Fluorescent probes for dopamine receptors: synthesis and characterization of fluorescein and 7-nitrobenz-2-oxa-1,3-diazol-4-yl conjugates of D-1 and D-2 receptor ligands

Abstract

Fluorescent probes have been designed and developed for dopamine D-1 and D-2 receptors. Fluorescein and/or NBD (7-nitrobenz-2-oxa-1,3-diazol-4-yl) derivatives of PPHT (D-2 agonist), spiperone (D-2 antagonist), SKF 38393 (D-1 agonist), and SKF 83566 (D-1 antagonist) were synthesized via their amino-functionalized analogues and all ligands were pharmacologically evaluated by measuring their ability to displace [3H]SCH 23390 and [3H]spiperone from D-1 and D-2 receptor sites in caudate putamen of monkeys (Macaca fascicularis). The fluorescein derivatives of PPHT and SKF 83566 and the NBD derivatives of spiperone and SKF 83566 retained the high affinity and selectivity of the parent ligands. The NBD derivatives of PPHT showed higher D-2 receptor affinity and selectivity than their parent ligands. The enantiomers of the fluorescent derivatives of PPHT were also synthesized and were found to exhibit stereoselectivity in binding to the D-2 receptor, with the S enantiomers having a considerably higher affinity than their R analogues. In contrast to these results, the fluorescein derivative of SKF 38393 showed only a low affinity for the D-1 receptor. These fluorescein- and NBD-coupled D-1 and D-2 receptor ligands have considerable significance as potential probes in the study of distribution of the receptors at the cellular/subcellular level and of their mobility in membranes in normal/diseased states by use of fluorescence microscopic and fluorescence photobleaching recovery techniques, respectively. The development of these novel fluorescent probes should also provide new leads for the design and synthesis of additional fluorescent ligands with better fluorescent properties and/or higher affinity/selectivity for the DA receptors.

A Fluorescent Ligand-Binding Alternative Using Tag-lite® Technology

“…Briefly, the CCK(26-33) peptide was derivatized with our red d2 dye (red-CCK (26)(27)(28)(29)(30)(31)(32)(33)). This fluorescent ligand was expected to display a good affinity for both SNAP-tagfused CCK1 and CCK2 receptors.…”

Discovery of indolylpiperazinylpyrimidines with dual-target profiles at adenosine A2A and dopamine D2 receptors for Parkinson's disease treatment

“…Among these, compounds 5 and 6 with hA 2A binding affinity in the low micromolar range were selected for the polymersome-based dopamine D 2 receptor binding assay. In such assay, boron-dipyrromethene N -( p -aminophenethyl)spiperone (BODIPY-NAPS, a fluorescent ligand) was incubated with D 2 receptor-functionalised polymersomes; spiperone is a selective D 2 -like antagonist with reported K i of 0.06 nM for D 2 receptor [ 24 ]. The mixture was then incubated with solutions containing eight different concentrations (ranging from 3 nM to 0.3 mM) of compounds 5 and 6 , and the measured fluorescence intensity against ligand concentration was plotted accordingly ( Fig 5A and 5B ).…”

“…Furthermore, (±)-2-( N -phenethyl- N -propyl)amino-5-hydroxytetralin hydrochloride ((±)-PPHT.HCl), a potent dopamine D 2 receptor agonist with a K i of 13.3 nM determined by competition binding experiments with [ 3 H]spiperone [ 24 ], was tested for its ability to displace BODIPY-NAPS. Similarly, a sigmoidal decrease in fluorescence with increasing concentration of (±)-PPHT.HCl was noted ( Fig 5C ); this observation was characteristic of D 2 agonist interactions in the D 2 R-functionalized polymersomes.…”

Design, synthesis and biological evaluation of bivalent ligands against A1–D1 receptor heteromers

“…In 1991, Neumeyer et al synthesized the derivative of SKF38393 to identify effective fluorescent probes. However, coupling of the large group to the 4' site of SKF38393 resulted in a considerable loss of affinity [20] . As a result, we did not synthesize the corresponding monovalent ligand compounds for the D 1 antagonist as a control.…”