Small molecule generators of biologically reactive sulfur species

Phototriggered Hydrogen Persulfide Donors via Hydrosulfide Radical Formation Enhancing the Reactive Sulfur Metabolome in Cells

Hydrogen persulfide (H2S2) is an important sulfur-containing signaling molecule that plays a crucial role in the homeostasis of various organ systems, such as the renal, cardiovascular, liver, and gastrointestinal systems. However, research on H2S2 in biological settings is still challenging due to its instability and high reactivity. Compounds that can controllably release H2S2 (also known as donors) are thus crucial research tools. Currently, available H2S2 donors are still very limited, with most of them relying on modified disulfide templates. These templates possess an unavoidable limitation of being susceptible to cellular disulfide exchange which can compromise their efficacy. In this work, we explored nondisulfide-based and nonoxidation-dependent templates for the design of H2S2 donors. We found that tertiary naphthacyl thiols could undergo phototriggered C-S homolytic cleavage to form H2S2 via hydrosulfide (HS) radicals. In addition, the release of H2S2 was associated with the formation of a product with strong blue fluorescence, which allowed for real-time monitoring of the release process. This reaction was demonstrated to proceed effectively in both buffers and cells, with the ability to enhance intracellular production of persulfides, including GSSH, CysSSH, H2S2, H2S3, etc. It provides a unique photocontrolled H2S2 donor system with distinct advantages compared to known H2S2 donors due to its good stability and spatiotemporal control ability.

Geminal-dithiol-based precursors for reactive sulfur species

Caged gem-dithiols have been developed as the donors of reactive sulfur species (RSS), but the chemistry of free gem-dithiols as RSS donors has not been well understood. Herein, we report the study of a free gem-dithiol, 1,3-diphenylpropane-2,2-dithiol, as the precursor for several RSS. It releases H2S under physiological conditions and can be converted to a mono-S-nitrosothiol, which serves as a NO donor. Furthermore, it can be converted to 3,3-dibenzyldithiirane, which is an active sulfur transfer reagent and can induce S-persulfidation.

2H-Thiopyran-2-thione sulfine, a compound for converting H2S to HSOH/H2S2 and increasing intracellular sulfane sulfur levels

Reactive sulfane sulfur species such as persulfides (RSSH) and H2S2 are important redox regulators and closely linked to H2S signaling. However, the study of these species is still challenging due to their instability, high reactivity, and the lack of suitable donors to produce them. Herein we report a unique compound, 2H-thiopyran-2-thione sulfine (TTS), which can specifically convert H2S to HSOH, and then to H2S2 in the presence of excess H2S. Meanwhile, the reaction product 2H-thiopyran-2-thione (TT) can be oxidized to reform TTS by biological oxidants. The reaction mechanism of TTS is studied experimentally and computationally. TTS can be conjugated to proteins to achieve specific delivery, and the combination of TTS and H2S leads to highly efficient protein persulfidation. When TTS is applied in conjunction with established H2S donors, the corresponding donors of H2S2 (or its equivalents) are obtained. Cell-based studies reveal that TTS can effectively increase intracellular sulfane sulfur levels and compensate for certain aspects of sulfide:quinone oxidoreductase (SQR) deficiency. These properties make TTS a conceptually new strategy for the design of donors of reactive sulfane sulfur species.

Fabrication of Ag nanostar and PEI-based SERS substrate for sensitive and rapid detection of SO2: Application for detection of sulfite residues in beer

Because of sulfite's potential toxicity, there is a growing concern about detecting and controlling its concentration in foods, alcoholic beverages, pharmaceuticals, and environmental samples to ensure public health. A branched polyethyleneimine-coated silver nano-star (AgNS@PEI) surface-enhanced Raman scattering (SERS) substrate was synthesized in this study for use as a sensitive, simple, rapid, stable, and reproducible non-destructible sulfite detection analytical technique. The seed morphology of the nano-star was created by using hydroxylamine (NH2OH) solution as a primary reducing agent, followed by a slow secondary reduction by trisodium citrate dihydrate (HOC(COONa)(CH2COONa)2 2H2O), resulting in the complete growth of the silver nano-star. For extra stability and selective absorption of sulfur dioxide from the headspace extraction of SO2 from sulfites, the nano-stars were thin coated with branched polyethyleneimine (b-PEI). The results showed that the thin-coated plasmonic substrates selectively absorb sulfur dioxide molecules, allowing sulfites in beer samples to be detected with a detection limit of 0.48 mg/L. Furthermore, the PEI-coated silver nano-star demonstrated increased stability and reproducibility, allowing for longer use of the substrate. Recovery experiments with recovery rates ranging from 95 to 112% and relative standard deviations ranging from 1.55 to 8.1% demonstrated that headspace extraction, selective SO2 absorption by the synthesized substrate, and subsequent SERS detections were reliable and valid for practical applications. Finally, this study developed an SO2-sensitive, selective, and robust Si@AgNS@PEI substrate for effective SERS detection and monitoring of sulfite levels in real-world environmental samples.

