A highly selective sulfinate ester probe for thiol bioimaging

Thionyl fluoride as a sulfur(IV) SuFEx hub for the efficient syntheses of sulfinamides and sulfinate esters

Herein, we demonstrate a method for the syntheses of sulfinamides and sulfinate esters using a novel sulfur(IV) fluoride exchange reaction with organometallic reagents. Our strategy involves the addition of an amine or alcohol nucleophile to thionyl fluoride, acting as a S(IV) SuFEx hub, followed by an organometallic reagent. This approach allows efficient access to sulfinamides (45-91% yields) and sulfinate esters (44-82% yields) in only 30 minutes. The sulfinamide and sulfinate esters also can be readily derivatized to the corresponding S(VI) sulfonamides, sulfonate esters, sulfonimidamides, and sulfonimidates without isolation of the intermediates.

Strategies for the direct oxidative esterification of thiols with alcohols

This review paper provides an overview of the main strategies for the oxidative esterification of thiols with alcohols. The review is divided into two major parts according to final products. The first includes the methods for the synthesis of sulfinic esters, while the second contains the procedures for the fabrication of sulfonic ester derivatives.

Constructing firefly luciferin bioluminescence probes for in vivo imaging

Bioluminescence imaging (BLI) is a widely applied visual approach for real-time detecting many physiological and pathological processes in a variety of biological systems. Based on the caging strategy, lots of bioluminescent probes have been well developed. While the targets react with recognizable groups, caged luciferins liberate luciferase substrates, which react with luciferase generating a bioluminescent response. Among the various bioluminescent systems, the most widely utilized bioluminescent system is the firefly luciferin system. The H and carboxylic acid of luciferin are critically caged sites. The introduced self-immolative linker extends the applications of probes. Firefly luciferin system probes have been successfully applied for analyzing physiological processes, monitoring the environment, diagnosing diseases, screening candidate drugs, and evaluating the therapeutic effect. Here, we systematically review the general design strategies of firefly luciferin bioluminescence probes and their applications. Bioluminescence probes provide a new approach for facilitating investigation in a diverse range of fields. It inspires us to explore more robust light emission luciferin and novel design strategies to develop bioluminescent probes.

Using a 3-hydroxyflavone derivative as a fluorescent probe for the indirect determination of aminothiols separated by ion-pair HPLC

Homocysteine, cysteine, cysteinyl-glycine, and glutathione are significant biological aminothiols (ATs) that are marker-molecules in Down syndrome, Alzheimer's disease, or have been implicated as risk factors in atherosclerosis and other vascular diseases, and therefore rapid determination of these molecules is desirable. After reduction of the disulfides, a widely used method utilizes derivatization with ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulfonate (SBD-F) as a fluorogenic probe prior to reversed-phase HPLC separation followed by fluorescence detection. The traditional HPLC determination of ATs is time consuming and economically expensive. We have developed an ion-pair HPLC method coupled with indirect fluorescence detection after post-column reaction with a 2,4-dinitrobenzenesulfonate derivative of a 3-hydroxyflavone. The accuracy, precision, post-column temperature and residence time, and limit-of-detection were evaluated. Sample throughput and reduced sample preparation time of over an hour for the existing methods to less than 20 minutes for the new method is also demonstrated. No statistical differences in HCy, Cys, or Cys-Gly determinations in plasma samples were observed between our method and the traditional HPLC method.

Electrochemical Synthesis of Sulfinate Esters: Nickel(II)-Catalyzed Oxidative Esterification of Thiols with Alcohols in an Undivided Cell

In this study, nickel-catalyzed electrochemical oxidative esterification of thiols with alcohols for the synthesis of sulfinate esters has been reported. The electrochemical oxidative esterification proceeded through a nickel-catalyzed oxidation of thiols using an undivided cell of graphite/nickel electrodes, where the nickel oxidation was studied by cyclic voltammetry. The method was conveniently and directly used for the one-pot synthesis of sulfinate esters of thiols.

Electrochemical Synthesis of Sulfinic Esters via Aerobic Oxidative Esterification of Thiophenols with Alcohols

A method for the electrochemical synthesis of sulfinic esters by aerobic oxidative coupling of thiophenols and alcohols has been developed. Using electrons as the redox reagent and O2 in air as the oxygen source, the reactions proceeded smoothly at room temperature, even for a gram-scale preparation. No use of catalyst, clean redox reagent, green and abundant oxygen source, and mild reaction conditions make this strategy eco-friendly.

