SYNTHESIS OF 2 ANALOGS OF ARACHIDONIC-ACID AND THEIR REACTIONS WITH 12-LIPOXYGENASE

Two analogues of arachidonic acid (AA) were synthesized and their reaction with purified porcine 12-lipoxygenase was investigated. The analogue (Z,Z,Z,E)-5,8,11,13 eicosatetraienoic acid 1 was found to be a substrate for the enzyme, being oxidized at one third the rate of AA. The structure of the lipoxygenation product, as well as its absolute stereochemistry, were determined by comparison of the enzymatic reaction product with a synthetic sample of known stereochemistry, prepared from L-arabinose. The oxygenation of 1 by 12-lipoxygenase occurred selectively at carbon 14 and yielded only the S-isomer. The second AA analogue (Z,Z,Z,E,E)-5,8,11,13,15 eicosapentaenoic acid 2 failed to give any detectable amount of product upon incubation with the enzyme. The results demonstrate that the 15-oxygenated function of 15-H(P)ETE is not a requirement for the stereoselective 14-oxygenation catalyzed by 12-lipoxygenase. Furthermore, these results support the proposal that AA binds in a horseshoe like conformation at the active site of lipoxygenase. © 1990.