Glu-derivative for the selective modification of the γ-carboxyl group. The OPp group can be removed selectively in the presence of Boc/OtBu with 1% TFA/DCM. Ocampo et al. applied OPp protection during the synthesis of a peptide-oligonucleotide conjugate and cleaved it with 3% trichloroacetic acid in DCM. Tofteng et al. generated a backbone pyroglutamyl imide moiety from C-terminal Glu after selective on-resin OPp removal.