A Copper (II) Ensemble-Based Fluorescence Chemosensor and Its Application in the 'Naked-Eye' Detection of Biothiols in Human Urine

Quick and effective detection of biothiols in biological fluids has gained increasing attention due to its vital biological functions. In this paper, a novel reversible fluorescence chemosensor (L-Cu2+) based on a benzocoumarin-Cu2+ ensemble has been developed for the detection of biothiols (Cys, Hcy and GSH) in human urine. The chemosensing ensemble (L-Cu2+) contains a 2:1 stoichiometry structure between fluorescent ligand L and paramagnetic Cu2+. L was found to exclusively bond with Cu2+ ions accompanied with a dramatic fluorescence quenching maximum at 443 nm and an increase of an absorbance band centered at 378 nm. Then, the in situ generated fluorescence sluggish ensemble, L-Cu2+, was successfully used as a chemosensor for the detection of biothiols with a fluorescence "OFF-ON" response modality. Upon the addition of biothiols, the decomplexation of L-Cu2+ led to the liberation of the fluorescent ligand, L, resulting in the recovery of fluorescence and absorbance spectra. Studies revealed that L-Cu2+ possesses simple synthesis, excellent stability, high sensitivity, reliability at a broad pH range and desired renewability (at least 5 times). The practical application of L-Cu2+ was then demonstrated by the detection of biothiols in human urine sample.

NBD-based fluorescent probes for separate detection of cysteine and biothiols via different reactivities

A NBD-based fluorescent probe is developed to seperately detect Cys and all biothiols via different reactivity.

Highly Sensitive Bioluminescent Probe for Thiol Detection in Living Cells

The sensitive detection of thiols including glutathione and cysteine is desirable owing to their roles as indispensable biomolecules in maintaining intracellular biological redox homeostasis. Herein, we report the design and synthesis of SEluc-1 (sulfinate ester luciferin), a chemoselective probe exhibiting a ratiometric and turn-on response towards thiols selectively in fluorescence and bioluminescence, respectively. The probe, which was designed based on the "caged" luciferin strategy, displays excellent selectivity, high signal/noise ratio (>240 in the case of bioluminescence), and a biologically relevant limit of detection (LOD, 80 nm for cysteine), which are all desirable traits for a sensitive bioluminescent sensor. SEluc-1 was further applied to fluorescence imaging of thiol activity in living human cervical cancer HeLa cell cultures, and was successfully able to detect fluctuations in thiol concentrations induced by oxidative stress in a bioluminescent assay utilizing African green monkey fibroblast COS-7 cells and human breast adenocarcinoma MCF-7 cells.

A NBD-S-rhodamine dyad for dual-color discriminative imaging of biothiols and Cys/Hcy

A fluorescent probe based on fast thiolysis of NBD thioether is developed for dual-color discriminative imaging of Cys and GSH.

Reaction-based ratiometric fluorescent probe for selective recognition of sulfide anions with a large Stokes shift through switching on ESIPT

Ratiometric fluorescent probe BNPT has been synthesized and characterized for S²⁻ sensing via ESIPT mechanism.

A fluorescent probe for specific detection of cysteine in the lipid dense region of cells

A new cysteine (Cys) specific chemodosimetric reagent () is used in imaging of endogenous Cys localized in the lipid dense region of the live Hct116 cells and the release of Cys within HepG2 cells from a drug following a biochemical transformation. A silica surface, modified with , could be used for quantitative estimation of Cys present in aqueous solution (pH 7.2) and in a human blood plasma (HBP).

Cellular Protection of SNAP-25 against Botulinum Neurotoxin/A: Inhibition of Thioredoxin Reductase through a Suicide Substrate Mechanism

Botulium neurotoxins (BoNTs) are among the most lethal toxins known to man. They are comprised of seven serotypes with BoNT/A being the most deadly; yet, there is no approved therapeutic for their intoxication or one that has even advanced to clinical trials. Botulinum neurotoxicity is ultimately governed through light chain (LC) protease SNARE protein cleavage leading to a loss of neurotransmitter release. Pharmacological attempts to ablate BoNT/A intoxication have sought to either nullify cellular toxin entry or critical biochemical junctions found within its intricate mechanism of action. In these regards, reports have surfaced of nonpeptidic small molecule inhibitors, but few have demonstrated efficacy in neutralizing cellular toxicity, a key prerequisite before rodent lethality studies can be initiated. On the basis of a lead discovered in our BoNT/A cellular assay campaign, we investigated a family of N-hydroxysuccinimide inhibitors grounded upon structure activity relationship (SAR) fundamentals. Molecules stemming from this SAR exercise were theorized to be protease inhibitors. However, this proposition was overturned on the basis of extensive kinetic analysis. Unexpectedly, inhibitor data pointed to thioredoxin reductase (TrxR), an essential component required for BoNT protease translocation. Also unforeseen was the inhibitors' mechanism of action against TrxR, which was found to be brokered through a suicide-mechanism utilizing quinone methide as the inactivating element. This new series of TrxR inhibitors provides an alternative means to negate the etiological agent responsible for BoNT intoxication, the LC protease.

