p-Hydroxyphenacyl bromide as photoremoveable thiol label: a potential phototrigger for thiol-containing biomolecules

p-Hydroxyphenacyl bromide is described as a photoremovable thiol protecting group on three biomolecules containing a free thiol group. The protecting group is efficiently incorporated by chemical coupling to the biomolecule in an ethanol–buffer mixture. The photofragmentations (λ=312 nm) were analyzed by UV, HPLC and MS methods, yielding over 70% of the free biomolecules. The concomitant formation of p-hydroxyphenylacetic thioesters derived from the corresponding thiols, as a sulfur-containing side-product, should not hinder the use of this protecting group for the caging of thiol-containing biomolecules.