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Isolation of unsaturated diols after oxidation of conjugated linoleic acid with peroxygenase
Author(s) -
Piazza George J.,
Nuñez Alberto,
Foglia Thomas A.
Publication year - 2003
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-003-1058-0
Subject(s) - conjugated linoleic acid , lipidology , clinical chemistry , conjugated system , chemistry , isolation (microbiology) , linoleic acid , biochemistry , organic chemistry , phosphatidyl choline , fatty acid , biology , bioinformatics , phospholipid , membrane , polymer
Oat seeds are a rich source of peroxygenase, an iron heme enzyme that participates in oxylipin metabolism in plants. An isomer of CLA, 9( Z ), 11( F )‐octadecadienoic acid ( 1 ), believed to have anticarcinogenic activity, was used as a substrate for peroxygenase in an aqueous medium using t ‐butyl hydroperoxide as the oxidant. After acidification of the reaction medium, the products were extracted with ethyl ether, converted to their methyl esters, and characterized using HPLC. Major products after reaction for 24 h showed resonances from 1 H NMR spectroscopy that were further downfield than the expected epoxides and were thought to be diol hydrolysis products. However, analyses by HPLC with atmospheric pressure chemical ionization MS (APCI‐MS) of the putative allylic diols or their bis‐trimethylsilyl ether derivatives gave incorrect M.W. The M.W. of the diols could be obtained by APCI‐MS after removal of unsaturation by hydrogenation or by EI‐MS after conversion of unsaturation by hydrogenation or by EI‐MS after conversion of the allylic 1,2‐diols to cyclic methyl boronic esters. Data from MS in conjunction with analyses using 1 H and 13 C NMR showed that the methylated products from 1 were methyl 9,10( threo )‐dihydroxy‐ 11( E )‐octadecenoate, methyl 9,10( erythro )‐dihydroxy‐11( E )‐octadecenoate, methyl 9,12( threo )‐dihydroxy‐10( E )‐octadecenoate. Solid‐phase extraction without prior acidification and conversion of the products to methyl esters allowed identification of the following epoxides: methyl 9,10( Z )‐epoxy‐11( E )‐octadecenoate ( 6M ), methyl 9,10( E )‐epoxy‐11( E )‐octadecenoate, and methyl 11,12( E )‐epoxy‐9( Z )‐octadecenoate. At times of up to at least 6h, 6M accounted for approximately 90% of the epoxide product. Product analysis after the hydrolysis of isolated epoxide 6M showed that hydrolysis of epoxide 6 could largely account for the diol products obtained from the acidified reaction mixtures.