We then examined the reaction on pentapeptides, focusing first on the more accessible lysine side chain in presence of protected N-terminus (Fig ). Peptides-EBX 3c-g bearing only aliphatic residues were obtained in 24-50% isolated yield. The reactions were nearly quantitative after only 20 minutes in open flasks, and mass loss occurred due to the instability of EBX cores on reverse-phase HPLC. Importantly, the reaction was selective for Lys in presence of nucleophilic amides (3h and 3i) or aromatic (3j-l) residues. We then examined the potentially more challenging functionalization of the N-terminus. Gratifyingly, peptide-EBXs 3n-p with a free N-terminal Phe were obtained in comparable yield, even in presence of unprotected Ser (3n) or protected-Lys (3o). The Lys side chain could also be functionalized on larger peptides, leading to 3q and 3r with respectively 9 and 10 amino acids. Although the synthesis of peptide-EBXs in solution was successful, a disadvantage was the significant mass loss upon HPLC purification. This was mostly due to partial degradation of the compound on HPLC. For example, when 10 mg pure compound 3g were submitted to HPLC, only 6.8 mg could be recovered. Therefore, we investigated if the reagent could be synthesized directly on solid phase (Fig ). In fact, peptide-EBX 3s functionalized on the N-terminus could be obtained on solid phase with high purity in 19% over 14 steps from commercial building blocks.