The Synthesis of a Coumarin Carbohydrazide Dinuclear Copper Complex Based Fluorescence Probe and Its Detection of Thiols

Small-molecule thiols, such as cysteine (CYS) and glutathione (GSH), are essential for maintaining the cellular redox environment and play important roles in regulating various cellular physiological functions. A fluorescence probe (compound 1-Cu²⁺) for thiols based on coumarin carbohydrazide dinuclear copper complex was developed. Compound 1 was synthesized from the reaction of 7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide with 4-tert-butyl-2,6- diformylphenol. Accordingly, the copper complex (compound 1-Cu²⁺) was prepared by mixing compound 1 with 2 equivalents copper ions. Compound 1 had strong fluorescence while compound 1-Cu²⁺ hardly possessed fluorescence owing to the quenching nature of paramagnetism Cu²⁺ to the fluorescence molecule excited state. However, the fluorescence intensity of compound 1-Cu²⁺ was increased dramatically after the addition of thiol-containing amino acids, but not the other non-sulfhydryl amino acids. UV-vis absorption and fluorescence spectra indicated that compound 1-Cu²⁺ had good selectivity and sensitivity for thiols such as glutathione in CH₃CN:H₂O (3:2, v/v) PBS solution. The fluorescence imaging experiments implied that compound 1-Cu²⁺ has potential application in thiol-containing amino acids detection in living cells.

Green synthesis of a benzothiazole based ‘turn-on’ type fluorimetric probe and its use for the selective detection of thiophenols in environmental samples and living cells

A highly sensitive ESIPT based fluorescent chemodosimeter (LOD 3.3 ppb) has been synthesized using “green” chemical route and employed to detect thiophenol in environmental samples and living cells.

A minimalist fluorescent probe for differentiating Cys, Hcy and GSH in live cells

A simple molecule, tetrafluoroterephthalonitrile (4F-2CN), was discovered to be an efficient fluorescent probe for detecting biological thiol species. The probe responded to Cys and emitted strong green fluorescence, whereas it reacted with Hcy/GSH and generated blue fluorescence. Addition of CTAB (cetyl trimethylammonium bromide) was observed to alter the fluorescence color of the reaction product of 4F-2CN and Hcy (from blue to green), but no alteration of the fluorescence color occurred for Cys and GSH. For the very first time, cell imaging experiments showed that the three commonly occurring thiols (Cys/Hcy/GSH) could be differentiated using a single fluorescent probe. In addition, the reaction product of 4F-2CN and Cys exhibits two-photon properties, offering a potentially useful tool for tissue imaging studies. To the best of our knowledge, 4F-2CN is currently the smallest fluorescent probe for thiol detection. We envision that this new and versatile probe will be a useful tool for further elucidating the roles of thiols in biology.

Acid-Activatable Michael-Type Fluorescent Probes for Thiols and for Labeling Lysosomes in Live Cells

A Michael addition is usually taken as a base-catalyzed reaction. Most fluorescent probes have been designed to detect thiols in slightly alkaline solutions (pH 7-9). The sensing reactions of almost all Michael-type fluorescent probes for thiols are faster in a high pH solution than in a low pH solution. In this work, we synthesized a series of 7-substituted 2-(quinolin-2-ylmethylene)malonic acids (QMAs, substituents: NEt2, OH, H, Cl, or NO2) and their ethyl esters (QMEs) as Michael-type fluorescent probes for thiols. The sensing reactions of QMAs and QMEs occur in distinct pH ranges, pH < 7 for QMAs and pH > 7 for QMEs. On the basis of experimental and theoretic studies, we have clarified the distinct pH effects on the sensing reactivity between QMAs and QMEs and demonstrated that two QMAs (NEt2, OH) are highly sensitive and selective fluorescent probes for thiols in acidic solutions (pH < 7) and promising dyes that can label lysosomes in live cells.

A highly selective fluorescence sensor for cysteine/homocysteine and its application in bioimaging

A new near-infrared (NIR) sensitive Cys/Hcy probe based on squaraine was rationally designed and synthesized.

A highly selective and sensitive fluorescent thiol probe through dual-reactive and dual-quenching groups

A fluorescent probe installed with dual-reactive and dual-quenching groups was rationally designed and synthesized for highly selective and sensitive sensing of biothiols.

A phenacrylate scaffold for tunable thiol activation and release

A thiol-selective 2-methyl-3-phenacrylate scaffold with spatiotemporal control over delivery of a cargo is reported. The half-lives of decomposition could be tuned from 30 min to 1 day and the scaffold's utility in thiol-inducible fluorophore release in cell-free as well as within cells is demonstrated.