An ROS-Responsive Donor That Self-Reports Its H2S Delivery by Forming a Benzoxazole-Based Fluorophore

Hydrogen sulfide (H2S), an endogenous signaling molecule, is known to play a pivotal role in neuroprotection, vasodilation, and hormonal regulation. To further explore the biological effects of H2S, refined donors that facilitate its biological delivery, especially under specific (patho) physiological conditions, are needed. In the present study, we demonstrate that ortho-substituted, aryl boronate esters provide two unique and distinct pathways for H2S release from thioamide-based donors: Lewis acid-facilitated hydrolysis and reactive oxygen species (ROS)-induced oxidation/cyclization. Through a detailed structure-activity relationship study, donors that resist hydrolysis and release H2S solely via the latter mechanism were identified, which have the added benefit of providing a potentially useful heterocycle as the lone byproduct of this novel chemistry. To highlight this, we developed an ROS-activated donor (QH642) that simultaneously synthesizes a benzoxazole-based fluorophore en route to its H2S delivery. A distinct advantage of this design over earlier self-reporting donors is that fluorophore formation is possible only if H2S has been discharged from the donor. This key feature eliminates the potential for false positives and provides a more accurate depiction of reaction progress and donor delivery of H2S, including in complex cellular environments.

Genome-wide characterization of the cytosolic sulfotransferase 1B member 1 (SULT1B1) family and its expression responses to sulfide stress in the razor clam Sinonovacula constricta

The razor clam (Sinonovacula constricta), a typical burrowing organism in the intertidal zones, is often exposed to sulfide environment and shows strong sulfide tolerance. Located downstream of the sulfur metabolism pathway, cytosolic sulfotransferase family 1B member 1 (SULT1B1) is a key enzyme catalysing the sulfonation reaction, and plays an important role in the biotransformation of endogenous substances such as thyroid hormones (THs). To investigate their roles in sulfide resistance, a systematic analysis of S. constricta SULT1B1s (ScSULT1B1s), including genomic distribution, phylogenetic relationships, gene structure, conserved motifs, and expression profiles under sulfide stress, was performed. A total of 10 ScSULT1B1 genes were found in the S. constricta genome. Sequence analysis showed that ScSULT1B1 gene family encoded 155-425 amino acids, containing four catalytic active sites (K, N, H, and S), one PAPS binding domain at the N-terminus, and one PAPS binding and dimerization domain at the C-terminus. The spatial-temporal expression patterns of ScSULT1B1s were further estimated by quantitative real-time PCR (qRT-PCR). Among them, partial ScSULT1B1s showed significantly high expression in the gill, hepatopancreas, and siphon. Furthermore, the response expression of certain ScSULT1B1s significantly fluctuated under sulfide stress. Together, our results suggest that ScSULT1B1s, by mediating the sulfonation reaction, may regulate THs levels to maintain basic metabolic and immune functions, making S. constricta highly sulfide tolerant.

H2S Donors with Cytoprotective Effects in Models of MI/R Injury and Chemotherapy-Induced Cardiotoxicity

Hydrogen sulfide (H2S) is an endogenous signaling molecule that greatly influences several important (patho)physiological processes related to cardiovascular health and disease, including vasodilation, angiogenesis, inflammation, and cellular redox homeostasis. Consequently, H2S supplementation is an emerging area of interest, especially for the treatment of cardiovascular-related diseases. To fully unlock the medicinal properties of hydrogen sulfide, however, the development and refinement of H2S releasing compounds (or donors) are required to augment its bioavailability and to better mimic its natural enzymatic production. Categorizing donors by the biological stimulus that triggers their H2S release, this review highlights the fundamental chemistry and releasing mechanisms of a range of H2S donors that have exhibited promising protective effects in models of myocardial ischemia-reperfusion (MI/R) injury and cancer chemotherapy-induced cardiotoxicity, specifically. Thus, in addition to serving as important investigative tools that further advance our knowledge and understanding of H2S chemical biology, the compounds highlighted in this review have the potential to serve as vital therapeutic agents for the treatment (or prevention) of various cardiomyopathies.

