title: Removal of the 5-nitro-2-pyridine-sulfenyl protecting group from selenocysteine and cysteine by ascorbolysis.
abstract: We previously reported on a method for the facile removal of 4-methoxybenzyl and acetamidomethyl protecting groups from cysteine (Cys) and selenocysteine (Sec) using 2,2'-dithiobis-5-nitropyridine dissolved in trifluoroacetic acid, with or without thioanisole. The use of this reaction mixture removes the protecting group and replaces it with a 2-thio(5-nitropyridyl) (5-Npys) group. This results in either a mixed selenosulfide bond or disulfide bond (depending on the use of Sec or Cys), which can subsequently be reduced by thiolysis. A major disadvantage of thiolysis is that excess thiol must be used to drive the reaction to completion and then removed before using the Cys-containing or Sec-containing peptide in further applications. Here, we report a further advancement of this method as we have found that ascorbate at pH 4.5 and 25 °C will reduce the selenosulfide to the selenol. Ascorbolysis of the mixed disulfide between Cys and 5-Npys is much less efficient but can be accomplished at higher concentrations of ascorbate at pH 7 and 37 °C with extended reaction times. We envision that our improved method will allow for in situ reactions with alkylating agents and electrophiles without the need for further purification, as well as a number of other applications. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.
authors.affiliation: Department of Chemistry, Cook Physical Sciences Bldg, University of Vermont, 82 University Place, Burlington, VT, 05405, USA.
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Ste Marie
authors.affiliation: Department of Chemistry, Cook Physical Sciences Bldg, University of Vermont, 82 University Place, Burlington, VT, 05405, USA.
authors.forename: Erik L
authors.initials: EL
authors.lastname: Ruggles
authors.affiliation: Department of Biochemistry, University of Vermont, 89 Beaumont Ave., Given Laboratory, Room B413, Burlington, VT, 05405, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Hondal
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D011725:Pyridines / Q000737:chemistry*; D017279:Selenocysteine / Q000737:chemistry*; D013997:Time Factors; D014269:Trifluoroacetic Acid / Q000737:chemistry
chemical_list: D004220:Disulfides; D011725:Pyridines; D017279:Selenocysteine; D014269:Trifluoroacetic Acid; D003545:Cysteine; D001205:Ascorbic Acid
keywords: ascorbate; cysteine; deprotection; disulfide; orthogonal; protecting group; selenocysteine