Sustainable Electrocatalytic Oxidant-Free Syntheses of Thiosulfonates from Thiols

Electrochemical promoted three-component reaction to unsymmetric thiosulfonates

Compounds comprising S-S bonds serve as significant pharmacological scaffolds in medicinal chemistry and natural products. We have devised an efficient electrochemical method for the construction of asymmetric disulfide bonds, leading to the synthesis of unsymmetric thiosulfonates. Compared with existing synthesis methods, our work not only avoids the use of metals and oxidants, but also realizes the operation of a one-pot three-component method, which makes this strategy extremely attractive.

I2-Cs2CO3 Mediated Intramolecular C2-Amination and Oxidative Rearrangement Cascade of C-3 Phenylthio Indoles: A Route to Synthesize Thiosulfonate-Embedded 2-Iminoindolin-3-ones

An efficient, transition-metal-free protocol employing I2/Cs2CO3 for the synthesis of thiosulfonate containing 2-iminoindolin-3-ones motifs has been developed from C-3 phenylthio indoles. The reaction proceeded through intramolecular cyclization involving C-N bond formation, leading to the formation of indole-fused benzothiazines as a key intermediate. Remarkably, Cs2CO3 played a crucial role in the reaction as an oxygen source, enabling oxidative rearrangement with [1,4]-sulfonyl migration to furnish the final products with the formation of multiple functional groups such as C═O, C═N, and S-SO2.

Catalyst-Free Synthesis of Thiosulfonates and 3-Sulfenylindoles from Sodium Sulfinates in Water

This paper presents a green and efficient aqueous-phase method for the synthesis of thiosulfonates, which has the benefits of no need for catalysts or redox reagents and a short reaction time, providing a method with great economic value for synthesizing thiosulfonates. Furthermore, 3-Sulfenylindoles can be easily synthesized using this method, which expands the potential applications of this reaction.

C-2 Thiophenyl Tryptophan Trimers Inhibit Cellular Entry of SARS-CoV-2 through Interaction with the Viral Spike (S) Protein

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19, by infecting cells via the interaction of its spike protein (S) with the primary cell receptor angiotensin-converting enzyme (ACE2). To search for inhibitors of this key step in viral infection, we screened an in-house library of multivalent tryptophan derivatives. Using VSV-S pseudoparticles, we identified compound 2 as a potent entry inhibitor lacking cellular toxicity. Chemical optimization of 2 rendered compounds 63 and 65, which also potently inhibited genuine SARS-CoV-2 cell entry. Thermofluor and microscale thermophoresis studies revealed their binding to S and to its isolated receptor binding domain (RBD), interfering with the interaction with ACE2. High-resolution cryoelectron microscopy structure of S, free or bound to 2, shed light on cell entry inhibition mechanisms by these compounds. Overall, this work identifies and characterizes a new class of SARS-CoV-2 entry inhibitors with clear potential for preventing and/or fighting COVID-19.

Synthesis of Unsymmetric Thiosulfonates Starting from N-Substituted O-Thiocarbamates: Easy Access to the S-SO2 Bond

Using phenyliodine diacetate as an oxidant and nickel acetate as a promoter, a wide range of unsymmetric thiosulfonates could be furnished easily in moderate to excellent yields starting from N-substituted O-thiocarbamates and sodium sulfinates. This protocol features mild conditions, short reaction times, and high atomic utilization, which can provide an alternative method for the synthesis of unsymmetric thiosulfonates. In addition, the reaction could be scaled up on a gram scale, showing potential application value in industry.

Smart Flow Electrosynthesis and Application of Organodisulfides in Redox Flow Batteries

Electrochemical techniques have been recognized as an environmentally friendly and sustainable synthetic way to form organodisulfides. However, searching for optimum conditions which suffers from time/material-consuming caused by the uncertainty of reactant consumption has hindered its rapid and large-scale development. Inspired by advanced nonaqueous redox flow batteries (NARFBs) technology, it is proposed a smart flow electrosynthesis (SFE) method of organodisulfides that the voltage curve of NARFBs can be utilized as a precise indicator to reflect the desired information about reactants and distinguish the end point of reaction automatically. This electrochemical method also exhibits certain universality and scalability. Additionally, organodisulfides generated in electrolytes can be used as active species for NARFBs without further purification, and their electrochemical properties are easily adjusted by changing raw materials, which effectively alleviate the waste in complex synthesis steps for optimizing and designing active materials separately. An organodisulfide dervied from isopropyl alcohol and carbon disulfide shows excellent cycling life (1000 cycles) with low capacity fade rate (0.024% per cycle). Taking advantages of the inherent NARFBs, this work not only proves a SFE strategy, but also supplies a green and low-cost molecular engineering scheme for designing electroactive materials for energy storage.