Single-Component Photo-Responsive Template for the Controlled Release of NO and H2S2

Redox signaling molecules include a number of reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS). These molecules work collectively in the regulation of many physiological processes. Understanding the crosstalk mechanisms in these signaling molecules is important but challenging. The development of donor compounds of ROS/RNS/RSS will aid the advances in this field. While many donors that can release one ROS/RNS/RSS have been developed, dual donors that can release two signaling species and facilitate their crosstalk studies are still very rare. Those limited examples lack the ability to precisely control the timing of two releases. In this work, a 2-methoxy-6-naphthacyl-derived tertiary SNO compound, Naph-SNO, was designed and evaluated as the dual donor for NO and H₂S₂. The 2-methoxy-6-naphthacyl structure was demonstrated to be a novel photoremovable protecting group that could directly uncage C-S bonds. Under the irradiation of lights with different wavelengths (visible or UV), Naph-SNO could release NO and H₂S₂ in a stepwise manner, or simultaneously (i.e., likely producing the crosstalk product HSNO/HSSNO). In addition, the release of payloads from the donor also produced an end product with blue fluorescence. Therefore, the release process could be easily monitored in "real time." This controllable photo-triggered release strategy has the potential to be used in the design of other RNS/RSS dual donors.

Sulfur incorporation into biomolecules: recent advances

Sulfur is an essential element for a variety of cellular constituents in all living organisms and adds considerable functionality to a wide range of biomolecules. The pathways for incorporating sulfur into central metabolites of the cell such as cysteine, methionine, cystathionine, and homocysteine have long been established. Furthermore, the importance of persulfide intermediates during the biosynthesis of thionucleotide-containing tRNAs, iron-sulfur clusters, thiamin diphosphate, and the molybdenum cofactor are well known. This review briefly surveys these topics while emphasizing more recent aspects of sulfur metabolism that involve unconventional biosynthetic pathways. Sacrificial sulfur transfers from protein cysteinyl side chains to precursors of thiamin and the nickel-pincer nucleotide (NPN) cofactor are described. Newer aspects of synthesis for lipoic acid, biotin, and other compounds are summarized, focusing on the requisite iron-sulfur cluster destruction. Sulfur transfers by using a noncore sulfide ligand bound to a [4Fe-4S] cluster are highlighted for generating certain thioamides and for alternative biosynthetic pathways of thionucleotides and the NPN cofactor. Thioamide formation by activating an amide oxygen atom via phosphorylation also is illustrated. The discussion of these topics stresses the chemical reaction mechanisms of the transformations and generally avoids comments on the gene/protein nomenclature or the sources of the enzymes. This work sets the stage for future efforts to decipher the diverse mechanisms of sulfur incorporation into biological molecules.

External stimuli-responsive gasotransmitter prodrugs: Chemistry and spatiotemporal release

Gasotransmitters like nitric oxide, carbon monoxide, and hydrogen sulfide with unique pleiotropic pharmacological effects in mammals are an emerging therapeutic modality for different human diseases including cancer, infection, ischemia-reperfusion injuries, and inflammation; however, their clinical translation is hampered by the lack of a reliable delivery form, which delivers such gasotransmitters to the action site with precisely controlled dosage. The external stimuli-responsive prodrug strategy has shown tremendous potential in developing gasotransmitter prodrugs, which affords precise temporospatial control and better dose control compared with endogenous stimuli-sensitive prodrugs. The promising external stimuli employed for gasotransmitter activation range from photo, ultrasound, and bioorthogonal click chemistry to exogenous enzymes. Herein, we highlight the recent development of external stimuli-mediated decaging chemistry for the temporospatial delivery of gasotransmitters including nitric oxide, carbon monoxide, hydrogen sulfide and sulfur dioxide, and discuss the pros and cons of different designs.

