The peptide pellets were dissolved in water/0.1% (v/v) TFA (at a concentration of about 5 mg/mL) and purified using the CombiFlash RF200 Flash Chromatography instrument (Teledyne Isco) equipped with a 50 g RediSep Rf Gold Reversed-Phase C18 column. 5 mL of peptide solution was loaded for each round of purification. At a 40 mL/min flow rate with H2O/0.1% TFA (solvent A) and acetonitrile (solvent B), the gradient used was: 0% solvent B from 0-3 min, ramped up to 100% solvent B at 9 min, ramped down to 0% solvent B at 11 min, and held at 0% solvent B until 15 min. Collected sample fractions were rotary evaporated to remove acetonitrile and trace amounts of TFA before lyophilizing. For cyclization, lyophilized peptides were reconstituted in a 10 mM borate buffer (pH 8.5) and stirred for 24 h. These peptides were then purified and lyophilized a second time.