, including binding mechanisms, kinetics and oligomerization. Novel fluorescent probes allow the development of more efficient, cheaper, reliable and scalable high-throughput screening systems, which speeds up the drug development process. In this study, we used a novel Cy3B labelled commercially available fluorescent ligand CELT-419 for developing dopamine D3 receptor-ligand binding assays with fluorescence polarization and quantitative live cell epifluorescence microscopy. The fluorescence anisotropy assay using 384-well plates achieved Z’ value of 0.71, which is suitable for high-throughput screening of ligand binding. The assay can also be used to determine the kinetics of both the fluorescent ligand as well as some reference unlabeled ligands. Furthermore, CELT-419 was also used with live HEK293-D3R cells in epifluorescence microscopy imaging for deep-learning-based ligand binding quantification. This makes CELT-419 quite a universal fluorescence probe which has the potential to be also used in more advanced microscopy techniques resulting in more comparable studies.

Applications of Isosteres of Piperazine in the Design of Biologically Active Compounds: Part 2

Applications of piperazine and homopiperazine in drug design are well-established, and these heterocycles have found use as both scaffolding and terminal elements and also as a means of introducing a water-solubilizing element into a molecule. In the accompanying review (10.1021/acs.jafc.2c00726), we summarized applications of piperazine and homopiperazine and their fused ring homologues in bioactive compound design along with illustrations of the use of 4-substituted piperidines and a sulfoximine-based mimetic. In this review, we discuss applications of pyrrolidine- and fused-pyrrolidine-based mimetics of piperazine and homopiperazine and illustrate derivatives of azetidine that include stretched and spirocyclic motifs, along with applications of a series of diaminocycloalkanes.

Intracellular dynamics of the Sigma-1 receptor observed with super-resolution imaging microscopy

Sigma-1 receptor (Sig1R) is an endoplasmic reticulum (ER)-related membrane protein, that forms heteromers with other cellular proteins. As the mechanism of action of this chaperone protein remains unclear, the aim of the present study was to detect and analyze the intracellular dynamics of Sig1R in live cells using super-resolution imaging microscopy. For that, the Sig1R-yellow fluorescent protein conjugate (Sig1R-YFP) together with fluorescent markers of cell organelles were transfected into human ovarian adenocarcinoma (SK-OV-3) cells with BacMam technology. Sig1R-YFP was found to be located mainly in the nuclear envelope and in both tubular and vesicular structures of the ER but was not detected in the plasma membrane, even after activation of Sig1R with agonists. The super-resolution radial fluctuations approach (SRRF) performed with a highly inclined and laminated optical sheet (HILO) fluorescence microscope indicated substantial overlap of Sig1R-YFP spots with KDEL-mRFP, slight overlap with pmKate2-mito and no overlap with the markers of endosomes, peroxisomes, lysosomes, or caveolae. Activation of Sig1R with (+)-pentazocine caused a time-dependent decrease in the overlap between Sig1R-YFP and KDEL-mRFP, indicating that the activation of Sig1R decreases its colocalization with the marker of vesicular ER and does not cause comprehensive translocations of Sig1R in cells.

Abnormal dopamine receptor signaling allows selective therapeutic targeting of neoplastic progenitors in AML patients

The aberrant expression of dopamine receptors (DRDs) in acute myeloid leukemia (AML) cells has encouraged the repurposing of DRD antagonists such as thioridazine (TDZ) as anti-leukemic agents. Here, we access patient cells from a Phase I dose escalation trial to resolve the cellular and molecular bases of response to TDZ, and we extend these findings to an additional independent cohort of AML patient samples tested preclinically. We reveal that in DRD2⁺ AML patients, DRD signaling in leukemic progenitors provides leukemia-exclusive networks of sensitivity that spare healthy hematopoiesis. AML progenitor cell suppression can be increased by the isolation of the positive enantiomer from the racemic TDZ mixture (TDZ⁺), and this is accompanied by reduced cardiac liability. Our study indicates that the development of DRD-directed therapies provides a targeting strategy for a subset of AML patients and potentially other cancers that acquire DRD expression upon transformation from healthy tissue.