Detection of glutathione, cysteine, and homocysteine by online derivatization-based electrospray mass spectrometry

RATIONALE

Electrospray ionization mass spectrometry (ESI-MS) is one of the most popular techniques for obtaining structural information, which is commonly used in bioanalysis and clinical diagnostics. However, for the detection of complicated samples with high reactivities (such as reactive sulfur species, RSS), traditional ESI-MS usually suffers from overlapped and inaccurate signals. In this study, based on the multiphase flow of extractive electrospray ionization (MF-EESI), an ambient MS technique of online derivatization was proposed to detect thiols without any other sample pretreatment.

METHODS

RSS molecules and the derivatization reagent of 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) were introduced into the internal and innermost capillary of the MF-EESI system, respectively. By a high-velocity nebulizing stream of N₂ gas through an external capillary, both flows of innermost biothiols and internal NBD-Cl were electrosprayed and mixed for online reactions. Therefore, the fast derivatization of thiols was used to generate stable ionized derivatives for MS detection.

RESULTS

By evaluating the changes in MS signals before and after the derivatization, the ions of RSS were identified simply and correctly. Without any sample pretreatment, the fast detection of cysteine, homocysteine, and glutathione has been achieved in the complicated samples.

CONCLUSIONS

The present online derivatization-based MF-EESI was successfully used for fast, simple, and accurate detection of biothiols. This presented a potential pathway for the fast identification of thiols in complicated samples.

A dual-response NIR probe reveals positive correlation between biothiols and viscosity under cellular stress change

A mitochondrial targeted NIR fluorescent probe NIR-NBD was designed and developed for the detection of biothiols and viscosity. Furthermore, a positive correlation between the biothiol level and viscosity under cellular stress change was found for the first time, which provides some important correlation analysis information in the pathophysiological state.

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

The Path to Controlled Delivery of Reactive Sulfur Species

Reactive sulfur species (RSS) play regulatory roles in many physiological and pathological processes. Since the discovery of hydrogen sulfide (H₂S) as a nitric oxide (NO)-like signaling molecule, understanding the chemical biology of H₂S and H₂S-related RSS, such as hydropersulfides (RSSH) and polysulfides (H₂S_n), has become a fast-growing research field. However, the research on these RSS has technical difficulties due to their high reactivity and instability. To solve this problem, considerable efforts have been put into the development of unique RSS releasing compounds (e.g., donors) or in situ RSS generation systems. This Account tells the story of our research group's effort to develop novel RSS donors.We began with exploring molecular entities that were stable by themselves but could be triggered by biologically relevant factors, such as pH, thiols, light, or enzymes, to release H₂S in a controllable fashion. These studies led to the discovery of a series of novel H₂S donors. We later expanded our interests to other RSS including RSSH, H₂S_n, RSeSH, HSNO, RSOH, etc. The fundamental chemistry of these RSS was studied and applied to the development of the corresponding donors. In addition to small molecule donors, we also worked on H₂S-releasing biomaterials and their applications. This Account summarizes our work and systematically explains how each RSS donor template was proposed and evaluated. The Account covers the following key points: (1) rational chemistry design of each RSS donor template, (2) evaluation and mechanistic insights of each donor template, and (3) properties and biological applications of the donors.

A near-infrared fluorescent probe targeting mitochondria for sulfite detection and its application in food and biology

Sulfur dioxide (SO2) is the main air pollutant in the environment, causing great harm to human health. Abnormal SO2 levels are usually associated with some respiratory diseases, cardiovascular diseases, and neurological disorders (even brain cancer). Therefore, monitoring SO2 levels is helpful to better understand its special physiological and pathological role. Although many fluorescent probes for SO2 have been reported, many of them were not ideal for in vivo imaging due to the short emission wavelength. In this work, a near-infrared fluorescent probe NIR-BN with emission wavelength of 680 nm was constructed by conjugating the benzopyrylium moiety and 6-hydroxy-2-naphthaldehyde. NIR-BN had high selectivity and rapidity for SO2 detection. In addition, the detection limit of NIR-BN was relatively low, which can be used for the determination of sulfite in different sugar samples with high accuracy. Of course, due to the excellent spectral and structural properties of NIR-BN, we have applied NIR-BN to the detection of SO2 in biological systems.

