Konfigurationsbestimmung von (2S,7aR)- und (2S,7aS)-2-Benzyl-5,6,7,7a-tetrahydro-pyrrolo[2,1-b]oxazol-3(2H)-on

Im Zusammenhang mit Untersuchungen zur asymmetrischen Synthese 2-substituierter Pyrrolidine1* haben wir, wie kürzlich berichtet2*, durch säurekatalysierte Cyclisierung von (S>1 die beiden Tetrahydropyrrolo[2,l-d} oxazol-3(2tf)-one (2S,7aS)-2 und (2S,7aR)-3 dargestellt. (2$,7aS)-2 und (ZS,7aÄ)-3 wurden entsprechend ihrem Produktanteil als Haupt- und Nebenisomer bezeichnet; die Konfigurationen wurden nicht zugeordnet Dazu waren weitere Untersuchungen nötig, die hier vorgestellt werden

Benocyclidine (BTCP) as Non‐labelled Reporter Ligand for MS Binding Assays for the PCP Ion Channel Binding Site of the Desensitized Torpedo Nicotinic Acetylcholine Receptor (nAChR)

In this study we present MS Binding Assays for the PCP ion channel binding site of Torpedo californica nicotinic acetylcholine receptor (nAChR) as an alternative to radioligand binding assays. As MS Marker Benocyclidine (BTCP) was employed, found to be more affine (Kd of 84.2 nM) than the radioligands, e. g. [3H]PCP, used so far in respective binding assays. Based on a highly sensitive and fast LC-ESI-MS/MS method for quantification of BTCP samples, BTCP MS Binding Assays for the PCP ion channel binding site of Torpedo nAChR could be established comprising saturation, kinetic and competition experiments. The affinities obtained in competitive BTCP MS Binding Assays for ligands addressing the PCP ion channel binding site of Torpedo nAChR were in excellent accord with those reported from radioligand experiments. Thus, the new BTCP MS Binding Assays represent a potent and reliable alternative to radioligand binding assays used so far for the characterization of ligand binding to the PCP ion channel binding site of the nAChR

Synthesis and biological evaluation of novel N-substituted nipecotic acid derivatives with tricyclic cage structures in the lipophilic domain as GABA uptake inhibitors

<jats:title>Abstract</jats:title><jats:p>A new class of GABA reuptake inhibitors with sterically demanding, highly rigid tricyclic cage structures as the lipophilic domain was synthesized and investigated in regard to their biological activity at the murine GABA transporters (mGAT1–mGAT4). The construction of these compounds, consisting of nipecotic acid, a symmetric tricyclic amine, and a plain hydrocarbon linker connecting the two subunits via their amino nitrogens, was accomplished via reductive amination of a nipecotic acid derivative with an <jats:italic>N</jats:italic>-alkyl substituent displaying a terminal aldehyde function with tricyclic secondary amines. The target compounds varied with regard to spacer length, the bridge size of one of the bridges, and the substituents of the tricyclic skeleton to study the impact of these changes on their potency. Among the tested compounds nipecotic acid ethyl ester derivates with phenyl residues attached to the cage subunit showed reasonable inhibitory potency and subtype selectivity in favor of mGAT3 and mGAT4, respectively.</jats:p&gt

Synthesis and biological evaluation of α- and β-hydroxy substituted amino acid derivatives as potential mGAT1-4 inhibitors

<jats:title>Abstract</jats:title><jats:p>In this study, we report the synthesis and biological evaluation of a variety of α- and β-hydroxy substituted amino acid derivatives as potential amino acid subunits in inhibitors of GABA uptake transporters (GATs). In order to ensure that the test compounds adopt a binding pose similar to that presumed for related larger GAT inhibitors, lipophilic residues were introduced either at the amino nitrogen atom or at the alcohol function. Several of the synthesized compounds were found to exhibit similar inhibitory activity at the GAT subtypes mGAT2, mGAT3, and mGAT4, respectively, as compared with the reference N-butylnipecotic acid. Hence, these compounds might serve as starting point for future developments of more complex GAT inhibitors.</jats:p&gt

Structural Modification of the Natural Product Valerenic Acid Tunes RXR Homodimer Agonism

Retinoid X receptors (RXR) are ligand-sensing transcription factors with a unique role in nuclear receptor signaling as universal heterodimer partners. RXR modulation holds potential in cancer, neurodegeneration and metabolic diseases but adverse effects of RXR activation and lack of selective modulators prevent further exploration as therapeutic target. The natural product valerenic acid has been discovered as RXR agonist with unprecedented preference for RXR subtype and homodimer activation. To capture structural determinants of this activity profile and identify potential for optimization, we have studied effects of structural modification of the natural product on RXR modulation and identified an analogue with enhanced RXR homodimer agonism

