Stability of\na Multiresponsive Sulfonium Vinyl Sulfide\nLinker toward Nucleophilic/Radical Thiols, Reactive Nitrogen Species,\nand in Cells under Pro-inflammatory Stimulation

Chemical linkages that respond to biological stimuli\nare important\nfor many pharmaceutical and biotechnological applications, making\nit relevant to explore new variants with different responsivity profiles.\nThis work explores the responsiveness of a TAT peptide-based sulfonium\nvinyl sulfide probe that responds to nucleophilic thiols, radical\nthiol species (RTS), and reactive nitrogen species (RNS). Under model\nconditions, response to nucleophilic thiols was very slow (hours/days),\nthough fast with down to molar equivalents of either RTS or RNS (minutes).\nThese reactions led to the traceless release of a methionine-containing\npeptide in the first two cases and to a hydroxy nitration adduct in\nthe third case. Despite the sensitive nature of the probe, it remained\nstable for at least ∼2 h in the presence of cells during TAT-mediated\ntrafficking, even under pro-inflammatory stimulation. The thiol-responsiveness\nis intermediate to that observed for disulfide linkers and conventional\ncysteine–maleimide linkers, presenting opportunities for biotechnological\napplications.