H2S and reactive sulfur signaling at the host-bacterial pathogen interface

Bacterial pathogens that cause invasive disease in the vertebrate host must adapt to host efforts to cripple their viability. Major host insults are reactive oxygen and reactive nitrogen species as well as cellular stress induced by antibiotics. Hydrogen sulfide (H2S) is emerging as an important player in cytoprotection against these stressors, which may well be attributed to downstream more oxidized sulfur species termed reactive sulfur species (RSS). In this review, we summarize recent work that suggests that H2S/RSS impacts bacterial survival in infected cells and animals. We discuss the mechanisms of biogenesis and clearance of RSS in the context of a bacterial H2S/RSS homeostasis model and the bacterial transcriptional regulatory proteins that act as "sensors" of cellular RSS that maintain H2S/RSS homeostasis. In addition, we cover fluorescence imaging- and MS-based approaches used to detect and quantify RSS in bacterial cells. Last, we discuss proteome persulfidation (S-sulfuration) as a potential mediator of H2S/RSS signaling in bacteria in the context of the writer-reader-eraser paradigm, and progress toward ascribing regulatory significance to this widespread post-translational modification.

Synthesis of Cyclic Sulfite Diesters and their Evaluation as Sulfur Dioxide (SO2 ) Donors

Although sulfur dioxide (SO₂ ) finds widespread use in the food industry as its hydrated sulfite form, a number of aspects of SO₂ biology remain to be completely understood. Of the tools available for intracellular enhancement of SO₂ levels, most suffer from poor cell permeability and a lack of control over SO₂ release. We report 1,2-cyclic sulfite diesters as a new class of reliable SO₂ donors that dissociate in buffer through nucleophilic displacement to produce SO₂ with tunable release profiles. We provide data in support of the suitability of these SO₂ donors to enhance intracellular SO₂ levels more efficiently than sodium bisulfite, the most commonly used SO₂ donor for cellular studies.

Activatable Small-Molecule Hydrogen Sulfide Donors

Significance: Hydrogen sulfide (H2S) is an important biological signaling molecule involved in many physiological processes. These diverse roles have led researchers to develop contemporary methods to deliver H2S under physiologically relevant conditions and in response to various stimuli. Recent Advances: Different small-molecule donors have been developed that release H2S under various conditions. Key examples include donors activated in response to hydrolysis, to endogenous species, such as thiols, reactive oxygen species, and enzymes, and to external stimuli, such as photoactivation and bio-orthogonal chemistry. In addition, an alternative approach to release H2S has utilized the catalyzed hydrolysis of carbonyl sulfide (COS) by carbonic anhydrase to generate libraries of activatable COS-based H2S donors. Critical Issues: Small-molecule H2S donors provide important research and pharmacological tools to perturb H2S levels. Key needs, both in the development and in the use of such donors, include access to new donors that respond to specific stimuli as well as donors with well-defined control compounds that allow for clear delineation of the impact of H2S delivery from other donor byproducts. Future Directions: The abundance of reported small-molecule H2S donors provides biologists and physiologists with a chemical toolbox to ask key biological questions and to develop H2S-related therapeutic interventions. Further investigation into different releasing efficiencies in biological contexts and a clear understanding of biological responses to donors that release H2S gradually (e.g., hours to days) versus donors that generate H2S quickly (e.g., seconds to minutes) is needed.

