title: Modification of N-terminal α-amino groups of peptides and proteins using ketenes.
abstract: A method of highly selective N-terminal modification of proteins as well as peptides by an isolated ketene was developed. Modification of a library of unprotected peptides XSKFR (X varies over 20 natural amino acids) by an alkyne-functionalized ketene (1) at room temperature at pH 6.3 resulted in excellent N-terminal selectivity (modified α-amino group/modified ε-amino group = >99:1) for 13 out of the 20 peptides and moderate-to-high N-terminal selectivity (4:1 to 48:1) for 6 of the 7 remaining peptides. Using an alkyne-functionalized N-hydroxysuccinimide (NHS) ester (2) instead of 1, the modification of peptides XSKFR gave internal lysine-modified peptides for 5 out of the 20 peptides and moderate-to-low N-terminal selectivity (5:1 to 1:4) for 13 out of the 20 peptides. Proteins including insulin, lysozyme, RNaseA, and a therapeutic protein BCArg were selectively N-terminally modified at room temperature using ketene 1, in contrast to the formation of significant or major amounts of di-, tri-, or tetra-modified proteins in the modification by NHS ester 2. The 1-modified proteins were further functionalized by a dansyl azide compound through click chemistry without the need for prior treatment.
authors.affiliation: Department of Chemistry, State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
authors.forename: Anna On-Yee
authors.initials: AO
authors.lastname: Chan
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Ho
authors.forename: Hiu-Chi
authors.initials: HC
authors.lastname: Chong
authors.forename: Yun-Chung
authors.initials: YC
authors.lastname: Leung
authors.forename: Jie-Sheng
authors.initials: JS
authors.lastname: Huang
authors.forename: Man-Kin
authors.initials: MK
authors.lastname: Wong
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che
mesh_terms: D005030:Ethylenes / Q000138:chemical synthesis / Q000737:chemistry*; D007659:Ketones / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D005030:Ethylenes; D007659:Ketones; D010455:Peptides; D011506:Proteins; C008223:ketene