Discovery of Fluorogenic Diarylsydnone-Alkene Photoligation: Conversion of ortho-Dual-Twisted Diarylsydnones into Planar Pyrazolines

A small library of diarylsydnones (DASyds) was constructed based on aryl-pairing combinations and subjected to click reaction toward alkenes under photo-irradiation with high efficiency. We were able to demonstrate the utility of DASyds for highly fluorescent turn-on ligation targeting the trans-cyclooct-4-en-l-ol moieties on protein.