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Leukemic progenitors are a critical cellular target of DRD2 antagonist TDZ

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DRD2 protein expression is a reliable biomarker of TDZ response

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DRD2 antagonism selectively triggers leukemic maturation programs via cyclic AMP

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An enantiomer of TDZ displays a superior efficacy:risk ratio relative to racemic TDZ

Quantitative analysis of fluorescent ligand binding to dopamine D3 receptors using live-cell microscopy

Dopamine receptors are G protein-coupled receptors that have several essential functions in the central nervous system. A better understanding of the regulatory mechanisms of ligand binding to the receptor may open new possibilities to affect the downstream signal transduction pathways. The majority of the available ligand binding assays use either membrane preparations, cell suspensions, or genetically modified receptors, which may give at least partially incorrect understanding of ligand binding. In this study, we implemented an assay combining fluorescence and bright-field microscopy to measure ligand binding to dopamine D₃ receptors in live mammalian cells. For membrane fluorescence intensity quantification from microscopy images, we developed a machine learning-based user-friendly software membrane tools and incorporated it into a data management software aparecium that has been previously developed in our workgroup. For the experiments, a fluorescent ligand NAPS-Cy3B was synthesized by conjugating a dopaminergic antagonist N-(p-aminophenethyl)spiperone with a fluorophore Cy3B. The subnanomolar affinity of NAPS-Cy3B makes it a suitable ligand for the characterization of D₃ receptors in live HEK293 cells. Using a microplate compatible automated widefield fluorescence microscope, together with the membrane tools software, enables the detection and quantification of ligand binding with a high-throughput. The live cell assay is suitable for the characterization of fluorescent ligand binding and also in the competition experiments for the screening of novel unlabeled dopaminergic ligands. We propose that this simple yet more native-like approach is feasible in GPCR research, as it enables the detection of ligand binding in an environment containing more components involved in the signal transduction cascade.

Photochemical [2 + 2] Cycloaddition of Alkenyl Boronic Derivatives: An Entry into 3-Azabicyclo[3.2.0]heptane Scaffold

The synthesis of 3-azabicyclo[3.2.0]heptyl boropinacolates and trifluoroborates via the [2 + 2] photocycloaddition of the corresponding alkenyl boronic derivatives and maleimides or maleic anhydride is described. Optimization of the reaction conditions (i.e., wavelength, concentration of the reagents, photosensitizer) was carried out, and the scope and limitations of the method were studied. Alkenyl boronic acid pinacolates were found to be more suitable for the [2 + 2] cycloaddition, providing better reaction outcomes compared to the trifluoroborates. The utility of this approach was shown by the preparation of bi- and trifunctional building blocks (21 examples), which could be easily synthesized on up to 60 g scale. These cycloadducts provide a convenient entry into the 3-azabicyclo[3.2.0]heptane scaffold through the C-C coupling or oxidative deborylation reactions.

Zinc(ii)-mediated diastereoselective Passerini reactions of biocatalytically desymmetrised renewable inputs

A chiral aldehyde, obtained in both enantiomeric forms from renewable 2,5-Bis(hydroxymethyl)tetrahydrofuran by a chemoenzymatic procedure, was submitted to a modified diastereoselective Passerini reaction employing zinc dicarboxylates.

Photochemical In-Flow Synthesis of 2,4-Methanopyrrolidines: Pyrrolidine Analogues with Improved Water Solubility and Reduced Lipophilicity

A practical synthesis of 2,4-methanopyrrolidines was elaborated. The key synthetic step was an intramolecular photochemical [2 + 2]-cycloaddition of an acrylic acid derivative in flow. In spite of a higher molecular weight, 2,4-methanopyrrolidines were shown to have higher solubility in water and lower lipophilicity than pyrrolidines, important characteristics of bioactive molecules in drug design.

