Acid catalysis of a linoleic acid hydroperoxide: formation of epoxides by an intramolecular cyclization of the hydroperoxide group

Abstract

Acid catalysis (0.1 M H2S04) of (13S)-(9Z,lLE)-13-hydroperoxy-9,ll-octadecadienoic acid (1) in methanol-water (9:1) did not afford appreciable yields of anticipated products, hexanal and (Z)-12-oxo-9-dodecenoic acid, via the known Hock rearrangement of hydroperoxides. Instead, intramolecular rearrangement of the 13-hydroperoxide into 12,13-epoxides, accompanied by solvent substitution, was the primary course of reaction (all products were isolated after conversion to methyl esters). Three isomeric methyl (Z)-12,13-epoxy-11 -methoxy-9-octadecenoates were isolated in 20.2 mol % yield; methyl (llR,12fi,13S)-(Z)-12,13-epoxy-ll-methoxy-9-octadecenoate (2a) comprised 81% of the three. The stereoselectivity observed in the formation of 2a implied anchimeric assistance by the epoxide group in substitution by methanol. Kinetic evidence, as well as a 20.4 mol % yield of stereoisomers of methyl (E)-13-hydroxy-9,12-dimethoxy-10-octadecenoates, was indicative of intermediate (E)-12,13-epoxy-9-methoxy-10-octadecenoic acids. These allylic epoxides could not be isolated, presumably because they solvolyzed rapidly in the presence of acid. On the other hand, the nonallylic epoxides 2a-c solvolyzed more slowly. The following reaction mechanism is proposed: (a) a conjugate acid forms by addition of a proton to a hydroperoxy group; (b) electrophilic attack on C-12 by a partially positive-charged -oxygen of the hydroperoxy group affords

Characterization of Hydroperoxides and Carbonyl Compounds Obtained by Lipoxygenase Extracts of Selected Microorganisms

“…Consequently, the quantity of carbonyl compounds produced as a result of the acidic conditions (pH 3.0) used in our experiment, was taken into consideration by using a control trial containing all the components except the enzyme preparation. The results (unshown) indicated that the acid degradation of 13-HPODE did not produce appreciable yields of hexana1 42 ) in comparison to those obtained by enzymatic activity. Figure 6 shows the GC elution profile of the DNPHderivatized carbonyl compounds obtained by the F. proliferatum extract; the DNPH-derivatized carbonyl standards as well as those produced by the microbial extracts showed similar chromatograms.…”

Liquid chromatography–tandem mass spectrometry determination of human plasma 1-palmitoyl-2-hydroperoxyoctadecadienoyl-phosphatidylcholine isomers via promotion of sodium adduct formation

“…5) [23,24]. PCOOH has been reported to be easily decomposed by several factors, such as acids [35], metal ions [36], and temperature [37]. Thus, we spiked standard PCOOH (16:0/13-HpODE PC) into plasma and checked PCOOH recovery under different extraction conditions (Scheme 1).…”

Fast atom bombardment and tandem mass spectrometry for determining structural modification of fatty acids

“…and more recently picolinyl derivatives of fatty acids (21)(22)(23) were established to be useful for locating the double bond position and other structural modifications. Chemical ionization (CI) mass spectrometry has been tipplied to the study of unsaturated fatty acids esters (11) and epoxy (24,25) and hydroxy (25)(26)(27)(28)(29) substituted esters. The principal advantages of CI are enhanced molecular weight information and limited fragmentation, which makes key fragments more apparent.…”