Other promising PTMs include lysine trimethylation or acetylation, both of which have been incorporated into the chemical synthesis of L-histones (Table , Entries 26-27). Preparation of the corresponding D-histones would require the synthesis of the lysine building blocks in D-form. A more challenging lysine PTM is site-specific ubiquitination. Chemical synthesis of branched ubiquitin chains in native L-form is well reported, employing a removable glycyl auxiliary onto the lysine side chain (Figure ). The auxiliary facilitates NCL with a ubiquitin thioester, following subsequent removal with TFA to generate a native glycine at the branched ligation site. However, during preparation of the mirror-image branched ubiquitin proteins, the auxiliary was replaced with a cysteine residue to circumvent the low efficiency of the ligations, leaving a non-native cysteine as a scar at the ligation site (Figure ). Palmitoylation also serves as a promising PTM for incorporation into D-proteins and has been applied to the synthesis of cysteine palmitoylated L-proteins (Table , Entries 31-32). Palmitic acid is achiral and could be conjugated to D-cysteine or other D-amino acid residues. Synthesis of palmitoylated D-proteins may find use in racemic protein crystallography which has been applied to reveal the structure of transmembrane protein domains in racemic detergents. In addition, palmitoylation is a useful modification for pharmacokinetic optimization of peptide drugs, including the FDA-approved Liraglutide. This modification may find use in prolonging the half-life of D-peptide drug candidates, as encountered with the conjugation of cholesterol to the promising D-peptide drug candidate, CPT31.