τBu₂SiF-Derivatized D₂-Receptor Ligands: The First SiFA-Containing Small Molecule Radiotracers for Target-Specific PET-Imaging

The synthesis, radiolabeling and in vitro evaluation of new silicon-fluoride acceptor (SiFA) derivatized D-2-receptor ligands is reported. The SiFA-technology simplifies the introduction of fluorine-18 into target specific biomolecules for Positron-Emission-Tomography (PET). However, one of the remaining challenges, especially for small molecules such as receptor-ligands, is the bulkiness of the SiFA-moiety. We therefore synthesized four Fallypride SiFA-conjugates derivatized either directly at the benzoic acid ring system (SiFA-DMFP, SiFA-FP, SiFA-DDMFP) or at the butyl-side chain (SiFA-M-FP) and tested their receptor affinities. We found D2-receptor affinities for all compounds in the nanomolar range (Ki(SiFA-DMFP) = 13.6 nM, Ki(SiFA-FP) = 33.0 nM, Ki(SiFA-DDMFP) = 62.7 nM and Ki(SiFA-M-FP) = 4.21 nM). The radiofluorination showed highest yields when 10 nmol of the precursors were reacted with F-18]fluoride/TBAHCO(3) in acetonitrile. After a reversed phased cartridge purification the desired products could be isolated as an injectable solution after only 10 min synthesis time with radiochemical yields (RCY) of more than 40% in the case of SiFA-DMFP resulting in specific activities >41 GBq/mu mol (>1,100 Ci/mmol). Furthermore, the radiolabeled products were shown to be stable in the injectable solutions, as well as in human plasma, for at least 90 min

Simultaneous LC-ESI-MS/MS Quantification of Levosimendan and Its Metabolites for Therapeutic Drug Monitoring of Cardiac Surgery Patients

Levosimendan is used in severe chronic cardiac insufficiency, also within the peri-operative setting. Real-life pharmacokinetic data in surgical patients is lacking, making therapeutic drug monitoring (TDM) of levosimendan, its pharmacologically active metabolite OR-1896, and its intermediate OR-1855 important. A simultaneous highly sensitive quantification of levosimendan and its metabolites in small-volume samples has not yet been described. Here, levosimendan (LLOQ 0.450 nM), OR-1896, and OR-1855 (LLOQ both 1.0 nM) were successfully quantified by LC-ESI-MS/MS after liquid-liquid extraction in 300 mu L of blood. A short C8 column under reversed-phase conditions enabled simultaneous and fast quantification of levosimendan in the negative and the metabolites in the positive ionization mode in a single run within 2 min. Interestingly and unexpectedly, constitutional isomers of levosimendan metabolites with identical mass transitions and similar retention times were observed in surgical patients' samples, which we identified as the metamizole metabolites 4-aminoantipyrine and 4-acetamidoantipyrine. A longer C8 column and a modified mobile phase enabled selective quantification of all analytes in a single run within 7 min. We developed, validated, and applied highly sensitive LC-ESI-MS/MS methods for simultaneous quantification of levosimendan and its metabolites, enabling efficient TDM of cardiac surgery patients even with additional metamizole administration

Azidobupramine, an Antidepressant-Derived Bifunctional Neurotransmitter Transporter Ligand Allowing Covalent Labeling and Attachment of Fluorophores

The aim of this study was to design, synthesize and validate a multifunctional antidepressant probe that is modified at two distinct positions. The purpose of these modifications was to allow covalent linkage of the probe to interaction partners, and decoration of probe-target complexes with fluorescent reporter molecules. The strategy for the design of such a probe (i.e., azidobupramine) was guided by the need for the introduction of additional functional groups, conveying the required properties while keeping the additional moieties as small as possible. This should minimize the risk of changing antidepressant-like properties of the new probe azidobupramine. To control for this, we evaluated the binding parameters of azidobupramine to known target sites such as the transporters for serotonin (SERT), norepinephrine (NET), and dopamine (DAT). The binding affinities of azidobupramine to SERT, NET, and DAT were in the range of structurally related and clinically active antidepressants. Furthermore, we successfully visualized azidobupramine-SERT complexes not only in SERT-enriched protein material but also in living cells stably overexpressing SERT. To our knowledge, azidobupramine is the first structural analogue of a tricyclic antidepressant that can be covalently linked to target structures and further attached to reporter molecules while preserving antidepressant-like properties and avoiding radioactive isotopes