Abstract
A method was developed for steric analysis of methyl 9-hydroxy-10, 12-octadecadienoate and methyl 13-hydroxy-9,11-octadecadienoate. The hydroxy esters were converted into the corresponding (−)-menthoxycarbonyl derivatives by treatment with (−)-menthylchloroformate. These derivatives were subjected to oxidative ozonolysis and the ozonolysis product was treated with diazomethane, affording (−)-menthoxycarbonyl derivatives of dimethyl 2-hydroxysebacate and methyl 2-hydroxyheptanoate. Gas-liquid chromatography allowed separation of the diastereoisomeric derivatives and thus provided a sensitive means for determination of the absolute configuration of the parent unsaturated hydroxy ester. The method was applied to the hydroxy esters derived from the hydroperoxides formed from linoleic acid by action of soybean and corn lipoxygenases. 13 L-Hydroperoxy-9,11-octadecadienoic acid was isolated as major product after incubation with soybean lipoxygenase whereas 9 D-hydroperoxy-10,12-octadecadienoic acid was the major compound isolated after incubation with corn lipoxygenase, in agreement with previous work. The major compounds were accompanied by small amounts of the other 9- and 13-hydroperoxy acid isomers. These hydroperoxides were largely racemic stereoisomers and were probably formed mainly by autoxidation of the linoleic acid during the incubation period and isolation procedures. During the work with corn lipoxygenase it was found that this enzyme has a substrate specificity different from that of soybean lipoxygenase. Linoleic acid and α-linolenic acid both served as substrates for the corn enzyme whereas γ-linolenic acid and arachidonic acid did not. Soybean lipoxygenase oxygenated the four acids at comparable rates.
Published Version
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