Chlorotrimethylsilane−Nitrate Salts as Oxidants: Direct Oxidative Conversion of Thiols and Disulfides to Sulfonyl Chlorides

Promising anti-proliferative indolic benzenesulfonamides alter mechanisms with sulfonamide nitrogen substituents

Agents that cause apoptotic cell death by interfering with tubulin dynamics, such as vinblastine and paclitaxel, are an important class of chemotherapeutics. Unfortunately, these compounds are substrates for multidrug resistance (MDR) pumps, allowing cancer cells to gain resistance to these chemotherapeutics. The indolesulfonamide family of tubulin inhibitors are not excluded by MDR pumps and have a promising activity profile, although their high lipophilicity is a pharmacokinetic limitation for their clinical use. Here we present a new family of N-indolyl-3,4,5-trimethoxybenzenesulfonamide derivatives with modifications on the indole system at positions 1 and 3 and on the sulfonamide nitrogen. We synthesized and screened against HeLa cells 34 novel indolic benzenesulfonamides. The most potent derivatives (1.7-109 nM) were tested against a broad panel of cancer cell lines, which revealed that substituted benzenesulfonamides analogs had highest potency. Importantly, these compounds were only moderately toxic to non-tumorigenic cells, suggesting the presence of a therapeutic index. Consistent with known clinical anti-tubulin agents, these compounds arrested the cell cycle at G2/M phase. Mechanistically, they induced apoptosis via caspase 3/7 activation, which occurred during M arrest. The substituents on the sulfonamide nitrogen appeared to determine different mechanistic results and cell fates. These results suggest that the compounds act differently depending on the bridge substituents, thus making them very interesting as mechanistic probes as well as potential drugs for further development.

Copper-Catalyzed Vicinal Thiocyanosulfonylation of Alkenes and Alkynes

Efficient copper-catalyzed radical thiocyanosulfonylation of alkenes and alkynes with potassium thiocyanate and sodium phenylsulfinate is described. The reactions provide general and convenient methods toward the synthesis of β-thiocyanoalkyl sulfones and β-thiocyanoalkenyl sulfones, respectively, in satisfactory yields. Based on conducted mechanistic experiments, a mechanism involving oxidative generation of sulfonyl radicals and subsequent addition to alkenes followed by Cu-assisted thiocyanation is proposed. Moreover, the practicability of the reaction is successfully demonstrated by its successful application on a gram scale.

Preparation of Sulfonyl Chlorides by Oxidative Chlorination of Thiols and Disulfides using HNO3/HCl/O2 in a Flow Reactor

A continuous flow metal-free protocol for the synthesis of sulfonyl chlorides from thiols and disulfides in the presence of nitric acid, hydrochloric acid and oxygen was developed. The influence of the reaction parameters was investigated under batch and flow conditions. Online 19F NMR was successfully implemented to investigate different reaction conditions within a single experiment. The sulfonyl chlorides were isolated (mostly in 70-81 % yield) after performing a simple aqueous washing procedure. In particular, the protocol was successfully operated for >6 hours to convert diphenyl disulfide to its corresponding sulfonyl chloride, achieving a throughput of 3.7 g h-1. The environmental impact of the protocol was assessed and compared to an existing continuous flow protocol using 1,3-dichloro-5,5-dimethylhydantoin (DCH) as reagent. The process mass intensity (PMI) for the newly-developed flow protocol (15) compared favorably to the DCH flow process (20).

Synthetic Approaches to the New Drugs Approved During 2021

Each year, new drugs are introduced to the market, representing structures that have affinity for biological targets implicated in human diseases and conditions. These new chemical entities (NCEs), particularly small molecules and antibody-drug conjugates, provide insight into molecular recognition and serve as potential leads for the design of future medicines. This annual review is part of a continuing series highlighting the most likely process-scale synthetic approaches to 35 NCEs that were first approved anywhere in the world during 2021.

