Site‐specific labeling of synthetic peptide using the chemoselective reaction between N ‐methoxyamino acid and isothiocyanate

Site‐specific labeling of synthetic peptides carrying N ‐methoxyglycine (MeOGly) by isothiocyanate is demonstrated. A nonapeptide having MeOGly at its N ‐terminus was synthesized by the solid‐phase method and reacted with phenylisothiocyanate under various conditions. In acidic solution, the reaction specifically gave a peptide having phenylthiourea structure at its N ‐terminus, leaving side chain amino group intact. The synthetic human β ‐defensin‐2 carrying MeOGly at its N ‐terminus or the side chain amino group of Lys 10 reacted with phenylisothiocyanate or fluorescein isothiocyanate also at the N ‐methoxyamino group under the same conditions, demonstrating that this method is generally useful for the site‐specific labeling of linear synthetic peptides as well as disulfide‐containing peptides. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.