Protecting groups are fragments that bind to functional groups and block their reactivity. Some are acid-labile protecting groups such as Boc and tert-Bu ester. Some are base labile protecting groups such as Fmoc and Fm ester. Some others are fluoride-labile protecting groups such as Tmsec and Tmse ester. To ensure specific coupling between the required carboxyl and amino groups, the protecting groups should be easy to attach and remove without changing the rest of the peptide.