Synthesis of Sulfonyl Halides from Disulfides or Thiols Using Sodium Hypochlorite Pentahydrate (NaOCl·5H2O) Crystals

Synthesis of sulfonyl halides using sodium hypochlorite pentahydrate (NaOCl·5H2O) crystals was studied in detail, considering the reaction rate and yield of the desired product. NaOCl·5H2O reacted with disulfides or thiols in acetic acid to produce sulfonyl chlorides. The yields of the desired sulfonyl chlorides were enhanced when the reaction was performed in (trifluoromethyl)benzene under a CO2 atmosphere. The generation of hypochlorous acid (HOCl) was essential for both reactions. Similarly, sulfonyl bromides were prepared via the reaction of disulfides or thiols with sodium bromide and NaOCl·5H2O crystals in acetic acid owing to the generation of hypobromous acid (HOBr). However, the reaction could not proceed in (trifluoromethyl)benzene under a CO2 atmosphere because bromine was produced instead of HOBr.

Synthesis of [ 2 H 5 ]baricitinib via [ 2 H 5 ]ethanesulfonyl chloride

Baricitinib, typically applied as a treatment for rheumatoid arthritis, has recently attracted the attention of clinicians and researchers as a potential treatment for COVID‐19. Naturally, there has been a need for the preparation of the isotope‐labelled analogue of baricitinib to probe the pharmacokinetics of baricitinib in this new role. As such, we have developed a simple synthetic route to deuterated [²H₅]baricitinib, facilitating its formation over four steps and in a 29% overall yield based on starting [²H₅]ethanethiol (19% if we start with [²H₅]bromoethane instead). A critical component of the overall process involves the synthesis of [²H₅]ethanesulfonyl chloride, and we describe in detail the two routes that were explored to optimize this step.

A continuous flow investigation of sulfonyl chloride synthesis using N-chloroamides: optimization, kinetics and mechanism

We develop a continuous flow protocol for the synthesis of sulfonyl chlorides from disulfides and thiols, using 1,3-dichloro-5,5-dimethylhydantoin (DCH) as a dual-function reagent for oxidative chlorination.

Radical-mediated vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes

The addition of sulfonyl radicals to alkenes and alkynes is a valuable method for constructing useful highly functionalized sulfonyl compounds. The underexplored alkoxy- and fluorosulfonyl radicals are easily accessed by CF₃ radical addition to readily available allylsulfonic acid derivatives and then β-fragmentation. These substituted sulfonyl radicals add to aryl alkyl alkynes to give vinyl radicals that are trapped by trifluoromethyl transfer to provide tetra-substituted alkenes bearing the privileged alkoxy- or fluorosulfonyl group on one carbon and a trifluoromethyl group on the other. This process exhibits broad functional group compatibility and allows for the late-stage functionalization of drug molecules, demonstrating its potential in drug discovery and chemical biology.

An unprecedented method for vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes has been developed to afford useful alkenylsulfonate esters and alkenylsulfonyl fluorides.

Facile Synthesis of Sulfonyl Chlorides/Bromides from Sulfonyl Hydrazides

A simple and rapid method for efficient synthesis of sulfonyl chlorides/bromides from sulfonyl hydrazide with NXS (X = Cl or Br) and late-stage conversion to several other functional groups was described. A variety of nucleophiles could be engaged in this transformation, thus permitting the synthesis of complex sulfonamides and sulfonates. In most cases, these reactions are highly selective, simple, and clean, affording products at excellent yields.

One-Pot Synthesis of Pentafluorophenyl Sulfonic Esters via Copper-Catalyzed Reaction of Aryl Diazonium Salts, DABSO, and Pentafluorophenol

Pentafluorophenyl (PFP) sulfonic esters were synthesized via a copper-catalyzed one-pot multicomponent reaction of aryl diazonium tetrafluoroborate, DABSO (DABCO·(SO₂)₂), and pentafluorophenol. The reaction system provided the desired pentafluorophenyl sulfonic esters in good yields and exhibited excellent functional group tolerance. In addition, the generated PFP sulfonic esters were successfully applied in Sonogashira, Suzuki, Chan-Evans-Lam, and decarboxylative coupling reactions.

Practical copper-catalyzed chloronitration of alkenes with TMSCl and guanidine nitrate

A practical chloronitration of alkenes catalyzed by cheap copper sulfate pentahydrate to provide vic-chloronitro compounds in good to excellent yields was developed, and the resulting products could be transformed into diverse nitro compounds.

