Phenylthioethyl (Pte)/Phenylsulfonylethyl (Pse) as Safety Catch Protecting Groups for Peptide Synthesis

A safety-catch protecting group allows for the use of the same reagent/chemical mechanism for the removal of different protecting groups in the same synthetic scheme. While the first of these is removed directly, the removal of the second requires previous manipulation to make the protecting group labile to the reagent. Herein, phenylthioethyl (Pte)- and phenylsulfonylethyl (Pse)-based protecting groups are described. While Pte is stable to piperidine, Pse, which is its oxidized form, is labile in the presence of DBU-methylpiperidine. This system allows the preparation of linear, branched, cyclic, and other complex peptides.