Peptide Cleavage and Protected Cleavage Procedures
In Fmoc synthesis, the removal of the peptide from the solid support is typically accomplished with trifluoroacetic acid (TFA). Because the side chain protecting groups used in Fmoc synthesis are acid labile, a single step both cleaves the peptide from the resin and removes the protecting groups. Various scavenger molecules are added to the TFA to prevent the cleaved protecting groups from reattaching to the peptide. The particular scavengers used depend on the specific peptide sequence. Common scavengers include water (scavenges t-butyl cations), triisopropyl silane (TIS, scavenges trityl and Pbf cations), ethane dithiol (EDT, scavenges t-butyl cations, reduces oxidation of Cys/Met side chains), dioxa-1,8-octane-dithiol (DODT, scavenges t-butyl cations, suppresses oxidation of Cys/Met side chains), phenol (protects Tyr and Trp side chains from oxidation), and thioanisole (aids in removal of Pbf protecting groups from Arg(Pbf), suppresses oxidation of Cys/Met side chains). Cleavage can be performed either at room temperature or heated to 38 °C. For heated cleavage, CEM recommends the RazorTM parallel peptide cleavage system for both single peptides and large batch cleavages. For heated cleavage, CEM recommends the Razor parallel peptide cleavage system for both single peptides and large batch cleavages.