Development and Application of Carbonyl Sulfide-Based Donors for H2S Delivery

In addition to nitric oxide and carbon monoxide, hydrogen sulfide (H2S) has been recently recognized as an important biological signaling molecule with implications in a wide variety of processes, including vasodilation, cytoprotection, and neuromodulation. In parallel to the growing number of reports highlighting the biological impact of H2S, interest in developing H2S donors as both research tools and potential therapeutics has led to the growth of different H2S-releasing strategies. Many H2S investigations in model systems use direct inhalation of H2S gas or aqueous solutions of NaSH or Na2S; however, such systems do not mimic endogenous H2S production. This stark contrast drives the need to develop better sources of caged H2S. To address these limitations, different small organosulfur donor compounds have been prepared that release H2S in the presence of specific activators or triggers. Such compounds, however, often lack suitable  control compounds, which limits the use of these compounds in probing the effects of H2S directly. To address these needs, our group has pioneered the development of carbonyl sulfide (COS) releasing compounds as a new class of H2S donor motifs. Inspired by a commonly used carbamate prodrug scaffold, our approach utilizes self-immolative thiocarbamates to access controlled release of COS, which is rapidly converted to H2S by the ubiquitous enzyme carbonic anhydrase (CA). In addition, this design enables access to key control compounds that release CO2/H2O rather than COS/H2S, which enables delineation of the effects of COS/H2S from the organic donor byproducts. In this Account, we highlight a library of first-generation COS/H2S donors based on self-immolative thiocarbamates developed in our lab and also highlight challenges related to H2S donor development. We showcase the release of COS in the presence of specific triggers and activators, including biological thiols and bio-orthogonal reactants for targeted applications. We also demonstrate the design and development of a series of H2O2/reactive oxygen species (ROS)-triggered donors and show that such compounds can be activated by endogenous levels of ROS production. Utilizing approaches in bio-orthogonal activation, we establish that donors functionalized with an o-nitrobenzyl photocage can enable access to light-activated donors. Similar to endogenous production by cysteine catabolism, we also prepared a cysteine-selective COS donor activated by a Strongin ligation mechanism. In efforts to help delineate potential differences in the chemical biology of COS and H2S, we also report a simple esterase-activated donor, which demonstrated fast COS-releasing kinetics and inhibition of mitochondrial respiration in BEAS-2B cells. Additional investigations revealed that COS release rates and cytotoxicity correlated directly within this series of compounds with different ester motifs. In more recent and applied applications of this H2S donation strategy, we also highlight the development of donors that generate either a colorimetric or fluorescent optical response upon COS release. Overall, the work described in this Account outlines the development and initial application of a new class of H2S donors, which we anticipate will help to advance our understanding of the rapidly emerging chemical biology of H2S and COS.

Cyclic Sulfenyl Thiocarbamates Release Carbonyl Sulfide and Hydrogen Sulfide Independently in Thiol-Promoted Pathways

Hydrogen sulfide (H2S) is an important signaling molecule that provides protective activities in a variety of physiological and pathological processes. Among the different types of H2S donor compounds, thioamides have attracted attention due to prior conjugation to nonsteroidal anti-inflammatory drugs (NSAIDs) to access H2S-NSAID hybrids with significantly reduced toxicity, but the mechanism of H2S release from thioamides remains unclear. Herein, we reported the synthesis and evaluation of a class of thioamide-derived sulfenyl thiocarbamates (SulfenylTCMs) that function as a new class of H2S donors. These compounds are efficiently activated by cellular thiols to release carbonyl sulfide (COS), which is quickly converted to H2S by carbonic anhydrase (CA). In addition, through mechanistic investigations, we establish that COS-independent H2S release pathways are also operative. In contrast to the parent thioamide-based donors, the SulfenylTCMs exhibit excellent H2S releasing efficiencies of up to 90% and operate through mechanistically well-defined pathways. In addition, we demonstrate that the sulfenyl thiocarbamate group is readily attached to common NSAIDs, such as naproxen, to generate YZ-597 as an efficient H2S-NSAID hybrid, which we demonstrate releases H2S in cellular environments. Taken together, this new class of H2S donor motifs provides an important platform for new donor development.

Dithioesters: simple, tunable, cysteine-selective H2S donors

Dithioesters have a rich history in polymer chemistry for RAFT polymerizations and are readily accessible through different synthetic methods. Here we demonstrate that the dithioester functional group is a tunable motif that releases H2S upon reaction with cysteine and that structural and electronic modifications enable the rate of cysteine-mediated H2S release to be modified. In addition, we use (bis)phenyl dithioester to carry out kinetic and mechanistic investigations, which demonstrate that the initial attack by cysteine is the rate-limiting step of the reaction. These insights are further supported by complementary DFT calculations. We anticipate that the results from these investigations will allow for the further development of dithioesters as important chemical motifs for studying H2S chemical biology.