Thiourea dioxide as a source of sulfonyl groups: photoredox generation of sulfones and sulfonamides from heteroaryl/aryl halides

Thiourea dioxide as the source of sulfonyl groups for the efficient synthesis of heteroaryl sulfones and sulfonamides from heteroaryl halides under visible light irradiation is reported. This transformation proceeds smoothly via heteroaryl sulfinate intermediates, which can be trapped in situ by various electrophiles. A broad reaction scope is demonstrated, especially for the electron-deficient heteroaryl halides. Mechanistic studies show that the radical coupling of the heteroaryl radical and sulfur dioxide radical anion may be the key step during the reaction process, as supported by EPR spectroscopy and DFT calculations.

Aromatic Chlorosulfonylation by Photoredox Catalysis

Visible-light photoredox catalysis enables the efficient synthesis of arenesulfonyl chlorides from anilines. The new protocol involves the convenient in situ preparation of arenediazonium salts (from anilines) and the reactive gases SO₂ and HCl (from aqueous SOCl₂ ). The photocatalytic chlorosulfonylation operates at mild conditions (room temperature, acetonitrile/water) with low catalyst loading. Various functional groups are tolerated (e.g., halides, azides, nitro groups, CF₃ , SF₅ , esters, heteroarenes). Theoretical and experimental studies support a photoredox-catalysis mechanism.

Synthesis of 3-((arylsulfonyl)methyl)indolin-2-ones via insertion of sulfur dioxide using anilines as the aryl source

Facile assembly of 3-((arylsulfonyl)methyl)indolin-2-ones via insertion of sulfur dioxide starting from anilines, N-arylacrylamides and DABCO·(SO₂)₂ is realized.

Rethinking Cysteine Protective Groups: S-Alkylsulfonyl-l-Cysteines for Chemoselective Disulfide Formation

The ability to reversibly cross-link proteins and peptides grants the amino acid cysteine its unique role in nature as well as in peptide chemistry. We report a novel class of S-alkylsulfonyl-l-cysteines and N-carboxy anhydrides (NCA) thereof for peptide synthesis. The S-alkylsulfonyl group is stable against amines and thus enables its use under Fmoc chemistry conditions and the controlled polymerization of the corresponding NCAs yielding well-defined homo- as well as block co-polymers. Yet, thiols react immediately with the S-alkylsulfonyl group forming asymmetric disulfides. Therefore, we introduce the first reactive cysteine derivative for efficient and chemoselective disulfide formation in synthetic polypeptides, thus bypassing additional protective group cleavage steps.

A copper(i)-catalyzed three-component reaction of triethoxysilanes, sulfur dioxide, and alkyl halides

A copper(i)-catalyzed three-component reaction of triethoxysilanes, DABCO·(SO₂)₂, and alkyl halides is reported. This transformation provides a facile route to sulfones under ligand-free conditions catalyzed by copper(i) oxide. The insertion of sulfur dioxide is efficient, and both triethoxyarylsilanes and triethoxyalkylsilanes are practicable during the coupling process.

A general route to sulfones via insertion of sulfur dioxide promoted by cobalt oxide

A cobalt-promoted coupling reaction of triethoxysilanes, sulfur dioxide, and electrophiles is developed. Different electrophilic partners including alkyl bromides, iodonium salts, and electron-poor (hetero)aryl chlorides work well under the standard conditions.

Synthesis of diverse pyrazole-4-sulfonyl chlorides starting from 2-(benzylthio)malonaldehyde

A series of pyrazole-4-sulfonyl chlorides was obtained by a convenient 2-step method starting from synthetically available 2-(benzylthio)malonaldehyde. The method can be applied for the effective multi-gram synthesis of diverse pyrazole-containing sulfonyl chlorides which are mostly not available by other methods.

A four-component reaction of aryldiazonium tetrafluoroborates, sulfur dioxide, 1,2-dibromoethane, and hydrazines

A four-component reaction of aryldiazonium tetrafluoroborates, sulfur dioxide, 1,2-dibromoethane, and hydrazines under metal-free conditions is described, leading to 2-arylsulfonyl hydrazones. This transformation proceeds via insertion of sulfur dioxide with good functional group tolerance.

Sulfinate derivatives: dual and versatile partners in organic synthesis

Recent advances in the preparation and synthetic uses of sulfinic acids and their derivatives are highlighted in this review. They are used as versatile partners in sulfonylative and desulfitative reactions.