Integrating biocatalysis and multicomponent reactions

While often multicomponent reactions (MCR) are used for the diversity-oriented synthesis of racemic (or achiral) molecular entities, this short review describes two alternative approaches for accessing enantiopure products exploiting the power of biocatalysis. Enzymes or microorganisms may be used for preparing enantiopure MCR inputs or for resolving racemic (or achiral) MCR adducts.

Intramolecular [2 + 2] and [4 + 2] Cycloaddition Reactions of Cinnamylamides of Ethenetricarboxylate in Sequential Processes

Intramolecular [2 + 2] and [4 + 2] cycloaddition reactions of cinnamylamides of ethenetricarboxylate in sequential processes have been studied. Reaction of 1,1-diethyl 2-hydrogen ethenetricarboxylate and trans-cinnamylamines in the presence of EDCI/HOBt/Et₃N led to pyrrolidine products in one pot, via intramolecular [2 + 2], [4 + 2], and some other cyclizations. The types of the products depend on the substituents on the benzene ring and the reaction conditions. Reaction of cinnamylamines without substituents on the benzene ring and with halogens and OMe on the para position at room temperature gave cyclobutane-fused pyrrolidines as major products via [2 + 2] cycloaddition. The reaction at 80 °C in 1,2-dichloroethane gave δ-lactone fused pyrrolidines as major products, probably via ring-opening of the cyclobutanes. Interestingly, reaction of 1,1-diethyl 2-hydrogen ethenetricarboxylate and cinnamylamines bearing electron-withdrawing groups such as NO₂, CN, CO₂Me, CO₂Et, and CF₃ on ortho and para positions in the presence of EDCI/HOBt/Et₃N at room temperature or at 60-80 °C gave tetrahydrobenz[f]isoindolines via [4 + 2] cycloaddition as major products. DFT studies have been performed to explained the observed [2 + 2]/[4 + 2] selectivity.

Lunasin-induced behavioural effects in mice: focus on the dopaminergic system

The present study for the first time is devoted to identify central effects of synthetic lunasin, a 43 amino acid peptide. A markedly expressed neuroleptic/cataleptic effect was observed at low (0.1-10 nmol/mouse) centrally administered doses in male C57Bl/6 mice. Lunasin considerably reduced the amphetamine hyperlocomotion but weakly apomorphine climbing behaviour. No influence on ketamine and bicuculline effects was observed. Binding assay studies demonstrated modest affinity of lunasin for the dopamine D₁ receptor (Ki=60 ± 15 μM). In a functional assay of cAMP accumulation on live cells lunasin antagonised apomorphine effect on D₁ receptor activation (pEC₅₀=6.1 ± 0.3), but had no effect in cells expressing D₂ receptors. The obtained data suggest that lunasin's action at least in part is provided via dopaminergic D1 receptor pathways. However, other non-identified mechanisms (probably intracellular) may play an important role in lunasin's central action. Nevertheless further studies of lunasin are promising, particularly taking into account a necessity for novel type of antipsychotic drugs.

Diastereoselective multicomponent cascade reaction leading to [3.2.0]-heterobicyclic compounds

A general three-component triple cascade reaction through an iminium-enamine-iminium sequential activation initiated by a hetero-Michael addition to α,β-unsaturated aldehydes affords [3.2.0]heterobicycles in high diastereoselectivity. The rate and diastereoselectivity of the reaction depended on the (E)-4-heterocrotonate and size of the secondary amine. The enantiomers of the major diastereoisomer of oxa- and azabicyclo[3.2.0]heptane derivatives were separated by enzymatic kinetic resolution with immobilized Candida antarctica Lipase B (CALB), with E values up to 153. The absolute configuration of the nonacylated enantiomer of oxabicyclo[3.2.0]heptane was determined by single crystal X-ray analysis.