C–H Fluoroalkylsulfinylation/Intramolecular Rearrangement for Precise Synthesis of Fluoroalkyl Sulfoxides

Discovery of a Distinctive Reagent for Divergent Arene Trifluoromethylsulfinylation

Simple and direct arene trifluoromethylsulfinylation is highly desirable in drug design but remains a major challenge. Herein, we report a modular, mild, innate C-H trifluoromethylsulfinylation of a wide variety of arenes via a distinctive trifluoromethylsulfinylating reagent N-hydroxyphthalimide-O-trifluoromethanesulfinate following divergent efficient pathways. This trifluoromethylsulfinylation can be conducted in a redox-neutral manner at room temperature with light-, metal-, and photocatalyst-free mild conditions. Mechanistic studies and density functional theory (DFT) calculations revealed that the success of this approach hinges upon the design of an activated trifluoromethanesulfite ester that proceeds via homolytic cleavage with a very low bond dissociation energy to generate a dummy aminoxyl radical (PINO) and active CF3S(O) radical, which could accidentally be transformed into a trifluoromethanesulfonic anhydride, CF3S(O)OS(O)CF3, for the transfer of the S(O)CF3 group into an exemplary set of strong EDG-substituted arenes. DFT computation corroborates that this novel reagent can be activated by TfOH via heterolytic cleavage to produce highly active CF3S(O)OTf, which is responsible for electrophilic trifluoromethylsulfinylation of the challenging weak EDG-substituted arene substrates through an electrophilic addition-elimination mechanism. Such C-H functionalization using N-hydroxyphthalimide-O-trifluoromethanesulfinate affords an innovative strategy and marked improvement over functionalization with previously developed reagents. Notably, simple and mild conditions, broad reactivities, good functional group compatibility, divergent reaction modes (homolysis and heterolysis), as well as late-stage trifluoromethylsulfinylation (LST) of complex biologically active molecules in these reactions underline the great potential of N-hydroxyphthalimide-O-trifluoromethanesulfinate for the preparation of functionalized drug-like molecules.

Arylsulfonothioates: Thiol-Activated Donors of Hydropersulfides which are Excreted to Maintain Cellular Redox Homeostasis or Retained to Counter Oxidative Stress

Despite their biological significance, the study of hydropersulfides (RSSH) is often limited due to their inherent instability. Here, we introduce arylsulfonothioates as thiol-activated RSSH donors and provide insight into cellular reactive sulfur species homeostasis. These precursors persulfidate physiologically relevant thiols (RSH) to form the corresponding RSSH. Real-time monitoring of hydrogen sulfide (H2S) generation via membrane inlet mass spectrometry (MIMS) was employed to follow RSSH production, revealing that electron-donating aryl substituents marginally slow RSSH release rates, whereas electron-withdrawing substituents slightly accelerate release. Furthermore, arylsulfonothioates with strong electron-withdrawing substituents offer superior protection against doxorubicin (DOX)-induced cardiotoxicity. Experiments using H9c2 cardiomyocytes affirmed the cell-permeability of arylsulfonothioates and their ability to increase intracellular RSSH levels and protein persulfidation levels. Notably, we observe the excretion of RSSH into the extracellular medium. Further investigations revealed the involvement of the cystine/glutamate antiporter SLC7A11, as cotreatment with its inhibitor, sulfasalazine, significantly reduce extracellular RSSH release. H9c2 cells exhibit tolerance to arylsulfonothioate 1g with an electron-withdrawing 4-cyano group at 1 mM; however, inhibition of the cystine antiporter results in a minor decrease in cell viability. Under oxidative stress conditions induced by DOX or hydrogen peroxide (H2O2), cotreatment with 1g diminishes the excretion of RSSH and confers cytoprotection against DOX or H2O2-mediated toxicity. Our findings show adaptive cellular responses to RSSH levels, demonstrating excretion under elevated conditions to maintain redox homeostasis and intracellular retention as a protective response during oxidative stress.

Clickable tryptophan modification for late-stage diversification of native peptides

As the least abundant residue in proteins, tryptophan widely exists in peptide drugs and bioactive natural products and contributes to drug-target interactions in multiple ways. We report here a clickable tryptophan modification for late-stage diversification of native peptides, via catalyst-free C2-sulfenylation with 8-quinoline thiosulfonate reagents in trifluoroacetic acid (TFA). A wide range of groups including trifluoromethylthio (SCF3), difluoromethylthio (SCF2H), (ethoxycarbonyl)difluoromethylthio (SCF2CO2Et), alkylthio, and arylthio were readily incorporated. The rapid reaction kinetics of Trp modification and full tolerance with other 19 proteinogenic amino acids, as well as the super dissolving capability of TFA, render this method suitable for all kinds of Trp-containing peptides without limitations from sequences, hydrophobicity, and aggregation propensity. The late-stage modification of 15 therapeutic peptides (1.0 to 7.6 kilodaltons) and the improved bioactivity and serum stability of SCF3- and SCF2H-modified melittin analogs illustrated the effectiveness of this method and its potential in pharmacokinetic property improvement.

Mechanistic Study on Selenium- and Sulfur-Mediated Isomerization of Hydroxamic Acids

An in-depth computational study reveals the intriguing mechanism of the recently reported isomerization of hydroxamic acids into para-aminophenols catalyzed by phenylselenyl bromide under mild conditions. The computations not only align with the reported experimental data, effectively explaining observed phenomena such as para-selectivity but also shed light on crucial aspects of the reaction mechanism that establish limitations on the scope of the studied rearrangement. Additionally, a joint theoretical/experimental study was performed to examine the potency of the phenylsulfenyl bromide to mediate the reaction under the same conditions.

β-Trifluorosulfinylesters: tuneable reagents for switchable trifluoromethylsulfinylation and C–H trifluoromethylthiolation

β-Trifluorosulfinylesters, a family of novel reagents from commercially available starting materials for direct trifluoromethylthiolation and trifluoromethylsulfinylation were developed.

Copper-catalyzed [1,3]-nitrogen rearrangement of O-aryl ketoximes via oxidative addition of N–O bond in inverse electron flow†

The [1,3]-nitrogen rearrangement reactions of O-aryl ketoximes were promoted by N-heterocyclic carbene (NHC)-copper catalysts and BF₃·OEt₂ as an additive, affording ortho-aminophenol derivatives in good yields. The reaction of substrates with electron-withdrawing substituents on the phenol moiety are accelerated by adding silver salt and modifying the substituent at the nitrogen atom. Density functional theory calculations suggest that the rate-determining step of this reaction is the oxidative addition of the N–O bond of the substrate to the copper catalyst. The negative ρ values of the substituent at both the oxime carbon and phenoxy group indicate that the donation of electrons by the oxygen and nitrogen atoms accelerates the oxidative addition.

[1,3]-Nitrogen rearrangement reactions of O-aryl ketoximes was catalytically promoted by IPrCuBr and BF₃·OEt₂. The oxidative addition of the N–O bond to the Cu catalyst is accelerated by donation of electrons from both nitrogen and oxygen atoms.

“Thiol-free synthesized” and sustainable thiolating synthons for nickel-catalyzed reductive assembly of sulfides with high efficiency

Unsymmetrical sulfides are widely found in the pharmaceutical industry, organic synthesis, and materials science.