title: The 4-pyridylmethyl ester as a protecting group for glutamic and aspartic acids: 'flipping' peptide charge states for characterization by positive ion mode ESI-MS.
abstract: Use of the 4-pyridylmethyl ester group for side-chain protection of glutamic acid residues in solid-phase peptide synthesis enables switching of the charge state of a peptide from negative to positive, thus making detection by positive ion mode ESI-MS possible. The pyridylmethyl ester moiety is readily removed from peptides in high yield by hydrogenation. Combining the 4-pyridylmethyl ester protecting group with benzyl ester protection reduces the number of the former needed to produce a net positive charge and allows for purification by RP HPLC. This protecting group is useful in the synthesis of highly acidic peptide sequences, which are often beset by problems with purification by standard RP HPLC and characterization by ESI-MS.
authors: East Carolina University, Chemistry, Greenville, NC, USA.
authors: Sriramya
authors: S
authors: Garapati
authors: Colin S
authors: CS
authors: Burns
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry*; D018698:Glutamic Acid / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D010455:Peptides; D001224:Aspartic Acid; D018698:Glutamic Acid
keywords: 4-picolyl ester; 4-pyridylmethyl ester; ESI-MS; acidic peptides; aspartic acid; glutamic acid; polarity switching; protecting group