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.

Cardiolipin: characterization of distinct oxidized molecular species

“…In vivo aldehydes, e.g., 4-hydroxynonenal and other thiobarbituric acid-reactive substances derived from linoleic acid oxidation, have been used as monitors of oxidative stress. These products, readily generated from linoleic acid in the presence of a one-electron reductant, routinely reduced metal ions like Fe(II) ( 49,50 ). The results of our studies suggest that production of aldehyde byproducts requires, in addition to oxygen radicals and/or singlet oxygen, a source of electrons to reduce the initial hydroperoxides.…”

Lipoxygenases Mediate the Effect of Essential Fatty Acid in Skin Barrier Formation

“…4B, inset) is characteristic of a conjugated enone with allylic epoxide (32). Its structural identification entailed reduction with sodium borohydride, transesterification to the methyl ester, and HPLC-UV and GC-MS analysis of the resulting epoxyalcohol methyl esters in comparison with authentic standards (Fig.…”

“…Intriguingly approximately half of the epoxy-ketone-EOS in mouse epidermis, together with epoxyketone-acyl acids, is directly coupled to proteins through a reversible linkage. Most likely, the chemistry involves Michael addition of the ␣,␤-unsaturated ketone to His on proteins (32). Notably, the CE protein involucrin is enriched in His (50).…”

Cardiolipin Remodeling in the Heart

“…71,72,81 Increased ROS production caused by partial block of electron flow through complex III 28,82 or complex IV 83,84 increases oxidative damage to CL. Products of ROS can react, in turn, with proteins 85-87 to generate Schiff bases [88][89][90] and similar adducts, providing mechanisms for the chemical loss of CL that would ''bypass'' MLCL and the potential for ''secondary remodeling.'' Furthermore, interaction with proteins would render this oxidatively modified CL nondetectable by the usual analytical approaches employed to detect oxidized CL.…”