Serendipitous Discovery of Photolytic Thiosulfoxide Formation: Application for Visible-Light-Inducible Manipulation of Supersulfide Level in Biological Systems

Tools to enable spatiotemporally controlled upregulation of supersulfides, which are highly reactive, unstable sulfur species, are needed to study the pathophysiological roles of post-translational protein modification with catenated sulfur atoms. Here, we set out to design N,N-diethylaminocoumarin (DEAC)-based visible-light-responsive N-acetylcysteine persulfide donors (NAC-SS-DEAC), and serendipitously found that upon visible light irradiation, they donate a sulfane sulfur (S0) atom to nucleophiles, including thiols and cyanate. Light-assisted tautomerization of the disulfide moiety of NAC-SS-DEAC to transiently afford unstable thiosulfoxide plays a key role in the S0 donation. We show that this reaction can be utilized to achieve visible-light-inducible manipulation of supersulfide levels in living cells.