Transpersulfidation or H2S Release? Understanding the Landscape of Persulfide Chemical Biology

Persulfides (RSSH) are biologically important reactive sulfur species that are endogenously produced, protect key cysteine residues from irreversible oxidation, and are important intermediates during different enzymatic processes. Although persul-fides are stronger nucleophiles than their thiol counterparts, persulfides can also act as electrophiles in their neutral, proto-nated form in specific environments. Moreover, persulfides are electrophilic at both sulfur atoms, and reaction with a thiolate can lead to either H2S release with disulfide formation or alternatively result in transpersulfidation. Despite the broad ac-ceptance of these reaction pathways, the specific properties that control whether persulfides react through the H2S releasing or transpersulfidation pathway remains elusive. Herein, we use a combined computational and experimental approach to directly investigate the reactivity between persulfides and thiols to answer these questions. Using DFT calculations, we demonstrate that increasing steric bulk or electron withdrawal near the persulfide can shunt persulfide reactivity through the transpersulfidation pathway. Building from these insights, we use a persulfide donor and TME-IAM trapping agent to experi-mentally monitor and measure transpersulfidation from a bulky penicillamine-based persulfide to a cysteine-based thiol, which to the best of our knowledge is the first direct observation of transpersulfidation between low molecular weight spe-cies. Taken together, these combined approaches highlight how the properties of persulfides are directly impacted by local environments, which has significant impacts in understanding the complex chemical biology of these reactive species.