An efficient method has been developed for the chemoselective cysteine modification of unprotected peptides and proteins in aqueous media through the formation of a vinyl sulfide linkage by using electron-deficient alkynes, including alkynoic amides, esters and alkynones. The terminal alkynone-modified peptides could be converted back into the unmodified peptides (81% isolated yield) by adding thiols under mild conditions. The usefulness of this thiol-assisted cleavage of the vinyl sulfide linkage in peptides has been exemplified by the enrichment of a cysteine-containing peptide (71% recovery) from a mixture of cysteine-containing and non-cysteine-containing peptides.
"Turn-on" FRET-based luminescent probes containing iridium(III) complexes for the detection of Cys and Hcy have been designed and synthesized. The relationship between the steric bulk of the probe and the corresponding emission intensity enhancement towards detection of Cys and Hcy has been studied.
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