The peptide chain was synthesized by SPPS on Rink Amide MBHA resin. Each amino acid coupling step was carried out with Fmoc-protected amino acid (2 eq), DIC (4 eq), ethyl cyanohydroxyiminoacetate (2 eq) in DMF at 75 °C (155 W) for 0.25 min and at 90 °C (30 W) for further 2 min. For the last lysine, the coupling was carried out at 75 °C (155 W) for 0.5 min and at 90 °C (30 W) for further 4 min. After each coupling step, the respective Fmoc protecting group was removed by 10% Piperazine (w/v) in ethanol:NMP (1:9). After the final Fmoc deprotection, cleavage was performed in TFA/H2O/TIS 95:2.5:2.5 solution for 2 h. The resin was removed by filtration and the filtrate was concentrated by N2 flow. The crude product was precipitated with cold diethyl ether, centrifuged (4,000 g for 10 min) and the supernatant was discarded. The precipitate was dissolved in water, filtrated through a 0.22 µm syringe filter and purified by RP-HPLC. Lyophilization of the pure product fractions afforded the desired compound as white powder, which was characterized by LC-MS (Supplementary Figure ).