Caged cysteine and thiophosphoryl peptides.

Photoreleasable molecules are important in studies of various biological phenomena, especially cell signaling. Here we report a generally applicable approach for 'caging' unprotected cysteine-containing or thiophosphorylated peptides in aqueous solution with 2-nitrobenzyl bromides. Photolysis of the caged peptides was achieved with near UV light with product quantum efficiencies of 0.064-0.62 under conditions that produced no damage to attendant biological macromolecules. Yields of uncaged peptides were 55-70%. Selective reaction of the side-chain of thiophosphoryl serine with 2-nitrobenzyl bromide in the presence of a cysteinyl residue was also demonstrated, establishing a means for functional caging of various signal transduction proteins without prior modification or mutagenesis.