Cross-linking of proteins by 3-(trifluoromethyl)-2,5-hexanedione. Model studies implicate an unexpected amine-dependent defluorinative substitution pathway competing with pyrrole formation.
Protein modification by the neurotoxic gamma-diketone 3-methyl-2,5-hexanedione (3-MHD) and its analogue 3-(trifluoromethyl)-2,5-hexanedione (3-TFMHD) was examined. Unlike 3-MHD, which forms lysine-based pyrroles that lead to autoxidation-dependent protein cross-linking, 3-TFMHD forms an autoxidatively inert pyrrole. The surprising finding that 3-TFMHD was nonetheless as effective as 3-MHD in cross-linking ribonuclease A suggested that protein lysine condensation with 3-TFMHD could take an alternate course competing with pyrrole formation. Model studies using neopentylamine led to the isolation of the expected 1-(2,2-dimethylpropyl)-2,5-dimethyl-3-(trifluoromethyl)pyrrole as well as the neopentylamine-3-TFMHD 2:1 adducts N,N'-bis(2,2-dimethylpropyl)-2-amino-3-acetyl-5-methylpyrrole (major) and N,N'-bis(2,2-dimethylpropyl)-3-(1-aminoethylidene)-5-methyl-4-pyrrolin-2-one (minor). The formation of these 2:1 adducts, the lysine analogues of which are believed to be mainly responsible for the observed protein cross-linking, is proposed to proceed via Schiff base formation, enamine fluoride elimination, second amine condensation, and hydrolysis.
Xu
Guozhang
G
Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Sayre
Lawrence M
LM
D003432:Cross-Linking Reagents / Q000494:pharmacology*; D006588:Hexanones / Q000494:pharmacology*; D008239:Lysine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D015394:Molecular Structure; D009498:Neurotoxins / Q000494:pharmacology*; D011506:Proteins / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry; D012260:Ribonucleases / Q000737:chemistry
C464119:3-(trifluoromethyl)-2,5-hexanedione; D003432:Cross-Linking Reagents; D006588:Hexanones; D009498:Neurotoxins; D011506:Proteins; D011758:Pyrroles; C464099:3-methyl-2,5-hexanedione; D012260:Ribonucleases; D008239:Lysine