Arachidonic acid epoxides. Demonstration through [18O]oxygen studies of an intramolecular transfer of the terminal hydroxyl group of (12S)-hydroperoxyeicosa-5,8,10,14-tetraenoic acid to form hydroxyepoxides.

Purified 12-hydroperoxyeicosa - 5, 8, 10, 14 - tetrae noic acid (12-HPETE) containing deuterium atoms at 5, 6, 8, 9, 11, 12, 14, and 15 was prepared by incubating octadeuterated arachidonic acid with a platelet preparation in air or [18O]oxygen gas. A mixture of 12-HPETE containing 16O16O:18O18O (5:4) was subsequently prepared and incubated with hematin in phosphate buffer (pH 7.4); in another experiment the same mixture of 12-HPETE was incubated with a rat lung preparation (0-30% ammonium sulfate) which lacked epoxide hydratase activity. Gas chromatography-mass spectrometry negative ion chemical ionization analysis of the extracted products after conversion into pentafluorobenzyl-trimethylsilyl derivatives indicated that the products from both incubations, i.e. 12-hydroxyeicosa - 5,8,10,14 - tetraenoic acid (12 - HETE), 8 - hydroxy - 11,12-epoxyeicosa - 5,9,14 - trienoic acid (8H-11,12-EPETE), 10H - 11,12-epoxyeicosa - 5,8,14 - trienoic acid (10H-11,12-EPETE), and 8,11,12-trihydroxyeicosa-5,9,14-trienoic acid, all retained either two [16O]oxygen or two [18O]oxygen atoms of starting 12-HPETE and that no mixed species existed which contained one [16O]oxygen and one [18O]oxygen atom. These results demonstrate for the first time in the arachidonic acid series an intramolecular transfer of the terminal hydroxyl group of the hydroperoxide of 12-HPETE to the C-8 or C-10 alkyl positions to form the hydroxyepoxides 8H-11,12-EPETE and 10H-11,12-EPETE. This reaction carried out by both hematin in the absence of protein and the rat lung preparation is suggestive of a metal-hydroperoxide-olefin "cage" complex facilitating a concerted reaction in which the terminal hydroxyl group of the hydroperoxide is trapped by alkyl free radical centers.