Structures, practical sources (gymnosperm seeds), gas-liquid chromatographic data (equivalent chain lengths), and mass spectrometric characteristics of all-cis Δ5-olefinic acids

Abstract

Structures, practical sources (gymnosperm seeds), gas-liquid chromatographic data (equivalent chain lengths), and mass spectrometric characteristics of all-cis ∆ ∆5-olefinic acidsIn view of the increasing interest of lipid researchers in the biological effects of all-cis ∆5-unsaturated polymethylene-interrupted fatty acids (∆5-UPIFA) from vegetable origin, this paper is concerned with their occurrence in practical sources (gymnosperm seeds), structures, and identification by gas-liquid chromatography (GLC) and mass spectrometry (MS). The use of equivalent chain lengths (ECL) determined by calculations based on available standards, in close agreement with data determined with easily available commercial gymnosperm seeds specific for each ∆5-UPIFA, allows identification of all ∆5-UPIFA. These tentative identifications are supported by GLC-MS of the appropriate (4,4-dimethyloxazoline and picolinyl ester) derivatives. ECL are particularly useful to identify ∆5-UPIFA in tissue lipids from animals experimentally fed oils containing these acids, with no interference with polyunsaturated fatty acids of endogenous origin.

Non-methylene-interrupted Fatty Acids with &Delta;5 Unsaturation in <i>Sargassum</i> Species

“…Figure 2 illustrates the mass spectrum of the DMOX derivative of Peak 36. The fragmentation pattern is very similar to that of 5,9-18:2 and different from that of 5,11-20:2 22 . The double bond at the Δ9 position can be confirmed by a gap of 12 amu between m/z 194 and 206 carbons 8 and 9 , which means that the double bond is between carbons 9 and 10.…”

“…A more abundant ion at m/z 234 cleavage beta to the double bond gives an additional diagnostic information for the double bond at the Δ9 position 22 . The ions produced by cleavage at the double bond per se are not easily distinguished when the double bond is closer to the carboxyl group than the Δ7 position in the chain 22 . Thus, in this study, it was not possible to confi rm a Δ5 unsaturation for Peak 36 with a gap of 12 amu.…”

“…However, this hardly matters as the prominent ion at m/z 180 base peak , which represents cleavage at the center of bis-allylic system, is sufficiently characteristic for a 5,9-NMI diene system in the molecule 22 . The odd-numbered ion at m/z 153 and the intense ion at m/z 166 also support the double bond at the Δ5 position 22,23 crocystum, S. turbinariodes, and S. cristaefolum was identical to 5,11-20:2 by comparing the ECL value and retention times of the acid obtained from a mollusk.…”

“…The double bond at the Δ9 position can be confirmed by a gap of 12 amu between m/z 194 and 206 carbons 8 and 9 , which means that the double bond is between carbons 9 and 10. A more abundant ion at m/z 234 cleavage beta to the double bond gives an additional diagnostic information for the double bond at the Δ9 position 22 . The ions produced by cleavage at the double bond per se are not easily distinguished when the double bond is closer to the carboxyl group than the Δ7 position in the chain 22 .…”

“…The odd-numbered ion at m/z 153 and the intense ion at m/z 166 also support the double bond at the Δ5 position 22,23 crocystum, S. turbinariodes, and S. cristaefolum was identical to 5,11-20:2 by comparing the ECL value and retention times of the acid obtained from a mollusk. Kaneniwa et al 6 also identifi ed 5,11-20:2 in several seaweeds, including Chlorophyta, Phaeophyta and Rhodophyta, by using the ECL value and retention time of the known acid obtained from sea urchin lipids.…”