Fluorogenic hydrogen sulfide (H2S) donors based on sulfenyl thiocarbonates enable H2S tracking and quantification

Hydrogen sulfide (H2S) is an important cellular signaling molecule that exhibits promising protective effects. Although a number of triggerable H2S donors have been developed, spatiotemporal feedback from H2S release in biological systems remains a key challenge in H2S donor development. Herein we report the synthesis, evaluation, and application of caged sulfenyl thiocarbonates as new fluorescent H2S donors. These molecules rely on thiol cleavage of sulfenyl thiocarbonates to release carbonyl sulfide (COS), which is quickly converted to H2S by carbonic anhydrase (CA). This approach is a new strategy in H2S release and does not release electrophilic byproducts common from COS-based H2S releasing motifs. Importantly, the release of COS/H2S is accompanied by the release of a fluorescent reporter, which enables the real-time tracking of H2S by fluorescence spectroscopy or microscopy. Dependent on the choice of fluorophore, either one or two equivalents of H2S can be released, thus allowing for the dynamic range of the fluorescent donors to be tuned. We demonstrate that the fluorescence response correlates directly with quantified H2S release and also demonstrate the live-cell compatibility of these donors. Furthermore, these fluorescent donors exhibit anti-inflammatory effects in RAW 264.7 cells, indicating their potential application as new H2S-releasing therapeutics. Taken together, sulfenyl thiocarbonates provide a new platform for H2S donation and readily enable fluorescent tracking of H2S delivery in complex environments.

Effects of sulfane sulfur content in benzyl polysulfides on thiol-triggered H2S release and cell proliferation

Investigations into hydrogen sulfide (H2S) signaling pathways have demonstrated both the generation and importance of persulfides, which are reactive sulfur species that contain both reduced and oxidized sulfur. These observations have led researchers to suggest that oxidized sulfur species, including sulfane sulfur (S0), are responsible for many of the physiological phenomena initially attributed to H2S. A common method of introducing S0 to biological systems is the administration of organic polysulfides, such as diallyl trisulfide (DATS). However, prior reports have demonstrated that commercially-available DATS often contains a mixture of polysulfides, and furthermore a lack of structure-activity relationships for organic polysulfides has limited our overall understanding of different polysulfides and their function in biological systems. Advancing our interests in the chemical biology of reactive sulfur species including H2S and S0, we report here our investigations into the rates and quantities of H2S release from a series of synthetic, pure benzyl polysulfides, ranging from monosulfide to tetrasulfide. We demonstrate that H2S is only released from the trisulfide and tetrasulfide, and that this release requires thiol-mediated reduction in the presence of cysteine or reduced glutathione. Additionally, we demonstrate the different effects of trisulfides and tetrasulfides on cell proliferation in murine epithelial bEnd.3 cells.

One- and two-photon responsive sulfur dioxide (SO2) donors: a combinatorial drug delivery for improved antibiotic therapy

Light-activated sulfur dioxide donors have been developed and explored their applicability for combinatorial antibiotic therapy with self-monitoring ability.

SO2 Donors and Prodrugs, and Their Possible Applications: A Review

SO2 is widely recognized as an air pollutant and is a known cause of acid rain. At a sufficiently high level, it also causes respiratory diseases. A much lesser known side of SO2 is its endogenous nature and possible physiological roles. There is mounting evidence that SO2 is produced during normal cellular metabolism and may possibly function as a signaling molecule in normal physiology. The latter aspect is still at the stage of being carefully examined as to the validity of classifying SO2 as a gasotransmitter with endogenous signaling roles. One difficulty in studying the biological and pharmacological roles of SO2 is the lack of adequate tools for its controllable and precise delivery. Traditional methods of using SO2 gas or mixed sulfite salts do not meet research need for several reasons. Therefore, there has been increasing attention on the need of developing SO2 donors or prodrugs that can be used as tools for the elucidation of SO2's physiological roles, pharmacological effects, and possible mechanism(s) of action. In this review, we aim to review basic sulfur chemistry in the context of sulfur signaling and various chemical strategies used for designing SO2 donors. We will also discuss potential pharmacological applications of SO2 donors, lay out desirable features for such donors and possibly prodrugs, analyze existing problems, and give our thoughts on research needs.

The benefits of macromolecular hydrogen sulfide prodrugs

Hydrogen sulfide has significant therapeutic potential that is continually being implicated in a variety of biochemical processes. This highlight article will present the benefits and opportunities in designing macromolecule based H₂S donors. Emphasis will be on how design of polymer systems can help drive the development of H₂S therapeutics. With a better range of donor systems this field will progress rapidly and new applications for H₂S therapeutics will be discovered.