title: A Type of Auxiliary for Native Chemical Peptide Ligation beyond Cysteine and Glycine Junctions.
abstract: Native chemical ligation enables the chemical synthesis of proteins. Previously, thiol-containing auxiliary groups have been used to extend the reaction scope beyond N-terminal cysteine residues. However, the N-benzyl-type auxiliaries used so far result in rather low reaction rates. Herein, a new N(α) -auxiliary is presented. Consideration of a radical fragmentation for cleavage led to the design of a new auxiliary group which is selectively removed under mildly basic conditions (pH 8.5) in the presence of TCEP and morpholine. Most importantly and in contrast to previously described auxiliaries, the 2-mercapto-2-phenethyl auxiliary is not limited to Gly-containing sites and ligations succeed at sterically demanding junctions. The auxiliary is introduced in high yield by on-resin reductive amination with commercially available amino acid building blocks. The synthetic utility of the method is demonstrated by the synthesis of two antimicrobial proteins, DCD-1L and opistoporin-2.
authors.affiliation: Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin (Germany).
authors.forename: Simon F
authors.initials: SF
authors.lastname: Loibl
authors.affiliation: Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin (Germany).
authors.forename: Ziv
authors.initials: Z
authors.lastname: Harpaz
authors.affiliation: Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin (Germany). oliver.seitz@chemie.hu-berlin.de.
authors.forename: Oliver
authors.initials: O
authors.lastname: Seitz
mesh_terms: D003545:Cysteine / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry*; D015394:Molecular Structure; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: D010455:Peptides; D003545:Cysteine; D005998:Glycine
keywords: Nα-auxiliaries; desulfurization; peptide ligation; protein synthesis; radical reactions