title: Synthesis of six epoxyketooctadecenoic acid (EKODE) isomers, their generation from nonenzymatic oxidation of linoleic acid, and their reactivity with imidazole nucleophiles.
abstract: As a class of linoleic acid oxidation products, epoxyketooctadecenoic acids (EKODEs), are formed in vivo and in vitro by a free radical mechanism initiated by either enzymatic or nonenzymatic pathways. They have so far been made available in small-scale quantities, often as isomeric mixtures, from reductive decomposition of linoleic acid-derived hydroperoxides. There is major interest in these compounds owing to their highly potent biological activities and their ability to covalently modify proteins. The synthesis of six EKODE regio- and stereoisomers, two trans alpha',beta'-epoxy-alpha,beta-enones, and two trans and the two cis gamma,delta,-epoxy-alpha,beta-enones was accomplished, with the key steps being Wittig-type reactions and aldol condensations. All six EKODE isomers were confirmed by HPLC to be generated in the autoxidation of linoleic acid promoted by Fe(II)/ascorbic acid through spiking in of authentic samples. On the basis of evidence for EKODE modification of protein His residues, the reactions of Nalpha-benzoyl-L-histidine with autoxidizing linoleic acid and with the individual EKODE isomers were compared, as were the kinetics of the various EKODE reactions with imidazole nucleophiles. The structures of His-EKODE-(E)-I adducts were confirmed to reflect conjugate addition (epoxide ring remains intact) through an NMR study of the reaction of imidazole with a generic EKODE-(E)-I analog. The synthesis of the EKODE isomers makes these important molecules available for further chemical and biological evaluation.
authors.affiliation: Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: De
authors.initials: D
authors.lastname: Lin
authors.forename: Jianye
authors.initials: J
authors.lastname: Zhang
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Sayre
mesh_terms: D007093:Imidazoles / Q000737:chemistry*; D019787:Linoleic Acid / Q000737:chemistry*; D015394:Molecular Structure; D009829:Oleic Acids / Q000138:chemical synthesis* / Q000737:chemistry*; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: C474654:12,13-epoxy-9- keto-10-octadecenoic acid; D007093:Imidazoles; D009829:Oleic Acids; D019787:Linoleic Acid