Synthesis And Applications Of Several Fluorescent Probes For Biological Thiols

Biological thiols, such as cysteine, homocysteine and glutathione, play vital roles in physiological and pathological processes which can maintain intracellular redox equilibrium. It is very important to detect cysteine, homocysteine and glutathione for obtaining a lot of significant physiological and pathological information, which would promote the development of medical industry. It has attracted more and more attention as fluorescent probes have many advantages, such as high selectivity, high sensitivity, low detection, enabling intracellular localization and so on. Fluorescent probes have been widely used in many sides, such as biomedical, environmental testing and other areas. In this work, we designed and synthesized two probes which were applied for detection of biological thiols or live-cell imaging. The main contents are summarized as follows:1. Two new fluorescence probes, probes1and probe2, with a mechanism of photoinduced electron transfer (PET) have been synthesized and characterized in this work. Probe1was composed of the7-nitro [1,2,5] oxadiazole and4-hydroxyphenyl maleimide. Probe2comprised three sections, chromophore, detection group and mitochondria-targeted moiety; naphthalimide as a chromophore for its good fluorescence properties, nitro group as a detection group for its strong electron-withdrawing, triphenylphosphine salts as a mitochondria-targeted moiety, and disulfide bond to bring probe to the mitochondria.2. The probe1is a turn-on fluorescent probe. PET occurred between the maleimide and the fluorophore by n-n*transition from the fluorophore to an ethylenically double bond, which reduced fluorescence quantum yield. The PET was hindered when cysteine reacted with maleimide-carbon double bond. An emission spectrum with max emission at554nm under the excititation of465nm was observed. The probe1can also be used to image Hela cells, indicating that the probe has membrane permeability and biocompatibility. This detection method based on probe1is fast, high sensitivity and simple.3. The displacement of the nitro group by thiols can be conducted under milder conditions, which can alter the electron push-pull character of the probe. The discrimination involves a blue-fluorescent thioether formation via nucleophilic aromatic substitution of the nitro group by thiol, followed by a second intramolecular nucleophilic aromatic substitution of alkylthio with the amino group to give the green-fluorescent4-amino derivative. The process of cysteine substituding nitro group to obtain amine substituent needed less time. However, the process of homocysteine substituding nitro group was stopped in the first step as the feasibility of intramolecular aromatic nucleophilic substitution of a thioether by an amino group facilitated by intramolecularity. The results enabled us to distinguish Cys, Hey and GSH especially from their different structural from others thiols. The new probe was successfully applied for the imaging of cysteine in Hela cells, indicating that the probe has perfect biocompatibility.