Uncaging carbon disulfide. Delivery platforms for potential pharmacological applications: a mechanistic approach

A benzimidazole-based Cu(II) complex catalyzed site-selective C-H sulfenylation of imidazo-[1,2-a]pyridines using CS2 as a sulfur source

A new benzimidazole-based Cu(II) complex catalyzed site-selective sulfenylation of imidazo[1,2-a]pyridines with benzyl/alkyl/allyl bromides and CS2 at 100 °C in DMF : H2O is reported. The present methodology has been developed for the synthesis of 3-sulfenyl imidazo[1,2-a]pyridines in good yields with a broad substrate scope. In this protocol, CS2, commonly known as a non-polar small molecule bioregulator (SMB), is converted to valuable sulfenylated imidazo[1,2-a]pyridine derivatives. In addition, theoretical investigations along with experimental evidence unfold the insights into the probable mechanistic pathway of site-selective sulfenylation from S,S-dibenzyltrithiocarbonate, which is particularly formed as an intermediate during the reaction.

Bioorthogonal Delivery of Carbon Disulfide in Living Cells

Carbon disulfide (CS2) is an environmental contaminant, which is deadly hazardous to the workers under chronic or acute exposure. However, the toxicity mechanisms of CS2 are still unclear due to the scarcity of biocompatible donors, which can release CS2 in cells. Here we developed the first bioorthogonal CS2 delivery system based on the "click-and-release" reactions between mesoionic 1,3-thiazolium-5-thiolates (TATs) and strained cyclooctyne exo-BCN-OH. We successfully realized intracellular CS2 release and investigated the causes of CS2-induced hepatotoxicity, including oxidative stress, proteotoxic stress and copper-dependent cell death. It is found that CS2 can be copper vehicles bypassing copper transporters after reacting with nucleophiles in cytoplasm, and extra copper supplementation will exacerbate the loss of homeostasis of cells and ultimately cell death. These findings inspired us to explore the anticancer activity of CS2 in combination with copper by introducing a copper chelating group in our CS2 delivery system.

Synergistic Activation of Nitrite and Thiocarbonyl Compounds Affords NO and Sulfane Sulfur via (Per)thionitrite (SNO- /SSNO- )

(Per)thionitrite (SNO- /SSNO- ) intermediates play vital roles in modulating nitric oxide (NO) and hydrogen sulfide (H2 S) dependent bio-signalling processes. Whilst the previous preparations of such intermediates involved reactive H2 S/HS- or sulfane sulfur (S0 ) species, the present report reveals that relatively stable thiocarbonyl compounds (such as carbon disulfide (CS2 ), thiocarbamate, thioacetic acid, and thioacetate) react with nitrite anion to yield SNO- /SSNO- . For instance, the reaction of CS2 and nitrite anion (NO2 - ) under ambient condition affords CO2 and SNO- /SSNO- . A detailed investigation involving UV/Vis, FTIR, HRMS, and multinuclear NMR studies confirm the formation of SNO- /SSNO- , which are proposed to form through an initial nucleophilic attack by nitrite anion followed by a transnitrosation step. Notably, reactions of CS2 and nitrite in the presence of thiol RSH show the formation of organic polysulfides R-Sn -R, thereby illustrating that the thiocarbonyls are capable of influencing the pool of bioavailable sulfane sulfurs. Furthermore, the availability of both NO2 - and thiocarbonyl motifs in the biological context hints at their synergistic metal-free activations leading to the generation of NO gas and various reactive sulfur species via SNO- /SSNO- .

Diaryl dithiocarbamates: synthesis, oxidation to thiuram disulfides, Co(III) complexes [Co(S2CNAr2)3] and their use as single source precursors to CoS2

Air and moisture stable diaryl dithiocarbamate salts, Ar₂NCS₂Li, result from addition of CS₂ to Ar₂NLi, the latter being formed upon deprotonation of diarylamines by ⁿBuLi. Oxidation with K₃[Fe(CN)₆] affords the analogous thiuram disulfides, (Ar₂NCS₂)₂, two examples of which (Ar = p-C₆H₄X; X = Me, OMe) have been crystallographically characterised. The interconversion of dithiocarbamate and thiuram disulfides has also been probed electrochemically and compared with that established for the widely-utilised diethyl system. While oxidation reactions are generally clean and high yielding, for Ph(2-naphthyl)NCS₂Li an ortho-cyclisation product, 3-phenylnaphtho[2,1-d]thiazole-2(3H)-thione, is also formed, resulting from a competitive intramolecular free-radical cyclisation. To demonstrate the coordinating ability of diaryl dithiocarbamates, a small series of Co(III) complexes have been prepared, with two examples, [Co{S₂CN(p-tolyl)₂}₃] and [Co{S₂CNPh(m-tolyl)}₃] being crystallographically characterised. Solvothermal decomposition of [Co{S₂CN(p-tolyl)₂}₃] in oleylamine generates phase pure CoS₂ nanospheres in an unexpected phase-selective manner.

