Environment-Sensitive Fluorescence of 7-Nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)-Labeled Ligands for Serotonin Receptors

Abstract

Serotonin is a neurotransmitter that plays a crucial role in the regulation of several behavioral and cognitive functions by binding to a number of different serotonin receptors present on the cell surface. We report here the synthesis and characterization of several novel fluorescent analogs of serotonin in which the fluorescent NBD (7-nitrobenz-2-oxa-1,3-diazol-4-yl) group is covalently attached to serotonin. The fluorescent ligands compete with the serotonin1A receptor specific radiolabeled agonist for binding to the receptor. Interestingly, these fluorescent ligands display a high environmental sensitivity of their fluorescence. Importantly, the human serotonin1A receptor stably expressed in CHO-K1 cells could be specifically labeled with one of the fluorescent ligands with minimal nonspecific labeling. Interestingly, we show by spectral imaging that the NBD-labeled ligand exhibits a red edge excitation shift (REES) of 29 nm when bound to the receptor, implying that it is localized in a restricted microenvironment. Taken together, our results show that NBD-labeled serotonin analogs offer an attractive fluorescent approach for elucidating the molecular environment of the serotonin binding site in serotonin receptors. In view of the multiple roles played by the serotonergic systems in the central and peripheral nervous systems, these fluorescent ligands would be useful in future studies involving serotonin receptors.

Environmentally sensitive photosensitizers enable targeted photodynamic ablation of Gram-positive antibiotic resistant bacteria

“…Another recent example was reported by Calvaresi and co-workers, who described a concanavalin A-Rose Bengal conjugate to selectively ablate Gramnegative bacteria due to the selective binding of concanavalin to the lipopolysaccharide surface [32]. Several groups have reported nitrobenzoxadiazoles as environmentally sensitive fluorophores [33][34][35]. This feature has been exploited to design activatable probes that turn on in hydrophobic environments and display enhanced signal-to-noise ratios over 'always-on' fluorophores [36,37]; however, the potential of nitrobenzoselenadiazoles as environmentally sensitive PS has not been studied to date.…”

Illuminating the monoamine transporters: Fluorescently labelled ligands to study dopamine, serotonin and norepinephrine transporters

“…In most cases, addition of the fluorescent tag adversely affects binding affinity, and thus, minimizing this decrease by choosing a position on the parent ligand that will have the least impact is critical to success 23,25,26 . In addition, SAR findings will provide guidance for the design of the synthetic scheme to obtain the final FLL that usually requires the addition of the fluorescent label as the final step 23,25,27 . This approach has generated a variety of fluorescent inhibitors of uptake‐1 MATs.…”

“…23,25,26 In addition, SAR findings will provide guidance for the design of the synthetic scheme to obtain the final FLL that usually requires the addition of the fluorescent label as the final step. 23,25,27 This approach has generated a variety of fluorescent inhibitors of uptake-1 MATs. Recent reports suggest that the linker length and composition contributes to the binding affinity and selectivity of the FLL.…”

Novel Derivatives of Nitrobenzofurazan with Chromogenic and Fluorogenic Properties

“…Furthermore, NBD-Cl serves as a reagent for the synthesis of other valuable benzo-oxadiazole-type compounds used in various physical, chemical, or biological processes [ 13 ]. For instance, medicines like cephalosporins [ 14 ], acetylcysteine, captopril [ 15 ], serotonin [ 16 ], glucosinolates [ 17 ], ciprofloxacin [ 18 ], or materials like mesoporous silica [ 19 ] or polymer microparticles [ 20 ] have been derivatized with NBD-chloride.…”