title: Model system for irreversible inhibition of Nek2: thiol addition to ethynylpurines and related substituted heterocycles.
abstract: Recent studies have shown that irreversible inhibition of Nek2 kinase [(Never in mitosis gene a)-related kinase 2], overexpression of which is observed in several cancers, can be achieved using Michael acceptors containing an ethynyl group, which target the enzyme's cysteine 22 residue lying near the catalytic site. The model studies described herein demonstrate an analogous capture of the ethynyl moiety in a series of ethynyl-heterocycles (e.g. 6-ethynyl-N-phenyl-9H-purin-2-amine) by N-acetylcysteine methyl ester in the presence of 1,4-diazabicyclo[2.2.2]octane in either dimethyl sulfoxide or N,N-dimethylformamide. Kinetic studies showed a 50-fold range in reactivity with 7-ethynyl-N-phenyl-3H-[1,2,3]triazolo[4,5-d]pyrimidin-5-amine being the most reactive compound, whereas 4-ethynyl-N-phenyl-7H-pyrrolo[2,3-d]pyrimidin-2-amine was the least reactive. Studies of the isomeric compounds, 2-(3-((6-ethynyl-7-methyl-7H-purin-2-yl)amino)phenyl)acetamide and 2-(3-((6-ethynyl-9-methyl-9H-purin-2-yl)amino)phenyl)acetamide, revealed the N(7)-methyl isomer to be 5-fold more reactive than the 9-methyl isomer, which is ascribed to a buttressing effect in the N(7)-methyl compound. Comparison of the crystal structures of these isomers showed that the ethynyl group is significantly displaced away from the methyl group exclusively in the N(7)-methyl isomer with an sp(2) bond angle of 124°, whereas the corresponding angle in the N(9)-methyl isomer was the expected 120°. The results of this study indicate heterocyclic scaffolds that are likely to be more promising for inhibition of Nek2 and other kinases containing a reactive cysteine.
authors.affiliation: Newcastle Cancer Centre, Northern Institute for Cancer Research, School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. bernard.golding@ncl.ac.uk.
authors.forename: Honorine
authors.initials: H
authors.lastname: Lebraud
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Coxon
authors.forename: Victoria S
authors.initials: VS
authors.lastname: Archard
authors.forename: Carlo M
authors.initials: CM
authors.lastname: Bawn
authors.forename: Benoit
authors.initials: B
authors.lastname: Carbain
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Matheson
authors.forename: David M
authors.initials: DM
authors.lastname: Turner
authors.forename: Celine
authors.initials: C
authors.lastname: Cano
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Griffin
authors.forename: Ian R
authors.initials: IR
authors.lastname: Hardcastle
authors.forename: Ulrich
authors.initials: U
authors.lastname: Baisch
authors.forename: Ross W
authors.initials: RW
authors.lastname: Harrington
authors.forename: Bernard T
authors.initials: BT
authors.lastname: Golding
mesh_terms: D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D000072379:NIMA-Related Kinases; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011687:Purines / Q000737:chemistry / Q000494:pharmacology*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D006571:Heterocyclic Compounds; D047428:Protein Kinase Inhibitors; D011687:Purines; D013438:Sulfhydryl Compounds; C089441:NEK2 protein, human; D000072379:NIMA-Related Kinases; D017346:Protein Serine-Threonine Kinases