Analysis of 1,2-diols of linoleic, alpha-linolenic and arachidonic acid by gas chromatography--mass spectrometry using cyclic alkyl boronic esters

Arachidonic acid is metabolized by hepatic and renal cortical microsomes in the presence of NADPH to vicinal dihydroxyeicosatrienoic acids as some of the major metabolites. Other polyunsaturated, long-chain fatty acids might be metabolized to vicinal dihydroxy acids (1,2-diols) in the same way. To facilitate identification of 1,2-diols in biological samples, a series of unsaturated 1,2-diols were synthesized from linoleic, alpha-linolenic and arachidonic acid and the electron-ionization mass spectra of cyclic methane- and n-butaneboronic ester derivatives and of trimethylsilyl (TMS) ether derivatives were compared. The TMS ether derivatives gave rise to weak molecular ions but prominent informative fragmentation ions were formed by alpha-cleavage as well as cleavage between the carbons with the TMS ethers. The TMS ether derivative of methyl 15,16-dihydroxy-9,12-octadecadienoate had a considerably larger carbon value than the other C18 diols, while the cyclic boronates were poorly separated on gas chromatography. The methane- and n-butaneboronic acid derivatives showed strong molecular ions and a characteristic but not very informative fragmentation, although the position of the hydroxyls could be deduced from one or two fragments formed by alpha-cleavage. Linoleic and alpha-linolenic acid are metabolized in the rabbit to many polar products by hepatic and renal cortical microsomes and NADPH. 12,13-Dihydroxy-9-octadecenoic acid and other metabolites of linoleic acid were identified by gas chromatography--mass spectrometry.