Prodrugs of Persulfides, Sulfur Dioxide, and Carbon Disulfide: Important Tools for Studying Sulfur Signaling at Various Oxidation States

Significance: Bioactive sulfur species such as hydrogen sulfide (H₂S), persulfide species (R-S_nSH, n ≥ 1), hydrogen polysulfide (H₂S_n, n ≥ 2), sulfur dioxide (SO₂), and carbon disulfide (CS₂) participate in various physiological and/or pathological pathways such as vasodilation, apoptosis, inflammation, and energy metabolism regulation. The oxidation state of the individual sulfur species endows them unique biological activities. Recent Advances: There have been great strides made in achieving molecular understanding of the sulfur-signaling processes. Critical Issues: The development of various chemical tools that deliver reactive sulfur species in a controllable manner has played an important role in understanding the different roles of various sulfur species. In this review, we focus on three types of sulfur species, including persulfide, SO₂, and CS₂. Starting with a brief introduction of their physiological functions, we will then assess the various drug delivery strategies to generate persulfide species, SO₂, and CS₂ as research tools and potentially as therapeutic agents. Future Directions: Development of donors of various sulfur species that respond to distinct stimulus is critical for this field. Another key to the long-term success of this field is the identification of an area of unmet medical need that can be addressed with these sulfur species.

Investigations into the carbonic anhydrase inhibition of COS-releasing donor core motifs

Carbonyl sulfide (COS) releasing scaffolds are gaining popularity as hydrogen sulfide (H₂S) donors through exploitation of the carbonic anhydrase (CA)-mediated hydrolysis of COS to H₂S. The majority of compounds in this emerging class of donors undergo triggerable decomposition (often referred to as self-immolation) to release COS, and a handful of different COS-releasing structures have been reported. One benefit of this donation strategy is that numerous caged COS-containing core motifs are possible and are poised for development into self-immolative COS/H₂S donors. Because the intermediate release of COS en route to H₂S donation requires CA, it is important that the COS donor motifs do not inhibit CA directly. In this work, we investigate the cytotoxicity and CA inhibition properties of different caged COS donor cores, as well as caged CO₂ and CS₂ motifs and non-self-immolative control compounds. None of the compounds investigated exhibited significant cytotoxicity or enhanced cell proliferation at concentrations up to 100 μM in A549 cells, but we identified four core structures that function as CA inhibitors, thus providing a roadmap for the future development of self-immolative COS/H₂S donor motifs.

Kinetic Insights into Hydrogen Sulfide Delivery from Caged-Carbonyl Sulfide Isomeric Donor Platforms

Hydrogen sulfide (H2S) is a biologically important small gaseous molecule that exhibits promising protective effects against a variety of physiological and pathological processes. To investigate the expanding roles of H2S in biology, researchers often use H2S donors to mimic enzymatic H2S synthesis or to provide increased H2S levels under specific circumstances. Aligned with the need for new broad and easily modifiable platforms for H2S donation, we report here the preparation and H2S release kinetics from a series of isomeric caged-carbonyl sulfide (COS) compounds, including thiocarbamates, thiocarbonates, and dithiocarbonates, all of which release COS that is quickly converted to H2S by the ubiquitous enzyme carbonic anhydrase. Each donor is designed to release COS/H2S after the activation of a trigger by activation by hydrogen peroxide (H2O2). In addition to providing a broad palette of new, H2O2-responsive donor motifs, we also demonstrate the H2O2 dose-dependent COS/H2S release from each donor core, establish that release profiles can be modified by structural modifications, and compare COS/H2S release rates and efficiencies from isomeric core structures. Supporting our experimental investigations, we also provide computational insights into the potential energy surfaces for COS/H2S release from each platform. In addition, we also report initial investigations into dithiocarbamate cores, which release H2S directly upon H2O2-mediated activation. As a whole, the insights on COS/H2S release gained from these investigations provide a foundation for the expansion of the emerging area of responsive COS/H2S donor systems.

Biological Thiols and Carbon Disulfide: The Formation and Decay of Trithiocarbonates under Physiologically Relevant Conditions

Carbon disulfide is an environmental toxin, but there are suggestions in the literature that it may also have regulatory and/or therapeutic roles in mammalian physiology. Thiols or thiolates would be likely biological targets for an electrophile, such as CS₂, and in this context, the present study examines the dynamics of CS₂ reactions with various thiols (RSH) in physiologically relevant near-neutral aqueous media to form the respective trithiocarbonate anions (TTC^-, also known as "thioxanthate anions"). The rates of TTC^- formation are markedly pH-dependent, indicating that the reactive form of RSH is the conjugate base RS^-. The rates of the reverse reaction, that is, decay of TTC^- anions to release CS₂, is pH-independent, with rates roughly antiparallel to the basicities of the RS^- conjugate base. These observations indicate that the rate-limiting step of decay is simple CS₂ dissociation from RS^-, and according to microscopic reversibility, the transition state of TTC^- formation would be simple addition of the RS^- nucleophile to the CS₂ electrophile. At pH 7.4 and 37 °C, cysteine and glutathione react with CS₂ at a similar rate but the trithiocarbonate product undergoes a slow cyclization to give 2-thiothiazolidine-4-carboxylic acid. The potential biological relevance of these observations is briefly discussed.