Stereoselective Multicomponent Assembly of Enantiopure Oxazolopiperidines and -azepines

A multicomponent reaction (MCR) based on a cyclohydrocarbonylation (CHC) driven by hydroformylation was set up toward the efficient diastereoselective preparation of oxazolopiperidines (<b>4a</b>–<b>e</b>) and -azepines (<b>7a</b>–<b>d</b>). The bicyclic oxazolidines were obtained from chiral <i>N</i>-alkenylamino alcohols via transient cyclic iminium intermediates that underwent an intramolecular cyclization from the appendant oxygen. On the basis of a series of different experimental conditions, the diastereocontrol observed during the formation of the oxazolidines is best explained by the stereoelectronic effect induced by an A^1,3-strain in a common cyclic iminium intermediate (<b>A</b>). This new sequence is suitable for diversity oriented syntheses, allowing the preparation of enantiopure (<i>S</i>)- and (<i>R</i>)-coniceine in five steps from commercially available material

From the Promiscuous Asenapine to Potent Fluorescent Ligands Acting at a Series of Aminergic G‑Protein-Coupled Receptors

Monoamine neurotransmitters such as serotonin, dopamine, histamine, and noradrenaline have important and varied physiological functions and similar chemical structures. Representing important pharmaceutical drug targets, the corresponding G-protein-coupled receptors (termed aminergic GPCRs) belong to the class of cell membrane receptors and share many levels of similarity as well. Given their pharmacological and structural closeness, one could hypothesize the possibility to derivatize a ubiquitous ligand to afford rapidly fluorescent probes for a large set of GPCRs to be used for instance in FRET-based binding assays. Here we report fluorescent derivatives of the nonselective agent asenapine which were designed, synthesized, and evaluated as ligands of 34 serotonin, dopamine, histamine, melatonin, acetylcholine, and adrenergic receptors. It appears that this strategy led rapidly to the discovery and development of nanomolar affinity fluorescent probes for 14 aminergic GPCRs. Selected probes were tested in competition binding assays with unlabeled competitors in order to demonstrate their suitability for drug discovery purposes

Time-Resolved FRET Binding Assay to Investigate Hetero-Oligomer Binding Properties: Proof of Concept with Dopamine D₁/D₃ Heterodimer

G protein-coupled receptors (GPCRs) have been described to form hetero-oligomers. The importance of these complexes in physiology and pathology is considered crucial, and heterodimers represent promising new targets to discover innovative therapeutics. However, there is a lack of binding assays to allow the evaluation of ligand affinity for GPCR hetero-oligomers. Using dopamine receptors and more specifically the D₁ and D₃ receptors as GPCR models, we developed a new time-resolved FRET (TR-FRET) based assay to determine ligand affinity for the D₁/D₃ heteromer. Based on the high-resolution structure of the dopamine D₃ receptor (D₃R), six fluorescent probes derived from a known D₃R partial agonist (BP 897) were designed, synthesized and evaluated as high affinity and selective ligands for the D₃/D₂ receptors, and for other dopamine receptor subtypes. The highest affinity ligand <b>21</b> was then employed in the development of the D₁/D₃ heteromer assay. The TR-FRET was monitored between a fluorescent tag donor carried by the D₁ receptor (D₁R) and a fluorescent acceptor D₃R ligand <b>21</b>. The newly reported assay, easy to implement on other G protein-coupled receptors, constitutes an attractive strategy to screen for heteromer ligands