Hydrogenolytic debenzylation of sulfur-containing peptides

S-protected cysteine derivatives are desulfurized by hydrogenation with Pd/H2 forming inhibiting thiols and alanine derivatives. In the case of protected cysteine peptides, this inhibition effect may be suppressed by adding BF3-etherate, the extent of suppression depending on the position of the cysteine and on the sequence length of the peptide derivative. With sufficient sequence distance from the cysteine sulfur, benzyl type protecting groups may be quantitatively removed from the cysteine sulfur by means of hydrogenolysis.