Direct conversion of sulfinamides to thiosulfonates without the use of additional redox agents under metal-free conditions

Direct conversion of sulfinamides to thiosulfonates is described. Without the use of additional redox agents, the reaction proceeds smoothly in the presence of TFA under metal-free conditions. This protocol possesses many advantages such as odourless and stable starting materials, broad substrate scope, selective synthesis, and mild reaction conditions.

Oxidative cross-coupling of thiols for S-X (X = S, N, O, P, and C) bond formation: mechanistic aspects

This review focuses on the reactive intermediates (disulfides, sulfenyl halides, thiyl radicals, sulfenium cations, and metal-organosulfur species) and the mechanisms of the recently reported oxidative couplings of thiols. These intermediates are generated by chemical oxidants, transition metal catalysts, electrochemistry, and photochemistry. Chemical oxidant-mediated reactions involve radical, halogenated, or cationic intermediates, or disulfides. Transition metal-catalyzed mechanisms proposed various metal-organosulfur intermediates to elucidate the reactivity and selectivity of metal catalysts. In electro- and photooxidation, direct oxidation/reduction mechanisms of reactants at the electrode or indirect oxidation/reduction of reactants in the presence of redox catalysts have been reported. The following sections are based on the products, thiosulfonates (S-S bond), sulfenamides, sulfinamides, and sulfonamides (S-N bond), sulfinates (S-O bond), thiophosphine oxides and thiophosphates (S-P bond), and sulfides, sulfoxides, and sulfones (S-C bond) and discuss the reaction mechanisms and the above-mentioned key intermediates for product formation. The contents of this review will provide helpful information, guiding the choice of oxidative coupling conditions for the synthesis of various organosulfur compounds with high yields and selectivity.

Recent Advances in the Electrochemical Synthesis of Organosulfur Compounds

Organosulfur compounds are being widely used in medicinal chemistry, as well as in organic transformations and in synthetic applications. Because of their interest in many areas, the development of sustainable and green synthetic methods to access various organosulfur compounds has a high influence on the chemistry community. Electroorganic synthesis has become a very valuable methodology for the synthesis of organosulfur compounds during the last decade. The use of electrochemical technology offers a green, sustainable and safe alternative to prepare and modify such compounds. This review summarises recent developments in the preparation of organosulfur compounds such as sulfoxides, sulfones, sulfinic esters, sulfonamides, thiosulfonates, sulfonyl fluorides and sulfoximines under electrochemical reaction conditions.

Diaryl disulfides and thiosulfonates as combretastatin A-4 analogues: Synthesis, cytotoxicity and antitubulin activity

Diaryl disulfides and diaryl thiosulfonates were synthesized with the two phenyl rings of all compounds bearing identical halide substituents. Because of structural similarity to the potent antimitotic natural product combretastatin A-4 (CA-4), the compounds were examined for inhibition of tubulin polymerization, and the thiosulfonates were more active than the disulfides. The nine thiosulfonates had IC50 values ranging from 1.2 to 9.1 µM, as compared with 1.3 µM obtained with CA-4. The compounds thus ranged from equipotent with CA-4 to 7-fold less active. The nine disulfides had IC50 values ranging from 1.2 to 5.1 µM, as compared with 0.54 µM obtained with CA-4. The compounds thus ranged from less than half as active as CA-4 to over 9-fold less active. The most active members of each group, 2 g and 3c, in the assembly assay were modeled into the colchicine site. Compound 3c had significant hydrophobic interactions with β-tubulin residues CYS 241 and ALA 250, and its thiosulfonate bridge made a hydrogen bond with β-tubulin residue ASN 258. Compound 2 g had hydrophobic interactions with β-tubulin residues ALA 250, CYS 241 and ALA 254, but there was no significant interaction of the disulfide bridge with tubulin.

An unexpected reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea under photoinduced conditions

A photoinduced synthesis of S-aryl thiosulfonates through a three-component reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea is achieved. In this transformation, a radical coupling pathway is proposed.