Formation of hydroperoxides with unconjugated diene systems during autoxidation and enzymic oxygenation of linoleic acid

Abstract

During the autoxidation of methyl linoleate two minor monohydroperoxides are formed. After reduction they have been separated from the major products by HPLC on a silica gel/AgNO 3 column. On the basis of 1H-NMR and mass spectral data they were identified as the methyl esters of 8- and 14-hydroperoxy-cis-9, cis-12-octadecadienoic acids (8- and 14-HPOD). Both minor hydroperoxides are as stable as the major monohydroperoxides, since the percentage of them in the monohydroperoxide fraction is not significantly changed by an increase in the reaction temperature or by addition of α-tocopherol. Each of the 8- and 14-HPODs accounted for about 1% of the monohydroperoxides. There was some evidence that during catalysis of lipoxygenase-2 the 8- and 14-HPODs are produced to the same extent as in the autoxidation experiments. Both minor hydroperoxides are absent in the reaction with lipoxygenase-1.