Wavelength-selective photoactivatable protecting groups for thiols.

We developed and characterized efficient, remarkably water-soluble photolabile protecting groups for thiols based on 2-nitrobenzyl and (coumarin-4-yl)methyl chromophores, among them two new ones. The protecting groups allow, due to their different absorption maxima, wavelength-selective photocleavage of binary mixtures of cysteine derivatives protected at the thiol function with various photolabile protecting groups by irradiation with light. The concept was also functional with the two different S-protected cysteine residues in derivatives of the model peptide resact. Selective photolysis could be achieved for the peptides Ac(0)-Cys(1)(BCMACMOC),Cys(8)(7,8BCMCMOC)-resact and Ac(0)-Cys(1)(C4MNB),Cys(8)(BCMACMOC)-resact by irradiation with light of > or = 402 nm or > or = 436 nm wavelength, respectively, followed by irradiation at lambda > or = 325 nm.