Cyclic Thiosulfinates and Cyclic Disulfides Selectively Cross-Link Thiols While Avoiding Modification of Lone Thiols

J Am Chem Soc. 2018 Jun 20;140(24):7377-7380. doi: 10.1021/jacs.8b01136. Epub 2018 Jun 11.


This work addresses the need for chemical tools that can selectively form cross-links. Contemporary thiol-selective cross-linkers, for example, modify all accessible thiols, but only form cross-links between a subset. The resulting terminal "dead-end" modifications of lone thiols are toxic, confound cross-linking-based studies of macromolecular structure, and are an undesired, and currently unavoidable, byproduct in polymer synthesis. Using the thiol pair of Cu/Zn-superoxide dismutase (SOD1), we demonstrated that cyclic disulfides, including the drug/nutritional supplement lipoic acid, efficiently cross-linked thiol pairs but avoided dead-end modifications. Thiolate-directed nucleophilic attack upon the cyclic disulfide resulted in thiol-disulfide exchange and ring cleavage. The resulting disulfide-tethered terminal thiolate moiety either directed the reverse reaction, releasing the cyclic disulfide, or participated in oxidative disulfide (cross-link) formation. We hypothesized, and confirmed with density functional theory (DFT) calculations, that mono- S-oxo derivatives of cyclic disulfides formed a terminal sulfenic acid upon ring cleavage that obviated the previously rate-limiting step, thiol oxidation, and accelerated the new rate-determining step, ring cleavage. Our calculations suggest that the origin of accelerated ring cleavage is improved frontier molecular orbital overlap in the thiolate-disulfide interchange transition. Five- to seven-membered cyclic thiosulfinates were synthesized and efficiently cross-linked up to 104-fold faster than their cyclic disulfide precursors; functioned in the presence of biological concentrations of glutathione; and acted as cell-permeable, potent, tolerable, intracellular cross-linkers. This new class of thiol cross-linkers exhibited click-like attributes including, high yields driven by the enthalpies of disulfide and water formation, orthogonality with common functional groups, water-compatibility, and ring strain-dependence.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Cross-Linking Reagents / chemical synthesis
  • Cross-Linking Reagents / chemistry*
  • Disulfides / chemical synthesis
  • Disulfides / chemistry*
  • Humans
  • Models, Chemical
  • Oxidation-Reduction
  • Quantum Theory
  • Sulfenic Acids / chemistry
  • Sulfhydryl Compounds / chemistry*
  • Sulfinic Acids / chemical synthesis
  • Sulfinic Acids / chemistry*
  • Superoxide Dismutase-1 / chemistry*


  • Cross-Linking Reagents
  • Disulfides
  • SOD1 protein, human
  • Sulfenic Acids
  • Sulfhydryl Compounds
  • Sulfinic Acids
  • thiosulfinic acids
  • Superoxide Dismutase-1